https://chemicalengineeringnob.com/2018/10/04/1794/

Heat exchanger is equipment that transfers energy from a warmer fluid to cooler fluid through a solid wall separating the two fluids; with maximum rate and minimum investment cost. The transferred heat maybe sourced from a condensation or vaporization process. This is majorly used and designed by chemical Engineers. Therefore, it is common practice in chemical engineering.

Examples includes: milk chillers, automobile radiators and intercooler.

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Types of heat exchanger
For the benefit and effective heat transfer process, it is necessary to classify heat exchangers according to:

Nature of heat transfer process: this deals with the mixing or contact between the fluid system. It could be direct or indirect contact. In direct contact, the hot and cold fluid mixes together in order to transfer heat due to temperature difference. The fluid are must be harmless to the system. For indirect contact, heat is transferred through the walls separating the fluids. The advantages of both classes are; easy construction, higher heat transfer coefficient (regenerators), and more surfaces are for heat transfer (recuperator).
Relative motion of the fluid: the movement of the fluid could be in the following ways;

https://chemicalengineeringnob.com/2018/10/04/1794/