Nova Kool Manufacturing ULC

Basic Refrigeration Principles

Most users normally associate refrigeration with cold and cooling, yet the practice of refrigeration engineering deals almost entirely with the transfer of heat. This seeming paradox is one of the most fundamental concepts that must be grasped to understand the workings of a refrigeration system.

Cold is really only the absence of heat, just as darkness is the absence of light, and dryness is the absence of moisture.

Latent Heat of Fusion & Latent Heat of Evaporation

Latent Heat of Fusion
A change of substance from a solid to a liquid, or from a liquid to a solid involves the latent heat of fusion. It might also be termed the latent heat of melting, or the latent heat of freezing.

When one pound of ice melts, it absorbs 144 BTU's at a constant temperature of 32° F., and if one pound of water is to be frozen into ice, 144 BTU's must be removed from the water at a constant temperature of 32° F. In the freezing of food products, it is only the water content for which the latent heat of freezing must be taken into account, and normally this is calculated by determining the percentage of water content in a given product.

Latent Heat of Evaporation
A change of a substance from a liquid to a vapor, or from a vapor back to a liquid involves the latent heat of evaporation. Since boiling is only a rapid evaporating process, it might also be called the latent heat of boiling, the latent heat of vaporization, or for the reverse process, the latent heat of condensation.

When one pound of water boils or evaporates, it absorbs 970 BTU's at a constant temperature of 212° F. (at sea level) and to condense one pound of steam to water 970 BTU's must be extracted from it.

Because of the large amount of latent heat involved in evaporation and condensation, heat transfer can be very efficient during the process. The same changes of state affecting water apply to any liquid, although at different temperatures and pressures.

The absorption of heat by changing a liquid to a vapor, and the discharge of that heat by condensing the vapor is the keystone to the whole mechanical refrigeration process, and the movement of the latent heat involved is the basic means of refrigeration.

Katey Werner