Do It Yourself Solar Energy

DIY Home Energy System

This ebook guide teaches you how to escape complete dependence the power grid and learn how to live mostly on your own power and make sure that you are dependent on Yourself. You will be able to slash your energy bill by over 75% and not have to depend on greedy energy companies. The largest energy corporations are a monopoly for a given area, so they do not need to care about customer service or doing right by the people they service. You will learn how to break this monopoly and depend on yourself. Make your home immune to power shortages, blackouts, and energy failures; live free of any worry that the grid will totally fail you! You will learn practical steps such as how to build your own solar panel for less than $60! Once you start relying more on solar power you will be able to easily protect your family from dangerous power outages, and live free! Read more...

DIY Home Energy System Overview

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My DIY Home Energy System Review

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Free Energy Change Ag

Free-energy change (AG) as a function of cluster (r* > r) or stable nucleus (r > r*) size, r* is critical nucleus size, and AG* is critical free-energy barrier for nucleation. Figure 1-19. Free-energy change (AG) as a function of cluster (r* > r) or stable nucleus (r > r*) size, r* is critical nucleus size, and AG* is critical free-energy barrier for nucleation.

The Distribution of Standard Free Energy

The standard free energy can be used to explain chromatographic retention in two different ways. Firstly, portions of the standard free energy can be allotted to specific types of molecular interactions between the solute molecules and the two phases. Secondly, the molecule can be divided into different parts and each part allotted a portion of the standard free energy. This approach allows the contributions Consider the distribution of the standard free energy throughout an -alkane molecule, allotting a portion to each methylene group and to the two methyl end-groups. Then, algebraically, this concept can be put in the following form where AG(methylenegroup) is the standard free energy of each methylene group, AG(methylgroup) is the standard free energy of each methyl group, is the number of methylene groups and m is the number of methyl groups (m 2 for an -alkane). The expected straight lines are produced at each temperature and the indices of determination are very close to unity....

The Distribution of Standard Free Energy Between Different Types of Molecular Interactions

In contrast to apportioning the standard free energy between different groups in the solute molecule, it can also be divided between the different types of forces involved in the solute phase-phase distribution. This approach has been elegantly developed by Martire in his unified theory of retention. In a simplified form, the standard free energy can be divided into portions that result from the different types of interaction, e.g. Nevertheless, it is important to realize that they are not different types of interaction, but are all polar interactions, electrical in nature but of different strengths. In fact, many more terms have been introduced to describe subtly different enthalpic and en-tropic contributions to retention. In some cases, these extra terms are often introduced to take into account many second-order effects. It must be emphasized, however, that standard free energy is a bulk property, and where a portion is allotted to a particular type of interaction, e.g....

Solar power

Solar collector consisting of a pool of salt water heated by the sun used either directly as a source of heat or as a power source for an electric generator. Also known as salt-gradient solar pond. 'so lar 'pSnd solar power mecheng The conversion of the energy of the sun's radiation to useful work. 'so-lar 'pau-ar solar power satellite eng A proposed collector of solar energy that would be placed in geostationary orbit where sunlight striking the satellite would be converted to electricity and then to microwaves, which would be beamed to earth. .so-lar .pau-ar 'sad-al.it solar sensor electr A light-sensitive diode that sends a signal to the attitude-control system of a spacecraft when it senses the sun. Also known as sun sensor. 'so-lar 'sen-sar solar still chem eng A device for evaporating seawater, in which water is confined in one or more shallow pools, over which is placed a roof-shaped transparent cover made of glass or plastic film the sun's heat evaporates the water, leaving...

Solar Energy

20-1 Some fields of solar energy Since no life could exist on earth without the energy from the sun, the use of solar energy is as old as life. Even centuries ago living quarters were often built to take advantage of the warmth of the sun. The sun has also dried fruits and other foods and evaporated water from brine to leave salt. Earlier in the twentieth century solar collectors were used for heating domestic hot water. Since the precipitous increase in the cost of energy from fossil fuel in the mid-1970s and the prospect of their continued increase, solar energy has become the focus of much interest as one of the renewable resources. Some of the areas of study and application of solar energy include direct conversion of solar energy into electricity, high-temperature collectors suitable for operating power generators, low-temperature flat-plate collectors, and design of buildings to use solar energy in a passive manner. Since the time of the day at which solar energy is available...

The Condition of the

We receive about 100 Watts of solar energy on each square meter of the Earth's surface, or a yearly total of about 25 X 1018 BTUs. Therefore, 1 of the solar energy received on the surface of the planet could supply our total energy needs. If collected on artificial islands or in desert areas around the Equator, where the solar radiation intensity is much higher than average, a fraction of 1 of the globe's surface could permanently supply our total energy needs. If the collected solar power were used to obtain hydrogen from water and if the compressed hydrogen were used as our electric, heat, and transportation energy source, burning this fuel would result in the emission of only clean, nonpolluting steam. Also, if the combustion took place in fuel cells, we could nearly double the present efficiency of electric power generation (about 33 ) or the efficiency of the internal combustion engine

026 Different Culture From The Private Ice

The imperative for power steering is removed by the ultra-light construction of the 'supercar', provided steering and handling dynamics are properly designed. In EV supercars, wheel motors might provide for ABS and ASR without further weight penalty. High intensity headlamp technology can considerable reduce power demand as can the use of fibre-optic systems which provide multiple illumination from a single light source. Light-emitting diode marker lamps can also save energy and experts believe that the energy consumption of air-conditioning systems could be reduced by 90 , if properly designed, and used in cars with sandwich panel roofs, heat-reflecting windows and solar-powered ventilation fans. But none of this compares with the savings made by high strength composite construction which has the potential to bring down average car weight from 3000 to 1000 lb. It is reported that many of the 2000 or so lightweight EVs operating in Switzerland already weigh only 575 lb without...

Renewable Energy Resources

There is a wide range of renewable energy sources currently in use and abundantly available for future use as mainstream energy sources. These include wood, wind, tidal power, hydropower, geothermal energy, hydrogen, and, the most abundant of all, solar energy. Solar energy is the source of almost all of the earth's energy. About one two-billionth of the sun's radiation impinges on the earth, about half of which is not reflected back into interstellar space by the earth's atmosphere. The total solar-radiation intensity on a surface normal to the sun's rays is about 434.6 Btu ft2-h (1,370 W m2 or 4,932 kJ m2-h). This quantity, called the solar constant, undergoes small (1 ) variations that primarily affect the short-wave portion of the spectrum. Also, since the earth-sun distance varies as does the angle between the earth's equatorial plane and the sun line, seasonally, there are corresponding variations in terrestrial solar-radiation intensity. Additionally, in passing through the...

AG GsGl Hs TSsSl AHTAS

At the freezing temperature, Tf, AG Gs - Gl 0, because the free energy of the two phases is the same, and AH TfAS, It is necessary to cool below Tf for solidification, because at Tf both the solid and liquid phases are present and in equilibrium. Below Tf, AG is not equal to zero (Fig. 1 shows that Gs < Gl) and is given by Eq 1 with T T, where T < Tf.

R 2 yTf VsAH fTf TEQ

Nucleation requires a thermal energy either equal to or greater than AG* in order for a spherical nucleus of radius r* to form. The AG* value is the activation energy, which, as Fig. 2 shows, is a positive quantity. The greater the degree of undercooling, the more negative the free energy, the less positive the AG* value, and the greater the rate of nucleation of the solid. For homogeneous nucleation, AG* is given by

Some Quantitative Parameters

If we define a binding free energy for the biospecific interaction as AG , and for nonspecific interactions as AG J, then the total binding energy is the sum of AG 0 and AG0. But the effective dissociation constant is equal to the product of Kds and Kdn, the constants for the specific and nonspecific interactions. A very weak nonspecific interaction in addition to the biospecific one can tip the balance between adsorption and nonadsorption.

