eupex koppeling H2DV-19-C Helical gearboxes H2

Flender/Flender Gear Units/Helical gearboxes H2

and defrost. The nned-tube evaporators have ns to increase the surface area of the evaporator and thus provide higher heat transfer rate. Evaporators are also classi-ed as direct-expansion or ooded types. In direct-expansion evaporators, there is no recir- culation of the refrigerant in the coils before its return to the compressor. The ooded type recirculate any liquid refrigerant in the coils until it vaporizes before returning it tothe compressor. Such system has greater heat transfer efciency. To maintain high ef- ciency, the evaporator should be defrosted periodically. Evaporators that are operating at 0C are subjected to the accumulation of frost or ice (. The frost may be removed by electric heaters, periodic ooding of the coils with water, directing of hot refrigerant intothe coils, or defrosting with brine or glycol solution (. Compressor types that are most commonly used are reciprocating, rotary, and cen- trifugal compressors. Compressors may be run by an electric motor or by an internalcombustion engine. The reciprocating compressors can be used over wide range of capac- ities but have high maintenance costs. Rotary compressors have lower maintenance costs but are not available in sizes lower than 2 kW (. There are three major types of condensers, water-cooled, air-cooled, and evapora- tive. In double-pipe condensers cold water is passed through pipe that is encased by alarger pipe that carries the refrigerant. Heat is transferred by conduction from one pipeto the other. Shell and tube condensers are also used. These are similar to double-pipe condensers except that the water pipes enter large shell that contains the refrigerant. The method of heat exchange is the same. Water-cooled condensers can be expensive,especially if water is limited or its disposal is difcult. Air-cooled condensers are usually coils that are exposed to air. The refrigerant ows through the coils and the heat is conducted from the surface of the coils to the air byconv