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

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

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Refrigeration and Air Conditioning
A good refrigerant should have

High specific volume and high latent heat of vaporisation
High latent heat of vaporisation and low freezing point
High operating pressures and low freezing point
Low C.O.P. and low freezing point

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