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

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

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

Extraction Equipment in Food Industries

Design of extraction equipment may vary depending on nature of raw material used and intended product characteristics. Equipment design and working principle also largely dependent on scale of production or processing (large scale / small scale) and economic feasibility. Some popular extraction equipment used in food industries are described below.

Bollman extractor: Bollman extractor consists of perforated bucket elevator in series into which the fresh solid are fed at one end while fresh solvent is added at another end. Solids are fed into each bucket which will be moving downward until half the way and later on, bucket will be moving upward. Read more

Extraction Techniques

Depending upon need and quantities of material to be handled, different extraction techniques are used in food industries. Some popular extraction techniques are
1. Single stage batch extraction
2. Multi stage cross flow extraction
3. Multi stage counter current extraction

1. Single stage batch extraction:
It is a batch extractor in which the solids are brought in contact with adequate quantity of solvent so as to leach out the solute from solid into the solvent. The process can be accompanied with heating or stirring as the process demands. When the extraction process reaches equilibrium, the solution is decanted and excess solvent from the solution is removed to obtain pure solute. Example; brewing tea or coffee, extraction of oleoresins. Read more

Non Thermal Preservation of Food-Pulsed Electric Field

In this method of food preservation, electric energy at low power is collected over an extended period and stored in capacitor. That same energy is discharged, almost instantaneously at high level of power. When exposed to electric field, plasma membrane of cell becomes permeable to small molecules and the permeation causes swelling and eventual rupture of cell membrane. Rupture of cell membrane depends on factors such as intensity of electric field, number of pulses and duration of pulses. The induced transmembrane potential larger than natural potential of cell membrane cause rupture of cell membrane. Generation of pulse electric requires two devices; a) Pulse power supply and b) Treatment chamber. Read more

Non Thermal Preservation of Food- High pressure processing (HPP)

High pressure presents unique advantage over conventional food processing including application at low temperature which improves the retention of food quality. High pressure treatment are independent of product size and geometry and their effect is uniform and instantaneous. The food is compressed by uniform pressure from every direction and then returns to original shape when pressure is released.
Processing operation: A sterile container filled with food is sealed and placed in the pressure chamber for pressurizing. Ethylene Vinyl Alcohol (EVOH) and Poly vinyl Alcohol (PVOH) films are recommended for packaging food for high pressure treatment. Also existing multilayer plastic and some aluminum packages may be used. No deformation of the package occurs because the pressure is uniform. The basis of applying high pressure to food is to compress the water surrounding the food. At room temperature, volume of water decreases.  Food is subjected to high pressure for a specified time period. The holding time in the pressure vessel depends on type of food and process temperature. At the end of processing time, the chamber is decompressed to remove treated batch. Read more