Chemical Engineering - Chemical Engineering Thermodynamics - Discussion

Specific heat is amount of heat required to raise the temp of refrigerant by 1 degree celsius; so if the specific heat of refrigerant is high enough; indicates that it is a desired property.

And if viscosity of refrigerant is high;indicating that I have to increase its temp for free flowing through cooling system but increasing the temperature is not a good option because if I do such then my aim of cooling system will be in vain. So high viscosity of refrigerant is undesired.

According to me, high viscosity leads to low temperature and for a cooling system low temperature is desired one. That's why I think high viscosity is desired.

High viscosity is obviously an undesirable property of good refrigerant as it increases the losses of energy converts the useful energy in to non-conservative frictional energy.

High specific heat is undesirable as it will take more energy to reduce the temperature but how is viscosity going to effect it?

First thing is that viscosity is a property of fluid. The viscosity for liquids decreases with increase in temperature. So it has property of absorbing temp. As here the temp is maintained in low for cooling purpose. The viscosity of liquid i.e. refrigerant is increased. So there will effect for the refrigerant purpose. C IS CORRECT.

Latent heat of vaporization should be as large as possible to minimize the area under super heat and the area reduction due to throttling. Also, the higher value of enthalpy of vaporization lowers the required flow rate per ton of refrigeration.

Thus the answer will be option B.

Ideally speaking, the maximum amount of heat is extracted when the refrigerant enters as saturated liquid and vapourises completely in the cooling coils.

Exit vapours has to be compressed, cooled and liquefied. So if the specific heat is more, the refrigerant cooling duty increases and size of the heat exchanger also increases.

Also if the refrigerant is subcooled, it occupies more number of cooling coils in liquid state without vapourizing during the next cycle thus reducing the heat extracted.

Then how is a higher specific heat refrigerant favourable?

As per my knowledge, option A and C both are correct.

If more viscosity then molecules are more so to flow temperature time is more requires.

High viscosity hinders the refrigerant's ability to flow easily, which can result in poorer heat transfer.

This reduces the overall efficiency of the refrigeration system, making it less effective at cooling or heating.