Shell & Tube Heat Exchanger Discussion
Hairpin Heat Exchanger
This heat exchanger can be described a single-pass heat exchanger but folded in half. The shell-side and tube-side fluid are in a counter-current arrangement. This allows for the efficient heat exchange between the two fluids, as the temperature difference between both fluids is as high as possible for log mean average (LMTD). This efficiency in heat transfer allows for a smaller heat exchanger in general. . Furthermore, the closures of a heat exchanger allow for thermal expansion of the material without causing any damage to the piece of equipment. These closures also allow for the tube bundles in the heat exchanger to be removed and then cleaned, which will help with the longer upkeep of this piece of equipment. However, the main disadvantage when it comes to using a hairpin heat exchanger are economic reasons. This piece of equipment is much more expensive than a simple single-pass shell-and-tube heat exchanger.
Therefore, based off these factors, it seems that it is best to use a hairpin exchanger when the sizing of the equipment is targeted to be as small as possible; costs are not the biggest factor; and only general heating is needed.
Single-Pass Heat Exchanger
A single-pass heat is made up of tube bundles carrying the tube-side fluid and a shell carrying the shell-side fluid. Due to this design, in some areas there will be counter-current arrangement between the two fluids while at other regions there will be a co-current arrangement. By comparing this to hairpin heat exchanger, we can already see that this system is less efficient at heat transfer. Therefore, for the same duty, the heat exchanger will need a higher surface area, and will need to be bigger in volume too. One advantage that arises is simply due to the simplicity of the design of a single-pass heat exchanger. It allows for easy disassembly and cleaning of the equipment, especially since there are no bends that exist within the system.
I would recommend using this type of heat exchanger when costs are a top priority and a simple heat exchanger is needed. Simple hear means that the temperature of the system will not vary greatly on a daily basis. Furthermore, if the system consists of high temperature change between the inlet and outlet, it may be worth considering another system in case of any damage that can arise.
Plate & Frame Heat Exchanger
In this piece of equipment, plates in parallel are held by a frame. This simple arrangement allows for the cost of a plate and frame heat exchanger to be lower than most heat exchangers (as all you would need is the frame and sheets of metal for the plate). Also, this type of design allows for the system to be expandable – i.e., we can add more or remove plates to reach a desired heat transfer between the two fluids. Finally, since the plates can be removed from the frame, the maintenance of this heat exchanger is easy, and therefore the maintenance of this piece of equipment will extend the longevity of the heat exchanger as it can .
The gap between each plate is very small. So, when fluid flows in between these plates, it causes for high turbulent flow to occur. This turbulent flow allows for not only efficient heat transfer, but this flow also reduces the amount of fouling in the system. The reduced risk of fouling further increases the longevity of this piece of equipment.
This type of exchanger is recommended only for liquid-liquid flow at low to medium pressure. Since the flow path in this exchanger is small, gas-gas heat exchange will be inefficient. Furthermore, due to the smaller size of this exchanger, solids suspended in a liquid might block certain holes or closures.