SECONDARY LIQUID-COOLING SYSTEM

The seawater system shown in figure 2-1 is a multiple-branch system. As such, it supplies a number of heat exchangers for other electronic equipment. To regulate the proper amount of seawater to each cool- ing system, an orifice plate is installed in the line between each heat exchanger and the duplex strainer. The heat exchangers are referred to as seawater-to- distilled-water heat exchangers. Another means of providing seawater is through the ship’s fire main, as shown in figure 2-2. The sea- water is taken from the fire main through a duplex strainer and a flow regulator (orifice plate) to and through the heat exchanger. It is then discharged overboard. The connection to the fire main is perma- nent. The ship’s fire pump, not shown in figure 2-3, is used to pump seawater into the fire main. The fire pump is similar in design to the previously mentioned seawater circulating pump, except it has a much larger capacity. Another means of obtaining seawater as a primary coolant for types I and II liquid-cooling systems is by an emergency connection, which is used if the normal seawater supply is lost. The connection is usually by means of a 1 1/2-inch fire hose. The emergency supply comes from an alternate portion of the ship’s fire main or a portable pump rigged by the ship’s damage con- trol party. The portable emergency hose is normally stored in the liquid-coolant machinery room. In types II and III liquid-cooling systems, chilled water is taken from the supply main of the air- conditioning, chilled-water systems. The chilled water is used as a backup source of cooling water for the primary cooling system shown in figure 2-2, and as a normal and backup source for the system shown in figure 2-3. The chilled water flows through the tubes of the heat exchanger (chilled water to distilled water), a flow regulator, and back to the chilled-water system. A temperature-regulating valve at the inlet of the heat exchanger regulates the flow of chilled water through the heat exchanger to maintain the required water temperature in the secondary system (distilled water). The ship’s air-conditioning, chilled-water circu- lating pump is used to pump the chilled water through the heat exchanger. The chilled-water system is a closed-loop water system because the water is recir- culated. The system must be kept tight and free from leaks to ensure satisfactory operation. SECONDARY LIQUID-COOLING SYSTEM The secondary liquid-cooling system transfers heat from the electronic equipment being cooled to the primary cooling system. The coolant normally used in the secondary system is distilled water, which is ultrapure and is maintained in that state by a de- mineralize. In some secondary systems, ethylene glycol is added to the water to prevent freezing when the system is exposed to freezing weather. The secondary liquid-cooling system is usually comprised of a distilled-water circulating pump, a compression or gravity-feed expansion tank, the elec- tronic equipment being cooled, a demineralizer, a temperature-control valve, the monitoring equipment with its associated alarms, and the heat exchanger, which is shared with the primary system. The second- ary system is a closed-loop water system, as compared to the seawater system, which is a one-pass, or open-loop, system. LIQUID-COOLING SYSTEM CONFIGURATIONS The U.S. Navy uses three basic configurations of liquid-cooling systems, and you could be involved with all three of them, depending on the number and types of electronic equipment to be cooled. The speci- fications for the type of system installed on your equipment will depend on the operational require- ments of the equipment. Some electronic equipments require very close regulation of the temperature of the distilled water, whereas others do not. 2-4