Problem 6.6 - Adiabatic Evaluation of a R134a Compressor

A young engineer was assigned to evaluate the compressor of a proposed R-134a refrigeration system shown below, and assumed it to be adiabatic.

• a) Under this assumption, and ignoring kinetic and potential energy effects, determine the specific work input to the compressor [48.3 kJ/kg].

• b) His supervisor checked the results and told him that his assumption was incorrect and not physically feasible. On the h-s diagram below draw the actual compression process (as assumed) as well as the equivalent isentropic compression process. Using this diagram, as well as relevant data evaluated at the inlet and outlet of the compressor, explain how she arrived at that conclusion.

Derive all equations used starting from the basic energy equation and the equation for entropy generated.