General Theory of Heat Exchangers

A heat exchanger is a device that transfers heat from one medium to another the medium may be a solid, liquid, or gas. Some of the most complex engineering design problems relate to heat exchangers. 

Fdeat exchangers are divided into the following types. 

Recuperator A wall separating the flowing fluids is the most commonly encountered problem. 

Regenerator The hot and cold fluids pass alternately through a space containing solid areas/particles, which provide alternately a heat sink and a heat source. An example of the rotating-type matrix is a cooling tower. 

The direction of flow is important, as it has a pronounced effect on the efficiency of a heat exchanger. The flows may be in the same direction (parallel flow, cocurrent), in the opposite direction (counterflow), or at right angles to each other (cross-flow). The flow may be either single-pass or multipass the latter method reduces the length of the pass. 

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