Ch 6. Entropy Multimedia Engineering Thermodynamics Entropy Tds Relations EntropyChange IsentropicProcess IsentropicEfficiency EntropyBalance (1) EntropyBalance (2) ReversibleWork
 Chapter 1. Basics 2. Pure Substances 3. First Law 4. Energy Analysis 5. Second Law 6. Entropy 7. Exergy Analysis 8. Gas Power Cyc 9. Brayton Cycle 10. Rankine Cycle Appendix Basic Math Units Thermo Tables Search eBooks Dynamics Statics Mechanics Fluids Thermodynamics Math Author(s): Meirong Huang Kurt Gramoll ©Kurt Gramoll

 THERMODYNAMICS - CASE STUDY Introduction Heat Exchange in the Evaporator According to a recent new law, refrigeration systems are no longer allowed to use refrigerant R-12 due to environmental concerns. A cryogenic manufacturing facility has to choose a new refrigerant to replace R-12 used in its refrigeration systems. Refrigerant R-134a is one choice which satisfies the energy requirement. To further evaluate this new refrigerant, the entropy changes need to be determined. What is known: Refrigerant R-134a enters the evaporator of the refrigeration system as a saturated liquid-vapor mixture at a pressure of 200 kPa. Refrigerant R-134a leaves the evaporator as saturated vapor at a pressure of 200 kPa. Refrigerant R-134a absorbs 150 kJ of heat from the cooled space. The cooled space of the refrigeration system is maintained at -4oC. Question Determine the entropy change of refrigerant R-134a. Determine the entropy change of the cooled space. Determine the total entropy change of the whole process. Approach The evaporator is a heat exchanger which has one inlet and one exit. Refrigerant R-134a enters the evaporator as a saturated liquid-vapor mixture and leaves the evaporator as saturated vapor. Hence the temperature in the evaporator remains constant at the saturation temperature of 200 kPa.