A water-cooled condenser consists of hot transfer tubes mounted within a steel. Condenser water passes thru the tubes, and the condensing refrigerant occupies the shell surrounding the tubes. Ht e shell is equipped with a hot gas inlet, liquid sump, purge connections, water regulating valve connection, and a pressure relief device. The shell-and-coil condenser had a spiral or trombone tube must be cleaned chemically instead of by reaming or brushing.
Shell-and-coil condensers are of relatively low cost and are often used in air conditioning applications. At a given entering water temperature and condensing temperature, condenser capacity is dedecreased by decreasing the water flow rate, thus increasing the water temperature rise. Condensing temperatures usually range from 100-110 F, but may be a low as 80 F for Once-thru City water condensing.
The water-cooled condenser and the cooling tower should be considered as a single heat rejection device for the purposes of selection and application. Therefore, the economics of condenser selection are reviewed under the subject of Cooling Towers. In a once-thru application, the entering water temperature used for selection should be the maximum water temperature prevailing at the time of maximum refrigeration load.
Selection of the number of water passes should be made with regard to the temperature and pressure of the water available. The low pressure and higher temperature water available from cooling towers generally dictates the least number of passes.
Normally, manufacturers base water-cooled condenser ratings on various conditions of the tube scaling on the water side. A fouling factor represents the resistance to heat floe presented by scaling. Since some surface fouling is present on tube surfaces from the beginning of operation, a minimum fouling factor of .0005 is suggested for selection.
Scale factors for various types of condensing water system are shown in Part 5. The factors shown should be tempered by operating conditions. A reduction in the factor is justified in the case of frequent cleaning, an unusually low condensing temperature, or when operation is less than 4000 hours annually.
Control of water flow thru condensers may be required to limit the condensing pressure to a
predetermined minimum. Two methods of restricting this flow are commonly used, a two-way throttling valve or a three-way diverting valve. The two-way valve is useful in maintaining condensing pressure in once-thru applications utilizing city, well, lake or river water.
In the case of city water, a prime objective may be to minimize water costs. The three-way valve is most often used with a cooling tower. It operates to direct water around the condenser as the condensing temperature is lowered. This allows the pump to maintain its flow and reduces problems of water distribution with multiple unit applications.
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