whereg/go = 1 lbf/lbm; but when using SI units,g/go is replaced by 9.80665 m/s2 (= g in the SI system). ATc is due to the compression of the liquid and is not a consequence of loss or dissipation as is the term involving the pump efficiency h (see Section 2.1). As shown in Reference 1 of Section 2.1, ATcis 3°F per 1000 psi (0.24°C per MPa) of pump pressure rise for hydrocarbon fuels. For boiler feedwater at 350°F (177°C), ATc = 1.6°F per 1000 psi (0.129°C per MPa), but it is much smaller for cold water. By consulting tables of properties for the liquid phase of the fluid being pumped and assuming the compression process between the actual inlet and discharge pressures to be isentropic, ATc can be determined. This is important if Eq. 33 is used to evaluate overall pump efficiency from temperature rise measurements. AT and ATc are often of the same order of magnitude at BEP, and serious errors have been made by excluding ATc from the efficiency computation. At very low, off-BEP flow rates, AT will be high in comparison to ATc; so, the latter can be safely ignored in temperature rise calculations at such low-efficiency conditions.

In practice, determination of efficiency from AT-measurements is accomplished by the direct thermodynamic method54, rather than by the ATc-method. Both approaches are based on the definition of pump efficiency as the ratio of an isentropic rise of total enthalpy (= gAH) to the actual rise of total enthalpy (Eq. 1 of Section 2.1), allowances being made for the usually small external power losses that do not appear in the pumped fluid (such as bearing drag) and the similarly small effects of heat transferred between pump and surroundings. In the direct thermodynamic method, the enthalpy rise Ah is found from the chain rule,

Survival Treasure

Survival Treasure

This is a collection of 3 guides all about survival. Within this collection you find the following titles: Outdoor Survival Skills, Survival Basics and The Wilderness Survival Guide.

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