Milk comes from cow at about 37°C and must be cooled within two hours to 4°C or lower and under hygienic condition. At this temperature any microorganism present will not multiply at dangerous rate and milk can be transported to processing plant safely. Read more
For refrigerants to be ideal, it should possesses following properties
1. Low boiling point
2. Low freezing point
3. High critical pressure and temperature (to avoid large power requirement)
4. Low specific heat (high specific heat decreases refrigerant effect per kg or refrigerant.
5. High latent heat (increases refrigerant effect per kg of refrigerant)
6. Pressure in evaporator and condenser should be low enough to reduce material cost and must be positive to avoid leakage of air into the system.
7. Low specific volume to reduce size of compressor.
8. High thermal conductivity to reduce area of heat transfer in evaporator and condenser.
9. Non-flammable, non-explosive, non-toxic and non-corrosive.
10. High miscibility with lubricating oil and should not have reacting property with lubricating oil in the temperature range of system.
11. High coefficient of performance (COP) to reduce cost of system
12. Readily available and cheap Read more
Any substance that absorbs heat through expansion or vaporization may be termed a refrigerant. In broad sense, refrigerant is also applied to secondary cooling medium as brine solution or cold water. As commonly interpreted, however, refrigerant includes only those working medium which passes through cycle of evaporation, recovery, compression and liquefaction. Thus circulating cold mediums, ice and solid carbon dioxide are not primary refrigerants. The primary refrigerants directly take part in refrigeration system whereas secondary refrigerants are first cooled with the help of primary refrigerant and are further used for cooling purposes.
Expansion devises are used in between evaporator and condenser in refrigeration system. These devices meters and regulates the flow of liquid refrigerant to an evaporator. The expansion device have following specific functions.
1. To reduce the pressure of liquid refrigerant coming from condenser.
2. To maintain desired pressure difference between high pressure and low pressure side of the system.
3. Capacity expansion devices are used to maintain the desired rate of flow and pressure drop across the system.
4. To control the flow of refrigerant according to variation of load on the evaporator. Read more
High side equipment: The pressure of the refrigerant in the condenser is very little that at the compressor discharge. The pressure at compressor discharge is higher than at any other part of the system. Hence the condenser and other equipment in the system between compressor discharge and expansion valve are referred to as high side equipment.
Low side valve equipment: Since the refrigerant in the evaporator is at low pressure compared to that in the condenser, the evaporator and auxiliaries between the expansion valve and the compressor intake are often referred to as low side equipment. Read more
The function of evaporator is to absorb heat from surrounding location or medium which is to be cooled by means of refrigerant. The refrigerant either boils as it flows through a pipe, tube or other type of space so that liquid is continuously wetting all the inside surface or it boils in a shell around submerged tubes through which the fluid to be cooling is flowing. Various methods are used for evaporators, depending upon the refrigerant to be used and evaporator application, but iron, steel and copper predominate. Read more
Basically, compressor in refrigeration system have following main function
1. Remove low temperature and low pressure refrigerant vapors from cooling coil through suction line.
2. Compress refrigerant vapors by increasing the pressure and temperature resulting in an increase of boiling point of refrigerant.
3. Discharge the refrigerant vapors of high temperature and pressure to condenser through discharge line.
Compression of refrigerant gas may be accomplished by any one of several different means such as positive displacement (reciprocating, rotary, gear types) and centrifugal (centrifugal compressor). The common type of compressors in use are
1. Reciprocating compressor
2. Rotary compressor
3. Centrifugal compressor
4. Screw compressor
5. Scroll compressor Read more