Saffron
01-11-2008, 04:58 AM
I'm doing a refrigeration paper on designing a facility and need some assistance with some evaporator questions.
The theoretical specs are 27ºC product enters a -20ºC room where it is stacked ready for air blast freezing. The blasts are to have a 5m/s air velocity, average air temp of -25ºC for 40 hrs and the ammonia suction operates at -10kPa. Heat Load calcs average out at 20kW with instantaneous peak load about 75kW.
The calc I need assistance with is the temperature difference across the evaporator. The expressions used are T(on) and T(off). Can T(on) be assumed to be room temperature (-20ºC) and how can one calculate t(off)?
The theoretical system is ammonia pumped through an expansion valve into the evaporator. The formula I have to calculate refrigerant mass flow rate is
Фe = mr (hd - hc).
Can hc be calculated using pump pressure plotted on a Mollier chart with hd the suction pressure on a Mollier chart?
Any assistance would be more than welcome. No computer models are allowed - all workings must be shown.:confused:
The theoretical specs are 27ºC product enters a -20ºC room where it is stacked ready for air blast freezing. The blasts are to have a 5m/s air velocity, average air temp of -25ºC for 40 hrs and the ammonia suction operates at -10kPa. Heat Load calcs average out at 20kW with instantaneous peak load about 75kW.
The calc I need assistance with is the temperature difference across the evaporator. The expressions used are T(on) and T(off). Can T(on) be assumed to be room temperature (-20ºC) and how can one calculate t(off)?
The theoretical system is ammonia pumped through an expansion valve into the evaporator. The formula I have to calculate refrigerant mass flow rate is
Фe = mr (hd - hc).
Can hc be calculated using pump pressure plotted on a Mollier chart with hd the suction pressure on a Mollier chart?
Any assistance would be more than welcome. No computer models are allowed - all workings must be shown.:confused: