A
shell and tube heat exchanger is a class of
heat exchangerA heat exchanger is a device built for efficient heat transfer from one medium to another. The media may be separated by a solid wall, so that they never mix, or they may be in direct contact. They are widely used in space heating, refrigeration, air conditioning, power plants, chemical plants,...
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 vesselA pressure vessel is a closed container designed to hold gases or liquids at a pressure substantially different from the ambient pressure.The pressure differential is potentially dangerous and many fatal accidents have occurred in the history of their development and operation...
) 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.
A
shell and tube heat exchanger is a class of
heat exchangerA heat exchanger is a device built for efficient heat transfer from one medium to another. The media may be separated by a solid wall, so that they never mix, or they may be in direct contact. They are widely used in space heating, refrigeration, air conditioning, power plants, chemical plants,...
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 vesselA pressure vessel is a closed container designed to hold gases or liquids at a pressure substantially different from the ambient pressure.The pressure differential is potentially dangerous and many fatal accidents have occurred in the history of their development and operation...
) 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
liquidLiquid is one of the principal states of matter. A liquid is a fluid that has the particles loose and can freely form a distinct surface at the boundaries of its bulk material. The surface is a free surface where the liquid is not constrained by a container....
s or
gasThis page is about the physical properties of gas as a state of matter. For the uses of gases, and other meanings, see Gas .A gas is one of four states of matter. Near absolute zero, a substance exists as a solid...
es on either the shell or the tube side. In order to transfer heat efficiently, a large
heat transferHeat transfer is the transition of thermal energy from a hotter object to a cooler object...
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
phaseIn the physical sciences, a phase is a region of space , throughout which all physical properties of a material are essentially uniform. Examples of physical properties include density, index of refraction, and chemical composition...
(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
boilerA boiler is a closed vessel in which water or other fluid is heated. The heated or vaporized fluid exits the boiler for use in various processes or heating applications.-Overview:-Materials:...
s, or cool a vapor to condense it into a liquid (called
condenserCondenser may refer to:*Condenser , a device or unit used to condense vapor into liquid. More specific articles on some types include:*Condenser , a range of laboratory glassware used to remove heat from fluids....
s), with the phase change usually occurring on the shell side. Boilers in steam engine
locomotiveA locomotive is a railway vehicle that provides the motive power for a train. The word originates from the Latin loco – "from a place", ablative of locus, "place" + Medieval Latin motivus, "causing motion", and is a shortened form of the term locomotive engine, first used in the early 19th...
s are typically large, usually cylindrically-shaped shell-and-tube heat exchangers. In large power plants with steam-driven
turbineA turbine is a rotary engine that extracts energy from a fluid or air flow and converts it into useful work.The simplest turbines have one moving part, a rotor assembly, which is a shaft or drum, with blades attached. Moving fluid acts on the blades, or the blades react to the flow, so that they...
s, shell-and-tube surface condensers are used to condense the exhaust
steamSteam is vaporized water. It is a transparent gas . At standard temperature and pressure, pure steam occupies about 1,600 times the volume of an equal mass of liquid water...
exiting the turbine into condensate
waterWater is an ubiquitous chemical substance that is composed of hydrogen and oxygen and is essential for all known forms of life.In typical usage, water refers only to its liquid form or state, but the substance also has a solid state, ice, and a gaseous state, water vapor or steam. Water covers 71%...
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 reactorPressurized water reactors comprise a majority of all western nuclear power plants and are one of two types of light water reactor , the other type being boiling water reactors . In a PWR the primary coolant is pumped under high pressure to the reactor core, then the heated water transfers...
s, large heat exchangers called
steam generatorA steam generator is a device used to boil water to create steam. It may refer to:*Boiler , a closed vessel in which water is heated under pressure...
s 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 a
turbineA steam turbine is a mechanical device that extracts thermal energy from pressurized steam, and converts it into rotary motion. Its modern manifestation was invented by Sir Charles Parsons in 1884....
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
bafflesA Baffle is an integral part of the shell and tube heat exchanger design. It is designed to support the tubular bundles and direct the flow of fluids for maximimum efficiency.-Use of baffles:The main roles of a baffle are to:...
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 differenceThe log mean temperature difference is used to determine the temperature driving force for heat transfer in flow systems, most notably in heat exchangers. The LMTD is a logarithmic average of the temperature difference between the hot and cold streams at each end of the exchanger. The larger the...
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.
Selection of tube material
To be able to transfer heat well, the tube material should have good
thermal conductivityIn physics, thermal conductivity, , is the property of a material that indicates its ability to conduct heat. It appears primarily in Fourier's Law for heat conduction.-Measurement:...
. Because heat is transferred from a hot to a cold side through the tubes, there is a
temperatureIn physics, temperature is a physical property of a system that underlies the common notions of hot and cold; something that feels hotter generally has the higher temperature. Temperature is one of the principal parameters of thermodynamics...
