Refrigeration and Air Conditioning
When the lower temperature of a refrigerating machine is fixed, then the coefficient of performance can be improved by

Operating the machine at lower speeds
Lowering the higher temperature
Raising the higher temperature
Operating the machine at higher speeds

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Refrigeration and Air Conditioning
In a vapour compression refrigeration system, a throttle valve is used in place of an expander because

The positive work in isentropic expansion of liquid is very small
It considerably reduces mass of the system
It improves the C.O.P., as the condenser is small
It leads to significant cost reduction

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Refrigeration and Air Conditioning
In order to cool and dehumidify a stream of moist air, it must be passed over the coil at a temperature

Which lies between the dry bulb and wet bulb temperatures of the incoming stream
Which is lower than the dew point temperature of the incoming stream
Of adiabatic saturation of incoming stream
Which lies between the wet bulb and dew point temperatures of the incoming stream

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