Closed circuit coolers are used in a wide range of continuous, intermittent and batch applications. They eliminate excess heat from a system to ensure the process operates safely and efficiently. This heat is generated mechanically, electrically or by a chemical reaction.
Circulating air is the primary coolant; it takes away the heat from the components it passes over. Water is normally the secondary coolant. It removes heat from the airstream as it passes through the closed circuit cooler, returning the airstream to within 5 to 10oC of the circulating water temperature.
The quality of the cooling water determines the materials used in the closed circuit cooler. Tube materials vary from copper through stainless steel to titanium.
Example of marine applications
Recirculating marine breaking resistors are an example of a process which is intermittent and where a large amount of thermal energy must be taken out from a closed system, in a short period of time. A centrifugal fan circulates large volumes of air through the resistor stack as the braking is applied and the heat is generated. The air removes the heat from the resistor stack and in turn, the air is cooled by a closed circuit air to water heat exchanger.
The cooling water for the majority of marine applications is seawater. 90/10 cupronickel is a standard tube material for clean seawater. However, in some instances, the requirement to minimise weight may have an impact. Titanium, while marginally reducing the heat transfer, can contribute to weight reduction in addition to corrosion and erosion resistance.
Because of the large amount of heat input, the recirculating air temperature rises to more than 100o C. Over a specified period, the circulating air is reduced in temperature to within 5 to 10o C of the circulating water temperature. The resistors are returned to their normal standby temperature profile so that they are available for operation when next called upon.