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
stressIn continuum mechanics, the concept of stress, introduced by Cauchy around 1822, is a measure of the average amount of force exerted per unit area of a surface within a deformable body on which internal forces act...
from high
pressurePressure is the force per unit area applied in a direction perpendicular to the surface of an object. Gauge pressure is the pressure relative to the local atmospheric or ambient pressure.- Definition :...
s 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,
pHpH is a measure of the acidity or basicity of a solution. It is defined as the cologarithm of the activity of dissolved hydrogen ions . Hydrogen ion activity coefficients cannot be measured experimentally, so they are based on theoretical calculations...
, etc.) to minimize deterioration such as
corrosionCorrosion is the disintegration of a material into its constituent atoms due to chemical reactions with its surroundings. In the most common use of the word, this means a loss of electrons of metals reacting with water and oxygen. Weakening of iron due to oxidation of the iron atoms is a...
. All of these requirements call for careful selection of strong, thermally-conductive, corrosion-resistant, high quality tube materials, typically
metalA metal is a chemical element that is a good conductor of both electricity and heat, forms cations and ionic bonds with non-metals. In chemistry, a metal is an element, compound, or alloy characterized by high electrical conductivity. In a metal, atoms readily lose electrons to form positive ions...
s, including copper alloy,
stainless steelIn metallurgy, stainless steel, also known as inox steel or inox, is defined as a steel alloy with a minimum of 11% chromium content by mass. Stainless steel does not stain, corrode, or rust as easily as ordinary steel...
, carbon steel, non-ferrous copper alloy,
InconelInconel is a registered trademark of Special Metals Corporation that refers to a family of austenitic nickel-chromium-based superalloys . Inconel alloys are typically used in high temperature applications. It is often referred to in English as "Inco"...
,
nickelNickel is a chemical element, with the chemical symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge. It is one of the four ferromagnetic elements at about room temperature, other three being iron, cobalt and gadolinium...
,
HastelloyHastelloy is the registered trademark name of Haynes International, Inc. The trademark is applied as the prefix name of a range of twenty two different highly corrosion-resistant metal alloys loosely grouped by the metallurgical industry under the material term “superalloys” or “high-performance...
and
titaniumTitanium is a chemical element with the symbol Ti and atomic number 22. Sometimes called the “space age metal”, it has a low density and is a strong, lustrous, corrosion-resistant transition metal with a silver color.Titanium can be alloyed with iron, aluminium, vanadium, molybdenum, among other...
. Poor choice of tube material could result in a
leakA leak is a hole or other opening, usually unintended and therefore undesired, in a container or fluid-containing system, such as a tank or a ship's hull, through which the contents of the container can escape or outside matter can enter the container. The word "leak" is also used as a verb;...
through a tube between the shell and tube sides causing fluid cross-contamination and possibly loss of pressure.
See also
- Heat exchanger
A heat exchanger is a device built for efficient heat transfer from one medium to another. The media may be separated by a solid wall, so that they never mix, or they may be in direct contact. They are widely used in space heating, refrigeration, air conditioning, power plants, chemical plants,...
- Surface condenser
- Boiler
A boiler is a closed vessel in which water or other fluid is heated. The heated or vaporized fluid exits the boiler for use in various processes or heating applications.-Overview:-Materials:...
or ReboilerReboilers are heat exchangers typically used to provide heat to the bottom of industrial distillation columns. They boil the liquid from the bottom of a distillation column to generate vapors which are returned to the column to drive the distillation separation....
- Plate and frame 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 fluids spread out over the plates. This facilitates...
- 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 volume ratio....
- Fouling
Fouling refers to the accumulation of unwanted material on solid surfaces, most often in an aquatic environment. The fouling material can consist of either living organisms or a non-living substance...
or scalingScaling may refer to:* Scaling , a linear transformation that enlarges or diminishes objects* Scaling , a network's ability to function as the number of people or computers on the network increases...
- Fired heater
- TEMA
TEMA may refer to:* Toyota Motor Engineering & Manufacturing North America* Tennessee Emergency Management Agency*TEMA, or the Turkish Foundation for Combating Soil Erosion, for Reforestation and the Protection of Natural Habitats is a non-governmental organization founded on 11 September 1992 by...
- Pressure vessel
A pressure vessel is a closed container designed to hold gases or liquids at a pressure substantially different from the ambient pressure.The pressure differential is potentially dangerous and many fatal accidents have occurred in the history of their development and operation...
- EJMA
- NTU method
The Number of Transfer Units Method is used to calculate the rate of heat transfer in heat exchangers when there is insufficient information to calculate the Log-Mean Temperature Difference...
as an alternative to finding the LMTD.
External links