INTRODUCTION—OUTLINE OF SOME DESCRIPTIVE SYSTEMS 11dharm
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The flow diagram of such a cycle is shown in Fig. 1.8.Expansion
valveReceiverCondenser
SNMCompressorEvaporator
L
Fig. 1.8. Simple vapour compression cycle.
The vapour at low temperature and pressure (state ‘M’) enters the compressor where it is
compressed isoentroprically and subsequently its temperature and pressure increase considerably
(state ‘N’). This vapour after leaving the compressor enters the condenser where it is condensed
into high pressure liquid (state ‘S’) and is collected in a receiver. From receiver it passes through
the expansion valve, here it is throttled down to a lower pressure and has a low temperature
(state ‘L’). After finding its way through expansion valve it finally passes on to evaporator where
it extracts heat from the surroundings and vapourises to low pressure vapour (state ‘M’).
Domestic Refrigerator :
Refrigerators, these days, are becoming the common item for house hold use, vendor’s
shop, hotels, motels, offices, laboratories, hospitals, chemists and druggists shops, studios etc.
They are manufactured in different size to meet the needs of various groups of people. They are
usually rated with internal gross volume and the freezer volume. The freezer space is meant to
preserve perishable products at a temperature much below 0°C such as fish, meat, chicken etc.
and to produce ice and icecream as well. The refrigerators in India are available in different sizes
of various makes, i.e., 90, 100, 140, 160, 200, 250, 380 litres of gross volume. The freezers are
usually provided at top portion of the refrigerator space occupying around one-tenth to one-third of
the refrigerator volume. In some refrigerators, freezers are provided at the bottom.
A domestic refrigerator consists of the following two main parts :- The refrigeration system.
- The insulated cabinet.
Fig. 1.9 shows a flow diagram of a typical refrigeration system used in a domestic refrigera-
tor. A simple domestic refrigerator consists of a hermetic compressor placed in the cabinet base.
The condenser is installed at the back and the evaporator is placed inside the cabinet at the top.
The working of the refrigerator is as follows :
— The low pressure and low temperature refrigerant vapour (usually R12) is drawn through
the suction line to the compressor. The accumulator provided between the suction line
and the evaporator collects liquid refrigerant coming out of the evaporator due to incom-
plete evaporation, if any, prevents it from entering the compressor. The compressor
then compresses the refrigerant vapour to a high pressure and high temperature. The
compressed vapour flows through the discharge line into condenser (vertical natural
draft, wire-tube type).
— In the condenser the vapour refrigerant at high pressure and at high temperature is
condensed to the liquid refrigerant at high pressure and low temperature.