Thermodynamic optimization of irreversible refrigerators

• Dimensionless equation that links COP, entropy rate variation and heat exchange.
• Maximum COP as function of parameter controlling thermal exchanges.
• Application at irreversible vapor compression refrigerator based on literature data.
• Results show the analysis is useful in diagnostic and designing of refrigerators.

An irreversible inverse cycle, operating at steady state conditions with finite thermal capacity heat sources, is analyzed in order to obtain an expression for the coefficient of performance accounting for the Second Law. Some dimensionless parameters are proposed to link the entropy variation rate and the temperature differences at the heat exchangers to the cycle efficiency. A maximum for efficiency appears when a parameter depending only on the temperature of the inlet streams at each heat exchanger is used. The influence of dimensionless parameters and irreversibilities on the maximum cycle efficiency is analyzed. A graphical analysis, based on data from literature, is presented to show the use of this thermodynamic optimization criteria in design and verification process of refrigerators.