A heat exchanger is a device that transfers part of the heat from a hot fluid to a cold fluid. It plays a vital role in chemical, petroleum, power, food and many other industrial processes. In chemical production, heat exchangers can be used as heaters, coolers, condensers, evaporators and reboilers, making them widely applied equipment.
Heat exchangers vary in structural design to suit different media, operating conditions, temperatures and pressures. They are classified in detail as follows:
Classification by Heat Transfer Principle
Recuperative Heat ExchangersRecuperative heat exchangers allow two fluids at different temperatures to flow in spaces separated by a solid wall. Heat is exchanged between the two fluids through conduction through the wall and convection over the wall surface.This category includes shell-and-tube, double-pipe and other types, and is the most widely used heat exchanger type.
Regenerative Heat ExchangersRegenerative heat exchangers transfer heat from a hot fluid to a cold fluid via a solid thermal storage medium. The hot fluid first heats the solid medium to a specified temperature, after which the cold fluid passes through and is heated.Common types include rotary and valve-switching regenerators.
Fluid-connected Indirect Heat ExchangersThese consist of two surface heat exchangers connected by a circulating heat carrier. The carrier absorbs heat from the high-temperature fluid and releases it to the low-temperature fluid in the second unit.
Direct-contact Heat ExchangersAlso known as mixing heat exchangers, these allow two fluids to come into direct contact and mix for heat transfer. Examples include cooling towers and gas condensers.
Compound Heat ExchangersThese combine both indirect steam-water heat transfer and direct water-water mixing heat exchange. Compared with indirect surface exchangers, they offer higher efficiency; compared with direct mixing units, they provide greater stability and lower unit noise.
Classification by Application
HeaterA heater raises a fluid to a required temperature without causing a phase change in the heated fluid.
PreheaterA preheater preheats a fluid to provide standard process parameters for subsequent operations.
SuperheaterA superheater heats a fluid (process gas or steam) to a superheated state.
EvaporatorAn evaporator heats a fluid above its boiling point to cause evaporation, typically involving a phase change.