105 Alternative and Sustainable Energy Used via the Grid

There is no reason at all why alternative sustainable forms of energy such as solar, wind, hydro, tidal, wave, biomass, waste and energy taken from under sea currents should not be used to provide energy to electric vehicles via the grid. In some ways this is a much better option than powering electric vehicles directly from small wind generators and solar panels, where the energy is wasted when the vehicle is not directly charging. With the grid the energy can be transferred from one use to another. When electricity is not being supplied to one consumer it will be supplied to another. When there is ample electricity from alternative sources it will be used, fossil-fuelled generators being switched off to save fuel. When there is less alternative energy the fossil-fuelled generators will be used, the customer not experiencing any break in supply during periods of little sun, wind or tide. Also, the grid allows electric vehicles to be supplied with energy from all available energy...

113 Fuzzylogicbased Rover Health And Safety

Various observable states, events, and terrain features can be considered for online assessment of a rover's operational status. Table 11.1 lists a number of possible health and safety indicators (HSIs) associated with rover on-board subsystems, which convey some aspect(s) of rover operational well being as it relates to safe terrain traversal. At any given moment, the amount of power available to a rover system is perhaps the strongest indicator of its operational health. Solar energy is the primary power source for planetary rovers, although some systems have the luxury of rechargeable batteries. The attitude (pitch and roll) of the vehicle chassis can be monitored in order to avoid instabilities associated with ascent descent of slopes, traversal of rocky terrain, and turning within vehicle curvature constraints. In addition to surface irregularities, the type and condition of the terrain surface provide clues for safety assessment. Human automobile drivers are able to...

643 Electrical propulsion system

Powering an aircraft with an electrical power system is not new. Several attempts were made in the early days of aviation to incorporate electrical power into aircraft. However, the main difficulty rested with the storage of electrical energy in bulky and heavy batteries. Even now, batteries are still too heavy to be used in general aviation aircraft as the main power source, except for aircraft with very short operating time. One aeronautical field in which electrical propulsion has become established over the past 20 years is for model aircraft flying. Progressive miniaturisation of electrical and electronic components has shown the advantages of the technology. The aircraft are environmentally cleaner, more reliable and easier to integrate the operating systems. More recently, a number of large aircraft have been designed and flown using solar panels as the power source. Reference to the Pathfinder, Solar Challenger and Penguin aircraft should be made to understand these...

Electromagnetic Interaction

We previously determined the amount of electromagnetic energy that reaches the vicinity of the earth when we calculated the solar constant. This energy retains the blackbody spectral characteristics it had when it left the sun, the only difference being that the energy levels over the range of wavelengths has decreased. As this energy encounters the earth, the interactions affect both the earth and the energy itself. In some cases, these interactions are useful to the space systems user. For example, remote sensing techniques measure the absorption or transmission of solar radiation through the atmosphere to infer some of the characteristics of the atmosphere from space, and most spacecraft use solar panels to convert some of this radiation to electricity to power the spacecraft systems. In other cases, solar radiations produce undesired effects. For instance, spacecraft may absorb excess infrared frequencies, necessitating the use of thermal control devices, and the ionosphere,...

Thermodynamics of Enantiomer Separation

Enantiomer separation by GC is brought about by the difference in the Gibbs free energy AR,S(AG) of the diastereomeric association equilibria between the en-antiomers (selectand) and the CSP (selector). An important prerequisite is a fast and reversible association equilibrium (fast kinetics). The chemical association equilibria in the stationary phase are described by Kr and KS, with R referring to the second eluted enantiomer and S to the first eluted enantiomer. For enantiomer separation, the Gibbs-Helmholtz equation 1 applies, where R is the universal gas constant, Tis the temperature (K), H is the enthalpy and S is the entropy.

611 Surface energy theories

An isolated droplet of a fluid is most stable when its surface free energy, and thus its area, is a minimum. In 1878 Gibbs (1948) suggested that the growth of a crystal could be considered as a special case of this principle the total free energy of a crystal in equilibrium with its surroundings at constant temperature and pressure would be a minimum for a given volume. If the volume free energy per unit volume is assumed to be constant throughout the crystal, then

61 Thermodynamics of Nucleation

It was shown in Chapter 5 that the equilibrium compositions xai and xia of ferrite and austenite respectively, are obtained using the common tangent construction. The same construction can be used to determine the change in free energy AG7 7 +a when austenite of composition x decomposes into the equilibrium mixture of ferrite and carbon-enriched austenite (7'), Fig. 6.2a. Fig. 6.2 Free energy diagrams illustrating the chemical free energy changes during the nucleation and growth of ferrite from austenite of composition x. The term 7' refers to austenite which is enriched in carbon as a result of the decomposition of austenite of composition x into a mixture of ferrite and austenite. Fig. 6.2 Free energy diagrams illustrating the chemical free energy changes during the nucleation and growth of ferrite from austenite of composition x. The term 7' refers to austenite which is enriched in carbon as a result of the decomposition of austenite of composition x into a mixture of ferrite and...

51 Deviations from Equilibrium

Equilibrium is said to exist in a system when it reaches a state in which no further change is perceptible, no matter how long one waits (Pippard, 1981). This could happen if the system sinks into a very deep free energy minimum. Whether this represents the lowest free energy state, it is impossible to say, and a question more of philosophy than of practical consequence. It is more appropriate to refer to the state of metastable equilibrium, which represents a local minimum in free energy but does not exclude the existence of other deeper minima. The laws governing metastable equilibria are exactly identical to those dealing with equilibrium so this procedure has no obvious difficulties. A bainitic microstructure is far from equilibrium. The free energy change accompanying the formation of bainite in an Fe-0.1C wt alloy at 540 C is 580Jmol_1, whereas that for the formation of an equilibrium mixture of allotriomorphic ferrite and austenite at the same temperature is 1050Jmol 1....

411 Fuel Cell Characteristics

Theoretically, fuel cells operate isothermally, meaning that all free energy in a fuel cell chemical reaction should convert into electrical energy. The hydrogen fuel in the fuel cell does not burn as in IC engines, bypassing the thermal to mechanical conversion. Also, because the operation is isothermal, the efficiency of such direct electrochemical converters is not subject to the limitation of Carnot cycle efficiency imposed on heat engines. The fuel cell converts the Gibbs free energy of a chemical reaction into electrical energy in the form of electrons under isothermal conditions. The maximum electrical energy for a fuel cell operating at constant temperature and pressure is given by the change in Gibbs free energy where n is the number of electrons produced by the anode reaction F is Faraday's constant, equal to 96412.2 C mol and E is the reversible potential. The Gibbs free energy change for the reaction H2(g)+(1 2)O2g H2O(l) at standard condition of 1 atmospheric pressure and...

86 The Effect of Hydrostatic Pressure

There is general agreement that the application of hydrostatic pressure causes a retardation of the bainite reaction (Jellinghaus and Friedewold, I960 Radcliffe et al., 1963 Nilan, 1967). The effect on the time-temperature-transformation diagram is illustrated in Fig. 8.12. The observed retardation is not in itself a feature unique to bainite. All transformations which are accompanied by a reduction in density are expected to be retarded by hydrostatic pressure, which opposes a volume expansion. The effect of hydrostatic pressure is two fold it reduces the diffusion coefficients by decreasing the available free volume (although the details remain to be established), and it influences the free energy change for transformation. If AGm is the molar Gibbs free energy change for a reaction, then since where AVm is the change in molar volume on transformation, V is the volume and P is the pressure. The way in which the free energy change for transformation is influenced by the pressure...

