Component of a Centrifugal Refrigerant System Compressor

Component of a Centrifugal Refrigerant System Compressor Points : Component of a Centrifugal Refrigerant System Compressor, Compressor, Condenser, Evaporator, Flash Cooler, Orifice Plates Or Floats Valves, Purge Unit Compressor The centrifugal compressor has a rotating impeller that imports a high velocity to the refrigerant vapor and thus increased its kinetic energy this energy is then converted o static pressure in the expanding section of the impeller housing and thereby develops the head necessary for the refrigeration cycle. Centrifugal compressors are classified as open and close. In the open type driver and compressor are separated with the driver exposed to the atmosphere the closed type, commonly called hermetic has the compressor and driver enclosed within a sealed casing open type centrifugal compressor can be driven engine or a gas turbine, the in the open compressor, a shaft is required between the driver and compressor a light weight, compact design is achieved by mounting the impellers and drive motor on the same shaft motor cooling can accomplished by circulating chilled water in a jacket surrounding the motor or by refrigerant vapor in a two stage hermetic to balance the thrust of one impeller againt the thrust the first stage impeller is compressed by the first stage and discharged into the suction side of the second stage where it is again compressed and discharge into the condenser. Condenser The condenser, a shell and tube heat exchanger, receives compressed refrigerant vapor from the compressor the vapor condenses inside the shall and is collected as a liquid before being fed to the evaporator the condenser water that carries away the heat of condensation is carried in tubes inside, the shell. To distribute vapor evenly over the entire condensing tube bundle, so all the tube are a will absorb heat a perforated baffle plate is placed directly opposite the discharge opening from the compressor this baffle spreads the vapor throughout the length of the shell, and is and effective method of preventing impingement of the vapor on the condenser tubes There is another baffle installed in the condenser the purpose of this baffle is to create a quiet zone at the end of the path of vapor travel it is in this that the condensable gases are accumulated to permit most effective purging non-condensable gases and water vapor must not be allowed to accumulate as they decrease the cycle efficiency. Evaporator The evaporator is of the semi-flooded type with the bottom rows of tubes submerged in refrigerant water to be chilled is pumped through the tubes heat is transferred from the water to the liquid refrigerant causing it to boil and vaporize a High rate of heat transfer is obtain under full load since the entire tube bundle is wetted with rapidly boiling refrigerant. Just as the distribution of refrigerant vapor over the length of the condenser is important in condenser design, so is the distribution of refrigerant over the entire length of the evaporation important to the efficient operation of the evaporator to accomplish this there is metal baffle in the bottom of the evaporator the purpose of this baffle is to distribute the liquid, refrigerant uniformly since it is practical draw refrigerant vapor off the evaporator only at one point, it is necessary to provide a means above the evaporator surface to insure uniform flow of refrigerant from, the surface the, suction connection of the compressor this is accomplished by the used of eliminators. Eliminators separate and liquid refrigerant that may be carried by the refrigerant vapor when boiling is most violent under full load. This only dry vapor reaches the suction side of the first stage compressor. Flash Cooler A flash cooler is sometimes called an economizer. It flashes a small portion of refrigerant t the intermediate pressure to cool the remaining liquid refrigerant to the saturated condition in order to provide a greater refrigeration effect for a two stage compressor a single-stage flash cooler is used for a three stage compressor a two stage flash cooler is used. Orifice Plates Or Floats Valves Orifice plates (arrange in series) or float valves are used as throttling devices in centrifugal chillers that employ flooded refrigerant feed this device control the amount of refrigerant feed to the liquid cooler according to the pressure to the liquid refrigerant in the condenser. Purge Unit At an evaporator temperature 40 * f(4.4*c) HCFC -! @ # has a saturated pressure of 5.8 Psia (4OKP a abs) which is for lower then atmospheric pressure non-condensable gas such as air and carbon dioxide may diffuse and leak gaps because condenser is always located at a higher of non-condensable gas into the system usually accumulates in the upper-part of the condenser.

The presence of non-condensable gas reduces the refrigerant, flow as well as the rate a of heat transfer in the evaporator and the condenser it also increase the pressure in the condenser all these result in’ a loss of refrigerant capacity and increase of power consumption.

This purge unit includes mainly a purge tank. which is a low temperature and low pressure chamber with a DX coil to condense the vapor refrigerant, a condensing unit to serve the DX coil, a vacuum pump to purge the non- condensable gases, and filter dryer to absorb moisture and to remove dirt non- condensable gases and gaseous refrigerant from the upper part of the condenser migrate to the low temperature and low pressure purge tank through a connected to the bottom of the tank when the latent heat of condensation is absorbed by the coil, the gaseous refrigerant condenses to the liquid and falls to the refrigerant is separated by the water separation tube and from the middle layer all non-condensable gases accumulate at the top of the tank because of their lower densities. The purge vacuum, pump operates periodically to extract the non-condensable gases, and rejects them to the atmosphere it may be operated automatically once a day. The purge unit can be operated at any time independently of the chillers operation.