Category: Dairy Engineering

Sep 08

Introduction to Vapor Absorption Refrigeration System (VARS)

The compressor in vapor absorption system consumes a lot of energy. To avoid this, vapor absorption refrigeration system has been developed. The absorption system uses heat energy supplied by a flame or some other source of heat.

Michel Faraday experiment on liquefaction of gas:

vapor absorption refrigeration system is based on the principle of experiment developed by Michel Faraday. He sealed in a bent test tube a compound of silver chloride (a white powder) and dry ammonia gas which have been absorbed by the powder. He heated the end of tube containing the powder and at the same time, cooled the opposite end of the tube with water. Ammonia vapor was released during the application of heat and was condensed to cool end of the tube. When the flame under the powder was extinguished, vapor that had not been liquefied was reabsorbed by the powder reducing the pressure on liquid ammonia. The liquid ammonia begins to boil, change back to vapor and was reabsorbed by the powder. The end of tube containing boiling liquid was intensely cold. The evaporating ammonia having drawn heat from the nearest substance, the test tube itself. Read more

Sep 07

Introduction to Vapor Compressor Refrigeration System (VCRS)

Refrigeration can be defined as the process of transferring heat from low temperature region to high temperature region. In other words, it is the process of cooling the substance. This can be achieved only if heat is removed from that substance.

Principle of refrigeration: Principle of refrigeration is based on second law of thermodynamics. It states that heat doesn’t flow from low temperature body to high temperature body without the help of external work. In refrigeration process, since heat has to be transferred from low temperature body to high temperature body some external work has to be done according to second law of thermodynamics as shown below (fig 2.) Here, the external work is done by compressor, condenser etc. The machine which works under this principle and serves the purpose of refrigeration is called refrigerator. Read more

Aug 09

Mixing and Homogenization

Mixing is a unit operation in which uniform mixture is obtained from two or more compounds by dispersing one within another. When two or more materials are mixed, the goal of mixing is to obtain homogeneous final mixture. Homogeneity is the quality of being homogeneous. A perfect homogeneous sample indicates the state of complete mixing. Mixing has no preservative effect on food. It is a processing aid to alter eating quality of food and to achieve different functional and sensory quality of food. In some food adequate mixing is necessary to ensure that the proportion of each component in the sample complies with legislative standards. Read more