Capacity Of The Compressor
The compressor is the heart of the refrigeration machine, it uses mechanical energy generated by the electric motor, pump refrigerant through the loop. Refrigerant absorbs heat at one place and releases it in another place. The most efficient construction is possible to have compressor large enough to handle the required amount of cooling. If the compressor is too large energy losses in excess friction, starting etc. If the compressor is too small, it does not produce sufficient cooling.
Basically, the compressor must remove vapour at the outlet of the evaporator fast enough to enable the refrigerant evaporates at the correct pressure. To do this, he must remove the refrigerant vapor as fast as the heat enters the evaporator for evaporation of the coolant.
The method of determining the compressor size can be simply stated: the evaporator, as a rule, designed to remove the 24-hour heat load in 16 - or 18-hour running period. The amount of time depends on the factors described in the previous paragraphs.
Suppose that effective heat capacity of the refrigerant 60 Btu/lb.
As each pound of refrigerant evaporates in the evaporator, it takes 60 BTU of heat from the evaporator. To remove this much heat, the compressor must handle all the vapor formed. Refrigerant tables these values, called "specific volumes." Specific volume value means that a certain pressure on the pound refrigerant as it evaporates, will form a certain number of cubic feet of steam.
For example, assume that 1 lb. R-12, vaporizing in 9.17 psi (23.87 psia or 164.7 kPa) and 0F (17.8C), forms of 1.637 ft3 couple in 10 minutes. Compressor, you must remove the 1,637 ft3 vapour at the outlet of the evaporator in the same period. Compressor size needed to do this depends on the steam volume pumped per revolution of the compressor. This is determined by the hole (diameter of the cylinder), stroke (distance passed by a piston), number of cylinders, the compressor speed (rpm), and its volumetric efficiency. As a cranked shaft of the compressor makes a complete revolution, the piston moves from the lowest point of its travel (lower dead point) to the highest point (TDP) and back to the lowest point again.
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Industrial