TYPES OF LIQUID COOLING SYSTEMS

Heat is removed from the heat exchanger by forcing cool outside air through the heat exchanger by an external blower. There is no physical contact between the internal and external air. In some applications, the internal air is replaced by an inert gas such as nitrogen to prevent oxidation. AIR-TO-LIQUID COOLING A more efficient heat transfer is possible by replacing the air-to-air heat exchanger with an air-to-liquid heat exchanger (fig. 1-5). In this method, the internal air is also circulated past the heat producing part and through a heat exchanger, but the heat is removed from the heat exchanger by a liquid coolant circulating through the heat exchanger. Air-to-liquid cooling systems usually employ built-in safety devices to shut down the equipment to prevent overheating.The overheating could be caused by low or no liquid flow, liquid too hot, an inoperative circulating fan, or reduced heat exchanger efficiency because of improper maintenance. This type of cooling system is normally found on large equipment instillations where a huge amount of heat is developed. Many radar transmitters, for example, require cooling of this type. The other types that we have discussed would not be able to dissipate the heat that a high-powered radar transmitter develops. A disadvantage of this type of cooling system is that they are larger and more complex. However, for this reason and because they are a part of the more complex systems, we describe the typical liquid cooling system used aboard ship. In this way, you will be given abetter understanding of the function of individual components within a system and the basic maintemnce required to maintain the system to a high state of readiness. LIQUID COOLING Cooling systems are essential to the satisfactory operation of all shipboard combat systems equipment. In fact, some form of cooling is required for all shipboard electronic equipment. As we have indicated, liquid cooling is especially efficient for the transfer of large amounts of heat. To maintain cooling systems, you must have a broad understanding of the different types of liquid cooling systems with which you are involved. A typical liquid cooling system is composed of two basic coolant systems. First, there is the primary system. It provides the initial source of cooling water that can be either seawater (SW) or chilled water (CW) from the ship’s air-conditioning plant, or a combination of both. Next, the secondary system transfers the heat load from the electronic equipment to the primary system. The coolant normally used in the secondary system is distilled water (DW). This distilled water is ultrapure and is maintained in that state by a demineralize. In some secondary systems, ethylene glycol is added to the water to prevent freezing when the system is exposed to freezing weather. TYPES OF LIQUID COOLING SYSTEMS In the U.S. Navy, there are three basic configurations of liquid cooling systems, and conceivably you could be involved with all three. The type or types with which you maybe involved, depends upon the number and types of electronic equipment to be cooled. The three types of systems areas follows: Type I—Seawater/distilled water (SW/DW) heat exchanger with SW/DW heat exchanger standby Figure 1-5.—Air-to-liquid cooling. 1-3