1133 Kinetics Rates of Corrosion

The construction of thermodynamic corrosion (Pourbaix) diagrams provides valuable information on whether or not a particular reaction is feasible. However, these diagrams do not provide any information on the rate at which a reaction may occur. For example, the reaction of gaseous hydrogen and gaseous oxygen to form water is accompanied by a large decrease in free energy, some 200 + kJ at 25 C. However, the rate of this reaction is so slow that it might be regarded as not occurring at all. Furthermore, these diagrams, given normally at 25 C, do not provide information on a time basis. In this respect it is therefore necessary to consider the kinetic aspects of corrosion. The standard half-cell potential for the oxidation of iron, E(a), is 0.44 V while that for the cathodic reaction, E(c) is 0.0 V 11 . The total cell potential E(cell) is given by E(cell) E(c) - E(a) 0-0 V - 0-44 V -0-44 V Based on Faraday's law, Eq. 11.2, a large negative free-energy value is obtained and the reaction...

52 Chemical Potential

There is then no net tendency for atoms to transfer from one allotrope to the other, because the free energy of the iron atom in a is precisely equal to that in 7. Similarly, for an iron-carbon solid solution, equilibrium is when there is no net tendency for either iron or carbon atoms to transfer between ferrite and austenite, even though the two phases may differ in composition. That is, the free energy of a carbon (or iron) atom must be identical in ferrite and in austenite at equilibrium. It is no longer the case that the ferrite and austenite have identical free energies at equilibrium. It therefore becomes useful when considering the thermodynamics of solid solutions to partition the free energy of phase into parts which are attributed to the individual components. This leads to the concept of a chemical potential. The molar Gibbs free energy of a binary solution can be written as a weighted average of its components A and B where is the chemical potential of element i in a...

Mechanism of Infiltration

Successful infiltration of a porous, skeletal solid with a liquid phase requires that the total surface-free energy of the system after infiltration be lower than the total surface-free energy before infiltration. The total includes the surface-free energies of the solid and the liquid phases, as well as the interfacial energy between the solid and liquid. This relationship is expressed by

68 Growth with Partial Supersaturation

(i) A transformation can occur without any composition change as long as there is a reduction in the free energy. The chemical potential is then nonuniform across phase boundaries for all of the atomic species. A net reduction in free energy is still possible because some of the species are trapped in the parent phase and others in the product. Thus, martensitic transformation of steel involves the trapping of carbon in the martensite and iron in the austenite. (ii) Equilibrium transformation requires the partitioning of solutes between the phases until the chemical potential for each species is uniform in all locations.

Spinodal decomposition

Where G is the Gibbs free energy per mole of solution and c is the solution concentration. On a phase diagram the locus of such points, representing the limit of stability, is referred to as the spinodal (see Figure 5.6). Thus, for spinodal decomposition to occur, a spontaneous phase transition is necessary and the condition should apply. Within the spinodal region any phase separation can lower the free energy of the system and no nucleation step is required. Outside Figure 5.6. (a) Free energy-composition-temperature surface, showing the location of the spinodal (b) temperature-composition graph of the spinodal Figure 5.6. (a) Free energy-composition-temperature surface, showing the location of the spinodal (b) temperature-composition graph of the spinodal

Eo RT2F ln[PHPHc RT2F ln[Pc12

Gibbs free energy converted to electricity For a hydrogen oxygen fuel cell with liquid water as product, the Gibbs free energy change is -237 kJ per mole, equivalent to -118.5 MJ kg hydrogen and the higher and lower heats of combustion are2 142.5 and 121.0 MJ kg, resulting in maximum theoretical efficiency of 83 basis HHV which most accurately represents the reaction, but for comparison to conventional power systems, would be equivalent to 98 basis LHV.

Basic Thermodynamic Theory of Solute Distribution in Liquid Chromatography

The expression that relates the change in standard free energy of a solute when transferring from one phase to the other, as a function of the equilibrium constant (the distribution coefficient, K) is as follows where R is the gas constant, T is the absolute temperature and AG0 is the standard free energy change. Now The enthalpy term represents the energy involved when the solute molecule interacts by electrical forces with a molecule of the stationary phase. However, when interaction takes place, the freedom of movement of the solute molecule is also reduced and it can no longer move in the same random manner that it did in the mobile phase. This new motion restriction is measured as an entropy change. Thus, the free energy change is made up of an actual energy change which results from the work done during the interaction of the solute molecules with those of the stationary phase, and an entropy change that accounts for the resulting restricted movement or loss of randomness, when...

Stage II Diffusion Controlled Mass Transport

The densification or collapse of interface cavities during the second stage of diffusion bonding is attributable to the lowering of the surface free energy by the decrease in surface area. This takes place with the formation of new, but lower-energy, solid-solid interfaces. Because the driving force is the same (reduction of surface energy) for all systems, the considerable differences in behavior in various types of systems are related to the different mechanisms of material transfer.

Consolidation Processes

Where 7is the material surface free energy, is the relative density (P Pih) at some point during the consolidation process, and A0 is the relative density (PjPih) at the onset of consolidation. This relation yields surface pressures of approximately 1 to 10 MPa for nanocrystalline powder.

Flow Velocity of the Mobile Phase

In normal practice a thin-layer plate is immersed in a tank filled to a height z0 with the developing solvent. It has been shown that the migration of the mobile phase in a thin-layer plate may be compared to penetration of a liquid by diffusion in interconnected capillaries. A liquid enters a capillary because in doing so it decreases its free energy and more molecules

81 The Mechanical Driving Force

Given that displacive transformations in steels cause large strains, it is natural to expect an interaction between any applied stress and the progress of the transformation, in a manner which is related uniquely to the transformation mechanism. The total driving force can be partitioned into a mechanical and the more usual chemical components (Patel and Cohen, 1953 Delaey and Warlimont, 1975 Christian, 1982). The physical reasoning behind this idea is that the movement of a glissile interface is a combined deformation and transformation process. The work done by the external stress may be added to the chemical free energy change in order to obtain the total free energy difference. The mechanical driving force is assumed to be given by the work done (AGMEch) by the external stress system in producing the macroscopic shape deformation

Types of Polymorphic Transformation

Phase transformations are driven by the tendency for minimization of the Gibbs free energy of the system. In the absence of a liquid phase, the transformation of one polymorph to another of lower Gibbs free energy is possible in principle, but such a process is generally very slow due to the high activation energy associated with nucleation and growth of a new polymorph within the solid matrix of the old one.

Concentration of Organic Modifier in the Mobile Phase

Where kwB is the retention factor for analyte B in a water-buffer mobile phase, SB is a constant for a given analyte-solvent combination, and is the organic modifier concentration in the mobile phase. The thermodynamic interpretation of eqn 7 is that the free energy of adsorption of the analyte B to the

1132 Thermodynamic Aspects

The tendency for a particular reaction to occur is determined by the free-energy change that takes place when reactants come into physical contact with each other, for example, a water droplet on a steel structure. Given that corrosion is an electrochemical process, consideration of the electrode potentials of the half-cell reactions (see below), which occur at the anodic and cathodic sites, provides a more direct approach to assessing the tendency of a reaction. A corrosion cell consists of two half-cell reactions, which may or may not occur on the same electrode (see Fig. 11.1). In the case of Fig. 11.1a the two half-cells A and C are connected to complete the corrosion cell via a metallic path (i.e., a wire). Each half-cell can be designated as Ea or Ec, relating to whether or not an oxidation (anodic) or reduction (cathodic) reaction occurs. The total cell potential when two half-cells are coupled together is given by Faraday's law relates the free-energy change of a corrosion...

512 Heterogeneous nucleation

As the presence of a suitable foreign body or 'sympathetic' surface can induce nucleation at degrees of supercooling lower than those required for spontaneous nucleation, the overall free energy change associated with the formation of a critical nucleus under heterogeneous conditions AGcrit, must be less than the corresponding free energy change, AGcrit, associated with homogeneous nucleation, i.e.

