5: Difference between plate heat exchanger and tubular heat exchanger?
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 water tight, 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 are 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 require 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& tube heat exchangers are extremely easy to maintain; removing the end covers reveals the tube core, which can be withdrawn for cleaning and routine maintenance.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.