Shell and tube heat exchanger

Shell and tube heat exchanger

A shell and tube heat exchanger is a class of heat exchanger designs. [ cite book|author=Sadik Kakaç and Hongtan Liu|title=Heat Exchangers: Selection, Rating and Thermal Design|edition=2nd Edition|publisher=CRC Press|year=2002|id=ISBN 0849309026] [cite book|author=Perry, Robert H. and Green, Don W.|title=Perry's Chemical Engineers' Handbook|edition=6th Edition| publisher=McGraw-Hill|year=1984|id=ISBN 0-07-049479-7] 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.

hell 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 does not 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 do not 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.

election 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 is 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.

ee also

*Heat exchanger
*Surface condenser
*Boiler or Reboiler
*Plate and Frame Heat Exchanger
*Plate fin heat exchanger
*Fouling or Scaling
*Fired Heater
*TEMA
*Pressure vessel
*EJMA
*NTU method as an alternative to finding the LMTD.

References

External links

* [http://www.cheresources.com/designexzz.shtml Basics of Shell and Tube Exchanger Design]
* [http://www.cheresources.com/heat_transfer_basics.shtml Basics of Industrial Heat Transfer]
* [http://www.cheresources.com/shell_tube_heat_exchanger_1.shtml Specifying a Liquid_Liquid Heat Exchanger]


Wikimedia Foundation. 2010.

Нужен реферат?

Look at other dictionaries:

  • Concentric tube heat exchanger — Concentric Tube (or Pipe) Heat Exchangers are used in a variety of industries for purposes such as material processing, food preparation and air conditioning.[1] They create a temperature driving force by passing fluid streams of different… …   Wikipedia

  • Heat exchanger — An interchangeable plate heat exchanger Tubular heat exchan …   Wikipedia

  • Plate fin heat exchanger — A plate fin heat exchanger is a type of heat exchanger design that uses plates and finned chambers to transfer heat between fluids. It is often categorized as a compact heat exchanger to emphasise its relatively high heat transfer surface area to …   Wikipedia

  • heat exchanger — a device for transferring the heat of one substance to another, as from the exhaust gases to the incoming air in a regenerative furnace. [1900 05] * * * Any of several devices that transfer heat from a hot to a cold fluid. In many engineering… …   Universalium

  • Plate heat exchanger — A plate heat exchanger is a type of heat exchanger that uses metal plates to transfer heat between two fluids. This has a major advantage over a conventional heat exchanger in that the fluids are exposed to a much larger surface area because the… …   Wikipedia

  • Dynamic scraped surface heat exchanger — The dynamic scraped surface heat exchanger (DSSHE) was designed to face some problems found in other types of heat exchangers. They increase heat transfer by: removing the fouling layers, increasing turbulence in case of high viscosity flow,… …   Wikipedia

  • Condenser (heat transfer) — For other Condensers not involving heat transfer, see Condenser (disambiguation). In systems involving heat transfer, a condenser is a device or unit used to condense a substance from its gaseous to its liquid state, typically by cooling it. In… …   Wikipedia

  • Heat transfer — is a discipline of thermal engineering that concerns the exchange of thermal energy from one physical system to another. Heat transfer is classified into various mechanisms, such as heat conduction, convection, thermal radiation, and phase change …   Wikipedia

  • Dynamic scraped surface heat exchangers — Introduction The most important technologies for indirect heat transfer use tubes (shell and tube exchangers) or flat surfaces (plate exchangers). Their goal is to exchange the maximum amount of heat per unit area by generating as much turbulence …   Wikipedia

  • Chiller — For other uses, see Chiller (disambiguation). York International water cooled chiller. A chiller is a machine that removes heat from a liquid via a vapor compression or absorption refrigeration cycle. This liquid can then be circulated through a… …   Wikipedia

Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”