04-01-2013, 03:55 PM
Simple Vapor Compression Refrigeration System
1Simple Vapor.pdf (Size: 190.86 KB / Downloads: 379)
A simple vapor compression refrigeration system consists of the following equipments:
i) Compressor ii) Condenser iii) Expansion valve iv) Evaporator.
The schematic diagram of the arrangement is as shown in Fig.6.5. The low
temperature, low pressure vapor at state B is compressed by a compressor to high
temperature and pressure vapor at state C. This vapor is condensed into high pressure
vapor at state D in the condenser and then passes through the expansion valve. Here,
the vapor is throttled down to a low pressure liquid and passed on to an evaporator,
where it absorbs heat from the surroundings from the circulating fluid (being
refrigerated) and vaporizes into low pressure vapor at state B. The cycle then repeats.
The exchange of energy is as follows:
a) Compressor requires work, δw. The work is supplied to the system from the
surroundings.
b) During condensation, heat δQ1 the equivalent of latent heat of condensation
etc, is lost from the refrigerator.
c) During evaporation, heat δQ2 equivalent to latent heat of vaporization is
absorbed by the refrigerant.
d) There is no exchange of heat during throttling process through the expansion
valve as this process occurs at constant enthalpy.
Sub-cooling of Liquids:
In the Fig.6.5.4(a) of simple vapor compression cycle, condensation process CD
resulted in the liquid at saturated state D. If it was possible to further cool down the
liquid to some lower value say upto D’, then the net refrigeration effect will be increased
as (hB – h’A) > (hB - hA). Hence, the sub cooling of the liquid increases the refrigerating
effect without increasing the work requirement.