Heat Exchanger

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A Model of Aircondition Heat Exchanger A heat exchanger is a device used to transfer heat between two or more fluids that can be single or two phase and depending on the exchanger type may be separated or in direct contact with each other. Devices involving energy sources such as nuclear fuel pins or fired heaters are not normally regarded as heat exchangers although many of the principles involved in their design are the same. In order to discuss heat exchangers it is necessary to provide some form of categorization that allows for a better understanding of these complex devices. There are two approaches that are normally taken when classifying heat exchangers. The first considers the flow configuration within the heat exchanger, while the second is based on the classification of equipment type primarily by construction. Both methods are considered here. Classification of Heat Exchangers by Construction In this section heat exchangers are classified mainly by their construction as explained in detail by Garland (1990). The first level of classification is to divide heat exchanger types into recuperative or regenerative categories. A Recuperative Heat Exchanger has separate flow paths for each fluid and fluids flow simultaneously through the exchanger exchanging heat across the wall separating the flow paths. On the other hand, a Regenerative Heat Exchanger has a single flow path which the hot and cold fluids alternately pass through. Heat Exchanger Classifications Figure 5 shows the different types of heat exchangers classified according to their construction. Regenerative Heat Exchangers In a regenerative heat exchanger, the flow path normally consists of a matrix that is heated when the hot fluid passes through it which is known as the "hot blow". This heat is then released to the cold fluid when this flows through the matrix which is called the "cold blow". Regenerative Heat Exchangers are sometimes known as Capacitive Heat Exchangers and are discussed in detail by Walker (1982). Regenerators are mainly used in gas/gas heat recovery applications in power stations and other energy-intensive industries. The two main types of regenerator are Static and Dynamic, both of which operate transiently unless great care is taken in their design resulting in cross contamination of the hot and cold streams. However, the use of regenerators is likely to increase in the future as attempts are made to improve energy efficiency and recover more low-grade heat. Because regenerative heat exchangers tend to be used for specialist applications recuperative heat exchangers are more common.