Heat Exchanger

Heat exchanger, abbreviated as HE or HEX, is a device used to transer heat from one medium to another at different temperatures.  The heat transfer can be air or a liquid such as water or oil.

A heat exchanger has many functions.  They are critical to the process industries as they used to condense, heat, cool, or chill a fluid.  It also can be used to change the phase of a fluid (liquid to vapor or vapor to liquid) like a boiler.  Heat exchangers can be a direct contact HEX or an indirect contact type HEX. 

In a direct contact heat exchanger, heat transfer continuously occurs by the mixing of two process streams.  An example of this is a cooling tower, commonly found in power plants where a stream of hot air is consistently mixed with cooler water.  The water cools the hot air and exits the top of the cooling tower.  Warm water exits the bottom of the tower, is recollected, cooled and used again. 

An indirect contact type heat exchanger transfers heat by maintaining a separation between the two process streams.  Examples of an indirect contact type HEX are Shell and Tube Heat Exchangers and Air Cooled Heat Exchanger (also known as a fin-fan)

 

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 Heat Exchanger Types

  • Adiabatic Heat Exchanger  -  It consists of a rotating wheel and an intermediate fluid that is stored to hold heat, it is then transferred to the other side of the heat exchanger for release.
  • Condenser, Boiler, and Evaporator  -  Condensers are heat exchange devices that take hot gas and cool it to the point of condensation, turning the gas or vapor into a liquid.  In evaporators and boilers, the heat transfer process is carried out by changing the liquid form from the liquid form to the gas or vapor form.
  • Direct and Indirect Heat Exchanger  -  Indirect-fired heaters use a flame in a burn chamber that warms the heat exchanger. The device draws cool air into two different chambers. The air passes over and around the heat exchanger and gets warm.  Direct-fired heaters heat the air that passes through an open flame.  Internal components within the heater control the warmed air, making it an efficient heating solution.
  • Double Pipe Heat Exchanger  -  Used for the transfer or exchange of heat between two liquids without mixing them.  They consist of two or more concentric, cylindrical pipes or tubes, one larger and the other smaller.  One fluid flows inside the tube and the other fluid flows outside,
  • Finned Heat Exchanger  -  They are designed for the maximum heat transfer surface area, which improves the efficiency of conducting heat in liquids with low thermal conductivity.  They have fins attached to the outer tube of the exchanger.  Adding fins facilitates the transfer of fluid outside the tube.
  • Microchannel Heat Exchanger  -  A multi-pass parallel-flow heat exchanger consisting of manifolds, an inlet and outlet, multi-port tubes with hydraulic channels, and fins.  All these parts are usually brazed together.
  • Phase Change Heat Exchanger  -  In a two-phase heat exchange process there is a phase change on the cold side, the warm side or both.
  • Pillow Plate Heat Exchanger  -  These exchangers are fully welded, so they form a wavy, pillow-shaped surface by an inflation process.
  • Plate Heat Exchanger  -  The metal plates form channels through which the interacting fluids can flow.  They use multiple layers of flat plates fixed to form a series of channels for the flow of fluids.
  • Shell and Tube Heat Exchanger  -  Has multiple tubes in which the two working fluids exchange heat by thermal contact which is placed within a cylindrical shell. As such, one fluid flows inside the tubes and the other through the shell.
  • Tube in Tube Heat Exchanger  -  Designed for sludge containing fibers and particles, used for heating and cooling purposes.  This exchangers has a tube mounted inside an outer shell tube.
  • Waste Heat Recovery Unit  -  These units reuse excess heat energy that would otherwise be disposed of or released into the atmosphere in the form of steam or smoke.

 

Heat Exchanger Standards

API Standards

  • API Std 530 - Calculation of Heater-tube Thickness in Petroleum Refineries
  • API Std 660 - Shell-and-Tube Heat Exchangers
  • API Std 661 - Petroleum, Petrochemical, and Natural Gas Industries—Air-cooled Heat Exchangers

ASTM Standards

  • ASTM B395 / B395M - Standard Specification for U-Bend Seamless Copper and Copper Alloy Heat Exchanger and Condenser Tubes
  • ASTM B543 / B543M - Standard Specification for Welded Copper and Copper-Alloy Heat Exchanger Tube
  • ASTM B743 - Standard Specification for Seamless Copper Tube in Coils
  • ASTM B903 - Standard Specification for Seamless Copper Heat Exchanger Tubes With Internal Enhancement
  • ASTM B919 - Standard Specification for Welded Copper Heat Exchanger Tubes With Internal Enhancement
  • ASTM B944 - Standard Specification for Copper-Beryllium Welded Heat Exchanger and Condenser Tube (UNS No. C17510)
  • ASTM B956 / B956M - Standard Specification for Welded Copper and Copper-Alloy Condenser and Heat Exchanger Tubes with Integral Fins

 

Heat Exchanger Glossary

A

B

  • Baffle Plate  -  Tubes pass through this plate for support.  It provides a blocked path for the shell-side medium, forcing the medium across the tubes for better heat exchanger performance.
  • Baffle Spacing  -  The space between baffle plates on a tube bundle.
  • Bundle Assembly  -  The tube assembly in removable bundle heat exchangers and consists of tubes, tubesheets, baffles, spacers, and tierods.

