006

Fig. k.2u. Isothcims for water on pressure-volume plane \prepared from the Electrical Research Association's Steam TaiuV.v, E. J. Arnold Ltd.. London. 1967).

fluids had been assessed including petrols (gasoline), spirits, liquid carbon dioxide, sulphur dioxide, but water was the preferred medium. In a discussion of the desirable fluid properties he mentioned, in passing, possibilities for compound working fluids of immiscible liquids, and for separate working fluids in the hot and cold regions (separated perhaps by buoyancy forces) raising intriguing prospects lor future research.

The very high pressures in dense-phase engines require the use of thick cylinder walls. Therefore, to minimize thermal conduction losses the displacer cylinder is bound to be a long cylinder of small diameter. Furthermore, because of the extremely high rates of pressure change, the swept volume of the piston will be very small. To reduce cylinder wall thickness and hence weight, a small diameter and relatively long stroke would be used.

effective form of power control for it would vary the mass How of lluid passing from the cold space to the hot space and hence the range of the pressure amplitude. The exact form of his power control system was not given but appeared to involve the use of a rack-and-pinion gear on the displacer rod.

The high density of the dense phase working fluid would almost certainly preclude operation at high speed. Therefore, the engines would likely be heavy, slow-running machines having thick cylinder walls and very high pressures. What then are the advantages of dense-phase machines that warrant further research attention? One advantage compared with gaseous machines is the very high rates of heat transfer attainable with liquids and their very high specific heats or heat capacities. Secondly, the seal problem for liquids are likely to be easier to handle despite the very high pressures involved. Thirdly, the fluid serves well as a lubricant. A unique and peculiar advantage of the liquid engine is the inherent self-pressurizing characteristic. This may be clearly seen by reference to Fig. S.20. Consider, for example, an engine at ambient temperature containing liquid water at atmospheric pressure. If the hot parts are heated the pressure level will increase automatically because the heated medium in the hot zone will expand and compress the remaining fluid in the engine as a result of the very high (dp/do) characteristic evident in Fig. K.20.

One likely application for a Malonc engine is a solar-powered water pump. A water pump using water as the working lluid has evident advantages. Moreover, it can be seen from Fig. 8.20 that appreciable changes in specific volume occur at moderate temperature changes. Therefore, relatively unsophisticated, low-cost solar collectors might be used although, of course, the power density and efficiency would be very low.

The attraction of such a system would be enhanced if the engine could be made self-starting. It is not evident how this might be done, although there is every reason to believe that novel and ingenious free-piston/free-displacer mechanisms could be made that would share with the Beale free-piston Stirling engine the characteristic of inherent self-starting capability (see Chapter I I). The field appears wide open for innovative research and novel developments in Malone dense-phase or liquid-cycle engines.

Solar Stirling Engine Basics Explained

Solar Stirling Engine Basics Explained

The solar Stirling engine is progressively becoming a viable alternative to solar panels for its higher efficiency. Stirling engines might be the best way to harvest the power provided by the sun. This is an easy-to-understand explanation of how Stirling engines work, the different types, and why they are more efficient than steam engines.

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