Refrigerator Troubleshooting Diagram

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Refrigerant blends

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Many of the new, alternative refrigerants are ‘blends’, which have two or three components, developed for existing and new plants as comparable alternatives to the refrigerants being replaced. They are ‘zeotropes’ with varying evaporating or condensing temperatures in the latent heat of vaporization phase, referred to as the ‘temperature glide’. Figure 3.3 shows the variation in evaporating and condensing temperatures.

To compare the performance between single component refrigerants and blends it will be necessary to specify the evaporating temperature of the blend to point A on the diagram and the condensing temperature to point B.

The temperature glide can be used to advantage in improving plant performance, by correct design of the heat exchangers. A problem associated with blends is that refrigerant leakage results in a change in the component concentration of the refrigerant. However, tests indicate that small changes in concentration (say less than 10%) have a negligible effect on plant performance.

The following recommendations apply to the use of blends:

• The plant must always be charged with liquid refrigerant, or the component concentrations will shift.
• Since most blends contain at least one flammable component, the entry of air into the system must be avoided.
• Blends which have a large temperature glide, greater than 5K, should not be used for flooded-type evaporators.

Written by sam

April 13th, 2011 at 4:58 am

Posted in Refrigeration

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Ideal properties for a refrigerant

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It will be useful to remind ourselves of the requirements for a fluid used as a refrigerant.

• A high density of suction gas
• Non-corrosive, non-toxic and non-flammable
• Critical temperature and triple point outside the working range
• Compatibility with component materials and lubricating oil
• Reasonable working pressures (not too high, or below atmospheric pressure)
• High dielectric strength (for compressors with integral motors)
• Low cost
• Ease of leak detection
• Environmentally friendly

No single fluid has all these properties, and meets the new environmental requirements, but this chapter will show the developments that are taking place in influencing the selection and choice of a refrigerant.

Written by sam

April 13th, 2011 at 4:48 am

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Evaporators

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The evaporator is that part of the system where the useful cooling is accomplished by removing the heat from the area to be cooled. This is done by bringing the temperature of the liquid refrigerant below the temperature of the surrounding medium. The heat passes into the liquid refrigerant and is absorbed as latent heat, changing the state of the refrigerant from a liquid into a vapor. It is then withdrawn by action of the compressor.

There are two general types of evaporators: dry and flooded. In the dry type, the refrigerant enters in the liquid state, and the design provides for complete evaporation with the vapors slightly superheated. In the flooded type, not all of the refrigerant is evaporated, and the liquid/vapor mixture leaving the evaporator flows into a surge drain from which the vapors are drawn into the compressor suction line; the liquid is recirculated through the evaporator.

Written by sam

February 13th, 2011 at 11:31 pm

Posted in Compressors

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