Heat Exchanger Fundamentals

By: Pravin Nagar


Heat Exchanger is the equipment in which heat (thermal energy) istransferred from one fluid to another fluid. These fluids are separated from each other with a metallic wall. To affect the exchange of heat, both the fluids must be at different temperatures. Heat will flow from hotter to the colder fluid.

Heat exchanger can be used for different purposes like, heating a colder fluid; cooling a hotter fluid; to condense a gaseous fluid; to boil a liquid and so on.

Type of heat exchangers

Although there are different types of heat exchangers, the construction of heat exchangers fall mainly into two categories: 1. Shell and tube; and 2. Plate

1. Shell and Tube Heat Exchangers

This is the most common type of heat exchanger construction and is suitable for high pressure applications.This type of heat exchanger consists of a set of tubes, called tube-bundle, arranged in a shell (pressure vessel). One fluid flows through the tubes, this fluid is called tube-side fluid; and other fluid flows over the tubes, this fluid is called shell-side fluid. Tube side fluid is separated from the shell side fluid by tubesheet at the end of the tubes. The tubes are welded or press fitted into the tube sheet to provide a leak tight joint. In the shell, tubes are supported by plates called baffles. These baffles reduce the vibration and direct the shell side fluid over the tubes for increased heat transfer efficiency. Generally Shell and tube heat exchangers are designed by TEMA standard and local and international codes for pressure vessels like, ASME BPVC, PD 5500, AD Merkblatt, etc.

There are mainly three types of shell and tube heat exchangers:

Fixed Tube-sheet Heat Exchanger:A fixed tube-sheet heat exchanger has straight tubes that are secured at both ends to tube-sheets welded to the shell. The tube-sheet may be welded to channel also. In this type of heat exchanger, tube bundle is fixed and cannot be removed. Hence it is generally used in clean service.In the event of large temperature differential between tube and shell material, higher longitudinal stresses will be developed in the shell and tube. To reduce these stresses, a flexible element called expansion joint is used on shell.

U-tube Heat Exchanger: In this type of heat exchanger, one tube-sheet is stationary andit has a bundle of U-shaped tubes. Tube bundle is removable for cleaning purpose. Hence it is used for dirty service on shell side. Because of U-bends, it is very difficult to clean inside of tube. Hence it is not suitable for dirty service on tube-side.

Floating Tube-sheet Heat Exchanger:In this type of heat exchanger, one tube-sheet is stationary and the other is free to float within the shell axially. Tube bundle is removable for cleaning purpose.As Floating tube-sheet heat exchanger can be cleaned from both tube and shell side, it can be used for services where both the shell and tube side fluids are dirty.

2. Plate type heat exchanger

A plate type heat exchanger consists of plates instead of tubes to separate the hot and cold fluids.Because of the larger surface area of the plate, this type of heat exchanger is capable of transferring more heat than similarly sized shell and tube heat exchanger. This type of heat exchanger is used for medium and low pressure applications.

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The author of this article is a professional writer who writes on industry related topics. He has couple years of experience writing on pressure vessel design, heat exchanger design, Mechanical drafting, engineering consultants and many more. His articles guide the reader in proper way.

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