(Solved): A direct expansion tubular evaporator with refrigerant R134a operates at the average saturation te ...

A direct expansion tubular evaporator with refrigerant R134a operates at the average saturation temperature of 5°C. The evaporator consisted of 120 tubes with inner diameter of 10 mm and length of 1 m. The average vapor fraction of refrigerant in the mixture (liquid-vapour) zone is 0.7. The superheated R134a vapour region occupies 30% of the volume of evaporator. The properties of R134a at 5°C are available in Table Q1. a) Calculate the total mass of R134a inside the evaporator (15 marks) Temp Quality Press Density Enthalpy Viscosity Therm Cond [C] [mol/mol] [MPa] [kg/m^3] [kJ/kg] [H Pas] [W/m-K] 5.000 0.0 0.3497 1278 206.8 254.4 0.08980 5.000 1.0000 0.3497 17.13 401.5 10.94 0.01195 Table Q1: Properties of R134a at 5°C b) The condenser is operating at 10 bar with 10 Kelvin of sub-cooling. Evaluate whether the mass of refrigerant in the evaporator calculated in Part(a) can produced 200 kW of heating effect at the condenser. The p-h diagram of R134a is available in the Appendix. (Take the mass flowrate of refrigerant (in kg/second) through condenser is equal to the mass of refrigerant inside the evaporator) (5 marks) c) What is the effect of superheated region in the condenser on the heating effect produced by this refrigeration cycle? (5 marks) p/bar 100 10 1 0.1 100 p-h Diagram for R134a Plotted by: J P M Trusler Reference state: h/(kJ-kg ¹) = 200 and s/(kJ-K¹-kg-¹) = 1.00 for saturated liquid at T = 0°C. TI°C 5/(kJ-K-¹-kg-¹) v/(m³-kg¹) Quality 30 20 -20 -50 406 -30 0.11 0.2 # 10 0.3 200 0.4 14 18 1.22 26 0.5 50 APPENDIX 80 0.6 60 70 90 0.9 100 0.7 0.8 300 h/(kJ-kg-¹) 110 120 -50 40 -30 -20 -10 0 400 10 02 20 QUE -0% 1.70 40 50 0.002 1.74 09 1.78 60 70% 80 06 1.82 0.005 1.900.01 1.94 0.02 1.98 XA 1.86 100 110 120- 130. 2.000.05 2.10 2.14 2.18 0.2 2.22 2.20 -0.1 Ot 2.30 500 ? Imperial College London 2003 40.5 150