A heat exchanger moves heat from one fluid to another without letting the two mix. Plants use them to cool oil, condense vapour, heat process streams and recover waste heat. There are several types, and the right one depends on pressure, temperature, how clean the fluids are, and the space available. This guide explains the main types, then looks at shell and tube designs in more detail, because they are the most common choice in oil, gas, petrochemical and power plants.
The main types of heat exchangers
- Shell and tube. A bundle of tubes inside a cylindrical shell. One fluid flows through the tubes and the other around them. It handles high pressure, high temperature and dirtier fluids.
- Double pipe (tube in tube). One pipe inside another, with the two fluids flowing in opposite directions. It suits small flows and very high pressures.
- Air-cooled. Hot fluid runs through finned tubes while fans blow ambient air across them. It saves cooling water. See our guide to air cooled heat exchangers and fin fan coolers.
- Plate. Stacked corrugated plates. It is compact and efficient with clean fluids at moderate pressure, and easy to clean and expand.
- Coil and spiral. Coiled tubes that save space, often used on packaged equipment.
How a shell and tube heat exchanger works
Hot fluid flows on one side of the tube wall and cold fluid on the other, so heat passes through the tube. Baffles inside the shell guide the shell-side fluid across the tubes, which improves heat transfer. The tubes are held in plates called tubesheets at each end. How these tubesheets and the bundle are arranged gives the different designs below.
Shell and tube designs
Fixed tubesheet
The tubes are fixed into a tubesheet at both ends of the shell. This design is simple and low in cost, but the outside of the tubes cannot be cleaned mechanically. It suits clean shell-side fluids. When the tubes and shell run at very different temperatures, an expansion joint in the shell may be needed.
U-tube
The tubes are bent into a U shape and fixed at one tubesheet only, so the bundle can expand freely. The bundle can be pulled out to clean the outside. The inside of the tubes is harder to clean, so it works best with a clean tube-side fluid.
Floating head
One tubesheet is free to move, so the bundle can expand and can be removed for cleaning both inside and outside. It suits dirty fluids and large temperature differences, and it costs more than a fixed tubesheet.
Extractable bundle
Any design where the tube bundle can be pulled out of the shell for inspection and cleaning is called an extractable bundle. Floating head and U-tube exchangers are both extractable types.
Kettle type
A kettle has an enlarged shell with space above the bundle where vapour separates from liquid. It is used as a reboiler or evaporator.
Flovex, the Italian manufacturer we represent, builds a standard production line in fixed bundle, extractable bundle, floating head and U-bundle designs, with smooth or finned tubes.
What TEMA means
TEMA is the Tubular Exchanger Manufacturers Association. Its standard sets design and construction rules for shell and tube exchangers and defines three classes. Class R is for severe petroleum and related processing duty, class B is for chemical process service, and class C is for moderate commercial and general process duty.
TEMA also gives each design a short letter code. For example, BEM describes a fixed tubesheet exchanger, and AES describes a floating head exchanger with a removable channel cover. When you ask for a quotation, giving the TEMA type and class removes a lot of guesswork. Flovex designs its engineered exchangers to TEMA.
API 660 and project specifications
API 660, also published as ISO 16812, covers shell and tube heat exchangers for refinery and petrochemical service. Oil and gas projects often add its requirements on top of TEMA, together with third-party inspection. Flovex manufacturing is ISO 9001 certified, holds the ASME U stamp with National Board registration, and is assessed under Module H of the EU Pressure Equipment Directive. The company has delivered more than 3,000 exchangers for API applications.
Tubes, fins and materials
Tubes can be smooth or finned. Fins add surface area to the outside of the tube, which makes the exchanger smaller and reduces the cooling water needed. Common tube materials include carbon steel, stainless steel, brass and cupronickel. For seawater and other demanding services, titanium, duplex and superduplex stainless steels are also used. The right material depends on the fluids and the water quality, so check it against a water analysis.
How to choose
- Heat duty: how much heat must be removed or added.
- The two fluids: their flow rates and inlet and outlet temperatures.
- Cleanliness: dirty fluids need a design that can be opened and cleaned.
- Pressure: the design pressure on each side and the pressure drop you can accept.
- Materials and standards: TEMA class, ASME, PED, API 660 and any inspection requirement.
Frequently asked questions
What is the most common type of heat exchanger?
Shell and tube exchangers are the most common in oil, gas, petrochemical and power plants because they handle high pressure, high temperature and dirty fluids.
What is the difference between a fixed tubesheet and a U-tube exchanger?
A fixed tubesheet exchanger has tubes fixed at both ends, so it is simple but the outside of the tubes cannot be cleaned mechanically. A U-tube exchanger has tubes fixed at one end only, so the bundle expands freely and can be pulled out for cleaning.
What does TEMA mean?
TEMA is the Tubular Exchanger Manufacturers Association. Its standard defines the design and construction of shell and tube heat exchangers and their classes R, B and C.
What is API 660?
API 660, also published as ISO 16812, is the standard for shell and tube heat exchangers in refinery and petrochemical service.
Power Energy Gulf supplies Flovex heat exchangers for industrial plants across Saudi Arabia and the GCC. See our industrial heat exchangers page, or contact us with your fluids, temperatures and flow rates and we will help you select a suitable unit.