91 Heating a Mixture of Austenite and Upper Bainitic Ferrite

If carbides precipitate during the bainite reaction then the final microstructure is unlikely to contain retained austenite. The sample must then be heated into the a + 7 phase field before austenite can nucleate first and then grow. Of course, if austenite exists in the starting microstructure, and if it remains stable during heating, then it can begin growth as soon as the free energy change becomes negative. For bainite, this may nevertheless require a substantial superheat because the transformation remains incomplete, i.e. it stops when x7 xTi rather than when x7 XAe3. The temperature therefore has to be raised until the carbon concentration of the residual austenite becomes equal to that given by the Ae3 phase boundary before the austenite can grow (Fig. 9.2).

57 Ostwalds rule of stages

0stwald (1896, 1897) attempted to generalize this sort of behaviour by propounding a 'rule of stages' which he stated as an unstable system does not necessarily transform directly into the most stable state, but into one which most closely resembles its own, i.e. into another transient state whose formation from the original is accompanied by the smallest loss of free energy. 0stwald recognized that there were many exceptions to this 'rule' and countless others have since been recorded. Thermodynamic explanations alone do not offer any theoretical support (Dufor and Defay, 1963 Dunning, 1969), but a combined thermodynamics-kinetics approach (Cardew and Davey, 1982) does appear to offer some justification, although the conclusion is that the rule has no general proof. A more recent proposal, based on the assumption of structural changes taking place in crystallizing solutions, has been offered as an alternative explanation by Nyvlt (1995) together with experimental evidence from...

64 Crystal habit modification 641 Crystal morphology and structure

A number of attempts have been made to predict the equilibrium form of a crystal. According to the Bravais rule (chapter 1), the important faces governing the crystal morphology are those with the highest reticular densities and the greatest interplanar distances, d i. Or, in simpler terms, the slowest-growing and most influential faces are the closest-packed and have the lowest Miller indices. The surface energy theories of crystal growth (section 6.1.1) suggest that the equilibrium form should be such that the crystal has a minimum total surface free energy per unit volume.

Kinetics of Nucleation and Polymorphism Pseudopolymorphism

A prerequisite for crystallization of a specific polymorphic phase is the formation of viable nuclei of that phase, nuclei being defined as the smallest molecular aggregates with a configuration resembling that of the final crystal. The probability of nucleation occurring increases with increasing supersaturation of the solution in such a solution, where incipient nuclei of all possible polymorphs may exist, kinetic factors determine which of these will become viable, i.e. lead to crystallization of a specific poly-morph. The critical parameter associated with the formation of a nucleus is the Gibbs free energy of activation, AG*. Nucleation, which proceeds with a rate dependent on AG*, may occur heterogeneously or homogeneously depending on whether random impurities or substrates promoting nucleation are present or not. In the former case, the mechanism of nucleation is associated with a reduction in AG*, relative to the uncatalysed process.

Continuum And Molecular Descriptions Of Smart Materials

Thermoplastic polymers are a class of materials whose behavior can be approximately represented by a CE like Eq. (9). These polymers are made of very long molecules, and have a backbone comprising several thousand atoms bonded covalently. These bonds have the possibility of rotating at the cost of some torsional energy, either by spontaneous thermal agitation or by the application of some external field (e.g., electrical) or deformation. Once the external effect disappears, these huge molecules tend to regain their average shape by releasing the torsional energy stored in the backbone of the molecule and adopting molecular conformations similar to the statistical coil (18). This tendency to go back to states of minimum free energy results in an approximately linear restoring force that acts on the whole molecule. This spring-like force opposes molecular stretching. If suspended in a liquid, that is, if the polymer molecule is in solution, it will also be subjected to random thermal...

Physical Principles

Experimentally, it has been observed that liquids placed on solid surfaces usually do not completely wet, but, rather, remain as a drop that has a definite contact angle between the liquid and solid phases (Ref 5). This condition is illustrated in Fig. 2. The Young and Dupre equation (Eq 1) permits the determination of change in surface free energy, AF, accompanying a small change in solid surface covered, AA (Ref 5). Thus,

The Basis of Chiral Recognition

The difference in free energy, AAG, needed for adequate chromatographic separation is influenced by the efficiency of the system employed. If the chromatographic system is of high efficiency, so that narrow peaks are observed, relatively small AAG values will afford acceptable analytical-scale enan-tiomer separations.

Process 2 Attachment Efficiency

These forces can accelerate, retard or even prevent the thinning of the liquid film between the particle and the bubble. From a thermodynamic point of view, the free energy of a liquid film differs from the bulk phase from which it is formed. This excess free energy was originally called the 'wedging apart' or 'disjoining' pressure by Derjaguin and represents the difference between the pressure within the film, pf, and that in the bulk liquid adjacent to the solid surface, p1. Note that for a bubble pushed against a fiat solid surface, immersed in water, pb, the pressure within the bubble, is equal to pf. Derjaguin and his school, as well as Scheludko, performed experimental measurements of disjoining pressures, providing both the first real verification of the DLVO theory of surface forces (named after Derjaguin, Landau, Verwey and Overbeek), as well as the first accurate experimental estimates of the Hamaker constant. The disjoining pressure (n)...

32 Solar Photovoltaics

Photovoltaic cells are devices that convert sunlight or solar energy into direct current electricity. They are usually found as flat panels, and such panels are now a fairly common sight, on buildings and powering roadside equipment, to say nothing of being on calculators and similar electronic equipment. They can also come as thin films, which can be curved around a car body. Solar radiation strikes the upper atmosphere with a value of 1300 Wm-2 but some of the radiation is lost in the atmosphere and by the time it reaches the Earth's surface it is less than 1000 Wm-2, normally called a 'standard sun'. Even in hot sunny climates solar radiation is normally less than this. Typical solar radiation on a flat plate constantly turned towards the sun will average around 750 Wm-2 on a clear day in the tropics and around 500 Wm-2 in more hazy climates such as the Philippines. For a flat plate such as a solar panel placed on a car roof, the sun will strike the plate at differing angles as the...

27 Radiation Climatology of Inclined Planes for Photovoltaics Applications

While national meteorological services normally concentrate on the provision of horizontal surface data, the practical utilisation of solar energy normally demands detailed design knowledge of the irradiation of inclined planes. Choice of a favourable collector orientation helps to reduce costs by increasing the radiant flux per unit collector area, so enabling a greater energy collection efficacy to be achieved per unit of investment. When the exposure of any site used for harnessing solar energy photovoltaically allows the most favourable orientations tend to be south facing in the northern hemisphere and north facing in the southern hemisphere. However, there are some climates where the afternoons are systematically cloudier than the forenoons. In these cases the true north-south orientation rule may be inappropriate. The appropriate choice of collector tilt and collector orientation is always an important decision. The most appropriate choice is strongly influenced by latitude. A...

Solar Thermal Energy Systems

Thermal energy generation from solar energy can be accomplished with a wide range of conversion devices, from passive and active space and water heating to high-pressure steam generation. Hot water is commonly generated using traditional solar plates, while high-pressure steam is raised in specially designed solar furnaces. Both systems operate by concentrating heat and transferring it to a fluid. A solar collector differs in several respects from more conventional heat exchangers. The latter usually accomplish a fluid-to-fluid exchange with high heat transfer rates and with radiation as an unimportant factor. In the solar collector, radiation is the primary mode of heat transfer. This radiant energy is then transferred to a fluid such as water or a water-glycol mixture. High-temperature systems feature heliostat, parabolic dish, or trough type collectors that intensely concentrate solar energy, allowing for generation of extremely high fluid temperatures sufficient to produce...

