R & A/C Quiz 2
(MEC 256model answer
Oct 2024)
Quiz 2, gr. 22
A vapor compression cycle using R12 operates with capacity of 500 ton refrigerant.
• The condenser Pressure is 0.7 MPa.
• The Refrigerant temperature at the compressor inlet is -5 °C. (just after the suction valve)
• After the isentropic compression process through the compressor had end, The
Refrigerant temperature increased to 80 °C (just before the discharge valve) .
• The refrigerant enters expansion valve at 0°C.
• Pressure drop across evaporator and condenser tubes is 0.01 and 0.2 MPa respectively .
• Pressure drop: across suction valve and across discharge valve is 0.01 Mpa and 0.1 Mpa
respectively.
• The increase in enthalpy in expansion valve is 10 Kj/Kg.
Quiz 2, gr. 22
Find:
1. mass flow rate kg/s
2. COP.
3. Compression power in KW.
4. Pressure of refrigerant at evaporator inlet
h3=200
h2=400
h4=210
(3 marks on chart)
h1=353
h3=200
h2=400
h4=210
(3 marks on chart)
h1=353
Total mark = 15 marks
• h1’=h1’’= 353 kj/kg
• h2’=h2”= 400 kj/kg,
• h3= 200 kj/kg
• h4=h3+10= 210 kj/kg
• m’= = Q L/(h1’-h4)=500*3.5/(353-210)=12.238 kg/s
• Cop= (h1-h4)/(h2-h1)= (353-210)/(400-353)=3.04
• Compressor power= m’ * (h2’-h1)= 12.238 *(400-353)=575.186 kw
• Pressure at evaporator inlet= 0.1 Mpa