solas
27-01-2010, 02:22 AM
Hello to all
I would appreciate your advice on a refrigeration problem.
I am working on a refrigeration assignment and would like a second opinion on the thermodynamic properties that I have selected from the tables.
The operating conditions are as follows;
Condensing temperature Tc: 30 degC
Evaporating temperature Te: 5 degC
Refrigerant type/tables: DuPont ***** R22. (T-22 SI units-kJ/kg)
Points on PH diagram:
a= hf Enthalpy of saturated liquid (kJ/kg)
b= hf Enthalpy of saturated liquid (kJ/kg)
c= hg Enthalpy of saturated vapour (kJ/kg)
d= h Enthalpy of superheated vapour (kJ/kg)
Values I got from the tables;
hf at Tc 30 degC = 236.6 (ha = hb = isenthalpic expansion) - page 5
hg at Te 5degC = 406.8 (hc) - page 4
h at Tc 30 degC / 1,200kPa = 422.9 9 (hd - isentropic compression) - page 14
Cooling COP = hc-hb / hd-hc
Substituting values
Ans. 10.57
The cop appears to be very high and I think it may be down to my incorrect interpretation of the tables. I would appreciate your comments on the accuracy of the above values and COP.
Your help would be greatly appreciated.
Thanks in advance.
I would appreciate your advice on a refrigeration problem.
I am working on a refrigeration assignment and would like a second opinion on the thermodynamic properties that I have selected from the tables.
The operating conditions are as follows;
Condensing temperature Tc: 30 degC
Evaporating temperature Te: 5 degC
Refrigerant type/tables: DuPont ***** R22. (T-22 SI units-kJ/kg)
Points on PH diagram:
a= hf Enthalpy of saturated liquid (kJ/kg)
b= hf Enthalpy of saturated liquid (kJ/kg)
c= hg Enthalpy of saturated vapour (kJ/kg)
d= h Enthalpy of superheated vapour (kJ/kg)
Values I got from the tables;
hf at Tc 30 degC = 236.6 (ha = hb = isenthalpic expansion) - page 5
hg at Te 5degC = 406.8 (hc) - page 4
h at Tc 30 degC / 1,200kPa = 422.9 9 (hd - isentropic compression) - page 14
Cooling COP = hc-hb / hd-hc
Substituting values
Ans. 10.57
The cop appears to be very high and I think it may be down to my incorrect interpretation of the tables. I would appreciate your comments on the accuracy of the above values and COP.
Your help would be greatly appreciated.
Thanks in advance.