Availability Limitations

If the liquid is water, evaporation can be carried out in large ponds using solar energy. Aqueous waste can also be evaporated in closed process vessels using steam energy. The resulting water vapor can be condensed for reuse. Energy requirements are minimized by techniques such as vapor recompression or multiple effect evaporators. Evaporation is applied to solvent waste contaminated with nonvolatile impurities such as oil, grease, paint solids or polymeric resins. Mechanically agitated or wipe-thin-film evaporators (Figure 11.15.4) are used. Solvent is evaporated and recovered for reuse. The residue is the bottom stream, typically containing 30 to 50 solids.

4 Efficiencies using the Shockley Solar Cell Equation

A further step in finding the appropriate efficiency limits for single-junction solar cells can be made by estimating the relevant terms in the Shockley ideal solar cell equation (Equation (1) in Chapter IIa-1). To this end, further remarks must be made about the solar spectrum and solar energy incident on the Earth's surface. The ultimate efficiency, discussed in Section 3, was based on the black-body photon flux (Equation (6)), a rigorous thermodynamic quantity but not a very good estimate of the solar spectrum as seen on Earth. By virtue of the large distance between the Sun and the Earth, the radiative energy incident on the Earth's surface is less than that of Equation (6), by a factor flo which describes the size of the solar disk (of solid angle cos) as perceived from the Earth

1472 Evaporators with direct heating

The use of solar heat for the production of Glauber's salt has been described by Holland1-22'23-1. Brine is pumped in hot weather to reservoirs of 100,000 m2 in area to a depth of 3-5 m, and salt is deposited. Later in the year, the mother liquor is drained off and the salt is stacked mechanically, and conveyed to special evaporators in which hot gases enter at 1150-1250 K through a suitable refractory duct and leave at about 330 K. The salt crystals melt in their water of crystallisation and are then dried in the stream of hot gas. Bloch et al.(24), who examined the mechanism of evaporation of salt brines by direct solar energy, found that the rate of evaporation increased with the depth of brine. The addition of dyes, such as 2-naphthol green, enables the solar energy to be absorbed in a much shallower depth of brine, and this technique has been used to obtain a significant increase in the rate of production in the Dead Sea area.

Engineering Societies and Associations

Societies and associations have exerted a strong influence on the development of the designer, engineer, and other professionals. As an example the ASME (American Society of Mechanical Engineers) publishes the periodicals in order to keep individuals informed of new developments and forward other important information. Examples of the periodicals include (1) Applied Mechanics Reviews (monthly), (2) CIME (Computers in Mechanical Engineering, published by Springer-Veriag, New York), (3) Mechanical Engineering (monthly), and (4) Transactions (quarterly). The Transactions include the following areas heat transfer, applied mechanics, bioengineering, energy resources technology, solar energy engineering, dynamic systems, measurement & control, and engineering materials and technology.

Renewable and Alternative Electric Generation Options

Conventional technology application options and certain others are being made cost-competitive with financial support from various federal and state agencies and local utilities. The renewable technology options, namely those that use geothermal, wind, water, and solar energy sources, have no fuel-cost component. Given the recent rise in world energy costs, following a long period of flat and even declining prices, life-cycle costs of renewables have improved relative to traditional fossil fuel-driven applications. Still, in some cases, this is not sufficient to overcome high initial capital and or ongoing operations and maintenance cost premiums. Whereas geothermal and solar energy can be used for a variety of thermal applications, electric generation is generally limited to abundant high-temperature sources. Geothermal energy sufficient for electric generation application is limited to specific regions (e.g., the Western United States), where high-temperature sources can be...

1625 Sizing and Economics

An article on how to identify cost-effective solar-thermal applications is given in the ASHRAE Journal9. In almost any solar energy system the largest single expense are the solar collector panels and support structure. For this reason the system is usually sized in terms of collector panel area. Pumps, piping, heat exchangers, and storage tanks are then selected to match. High interest rates tend to reduce the economic viability of solar systems. High fuel costs obviously have the opposite effect, as does a longer life of the equipment. Federal and state tax credits would also have an important effect on the economics of solar energy as an

Groundsource Heat Pumps

Ground-source heat pumps are known by a variety of names geoexchange heat pumps, ground-coupled heat pumps, geothermal heat pumps, earth-coupled heat pumps, ground-source systems, groundwater source heat pumps, well water heat pumps, solar energy heat pumps, and a few other variations. Some names are used to describe more accurately the specific application however, most are the result of marketing efforts and the need to associate (or disassociate) the heat pump systems from other systems. This chapter refers to them as ground-source heat pumps except when it is necessary to distinguish a specific design or application of the technology. A typical ground-source heat pump system design applied to a commercial facility is illustrated in Figure 28.1.

Costs and Market Penetration Issues

Similar to wind power resources, the availability of solar energy is orders of magnitude greater than the country's current electricity requirements. In fact, it is estimated that PV modules covering just a few tenths of a percent of the land in the United States could supply for all of the nation's electricity requirements. As conversion efficiencies improve, this number will continue to get smaller. Perhaps, as capacity costs continue to come down while conventional energy costs rise, such concepts will be viewed as more realistic. However, large-scale market penetration has been difficult to date.

106Using Sustainable Energy with Fuelled Vehicles

The latter method can be carried out using sustainable forms of energy such as those discussed above. One advantage of using hydrogen as a fuel is that its production can be matched to alternative energy availability. For example it can be produced at times of high wind or solar energy availability. It can also be produced by conventional generating plant at off peak times, which enhances the general efficiency of electricity production.

13 Selfassembled Fullerene Architectures

More recently, Schuster and coworkers202 have successfully used this metal-templated strategy to build similar structures containing fullerenes as stoppers but including a porphyrin unit into the macrocycle. The fullerenes were functionalized using the Bingel reaction. These systems containing porphyrins are used to transmit and process solar energy into other energy sources. This topic will be analyzed in depth in forthcoming sections.

155 The Nuclear Controversy

First was the youth movement against authority and constraints. In that generation's search for a simpler and more primitive or natural life style, the use of wood and solar energy was preferred to energy based on the high technology of the establishment. Another target for opposition was the military-industrial complex, blamed for the generally unpopular Viet Nam War. A 1980s version of the anti-establishment philosophy advocated decentralization of government and industry, favoring small locally controlled power units based on renewable resources.

Availability and Reliability

Energy source interruption can result from market curtailments (e.g., interruptible natural gas service contracts), delivery system physical failure or a variety of force majeure conditions. With certain renewable resources, availability is limited due to dependence on energy sources subject to variation (e.g., sun and wind) as opposed to easily stored and metered fossil fuels. For example, with PVs and solar thermal steam generator systems, availability is limited to about 25 or 35 , regardless of equipment reliability, even in the most optimal solar energy locations. With WECS, availability can be much higher, but can still be subject to wide variability and unpredictability of prevailing wind speeds. Hydropower plants may have very high availability, but, like wind, can vary depending on site-specific factors, such as seasonal or daily water level variations.

279References for Chapter

Robert Stobaugh and Daniel Yergin, Editors, Energy Future, Report of the Energy Project at the Harvard Business School, Ballantine Books, New York, 1980. This edition is an update of the original (1979). The authors recognize the need to reduce imported oil, believe there is little chance to increase domestic production, find both coal and nuclear objectionable because of health and environmental side-effects, support conservation measures strongly, and urge development of solar energy.

Production Sintering Practices Sintering of Nickel and Nickel Alloys

Composition and dew point of a sintering atmosphere determine whether reducing or oxidizing conditions prevail during sintering of a given material. The Richardson free energy chart should be consulted for proper conditions. For example, in sintering of nickel at 1000 C (1830 F), according to the Richardson free energy chart, the hydrogen-to-water and carbon monoxide-to-carbon dioxide ratios must be > 0.01 to prevent oxidation of nickel. A reducing gas containing approximately 5 hydrogen, 5 carbon monoxide, 8 carbon dioxide, and the remainder nitrogen easily meets these requirements.

