Answer to Question #296291 in Thermal Power Engineering for mahf

Question #296291

Refrigerant-134a is to be cooled by water in a condenser. The refrigerant enters the condenser with a mass flow rate of 6 kg/min at 1 MPa and 70ºC and leaves at 35°C. The cooling water enters at 300 kPa and 15°C and leaves at 25ºC. Neglecting any pressure drops, determine (a) the mass flow rate of the cooling water required and (b) the heat transfer rate from the refrigerant to water


1
Expert's answer
2022-02-14T00:01:02-0500

Part A


Taking the compressed water as a saturated liquid:

Internal energy at 15°C,  hf1=62.982kJkg115°C,\>\>h_{f1}=62.982kJkg^{-1}


Internal energy of water at 25° C,

hf2h_{f2} =104.83kJ/kg=104.83kJ/kg


The refrigerant enters the condenser as superheated vapor at 70°C and leave as compressed liquid at 35°C.


Internal energy of superheated vapor R -134a at 70°C

hf3h_{f3} =303.87kJ/kg=303.87kJ/kg


Internal energy of compressed liquid R-134a at 35°C

hf4=100.88kJ/kgh_{f4}=100.88kJ/kg


Taking mw=m_w= Flow rate of water


mw(104.8362.982)=6(308.87100.88)m_w(104.83-62.982)=6(308.87-100.88)


mw=29.1kg/minm_w=29.1kg/min


Part B

Change in energy of water =(104.8362.982)kJ/kg=(104.83-62.982)kJ/kg

Rate of flow of water =29.1kg/min=29.1kg/min


Heat transfer rate =29.1×(104.8362.982)=29.1×(104.83-62.982)

=1217.8kJ/min=1217.8kJ/min




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