Mechanical Engineering - Heat Transfer, Refrigeration and Air Conditioning - Discussion

1. 

R-12 is generally preferred over R-22 in deep freezers since

[A]. it has low operating pressures
[B]. it gives higher coefficient of performance
[C]. it is miscible with oil over large range of temperatures
[D]. all of the above

Answer: Option C

Explanation:

No answer description available for this question.

Kamran said: (Feb 19, 2016)  
Why R12 is better than R22?

Metal Head said: (Apr 5, 2016)  
Explain the answer.

Neeraj said: (Feb 22, 2017)  
Properties of R12 and its Advantages.

Here are some of the important properties of the refrigerant R12:

1) Safe properties: Refrigerant R12 is nontoxic, nonflammable, and non-explosive. This makes it highly popular for the domestic as well as the commercial applications.

2) Stability: R12 is highly stable chlorofluorocarbon and it does not disintegrate even under the extreme operating conditions. However, if it is brought in contact with the flame of fire or the electrical heating element, it disintegrates into the toxic products. Thus whenever there is leakage of R12 refrigerant it is advised to put all the flames off and keep the doors open so that it can escape to the open atmosphere.

3) Suitable for wide range of operating conditions: R12 has the boiling point of -21.6 degree F (-29.8 degree C) due to which it condenses at the moderate pressures at the atmospheric temperature. This means the discharge pressure of the compressor should be only moderate so as to produce the condensation of the refrigerant in the condenser at the atmospheric temperature. This helps in using the compressor of low compression ratio that has higher efficiency. Due to this property of refrigerant R12, it is used in wide range of applications like high-temperature, medium temperature and low-temperature applications. It can be used will all types of compressors like reciprocating, centrifugal and rotary.

4) Miscibility with oil: Refrigerant R12 is miscible with the compressor oil under all the operating conditions. There are two advantages of this property of R12. Firstly, there is no problem of the oil return back to the compressor. Some particles of the oil from compressor tend to get carried away with the discharged refrigerant, because of the property of miscibility of R12, these particles return back to the compressor easily. The second advantage of miscibility is that the refrigerant flowing through the condenser and the evaporator is free of the oil particles. The oil particles within the refrigerant reduce the heat transfer from it, but such problem does not occur with R12 refrigerant. Due to this the heat transfer capacity of the condenser and evaporator is increased, which ultimately helps increase the efficiency of the refrigeration plant.

Disadvantages of Refrigerant R12:

1) Low refrigerating effect per pound: The refrigerating effect of R12 per pound of its weight is low compared to the other refrigerants. However, this is not the major disadvantage as it can be used constructively in some cases. In the smaller systems, the greater weight of the R12 helps to control the refrigeration system in a better way. In the larger systems, this disadvantage is offset by the higher vapour density of the refrigerant thus the compressor displacement required per tonne of refrigeration with the R12 refrigerant is not much higher than compared with the other refrigerants. The high heat transfer rates in the condenser and the evaporator due to the absence of the oil also helps reduce the effects of this disadvantage.

2) R12 is CFC: R12 is the most widely used refrigerant, unfortunately, it is the CFC and it has unusually high potential to cause the depletion of the ozone layer. R12 is being replaced by other refrigerants and some of the suggested replacements for R12 are: R-134a,

Raushan Kumar said: (Dec 2, 2018)  
R12 and R22 is harmful gasses.

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