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.
  • Batch Furnace  -  A heat treating furnace where the load enters the quench tank at predetermined times, all at once.
  • Bundle Assembly  -  The tube assembly in removable bundle heat exchangers and consists of tubes, tubesheets, baffles, spacers, and tierods.
  • Burnout Point  -  At this point in the boiling process, vapor will form to such an extent that it hinders contact between the liquid refrigerant and the heat transfer area, leading to lower heat transfer efficiency.

C

  • Cavitation  -  The creation and collapse of bubbles in a liquid.  Localized cavities of vapor form on the low pressure side of the pump (suction) and collapse on themselves as energy is added to the fluid.
  • Circulation Number  -  In flooded systems, the number of times a specific volume has to pass the evaporator to be fully evaporated.
  • Closed Temperature Program  - When the primary and the secondary fluid temperatures are close to each other.
  • Compressor  -  A device that forces air or gas into a smaller area increasing the volume and creating a usable force of energy.
  • Condenser  -  A device that transfers unwanted heat out of a refrigeration system to a medium (either air, water, or a combination of air and water) that absorbs the heat and transfers it to a disposal point.
  • Condenser Coil  -  A series or network of tubes filled with refrigerant, normally located outside the home, which removes heat from the hot, gaseous refrigerant so that the refrigerant becomes liquid again.
  • Critical Heat Flux  - At this point, vapor will form to such an extent in the evaporator that it hinders contact between the liquid refrigerant and the heat transfer area, leading to lower heat transfer efficiency.
  • Critical Pressure  -  The pressure of substance at the critical point.
  • Critical Temperature  -  The temperature of substance at the critical point.

D

  • Dew Point  -  The temperature at which air must be cooled to become saturated with water vapor.  It is porportional to the amount of water vapor in a given amount of air and when the dew point is raised the more water vapor present, also the opposite.

  • Downstream Pressure  -  The pressure exiting the outlet side of the heat exchanger.
  • Dry Bulb Temperature  -  The temperature of air measured by a thermometer shielded from radiation and moisture.

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.
  • External Pressure Equalixation  -  An expansion valve with external pressure equalization compares the bulb pressure with the suction line pressure in order to control the superheat. Recommended in connection with BPHE evaporators due to the extra V-ring pressure drop.

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.
  • Flue  -  Any vent or passageway that carries the products of combustion from a furnace.
  • 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.
  • Foaming  -  Droplets of refrigerant entering the oil sump, where they are immediately evaporated.
  • Forced Circulation System  -  The forced-flow system is similar to a thermosiphon, but the forced-flow system has a pump installed before the evaporator.
  • Forward Temperature  -  Temperature of the hot fluid when it enters the device, radiator, or heat exchanger.

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 Gain  -  Heat added to the conditioned space by infiltration, solar radiation, occupant respiration and lighting.
  • 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.
  • Hydraulic Block  -  A boiler, block consisting of connections to the Brazed Plate Heat Exchanger, instead of pipes, in order to save space. It contains a number of functions, such as threeway valve, bypass valve, fill-up valve and temperature sensors.

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.
  • Liquid Hammer  -  In compressors, if a considerable amount of liquid enters the compressor house, a very large pressure can be built up when the piston reaches its top position. This phenomenon is called liquid hammer, and may cause severe damage to the valves or crankshaft.

M

N

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

O

  • Oil Separator  -  Separates oil from refrigerant and returns it to the compressor.
  • Open Compressor  -  The motor and compressor house are mounted without a shell, although the shaft has a seal.
  • Operasting Point  -  In a refrigerant system: the equilibrium point, where the performance of the evaporator matches the performance of the compressor.
  • 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.
  • Superheated Gas  -  When a dry saturated gas is heated at constant pressure, its temperature rises and it becomes superheated.

 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.
  • Thermocouple  -  The junction between two metals generates a voltage that is a function of temperature.  Thermocouples rely on this effect. Almost any metals can be used to make a thermocouple. 
  • 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.
  • Two-phase Static Head  -  A pressure head created by a liquid/gas mixture.

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

  • Water Hammer  -  A valve is suddenly opened or closed.  This can creates a repeating pressure wave of the liquid in the pipe that could cause a rupture to the pipe or even damage equipment.
  • Water Hammer Arrester  -  Absorbs unstable pressure due to sudden closing of gate, and moderates the impact of the fluid inside the pipe.
  • Wet Bulb Temperature  -  A temperature that takes into account the relative humidity and the dry bulb temperature.  At any given ambient temperature, less relative humidity results in a greater difference between the dry-bulb and wet-bulb temperatures.

X

Y

Z

 

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

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