Heat Exchangers

A heat exchanger divides the stream having waste heat and the medium to which it is to be transferred, though permits the transfer of heat across the division boundaries, industrial heat exchangers are termed by many names: regenerators, recuperators, waste-heat steam generators, heat wheels, condensers, temperature and moisture exchangers, and so on. Whatever name they might have, they all perform one fundamental function: the transfer of heat.

Heat Exchangers are characterized as single or multi-pass; liquid to gas, gas to gas, liquid to liquid, evaporator, condenser, parallel flow, counter-flow, or cross-flow. The terms ‘single pass’ or ‘multi-pass’ refer to the heating or cooling media passing over the heat transfer surfaces once or a number of times. Multi-pass flow includes the use of internal baffles. Gas to gas, liquid to gas, and liquid to liquid refer to the two fluids among which heat is transferred in the heat exchanger, and entails no phase changes take place in such fluids. An evaporator is a heat exchanger in which heat is transferred to an evaporating (or boiling) liquid; in a condenser, heat is transferred from a condensing vapor. A parallel-flow heat exchanger is one in which both fluids flow in around similar direction. A counter-flow heat exchanger is one in which two fluids move in reverse directions. Whenever the two fluids move at right angles to each other, the heat exchanger is considered to be of the cross-flow kind.