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THE FINKIit.STI.ilN AD1ABATIC CYCLE

Finkelstein (1960a) devised a generalized thermodynamic analysis of Stirling engines in which the processes of compression and expansion were not confined to isothermal conditions. In this generalized analysis the processes of compression anil expansion in //it- engine cylinders could be specified to occur anywhere between the two limiting cases:

(a) isothermal (infinite rates of heat transfer between the working gas and the cylinder walls).

(b) adiabatic (zero rates of heat transfer between the working gas and the cylinder walls).

The model assumed that, in the heater and cooler, infinite lieat transfer and isothermal conditions prevailed so that fluid in the heat exchangers was always at the upper temperature 7'n or the lower temperature Tc.. 'I he temperature of the working fluid in the cylinders varied during the cycle and could be greater or less than (in the expansion space) or Tt (in the compression space).

Finkelstein's generalized analysis retained all the other significant assumptions enumerated above for the Schmidt cycle so that it remained highly idealized. Nevertheless the possibility for non-isothermal processes represented the most significant theoretical development in nearly a century.

The limiting isothermal case of Finkelstein's theory corresponded exactly to the Schmidt cycle and equations were given for the adiabatic limiting case and for other cases intermediate between these limits. The theory was readily amenable to numerical analysis by standard methods. Significant simplification of the generalized analysis was attained by the assumption of adiabatic conditions (zero heal transfer) in the compression and expansion cases.

fn his presentation. Finkelstein included only »>rie Set of numerical results. This referred to a heat pump with the temperature ratio r = /'f/7'c — 2. The coefficient of performance of 1.0 with isothermal processes was reduced to 0.543 with adiabatic processes. Similarly Stoddart (I960) found that a Stirling engine prime mover having a Schmidt cycle (Carnot) efficiency of 50 per cent with isothermal compression and expansion

THEORETICAL ANALYSIS OF STIRLING ENGINES 59

## 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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