ali_g
24-11-2010, 07:08 PM
Hello,
I am a mature student and I’m trying to get to grips with a refrigeration problem I've been given.
I would much prefer an explanation than an outright answer.
But failing that, I might be able to reverse engineer an answer.
Bear in mind that this is a university apparatus so looks nothing like a refrigerator, here goes...
I am required to find electrical power of the electric motor (W_elec) using the equation W_elec = I_c x V x P_f.
Where I_c is the current measured at the compressor and V is the supply voltage.
Knowing this, I need to find the power factor (P_f) so I can draw a performance curve graph of motor shaft power v power factor.
I do not have access to the motor or an energy monitor; all results MUST be calculated.
I think I’m required to figure out how much energy it transferred into the refrigerant but don’t know how to go about it.
I have 4 enthalpy readings and 2 pressure readings that I have added to an enthalpy chart (refrigerant R134a).
I have details for the compressor;
Bore = 40mm; stroke = 30mm; total swept volume = 75.5x10^-6 m^3 ; pulley ratio between compressor & motor = 3.17; torque arm radius = 0.165m.
Compressor friction force = 5N
I have recorded and calculated many values:
Motor Shaft Power
Heat transfer rate to Cooling Water
Evaporator Heat Input
Energy transferred into refrigerant by compressor
Heat transfer rate from condenser to surroundings
Heat transfer rate into evaporator
Coefficient of Performance (COP) of refrigerator unit based on indicated power
Coefficient of Performance (COP) of refrigerator unit based on motor power
Volumetric efficiency of compressor
Still have to find:
Coefficient of Performance (COP) of refrigerator unit based on electrical input power (need electric power of motor)
Isentropic efficiency of compressor (need to find h_ (2^’) from enthalpy chart)
But have no idea where to go from here.
Any help will be much appreciated.
Thanks in advance.
I am a mature student and I’m trying to get to grips with a refrigeration problem I've been given.
I would much prefer an explanation than an outright answer.
But failing that, I might be able to reverse engineer an answer.
Bear in mind that this is a university apparatus so looks nothing like a refrigerator, here goes...
I am required to find electrical power of the electric motor (W_elec) using the equation W_elec = I_c x V x P_f.
Where I_c is the current measured at the compressor and V is the supply voltage.
Knowing this, I need to find the power factor (P_f) so I can draw a performance curve graph of motor shaft power v power factor.
I do not have access to the motor or an energy monitor; all results MUST be calculated.
I think I’m required to figure out how much energy it transferred into the refrigerant but don’t know how to go about it.
I have 4 enthalpy readings and 2 pressure readings that I have added to an enthalpy chart (refrigerant R134a).
I have details for the compressor;
Bore = 40mm; stroke = 30mm; total swept volume = 75.5x10^-6 m^3 ; pulley ratio between compressor & motor = 3.17; torque arm radius = 0.165m.
Compressor friction force = 5N
I have recorded and calculated many values:
Motor Shaft Power
Heat transfer rate to Cooling Water
Evaporator Heat Input
Energy transferred into refrigerant by compressor
Heat transfer rate from condenser to surroundings
Heat transfer rate into evaporator
Coefficient of Performance (COP) of refrigerator unit based on indicated power
Coefficient of Performance (COP) of refrigerator unit based on motor power
Volumetric efficiency of compressor
Still have to find:
Coefficient of Performance (COP) of refrigerator unit based on electrical input power (need electric power of motor)
Isentropic efficiency of compressor (need to find h_ (2^’) from enthalpy chart)
But have no idea where to go from here.
Any help will be much appreciated.
Thanks in advance.