We consider a vapour compression refrigeration cycle, as illustrated below (ref. Smith, van Ness and Abbott) Thea Valve Compresor Evaporate Figure The refrigerant is FREON-22, the temperature in the evaporation process is 250 K while the temperature of the condenser is 310 K. a) Assume the compression step is isentropic, so that we follow the dashed lines in the figures from 2 to 3'. Use preos.xlsx and reference state 1 to calculate the pressures, temperatures, molar entropies and molar enthalpies at points 1, 2, 3' and 4. These data should be presented in a table. This table should also give the state of the system at these points (i.e. vapour, liquid or a mixture) and, in the case of a vapour liquid mixture, should also give the proportion of vapour and liquid. Brief descriptions should be given explaining how you got these quantities, including, where appropriate, the mathematical equations used. Relevant copies of the preos.xlsx output should be provided as an appendix. (8 marks) b) Use these data to calculate the coefficient of Performance (COP) of the cycle. (1 mark) c) Now assume the compressor has an efficiency of 0.8, so the compression step now goes from 2 to 3. Calculate the molar entropy at point 3 and re-calculate the COP. (4 marks) d) Would replacing the throttle by an expander improve the COP of the vapour-liquid refrigeration cycle? Give reasons for your answer. (2 marks)