Shell and Tube Heat Exchangers

A heat exchanger is a device for transferring heat energy from a liquid or gas, to another liquid or gas without the two ever coming into contact with each other. A typical shell and tube heat exchanger will contain a tube bundle inside an outer shell, or body. Cold water flows through these tubes, whilst hot water, or gas flows around the outside of the tubes, enabling the heat from the hot water or gas to be transferred to the colder water inside the tubes.

A good example of how the process works are swimming pools, where most are heated via a boiler, using Gas, LPG or Biomass as the energy source. In theory, the most efficient way to heat the pool would be to circulate the pool water directly through the boiler. But were this to happen, the chemicals used in the pool water to keep it safe for use, would quickly corrode and damage vital parts inside the boiler, leading to premature failure and a costly replacement.

However, by using a heat exchanger to act as an ‘interface’ between the boiler water circuit and the pool water circuit, the boiler is protected from damage and the pool water is quickly heated up to the required temperature; the pool water passing through the central ‘tube core’, whilst the hot boiler water circulates around the outside of the tubes, transferring heat energy to the pool water.

More examples of applications where Bowman heat exchangers are used.

In certain conditions where there is a significant temperature differential between the cooling medium and liquid being cooled, a shell and tube heat exchanger is often the more cost-effective cooling solution compared to a plate heat exchanger. This is due to the small flow path within the plate heat exchanger which creates significant amounts of turbulence, leading to high pressure drop within the unit.

As the name suggests, plate heat exchangers are constructed from a series of thin metal plates. Usually made in stainless steel, each plate contains an intricate pressed pattern, and to ensure the unit is watertight, rubber gaskets are ‘sandwiched’ between all the metal plates, which are then compressed together in a rigid frame to form an arrangement of parallel flow channels with alternating hot and cold fluids.

In contrast, shell and tube design heat exchangers consist of two primary components; the outer body (or shell) and tube core (or bundle) inside the shell. Cooling media flows through the tube core, whilst the hot fluid enters the shell via an inlet port, flowing through and around the outside of the tube core through a series of baffle plates, before leaving the shell via outlet port. For maximum heat transfer efficiency the hot and cold fluids travel in a ‘counterflow’ direction through the heat exchanger. For more information on counterflow.

Whilst plate heat exchangers can be quite compact and have the ability to be increased in size, should cooling requirements change, they will be more costly to maintain than the equivalent shell and tube heat exchanger, as typically the rubber gaskets age, harden and need replacing every 2 years. This is a time-consuming and costly exercise, putting the heat exchanger out of service for longer periods. Additionally, leak detection can be more difficult and requires skilled labour to undertake the work. And, due to greater water flow resistance inside the heat exchanger, there is an increased chance of fouling, reducing the efficiency of the unit.

In contrast, shell & tube heat exchangers are extremely easy to maintain; removing the end covers reveals the tube core, which can be withdrawn for cleaning and routine maintenance. Heat transfer efficiency of a quality shell & tube heat exchanger, such as Bowman, is extremely good, whilst the units themselves are tough, providing long life durability. Shell and tube heat exchangers can also be used with the most demanding cooling media, including sea water and mineral rich or contaminated water.

More information on Bowman’s range of shell & tube heat exchangers.