Question

using a t-s diagram explain why cascading is used in refrigeration explain the criteria used in industry in selectin refrigerants for a particular application if it is desired to cool airto a temperature of -30 c will r-134a be a good choice you may use a property tablein relation to to answering this question

Answer 1

Some common criteria used for selection of the refrigerant are:-

1. Temperature that is to be maintained in the refrigerated space. - As various refrigerants have different working temperatures.

2. Toxicity of the Refrigerant - We do not prefer toxic refrigerants for domestic purposes.

3. Latent Heat of Vaporisation - the latent heat of vaporisation should be as high as possible.

4. Flammability - An ideal refrigerant should not have any danger of explosion.

5. Cost & Availability - The refrigerant must be readily available and reasonable priced.

R134a has a boiling point of -26.3 . The desired property of a refrigerant is that the boiling point of a refrigerant should be below the target temperature. As in this case the target temperature is below the boiling point of the refrigerant hence using R 134a for cooling air to -30 , is not suitable.