Refrigeration & Equipment Engineering

Unit 4 - Refrigerants

4.2.5.Secondary refrigerant
Brine is a secondary refrigerant and is generally used where temperature is required to be maintained below the freezing point of water (0^oc). In case the temperature involved is above the freezing point of water, then water is commonly used as a secondary refrigerant.

Brine is a solution of salt and water. It may be noted that when a salt is mixed with water, then the freezing temperature of the solution becomes lower,because when the salt is dissolving in water it takes off its latent heat from the solution and cools it below the freezing point of water.

The brine commonly used are calcium chloride (CaCl₂) and sodium chloride (NaCl) the CaCl₂ has the eutectic temperature of -55^oc at salt concentration of 30% by mass. This type of brine is primarily used where temperature below -18^oc is required.It is generally used in industrial process cooling and product freezing.

The sodium chloride brine has the eutectic temperature of -21.1^oc at –salt concentration of 23% by mass.