Brines As A Secondary Refrigerants
Due to its high triple point of water cannot be used as a secondary refrigerant in any application where the required temperature is below freezing. Therefore, brine solution is often used in these applications. Brine is the name given to a solution of salt dissolved in water. When the salt dissolves in water, the freezing temperature of the solution obtained is lower than clean water. Since the percentage of salt in the water unit is gradually increasing, freeze coolant temperature is gradually decreasing. However, as soon as the salt concentration, increase beyond a certain limit, freeze coolant temperature begins to rise.
Brine, existing in the critical concentration is called the eutectic solution. In any salt concentration is above or below it eutectic concentration, the freezing temperature of the solution increases. Solubility of salts in the water decreases as the temperature of the solution decreases. Thus, the temperature at which ice crystals begin to form depends on the concentration of salts and the relative solubility of salts in the water.
When the contents of salt in brine less than the eutectic solution, the excess water precipitates out of solution in the form of ice crystals as the heat for cooling. As the temperature decreases, die continued deposition of crystals of ice causes the die concentration of salt in the remaining decision to increase.
This reaction continues until the eutectic temperature is reached. In diis point, slush, consisting of ice and eutectic exists in brine hmm barrel. Further removal of heat from this mixture will result in the crystallization of eutectics brine. The solidification of the eutectic brine latent heat process, and it happens at a constant temperature. Similarly, when the content of salt in brine, exceeds the amount needed for the eutectic solution, salt starts to precipitate out of solution in the form of crystals of salt in some temperature above eutectic temperature. This is the precipitation of salt, as the temperature decreases produces eutectic mixture of salt and brine. Any warmth, emanating from the eutectic mixture after the temperature reached results in a constant temperature of crystallization of eutectics brine. Is to die to the process used with plate evaporators used in transport refrigeration.
Two types of brine are usually used in refrigeration, calcium chloride and sodium chloride. Calcium chloride (CaCl2) brine is mainly used in the industrial process cooling, freezing and storage of the product and in other applications where the temperature is below 0F (17.8C) are mandatory. The low freezing temperature (eutectic temperature), which can be obtained from the salt, calcium chloride solution 67F (55C). The salt concentration in the eutectic solution by about 30% by weight. The freezing temperature of various concentrations and other important properties of calcium chloride brine. The main disadvantage of calcium chloride brine his dehydrating effect and inclination to distribute the bitter taste of the food, with which it comes in contact. Any food freezing applications using calcium chloride brine need a design that prevents the brine from coming in contact with the cold production.
Sodium chloride (table salt) in brine not contaminate the food. Therefore, sodium chloride (NaCl brine is widely used in applications where cooling and freezing of meat, fish and other food products is carried out through the brine spray or fog. The lowest temperature is received with the salt solution of sodium chloride about 6F (21.1C). The salt concentration in the eutectic solution is approximately 23% by weight.
And salt content of these decisions increases, specific density, specific heat and thermal conductivity of brines reduction. Therefore, as the freezing temperature of the heat carrier reduced its capacity should increase to receive the required cooling effect. The salt concentration in the brine solution, together with its thermal properties can be determined by measuring the specific gravity of the brine with a water meter and looking at the thermal characteristics...