Ammonia Production Haber Process

Reactor For Petrochemicals

The production of ammonia is of historical interest because it represents the first important application of thermodynamics to an industrial process. Considering the synthesis reaction of ammonia from its elements, the calculated reaction heat (AH) and free energy change (AG) at room temperature are approximately -46 and -16.5 KJ mol, respectively. Although the calculated equilibrium constant Kc 3.6 x 108 at room temperature is substantially high, no reaction occurs under these conditions, and the rate is practically zero. The ammonia synthesis reaction could be represented as follows

Development of Theoretical Background in the Field of Ion Exchange

Some years later another model of ion exchange appeared, built on a molecular background rather than the macroscopic Gregor model. The model of Kachalsky (mid-1950s) presumes that the energy of electrostatic interaction which imparts changes in free energy of the system is uniformly distributed over the polymer chain between the ionogenic groups. The model describes the resin as a linear polyelectrolyte and provides an accurate description of ion exchangers with a small number of cross-linking bonds.

612 Adsorption layer theories

Expressions for the energy requirement of two-dimensional nucleation and the critical size of a two-dimensional nucleus may be derived in a similar manner to those for homogeneous three-dimensional nucleation (section 5.1.1). The overall excess free energy of nucleation may be written

65 Polymorphs and phase transformations

Under specified conditions of temperature and pressure, except at a transition point, only one polymorph is thermodynamically stable. All others are unstable and potentially capable of transforming to the stable polymorph. Whether they will do so, however, is another matter entirely. The more stable polymorph has the lower free energy at a given temperature. If polymorph II is more stable than polymorph I then the chemical potential of the species in the solid phase II is lower than that in solid phase I, i.e.

Stationary Power Generation

Cryogenic Stirling Engine

A major solar energy conversion demonstration is in progress for the U.S. Department of Energy in a program managed by the California Institute of Technology, Jet Propulsion Laboratory. This program includes the construction and evaluation in California of twenty-three 50 kW Stirling engines used in con junction with a similar number of solar collectors each 16 m (52 ft) in diameter. The engines to be used for this program are United Stirling P75, Siemens-type, four-cylinder machines derated to 50 kW. 'ITie program contractor is Ford Aeroneutronics. No doubt technical papers on this program will be appearing in the technical press in due course. The use of 23 engines provides a good probability for 20 systems to be operating continuously at any one time to provide a 20x50 1 mW capacity. It is said that electrical storage is to be included for power supply during the dark hours. Fig. 19.6. Stirling engine with solar energy input. with solar power systems offers a number of...

612 Evolution of the Nucleus

Widmanstatten Ferrite

Fig. 6.4 The free energy change necessary in order to obtain a detectable degree of transformation. Each point represents a different steel and there is no distinction made between Widmanstatten ferrite or bainite. (a) Calculated assuming the partitioning of carbon during nucleation. (b) Calculated assuming that there is no change in composition during nucleation. After Bhadeshia, 1981a. Fig. 6.4 The free energy change necessary in order to obtain a detectable degree of transformation. Each point represents a different steel and there is no distinction made between Widmanstatten ferrite or bainite. (a) Calculated assuming the partitioning of carbon during nucleation. (b) Calculated assuming that there is no change in composition during nucleation. After Bhadeshia, 1981a. where G w is the stored energy of Widmanstatten ferrite (about 50 Jmol-1). The first of these conditions ensures that the chemical free energy change exceeds the stored energy of the Widmanstatten ferrite, and the...

Displacement Reactions

The displacement reactions studied by MA are characterized by a large negative free energy change at room temperature and are therefore thermodynamically feasible at room temperature. However, commercial operations by pyrometallurgical techniques are conducted at elevated temperatures to overcome the kinetic barriers and achieve sufficiently high reaction rates. Mechanical alloying can provide the means to substantially increase the reaction kinetics of the displacement reactions because the repeated fracturing and welding of powder particles increases the area of contact between the particles and allows fresh surfaces to come into contact repeatedly. This allows the reaction to proceed without diffusion through the product layer. Additionally, the high defect densities induced during MA accelerate the diffusion process. As a consequence, these reactions will now occur at room temperature. If a reaction cannot occur at room temperature, the particle refinement and consequent reduction...

682 The Interface Response Functions

Where G* is an activation free energy and the pre-exponential factor V0 can be taken to be 30 ms-1 based on experimental data from single-interface martensitic transformations (Grujicic et al, 1985). The activation energy G* is a function of the net interfacial driving force G through the relation (Kocks et al, 1975) where G0* is the activation free energy barrier to dislocation motion in the absence of an interfacial driving force. The constants y and z define the shape of the force-distance function and for solid-solution interactions in the The diffusion field velocity depends on the compositions of the phases at the interface. These compositions are illustrated in Fig. 6.22, on a free energy diagram as a function of the amount Gdd of free energy dissipated in the diffusion

Stirling Engines For Space Power

The earlier program, sponsored by the U.S. Air Force, was executed by the Allison Division of General Motors and was directed to the design and development of a 3 kW (4 hp) solar space power-system. The Stirling engine, shown in Fig. 18.1, was a single-cylinder piston-displacer machine with rhombic drive and antecedents that were recognizably Philips. The engine used helium as the working fluid and was heated by solar energy concentrated by a large Fresnel lens. A comprehensive report (Parker and Malik 1962), in ten volumes, was prepared on the project and even at this late stage remains an interesting and worthwhile reference source. Volume I deals with the design of the engine and Volume 10 the test and evaluation of the prototype machine. So far as is known the unit never went beyond a first prototype and was never developed to the flight hardware stage. transfer heat from the solar energy absorber to the heater head of the engine. 'Hie use of an intermediate heating fluid is now...

Adsorptivebubble Separation Methods

FIG. 22-40 Normalized free-energy difference between distributed (II) and nondistributed (I) states of the solid particles versus three-phase contact angle (collection at the interface is not considered). A negative free-energy difference implies that the distributed state is preferred over the nondistributed state. Note especially the significant effect of n, the ratio of the liquid droplet to solid-particle radius. From Jacques, Hovarongkura, and Henry, Am. Inst. Chem. Eng. J., 25(1), 160 (1979). FIG. 22-40 Normalized free-energy difference between distributed (II) and nondistributed (I) states of the solid particles versus three-phase contact angle (collection at the interface is not considered). A negative free-energy difference implies that the distributed state is preferred over the nondistributed state. Note especially the significant effect of n, the ratio of the liquid droplet to solid-particle radius. From Jacques, Hovarongkura, and Henry, Am. Inst. Chem. Eng. J., 25(1), 160...

23 Combustion Properties

Adiabatic Equilibrium Images

The actual composition of the exhaust products from the combustion reaction depends on several factors including the oxidizer composition, the temperature of the gases, and the equivalence ratio. A diagram showing an adiabatic equilibrium combustion reaction is presented in Fig. 2.13. An adiabatic process means that no heat is lost during the reaction, or that the reaction occurs in a perfectly insulated chamber. This is not the case in an actual combustion process where heat is lost from the flame by radiation. Figure 2.14 shows the predicted major species for the adiabatic equilibrium combustion of CH4 as a function of the oxidizer composition. The calculations were made using a NASA computer program that minimizes the Gibbs free energy of a gaseous system 26 . An equilibrium process means that there is an infinite amount of time for the chemical reactions to take place, or the reaction products are not limited by chemical kinetics. In reality, the combustion reactions are completed...

