Question

5. A commercial refrigerator uses 134a refrigerant to keep the space refrigerated at −30 ° C by rejecting its waste heat into cooling water entering the condenser at 101,325 kPa, at the rate of 0.25 kg / s. The refrigerant is fed to the compressor at -25 ° C and 100 kPa. Use a software and determine the quality of the refrigerant at the inlet of the evaporator and the COP of the refrigerator using the conditions shown in the figure.

26°C Water 18°C 1.2 MPa 42°C Condenser Expansion valve Evaporator со с Compressor

Answer 1

Since no software is mentioned specifically in the question, I am using EES (Engineering Equations Solver) software for calculation of this answer.

Code:

Plots Windows Help Exampl Egy EES Commercial Version: - [Equations Window] Egy File Edit Search Options Calculate Tables BOE BOOBS {Given Data} P_cond = 1200 P_evap = 100 T_comp_in = -25 T_cond_out = 42 {Internal Calculations} h_comp_in = ENTHALPY(R134a, T=T_comp_in P=P_evap) S_comp_in= ENTROPY(R134a, T=T_comp_in.P=P_evap) s_comp_in= ENTROPY(R134a.h=h_comp_out, P=P_cond) h_cond_out = ENTHALPY(R134a.T=T_cond_out,P=P_cond) h_cond_out = h_evap_in {Calculation of Quality} h_evap_in = ENTHALPY(R134ax = Quality,P=P_evap) {Calculation of COP} 1/COP = (h_comp_out-h_comp_in)/(h_comp_in - h_evap_in)

The results:

L.... L EE, EES Commercial Version: File Edit Search Options Calculate Tab OS 300 ✓ Egy Solution Unit Settings: [kj]/[C]/[kPa]/[kg]/[degree COP = 2.372 comp.in = 235.5 [kJ/kg] "comp.out = 287.9 cond,out = 111.2 hevap.in = 111.2 Pcond = 1200 Pevan = 100 Quality = 0.4326 $comp.in = 0.9562 [kJ/kg-K] Tcomp.in=-25 Tcond,out = 42 Calculation time - 0 sec

The answers:

• COP = 2.372
• Quality = 0.4326

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