Heat Exchanger

Heat exchanger is a device, which is used to transfer heat between two media by the processes of conduction, convection, and radiation, and through utilizing maximum surface area contact. Heat exchangers have wide applications in space heating, refrigeration, air-conditioning, and power plant engineering, automobiles, etc.
These can be classified according to their basic design features, or by the type of flow relation between the coolant and hot fluid/surface. Some of the prominent types are:

Parallel Flow Heat Exchangers:

In this type, the two fluids enter the exchanger from the same end, and travel in parallel to one another towards the other end. The temperature gradient varies with position across the heat transfer surface , but an appropriate mean temperature can be defined, using LMTD or NTU methods.

Counter Flow Heat Exchangers:

In this type, the coolant and the hotter fluid enter the exchanger through different ends. It is one of the most efficient designs, as maximum heat transfer takes place in it. The coolant achieves the temperature of hotter fluid after reaching the inlet of hotter fluid and vice-versa, accounting least approximations.

Shell and Tube Heat Exchangers:

It consists of a bundle of tubes placed inside a shell. One of the fluids, flows through the tubes, while another fluid, flows over the tubes, which transfers heat between the two fluids. The set of tubes is called a tube bundle, and may be composed of several types of tubes, which may be arranged plain, longitudinally finned, etc.