Everything about Shell And Tube Heat Exchanger totally explained
A
shell and tube heat exchanger is a class of
heat exchanger designs. It is the most common type of heat exchanger in oil refineries and other large chemical processes, and is suited for higher-pressure applications. As its name implies, this type of heat exchanger consists of a shell (a large
pressure vessel) with a bundle of
tubes inside it. One fluid runs through the tubes, and another fluid flows over the tubes (through the shell) to transfer heat between the two fluids. The set of tubes is called a tube bundle, and may be composed by several types of tubes: plain, longitudinally finned, etc.
Theory and Application
Two fluids, of different starting temperatures, flow through the heat exchanger. One flows through the tubes (the tube side) and the other flows outside the tubes but inside the shell (the shell side). Heat is transferred from one fluid to the other through the tube walls, either from tube side to shell side or vice versa. The fluids can be either
liquids or
gases on either the shell or the tube side. In order to transfer heat efficiently, a large
heat transfer area should be used, leading to the use of many tubes. In this way, waste heat can be put to use. This is an efficient way to conserve energy.
Heat exchangers with only one
phase (liquid or gas) on each side can be called one-phase or single-phase heat exchangers. Two-phase heat exchangers can be used to heat a liquid to boil it into a gas (vapor), sometimes called
boilers, or cool a vapor to condense it into a liquid (called
condensers), with the phase change usually occurring on the shell side. Boilers in steam engine
locomotives are typically large, usually cylindrically-shaped shell-and-tube heat exchangers. In large
power plants with steam-driven
turbines, shell-and-tube
surface condensers are used to condense the exhaust
steam exiting the turbine into condensate
water which is recycled back to be turned into steam in the steam generator.
Shell and tube heat exchanger design
There can be many variations on the shell and tube design. Typically, the ends of each tube are connected to
plenums (sometimes called
water boxes) through holes in
tubesheets. The tubes may be straight or bent in the shape of a U, called U-tubes.
In nuclear power plants called
pressurized water reactors, large heat exchangers called
steam generators are two-phase, shell-and-tube heat exchangers which typically have U-tubes. They are used to boil water recycled from a surface condenser into steam to drive the turbine to produce power.
Most shell-and-tube heat exchangers are either 1, 2, or 4 pass designs on the tube side. This refers to the number of times the fluid in the tubes passes through the fluid in the shell. In a single pass heat exchanger, the fluid goes in one end of each tube and out the other.
Surface condensers in power plants are often 1-pass straight-tube heat exchangers (see
Surface condenser for diagram).
Two and four pass designs are common because the fluid can enter and exit on the same side. This makes construction much simpler.
There are often
baffles directing flow through the shell side so the fluid doesn't take a short cut through the shell side leaving ineffective low flow volumes.
Counter current heat exchangers are most efficient because they allow the highest
log mean temperature difference between the hot and cold streams. Many companies however don't use single pass heat exchangers because they can break easily in addition to being more expensive to build. Often multiple heat exchangers can be used to simulate the counter current flow of a single large exchanger.
Selection of tube material
To be able to transfer heat well, the tube material should have good
thermal conductivity. Because heat is transferred from a hot to a cold side through the tubes, there's a
temperature difference through the width of the tubes. Because of the tendency of the tube material to thermally expand differently at various temperatures,
thermal stresses occur during operation. This is in addition to any
stress from high
pressures from the fluids themselves. The tube material also should be compatible with both the shell and tube side fluids for long periods under the operating conditions (temperatures, pressures,
pH, etc.) to minimize deterioration such as
corrosion. All of these requirements call for careful selection of strong, thermally-conductive, corrosion-resistant, high quality tube materials, typically
metals. Poor choice of tube material could result in a
leak through a tube between the shell and tube sides causing fluid cross-contamination and possibly loss of pressure.
Further Information
Get more info on 'Shell And Tube Heat Exchanger'.
|
External Link Exchanges
Do you know how hard it is to get a link from a large encyclopaedia? Well we're different and will prove it. To get a link from us just add the following HTML to your site on a relevant page:
<a href="http://shell_and_tube_heat_exchanger.totallyexplained.com">Shell and tube heat exchanger Totally Explained</a>
Then simply click through this link from your web page. Our crawlers will verify your link, extract the title of your web page and instantly add a link back to it. If you like you can remove the words Totally Explained and embed the link in article text.
As long as your link remains in place, we'll keep our link to you right here. Please play fair - our crawlers are watching. Your site must be closely related to this one's topic. Any kind of spamming, dubious practises or removing the link will result in your link from us being dropped and, potentially, your whole site being banned. |
