Examining 4 Types of Heat Exchanger
Heat exchangers are responsible for transferring thermal energy from one medium to another, most commonly via conduction or convection. In general, heat exchangers may employ coils, fins, tubing, or hollow envelopes to facilitate the transfer of heat while keeping the internal mediums separate. Heat exchanger applications can range in use from basic residential and commercial HVAC systems to large industrial process utility systems.
While all heat exchangers operate under the same basic principles, the design characteristics, transfer mechanisms, materials and components will vary depending on the application or use of the system, and the medium to be heated or cooled. Heat exchangers are commonly classified based on these characteristics, and below we will take a look at four different types. [1]
1) Finned Tube / Air Cooled:
Mediums: Transfers heat from a liquid to an air/gas
Function: These heat exchangers pump liquid through a series of pipes while air or gas is fanned over the pipework to cool the liquid. They have fins that extend from the pipework and into the air/gas flow, thus maximizing the available surface area of the pipework, and in turn increasing the efficiency of the system. Sometimes they are found enclosed within ductwork, or the pipework is directly exposed to a free-flowing body of air/gas.
Uses: Finned Tube / Air Cooled Heat Exchangers are commonly found in systems that exhaust hot gases, recovering the heat from the exhaust and ‘transferring’ it to a liquid. Using a heat exchanger in this situation conserves more energy, creating a more efficient system. You can find these heat exchangers in “chemical applications, petrochemical cooling, steam cooling, in textiles processing, grain drying, concrete curing, paper manufacture and food processing.” [2]
2) Shell and Tube:
Mediums: Transfers heat from a liquid to a liquid/gas (fluid)
Function: Fluid passes through a bundle of tubes enclosed within a shell. The other medium is pumped into the shell, flowing in the counter direction of the tube bundle. Heat transfers from one fluid to the other.
Uses: Shell and Tube exchangers are known to be used in situations with high-pressure fluids or vacuums. Also, given the containment properties of shell and tube exchangers, they are equally ideal for situations where the fluids are extremely hot or dangerous to human health. These are frequently used within the oil, gas and chemical industries. [2]
3) Plate or Gasket Plate:
Mediums: Transfers heat from a liquid to a liquid/gas (fluid)
Function: Liquid passes through a series of rectangular envelopes, or plates, connected by gaskets. The mediums flow through the envelopes in alternating order - i.e. medium 1 would flow through the 1st and 3rd envelope, and medium 2 would flow through the 2nd and 4th, and so on. This method of transferring heat from one medium to another is very efficient.
Uses: Plate and gasket exchangers are commonly used in liquid to liquid applications, such as in transferring the heat from hot process water to main line distribution. Also, plate exchangers are useful in cooling oils with water since the two mediums naturally don't mix. [2]
4) Spiral Heat Exchanger:
Mediums: Fluid to Fluid
Function: This heat exchanger uses two concentric spiral channels to transfer heat, one spiral for one fluid and the other spiral for the other fluid. The two spiraled channels are wrapped around themselves to form a cylinder, with caps on either side to hold the structure together. The fluid flows in either a co-current flow, countercurrent flow, or cross flow, depending on which is most appropriate for the application. Co-current flow is when both fluids enter from the circumference of the spiral and exit from the center. Countercurrent flow has one fluid traveling from the circumference to the center, and the other fluid travels from the center to the circumference. Crossflow has one fluid traveling through the center of the cylinder, perpendicular to the spiraled channels filled with the other fluid.
Uses: Spiral exchangers are used in compact spaces with fluids that could leave a residue within the heat exchanger. These heat exchangers are smaller in footprint than other types with the same heat exchange area. The caps of the device can be removed, exposing the channels from the side for easy cleaning and access to the internals of the component - making this heat exchanger ideal for dirty fluids.
To Conclude
When deciding which heat exchanger is right for your process, it's crucial to work with engineers and designers who have multi-disciplinary experience in the design and construction of commercial, institutional and industrial facilities. Deep understanding and technical expertise within advanced process facility environments leads to better decision making when it comes to proper process utility design, implementation and operation. If you need a team of engineers who are comfortable in any environment, please feel free to connect with us to learn more about what we can do for you:
[1] https://www.thomasnet.com/articles/process-equipment/understanding-heat-exchangers/
[2] https://www.turnbull-scott.co.uk/about-us/types-of-heat-exchanger/