Fundamentals of Corrosion of Coating Substrate Systems

Corrosion is based on the reaction of a metallic material or layer with its environment. The metal atoms of a component change from the metallic state into an oxidized state. The products may be dissolved species or solid corrosion products. The driving force of this process is the tendency of the system to lower its free energy.

Solar Cell Power Systems Design

The power subsystem takes the stabilization method as an input cue from the ARC subsystem to determine the area and mass scaling factors that will be used for power subsystem calculations. Solar panel area and mass scaling factor dependency on the selected stabilization method is approximately satellite's end-of-life (EOL) power requirement, working backward to determine the satellite's beginning-of-life (BOL) power requirement. BOL power is higher because solar cells degrade over the mission lifetime (influenced by solar cell type, mission altitude, and inclination), and the solar panels must be large enough to guarantee adequate EOL power. When the BOL power requirements are known, the next step is to size the solar array, batteries, power regulation, control, and distribution systems. Solar cell BOL watts area and watts mass are selected from a database, such as the example provided by Table 8-4 which lists average values for various solar cell types and array architectures. Solar...

134 Breeding and Uranium Resources

It is not possible to predict the rate of adoption of fast breeder reactors for several reasons. The capital costs and operating costs for full-scale commercial systems are not firmly established. The existence of the satisfactory LWR and the ability of a country to purchase slightly enriched uranium or MOX tends to delay the installation of breeders. It is conceivable, however, that the conventional converter reactors could be replaced by breeders in the coming century because of fuel resource limitations. It is possible that the breeder could buy the time needed to fully develop alternative sources such as nuclear fusion, solar power, and geothermal energy. In the next chapter the prospects for fusion are considered.

41 Energy Conservation ENC

Identify and describe both the positive and negative impacts of the two alternative means of power generation photovoltaic solar panels and hydroelectric dams. The principal materials used in photovoltaic solar panel power generation are the photovoltaic cells and water (for cooling). The potential impacts of solar cell power generation must be considered, as well as the potential impacts of the manufacturing of the cells themselves, and any batteries used to store energy during low solar radiation periods. Some negative impacts may include 3. Generation of hazardous waste from mining and production of materials in batteries used to store energy for later delivery to the public when solar energy is not available

02 Design theory and practice

Configurations was made abundantly clear from the reaction to the otherwise ingenious and low cost Sinclair C5 electric vehicle. While clearly launched as a motorized tricycle, with a price appropriate to that vehicle category, the C5 was nearly always referred to by its media critics as an 'electric car' when operationally it was more appropriate for use on reserved cycleways of which, of course, there are hardly enough in existence to create a market. While the Sunracer Challenge in Australia has shown the remarkable possibilities even for solar-batteried electric vehicles, it is doubtful whether the wider public appreciate the radical design of structure and running gear that make transcontinental journeys under solar power a reality, albeit an extremely expensive one for a single seater. Electric cars are perceived as 'coming to their own' in urban environments where high traffic densities reduce average speeds and short-distance average journeys are the norm. There is also...

Stirling Finkelstein 1959

Civil Engineering Engines

Crank-driven engines can be of the type used by Stirling, with a regenerative displacer, or may have a separate external regenerator of the Rankine-Napier type. The possibility exists for the necessary volume variations to be gained by an oscillating-cvlindei mechanism, but, so lar as is known, machines of this type have not been developed. Ihc free-piston engine is another interesting configuration. Such machines have been brought to an operational stage by William Beale of Sunpower Inc Athens. Ohio, and seem promising for wide future application. Machines of this type are being developed for solar power conversion, air-conditioning, and heat pumps, as described in Chapter 1 I.

1523 Crystal nucleation

Where AG is the overall excess free energy associated with the formation of the crystalline body, a is the interfacial tension between the crystal and its surrounding supersaturated fluid, and AGv is the free energy change per unit volume associated with the phase change. The term 4nr2a, which represents the surface contribution, is positive and is proportional to r2 and the term (4n 3)r3 AGv which represents the volume contribution, is negative and is proportional to r3. Any crystal smaller than the critical nucleus size rc is unstable and tends to dissolve whilst any crystal larger than rc is stable and tends to grow. Combining equations 15.7 and 15.8, and expressing the rate of nucleation J in the form of an Arrhenius reaction rate equation, gives the nucleation rate as

51 Primary nucleation 511 Homogeneous nucleation

Homogeneous Nucleation

Crystallization from melts and solutions. The free energy changes associated with the process of homogeneous nucleation may be considered as follows. The overall excess free energy, AG, between a small solid particle of solute (assumed here, for simplicity, to be a sphere of radius r) and the solute in solution is equal to the sum of the surface excess free energy, AGs, i.e. the excess free energy between the surface of the particle and the bulk of the particle, and the volume excess free energy, AGV, i.e. the excess free energy between a very large particle (r to) and the solute in solution. AGs is a positive quantity, the magnitude of which is proportional to r2. In a supersaturated solution Gv is a negative quantity proportional to r3. Thus where AGV is the free energy change of the transformation per unit volume and 7 is the interfacial tension, i.e., between the developing crystalline surface and the supersaturated solution in which it is located. The term 'surface energy' is...

Multiphase Flow Concepts

On all interfaces between solids and fluids, and between immiscible fluids, there is a surface free energy resulting from electrical forces. These forces cause the surface of a liquid to occupy the smallest possible area and act like a membrane. Interfacial tension (IFT) refers to the tension between liquids at a liquid liquid interface. Surface tension refers to the tension between fluids at a gas liquid interface.

62 Possible Mechanisms of Nucleation

Widmanstatten Ferrite

Phase fluctuations occur as random events due to the thermal vibration of atoms. An individual fluctuation may or may not be associated with a reduction in free energy, but it can only survive and grow if there is a reduction. There is a cost associated with the creation of a new phase, the interface energy, Fig. 6.6 (a) Free energy curves for the nucleation of Widmanstatten ferrite and bainite in a low alloy steel for which the AGm and GN curves exhibit a double intersection, (b) Calculated TTT diagram for the same steel, showing how Widmanstatten ferrite and bainite form separate C curves, The Widmanstatten ferrite and bainite C curves would ordinarily be just one curve, joined by the line wxyz. After Ali and Bhadeshia (1991). Fig. 6.6 (a) Free energy curves for the nucleation of Widmanstatten ferrite and bainite in a low alloy steel for which the AGm and GN curves exhibit a double intersection, (b) Calculated TTT diagram for the same steel, showing how Widmanstatten ferrite and...

611 Transformation Start Temperature

Widmanstatten Ferrite

Nucleus can develop into either phase depending on the prevailing thermodynamic conditions. The analysis proves that carbon must partition during the nucleation stage in order always to obtain a reduction in free energy. The situation illustrated in Fig. 6.4b is not viable since diffusionless nucleation would in some cases lead to an increase in the free energy. The plots in Fig. 6.4 are generated using data from diverse steels. Figure 6.4a represents the free energy change AGm at the temperature where displacive transformation first occurs. The free energy change can be calculated from readily available thermodynamic data. It follows that Fig. 6.4a can be used to estimate for any steel. The equation fitted to the data in Fig. 6.4a is (Ali and Bhadeshia, 1990)

Thermodynamic Aspects of Polymorphism

What Represents Gibbs Free Energy

Thermodynamic treatment of a system displaying polymorphism is based on considerations of the Gibbs free energy, Gi, of each polymorph as well as the variation of Gi with the thermodynamic variables temperature (T) and pressure (p). Furthermore, since each polymorph is distinct, each has a characteristic value for its entropy, Si ( > 0), under any given conditions of T and p. Considering constant pressure, the thermodynamic relationship (3Gl dT)p Si therefore indicates that the slope of the G-T curve for each polymorph of a compound at any given value of T is (a) negative and (b) different. The stable phase at any given temperature is that polymorph with the lowest value of G, and since the G-T curves for the various polymorphs will generally intersect one another at various temperatures owing to their different slopes, it follows that at a given T, one polymorph will be stable and all others metastable with respect to it. When two G-T curves intersect, the polymorphs they represent...

