April 13, 2018
Comparative posts always present a challenge. Point in case, there are differences between tube and shell type heat exchangers. Tempting though it might be to just rattle off a list of contrasting vessel characteristics, we want to draw a definitive line between heat exchanger types. So, instead of throwing text against a wall and seeing what sticks, let's properly establish those equipment defining borders.
Engineering terms provide valuable clues. In this case, the layout of the heat exchanger type is in the title. A tube stack is mounted inside a cylindrical shell, so the "shell" section is a pressure vessel. Picture, if you will, two fluid interacting. The first fluid medium fills the interior of the shell, and the second fluid is channelled through those internally mounted tubes. Heat is then "exchanged" between the two thermally active mediums, with the many tubes acting as a kind of folded surface.
There are variations on the above design. Prefixed letters classify the heat exchanger types that fit in this category. For example, the U-type model simply sends a bank of tubes through the tube sheet and into the cylindrical shell, at which point the pipes curve back and return to the output plenum. Essentially, the tubes are U-shaped, with a limited number of shell baffles guiding the hot fluid. It's a single-pass design, which means the pipes only pass through the shell fluid once. Just to illustrate this point, picture a 4-pass system, a tube stack that travels 4 times, end-to-end, inside the exchanger shell. Lastly, the lettering issue is used again in header design. Covering most of the alphabet, the letters are used to identify a number of contrasting header configurations.
If a large heat transference ratio is required, tube and shell heat exchangers are a logical engineering choice. But there's still the matter of additional codifiers, of more letters and more numbers. Guided by the TEMA standards and ASME directives, rear and front header types compete with shell types. Vessel sizes, geometrical configurations, and pressure drops all regulate that latter variable. Then there's the tube pitch, the addition of fins, tube patterns, and several other variables to assess. Even baffle types enter this design formula.
And so it goes, with more details layered on top of the fundamental design principles. Tie rods and spacers, shell nozzles and expansion joints, the different elements in this extended family really draw a line between tube and shell heat exchanger types. From the vessel to the tubes and baffles, every element affects heat transfer efficiency.
Fusion - Weld Engineering Pty Ltd
ABN 98 068 987619
1865 Frankston Flinders Road,
Hastings, VIC 3915
Ph: (03) 5909 8218
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