Question:-
Consider the following statements
1. Practically all common refrigerants have approximately the same COP and power requirement
2. Ammonia mixes freely with lubricating oil and this helps lubrication of compressors
3. Dielectric strength of refrigerants is an important property in hermetically scaled compressor units
4. Leakage of ammonia can be detected by halide torch method
Of these statements
Option (A)
1, 2 and 4 are correct
Option (B)
2 and 4 are correct
Option(C)
1, 3 and 4 are correct
Option(D)
1 and 3 are correct
Correct Option:
(D)
Question Solution:
(i) Practically all common refrigeration have approximately the same COP and power requirement
Refrigrant COP kW/Ton
Carnot 5.74 0.75
CO2 2.56 1.4
SO2 4.87 0.74
F-11 5.09 0.71
F-12 4.7 0.76
F-22 4.6 0.77
F – 113 4.92 0.73
(ii) Ammonia (R-717) is lighter than oil, therefore its separation does not create any problem. The excess oil in the evaporator may be removed by opening a value in the bottom of the evaporator
(iii) The dielectric strength of the refrigerant becomes an important factor when it is used in hermetically scaled unit where the motor is exposed to the refrigerant
The dielectric strength of different refrigerant vapours are compared with dielectric strength of nitrogen therefore the relative dielectric strength of refrigerant vapour are given by a ratio by
= (Dielectric strength of refrigerant vapour /Dielectric strength of nitrogen)
(iv) The leaks of ammonia refrigerant may be quickly and easily detected by use of quickly and easily detected by use of burning, sulphur candle which in the presence of ammonia forms white fumes of ammonia sulphite
The leakage of fluorocarbon refrigerants may be detected by soap solution a or an elastic leak sector.
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