Phase Diagram Civil Engineering

A phase boundary must extrapolate into a two-phase field after crossing an invariant point. The validity of this feature, and similar features related to invariant temperatures, is easily demonstrated by constructing hypothetical free-energy diagrams slightly below and slightly above the invariant temperature and by observing the relative positions of the relevant tangent points to the free energy curves. After intersection, such boundaries can also be extrapolated into metas-table regions of the phase diagram. Such extrapolations are sometimes indicated by dashed or dotted lines.

Adhesion Means In Civil Engg

The excess energy associated with an interface is formally defined in terms of a surface energy. This may be expressed in terms either of Gibbs, GE, or Helmholtz, free energies. In order to circumvent difficulties associated with the unavoidably arbitrary position of the 'surface' plane, the surface energy is defined as the surface excess 7,8 , i.e the excess (per unit area) of the property concerned consequent upon the presence of the surface. Thus Gibbs surface free energy is defined by where A is the area of the surface, G is the total value of the Gibbs free energy in the system and Gb is the value the total Gibbs free energy would have if all the constituent particles (atoms, molecules etc.) were in the same state as they are in the bulk of the phase.

4 The Stochastic Generation of Solar Radiation Data

There is normally considerable variation in the global irradiation from day to day especially at high latitudes. The alternation of anti-cyclonic and cyclonic conditions causes large variations in cloud amount and in sunshine amounts. This results in a highly variable supply in the available daily solar energy in such regions. This is especially true for areas exposed to a strong maritime influence. The desert climates in contrast show much less day to day variation in irradiance. Some humid tropical climates have some cloud nearly every day. In such regions, cloudiness often develops progressively across the day due to vertical convection as the ground warms. Other climates are linked to strongly defined wet and dry seasons, for example the Monsoon climates of South-East Asia. There still remains a lot of work to be done in developing sound stochastic models covering the wide range of climates found across the world.

663 Growth Rate of Sub Units of Bainite

There are interesting observations on the thickening of bainite sub-units. The thickness can increase even after lengthening has halted. An elastically accommodated plate tends to adopt the largest aspect ratio consistent with a balance between the strain energy and the free energy change driving the transformation, Fig. 6.17, in order to achieve thermoelastic equilibrium (Olson and Cohen, 1977).

97 Other Propulsion Devices

Wind is not the only free energy source available to ships and a system invented by a Norwegian engineer utilises wave power. This device is said to be limited to ships of up to 50 m in length and it must be admitted that its extension to larger ships would seem unlikely. The device consists of a moveable foil placed horizontally on an axis beneath the vessel and arranged to have an angle of attack which results in its vertical movement as the ship moves in the waves providing a horizontal force imparting forward movement.

Properties And Uses Of Carbon Black

Carbon black is also used as a pigment for paints and printing inks, as a nucleation agent in weather modifications, and as a solar energy absorber. About 70 of the worlds' consumption of carbon black is used in the production of tires and tire products. Approximately 20 goes into other products such as footwear, belts, hoses, etc. and the rest is used in such items as paints, printing ink, etc. The world capacity of carbon black was approximately 17 billion pounds in 1998.13 U.S. projected consumption for the year 2003 is approximately 3.9 billion pounds.

1532 Evaporating crystallisers

If the solubility of a solute in a solvent is not appreciably decreased by lowering the temperature, the appropriate degree of solution supersaturation can be achieved by evaporating some of the solvent and the oldest and simplest technique, the use of solar energy, is still employed commercially throughout the world(66). Common salt is produced widely from brine in steam-heated evaporators, multiple-effect evaporator-crystallisers are used in sugar refining and many types of forced-circulation evaporating crystallisers are in large-scale use(3'40'67). Evaporating crystallisers are usually operated under reduced pressure to aid solvent removal, minimise heat consumption, or decrease the operating temperature of the solution, and these are described as reduced-pressure evaporating crystallisers.

Types of Heat Source and Heat Sink Media

Solar Energy Solar energy can be an effective heat pump heat source. When available, it provides heat at a higher temperature than other conventional sources, which produces a greater heating COP. The advantage of using solar as a heat pump heat source instead of directly for heating is that collector efficiency and capacity is increased due to a lower temperature requirement.

Very Little Diffusion Occurs Across The Bond Interface

Oberg et al. (Ref 34) used the Miedema model for alloy formation to explain the metallurgical details of explosion bonds. In their analysis, they suggest strong correlations between interfacial bond strength and the formation energies between binary alloy constituents. If the theoretical formation energy, yAB, is high, then a low bonding success would be predicted, indicating that low formation energies are preferred. Also, if the chemical portion of the interfacial free energy, gAhr,

44 Thermodynamics of fuel cells

A true direct energy conversion device is one which can convert the Gibbs free energy of a chemical reaction directly into work. A fuel cell converts the Gibbs free energy of a chemical reaction into a stream of electrons under isothermal conditions. The change in Gibbs free energy of a reaction is given by

Editors

Kreider, Ph.D., P.E. is professor of engineering and founding director of the University of Colorado's (CU) Joint Center for Energy Management. He is cofounder of the Building Systems Program at CU and has written seven textbooks on alternative energy, two books on building systems and other energy related topics, and more than 175 technical papers. He is president of Kreider and Associates, LLC, an energy consulting company. For 10 years he was a technical editor of the ASME Transactions Journal of Solar Energy Engineering.

11 Forces and Energy

Energy can be classified according to the primary source. We have already noted two sources of energy falling water and the burning of the chemical fuel gasoline, which is derived from petroleum, one of the main fossil fuels. To these we can add solar energy, the energy from winds, tides, or the sea motion, and heat from within the earth. Finally, we have energy from nuclear reactions, i.e., the burning of nuclear fuel.

Scott Frazier

DOE) funds a program where universities around the country operate Industrial Assessment Centers which perform free energy audits for small and medium sized manufacturing companies. There are currently 30 IACs funded by the Industrial Division of the U.S. DOE.

Attainable Regions

Clearly the choice of a suitable reagent is critical and is highly specific to a particular separation. Although the choice of reagent(s) for a particular separation usually has evolved with experience, the search for ever more effective reagent mixtures is an area of continuing research and development. A sound basis for these investigations is to develop an understanding of the free energy changes at the solid-water and bubble-water interfaces, consequent on changes of the reagent types and conditioning procedures.

Distance

Figure 1-17. (a) Free-energy variation with atomic distance in the absence of an applied field, (b) Free-energy variation with atomic distance in the presence of an applied field. Figure 1-17. (a) Free-energy variation with atomic distance in the absence of an applied field, (b) Free-energy variation with atomic distance in the presence of an applied field. The discussion to this point is applicable to motion of both impurity and matrix atoms. In the latter case we speak of self-diffusion. For matrix atoms there are driving forces other than concentration gradients that often result in transport of matter. Examples are forces due to stress fields, electric fields, and interfacial energy gradients. To visualize their effect, consider neighboring atomic positions in a crystalline solid where no fields are applied. The free energy of the system has the periodicity of the lattice and varies schematically, as shown in Fig. l-17a. Imposition of an external field now biases the system such...

Products

Free-energy path for thermodynamically favored reaction 1 2. where G* is the free energy of activation. As before, the Boltzmann factors represent the probabilities of surmounting the respective energy barriers faced by reactants proceeding in the forward direction, or products in the reverse direction. When chemical equilibrium prevails, the competing rates are equal and rN 0. Therefore,

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