Suppose a R-134a refrigeration system looks like Figure below, and has the follo

Question

Suppose a R-134a refrigeration system looks like Figure below, and has the following
fluid states:
1. entering the compressor, saturated vapor at 280kPa
2. exiting the compressor, 800 kPa, 40oC (superheated)
3. exiting the condenser, 800 kPa, x=0
4. exiting the adiabatic throttling process at 280 kPa
Determine (a) all 4 states specific enthalpies, (b) the evaporator cooling heat transfer
per unit mass, (c) the compressor work per unit mass, (d) the COP in cooling.

Suppose a R-134a refrigeration system looks like Figure below, and has the following fluid states: entering the compressor, saturated vapor at 280kPa exiting the compressor, 800 kPa, 40 degree C (superheated) exiting the condenser, 800 kPa, x=0 exiting the adiabatic throttling process at 280 kPa Determine (a) all 4 states specific enthalpies, (b) the evaporator cooling heat transfer per unit mass, (c) the compressor work per unit mass, (d) the COP in cooling.

Explanation / Answer

(a)

Using the Refrigeration table (Poprties of R-134A)

H1(Specific enthalpy at entering of compressor)=249.72 KJ/Kg

H2(Specific enthalpy at outlet of compressor,in superheated region)=276.45 KJ/Kg

H3(sp. enthalpy at exit of condensor)=95.47 KJ/Kg

H4=H3(throttlinh process)=95.47 Kj/kg

(b)

evaporator cooling heat transfer per unit mass=H2-H3=180.98 KJ/Kg (Ans)

(c)
the compressor work per unit mass=H2-H1=26.73 KJ/kg (Ans)

(d)COP of cooling=heat rejected/work input=180.98/26.73=6.77 (Ans)

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