TYPE I LIQUID-COOLING SYSTEM

TYPE I LIQUID-COOLING SYSTEM The type I liquid-cooling system is a seawater/ distilled-water (SW/DW) heat exchanger with an SW/ DW heat exchanger standby. This system is used for electronic system installations that can be operated satisfactorily with seawater temperature as high as 95°F, which should result in a distilled-water supply temperature to the electronics of approximately 104°F. Refer to figure 2-1 as you study this section. Starting with the distilled-water pumps, distilled water under pressure flows to the temperature-regu- lating valve. The temperature-regulating valve is in- stalled to partially bypass distilled water around the seawater-to-distilled-water heat exchanger so that a constant water temperature can be supplied to the electronic equipment. As the temperature in the dis- tilled water increases, more water is directed to the heat exchanger and less to the bypass line, thus main- taining the output water temperature constant. The standby heat exchanger is usually of the same design and is used when the on-line heat exchanger is inoperable or is undergoing maintenance. The size of the heat exchanger is designed to handle the full cooling load of the electronic equipment plus a 20- percent margin. From the heat exchanger, the water then goes through various monitoring devices, which check the water temperature and flow. The water temperature and flow depend on the re- quirements of the electronic equipment being cooled. After the water moves through the equipment, it is drawn back to the pump on the suction side; thus, a continuous flow of coolant is maintained in a closed- loop system. An expansion tank in the distilled-water system compensates for changes in the coolant volume and provides a source of makeup water in the event of a secondary system leak. When the expansion tank is located above the highest point in the secondary system and vented to the atmosphere, it is called a gravity tank. If it is below the highest point in the secondary cooling system, it is called a conpression tank because it requires an air charge on the tank for proper operation. The demineralizer is designed to remove dissolved metals, carbon dioxide, and oxygen. In addition, a submicron filter (less than one-millionth of a meter) is installed at the output of the demineralizer to pre- vent the carry-over of chemicals into the system and to remove existing solids. TYPE II LIQUID-COOLING SYSTEM The type II liquid-cooling system is an SW/DW heat exchanger with a chilled-water/distilled-water (CW/DW) heat exchanger standby. This system is used in installations that cannot accept a DW tempera- ture higher than 90°F. Refer to figure 2-2 as you study this section. The secondary cooling system of the type II liquid-cooling system is similar to that of the type I secondary liquid-cooling system and uses many of the same components—the major difference is in the operation of the CW/DW heat exchanger. The second- ary coolant is in series with the SW/DW heat ex- changer and automatically supplements the cooling operation when the SW/D Wheat exchanger is unable to lower the temperature of the distilled water to the normal operating temperature. The CW/DW temperature-regulating valve allows more chilled water to flow into the primary cooling system to the CW/DW heat exchanger. This causes the temperature in the secondary system to go down. Normally, this action occurs only if high seawater temperatures are encountered in tropical waters. The CW/DW heat exchanger is also used in an SW/DW heat exchanger malfunction. TYPE III LIQUID-COOLING SYSTEM The type III liquid-cooling system is a CW/DW heat exchanger with a CW/DW heat exchanger stand- by, and is used in installations where the temperature range is critical. It requires close regulation of the DW coolant to maintain temperatures between established limits. For example, the temperature limits might be between 70°F and 76°F. This system is used where tighter control is required. Refer to figure 2-3 as you study this section. 2-5