Polytropic expansion and compression

If no Mollier diagram is available, it is more difficult to estimate the ideal work in compression or expansion processes. Schultz (1962) gives a method for the calculation of the polytropic work, based on two generalised compressibility functions, X and Y which supplement the familiar compressibility factor Z. 

At conditions well removed from the critical conditions equations 3.36, 3.37 and 3.38 reduce to  

10 REM SHORT ENERGY PROGRAM, REWRITTEN IN GWBASIC, MARCH 92 20 PRINT HEAT BALANCE PROGRAM, BASIS kmol/h, TEMP K, DATUM 298 K  

50 PRINT INPUT HEAT CAPACITY DATA FOR EQUATION A+BT+CT 2+DT 3  

80 PRINT FOR COMPONENT I INPUT A, B, C, D, INCLUDING ANY ZERO VALUES  

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Polytropic process. Compression and expansion are important processes in chemical industry. The changes in enthalpy and... 

Close to the critical conditions, these equations should not be used. The procedure for calculation of polytropic work of compression or expansion close to the critical point is more complex (Shultz, 1962), and it is easiest to make such calculations using process simulation programs. 

Adiabatic expansion of the air in the engine causes a maximum temperature drop of the exhaust. Adiabatic compression causes a maximum temperature rise of the compressed air. These effects combine to cause the greatest work loss of any compressed-air system, when pressurized air must be cooled back to atmospheric temperature. The energy analysis parallels the one just made for the polytropic system. This shows that net areas on both PV and TS graphs measure the work lost. 

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