The refrigerant used in small tonnage commercial machines (hermetically sealed units) is
A. Ammonia
B. Carbon dioxide
C. Sulphur dioxide
D. R-12
Answer: Option D
Solution (By Examveda Team)
R-12 (Dichlorodifluoromethane) has been traditionally used in small tonnage commercial machines and hermetically sealed refrigeration units such as domestic refrigerators and small air-conditioning systems.It is preferred because it is non-toxic, non-flammable, chemically stable, and has good thermodynamic properties, making it highly suitable for sealed systems where maintenance is minimal.
Other options like Ammonia are toxic, Carbon dioxide operates at very high pressures, and Sulphur dioxide is corrosive and toxic, which makes them unsuitable for small hermetically sealed units.
Although R-12 is now phased out due to its ozone depletion potential, it remains the correct theoretical answer for traditional refrigeration systems in examination contexts.
This Question Belongs to Mechanical Engineering >> Refrigeration And Air Conditioning
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Comments (2)
Nusselt number (NN) is given by
A. $${{\text{N}}_{\text{N}}} = \frac{{{\text{h}}l}}{{\text{k}}}$$
B. $${{\text{N}}_{\text{N}}} = \frac{{\mu {{\text{c}}_{\text{p}}}}}{{\text{k}}}$$
C. $${{\text{N}}_{\text{N}}} = \frac{{\rho {\text{V}}l}}{\mu }$$
D. $${{\text{N}}_{\text{N}}} = \frac{{{{\text{V}}^2}}}{{{\text{t}}{{\text{c}}_{\text{p}}}}}$$
In case of sensible heating of air, the coil efficiency is given by (where B.P.F. = Bypass factor)
A. B.P.F. - 1
B. 1 - B.P.F.
C. $$\frac{1}{{{\text{B}}{\text{.P}}{\text{.F}}{\text{.}}}}$$
D. 1 + B.P.F.
The undesirable property of a refrigerant is
A. Non-toxic
B. Non-flammable
C. Non-explosive
D. High boiling point
The desirable property of a refrigerant is
A. Low boiling point
B. High critical temperature
C. High latent heat of vaporisation
D. All of these
D) R 12 used in past currently R-134 is used
R12 must be the answer