Refrigerant motor-driven compressor

Refrigerant motor-driven compressor Refrigerant condenser Refrigerant letdown valve Evaporator Refrigerant receiver... 

The motor-driven compressor boosts the pressure of the refrigerant vapors from the evaporator pressure, up to the condenser pressure. 

Many refrigeration compressors are horsepower-limited. This means the driver cannot put out enough work to drive the compressor as fast as desired. A motor-driven compressor is horsepower-limited when it trips off, because it is drawing too much current. 

Cooling. A compression refrigeration system, driven by an electric motor, suppHes cooling for either direct expansion or ice bank systems (Fig. 12). In the former, the milk is cooled by the evaporator (cooling cods) on the bulk tank liner opposite the milk side of the liner. The compressor must have the capacity to cool the milk as rapidly as it enters the tank. 

A motor-driven refrigeration compressor may be tripped off when the trip (or fuse) is set too low. Check this with an ammeter. The rated amperage (or horsepower) of the motor can be exceeded by trading the motor s operational life for increased horsepower. If refrigeration capacity is valuable. 

Let s say we have a centrifugal refrigeration compressor, driven by a motor. The motor is tripping off because of high amperage. Should we open or close the suction throttle valve shown in Fig. 22.2 Answer— close it. Of course, both the evaporator vapor outlet temperature and the process fluid outlet temperature will increase. But that is the price we pay for having too small a motor driver on the compressor. Does this mean that when our home air conditioner gets low on freon, our electric bill drops Correct. But the price we pay is a hot home. 

The fluid that flows through the coils in the back of a refrigerator removes heat from the interior by the same process. In fact, the refrigerant used in freezers will absorb so much heat that it can freeze skin. The fluid is compressed by the compressor, then allowed to expand through the coils. The compression is driven by an electric motor, and the expansion is driven by entropy the gas phase is a more disordered state than the liquid phase. 

HERMETIC SYSTEM - Refrigeration system which has a compressor driven by a motor contained in compressor dome or housing. 

For compressors driven by an ordinary (nonvariable speed) motor, the speed of the compressor is fixed. However, there is a method one can employ to overcome capacity limitations imposed by fixed speed compressors (and compressors running at their maximum rated speed). This method is to change the composition of the circulating refrigerant. Details are discussed later in this chapter. 

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