Refrigeration and Air Conditioning
A good refrigerant should have

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

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Refrigeration and Air Conditioning
The C.O.P. of an absorption type refrigerator is given by (where T₁ = Temperature at which the working substance receives heat, T₂ = Temperature of cooling water, and T₃ = Evaporator temperature)

[T₁ (T₁ - T₂)] / [T₃ (T₂ - T₃)]
[T₃ (T₁ - T₂)]/ [T₁ (T₂ - T₃)]
[T₃ (T₂ - T₃)] / [T₁ (T₁ - T₂)]
[T₁ (T₂ - T₃)] / [T₃ (T₁ - T₂)]

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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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