Circulation oils
Leaving the compressor, the discharge line should be led down where possible. It will allow to avoid accumulation of oil or pressure liquid refrigerant in the compressor during idle periods. Where capacitor above the compressor, you must have a sufficient rate in the line from the compressor, or oil separator to ensure that oil is carried forward. The check valve can be installed as a guarantee to prevent oil flowing back. Horizontal lines should downward slope in the direction of flow. Traces of oil, which come in the condenser will settle on the surface cooling and drop to the bottom in the form of liquid or dissolve in the condensed refrigerant. In any case, these two fluids will then pass to the expansion valve and the evaporator. Here, the refrigerant vapour changes, but most of the oil will remain as a liquid, containing dissolved refrigerant. Slight traces of oil, as low vapour pressure with suction gas. It is necessary to limit the accumulation of liquid oil in the evaporator, as it will accumulate quickly, reducing heat transfer and violations.
With ammonia, oil falls to the bottom and does not go into solution with the refrigerant.
Ammonia condensers, receivers and flooded evaporators can be distinguished by the provision of oil drain pots and connections in the bottom point. Automatic drainage and oil return will depend on the different densities of small and very rarely installed. Removal of oil from the collection of pots and low point drains periodic manual function and as part of regular maintenance. Some of the ammonia systems are designed for oil return through the maintenance of the gas velocity, for example, direct and a liquid expansion overfeed evaporators. Halocarbons all fairly mixed with oil to prevent the possibility of separate drainage and in any case they are rarely used with flooded evaporators.
The most common way of getting oil from the evaporator, compressor, to keep it in motion, providing a continuous velocity of the fluid in all parts of the schema using direct expansion evaporator. This dynamic method of treatment is a decisive factor in the design of almost all freon evaporators.
The critical section of the chain, where no liquid refrigerant to help move oil, i.e. evaporator and suction back to the compressor. Suction pipe must have a slope down compressor, but do not allow liquids to flooding of the compressor. Minimum gas velocities of about 3.5 m/s required. Where the compressor, evaporator below vertical sections provide sufficient speed analyser, as a rule, not less than 7 m/s you want to drop of oil will be back dry gaseous refrigerant in the compressor. On Fig. 11.1 shows piping arrangements that can be used to transport oil.
In some situations, liquid separator (see Chapter 9) is used to prevent large volumes of oil and/or refrigerant from suddenly compressor at start or immediately after thawing, for example. This system behavior is called ingress of liquid refrigerant compressors invariably designed to handle this to some extent.
With some small refrigeration circuits that can operate on the reduction of gas consumption for capacity controlled, it may not be possible to maintain a minimum rate for oil transportation back to the compressor, and it will settle in the chain. This is especially true with variable speed compressors, where many low speed allowed. Reversing the refrigerant type circuits (i.e. cooling/heat pumps)are another example. Measures should be aimed at improving or reverse gas flow periodically move, this oil....
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