C

  • Critical Pressure  -  The pressure of substance at the critical point.
  • Critical Temperature  -  The temperature of substance at the critical point.

D

  • Downstream Pressure  -  The pressure exiting the outlet side of the heat exchanger.

E

  • End Plate  -  Covers that have been welded to the end of the heat exchamnger.  Most end plates are used on bonnet assemblies.
  • Expansion Valve  -  A valve that maintains the pressure difference between the high-pressure and low-pressure sides in a condenser/evaporator system.

F

  • Fin-fan Heat Exchanger  -  A fin-fan is a type of heat exchanger that forces air over a set of coils to cool the process.  It is also referred to as an air cooled heat exchanger.
  • Flow Rate  -  The amount of fluid that flows in a given time past a specific point.
  • Fluid  -  A substance that deforms and changes position when put under stress.
  • Fluid Pressure  -  Fluid at rest, exerts a force perpendicular to any surface in comes in contact with.

G

  • Gasket  -  A seal between two components, usually bolted.

H

  • Heat  -  A form of energy that causes physical change in what is being heated.  The lack of heat is cold.
  • Heat Transfer  -  The exertion of power that is created by heat, or the increase in temperature.  It is the transfer of heat from one system to another.  There are four ways to transfer heat: conduction, convection, mixing, and radiation.
  • Heat Transfer by Conduction  -  It is the flow of energy between two objects, or within one object, where there is a temperature differential.
  • Heat Transfer Rate  -  The amount of hear transfered per unit of time per fluid or material.

Il

  • Inlet Pressure  -  See upstream pressure

J

K

L

  • Latent Heat  -  The energy absorbed or released by a substance during a constant temperature or phase change from a solid to liquid, liquid to gas or vise versa.
  • Line Pressure  -  The pressure in the supply line.

M

N

  • Nipple  -  A short length of pipe either fully threaded (close nipple) or  thread both ends.

O

  • Operating Pressure  -  The operating pressure of equipment occurs when the plant or process is operating at steady state conditions.
  • Outlet Pressure  -  See downstream pressure

P

  • Packed End  -  The end of a heat exchanger which contains the packing joint.
  • Pressure  -  It is the force exerted perpendicular to the surface of an object and is expressed as force per unit area.

Q

  • Quad Layout  -  A quadrant type layout.  Four separate quarters of a tube layout with pass lanes between them.

R

S

  • Saturated Vapor  -  A vapor at a temperature of the boiling point on the verge of condensing.
  • Shell and Tube Heat Exchanger TEMA Designation  -  There are many different types of shell and tube heat exchanger configurations.  To help standardize the types of configurations, the Tubular Exchanger Manufactures Association has devised a standard nomenclature to briefly describe heat exchangers.
  • Shell Assembly  -  The assembly into which the tube bundle fits. The shell also contains the shell-side connections.

  • Shell Head  -  A formed plate welded to the shell, or bonnet, pipe. It can be many styles or shapes, including flanged and dished, elliptical, ellipsoidal and hemispherical.  Generally, as a head gets flatter, it gets weaker; therefore, designers can use a flat-end plate or a thinner formed head to do the same job.

  • Specific Heat  -  The amount of heat required to raise the temperature of a material 1 degree.
  • Steam  -  The invisible vapor (gas) when water is heated to its boiling point and passes from a liquid to a gaseous state.
  • Steam Density  -  Has a higher density than water vapor, the higher the pressure the higher the steam density.

T

  • Temperature  -  The amount of heat or cold, but it is neither heat or cold.  Temperature is expressed as a number that is related to energy and porportional to a type of energy, but it is not energy.
  • Tensile Strength  -  The maximum stress a material can resist before it starts to elongate.
  • Thermal Resistance  -  Measures the temperature difference by which an object or material resists a heat flow.
  • Tie Rod  -  Bars mounted between the tube sheets to support the baffles.
  • Tie Tube  -  A tie tube takes the place of the tie rod in a small diameter heat exchanger, and serves the same purpose.
  • Tube Bundle  -  Heat exchangers consist basically of housing and tube bundle.  The housing is a welded construction and includes all connecting, joining and fastening elements.
  • Tube Layout  -  Shows the positioning of the tubes inside the heat exchanger and the locations of the tie rods.

  • Tube Side  -  The fluid that circulates through the inside of the tubes of the heat exchanger.

U

  • Upstream Pressure  -  The pressure entering the inlet side of the heat exchanger.

V

  • Viscosity  -  The measure of the internal friction/resistance to the flow of a liquid.

W

X

Y

Z

 

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Title
Fin-fan Heat Exchanger
Shell and Tube Heat Exchanger
Shell and Tube Heat Exchanger TEMA Designation

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