Different types of heat exchangers are used on board a ship. The type of heat exchange used for a particular usage depends on the application and requirement. In this article we talk about different types of heat exchangers used on a ship.
The types of exchangers are mainly defined by their construction and are as follows:
1) Shell and Tube Type Heat Exchanger
This is the most popular type design with a shell accompanying several tubes and the flow of liquid to be cooled is mainly through tubes, whereas the secondary liquid flows over the tube inside shell.
Shell and tube type heat exchanger is extremely economical to install and easy to clean; however the frequency of maintenance is higher than other types.
2) Plate Type Heat Exchanger
Plate type exchanger consists of thin corrugated plates joined parallel together, creating cavity for fluid flow inside it. Alternate sides of the plate carries two different fluids, between which, heat transfer is carried out.
Installation of this type of heat exchanger is expensive than shell and tube type, but maintenance cost is much lower.
Efficiency of plate type is higher than shell and tube type for same size of unit and can withstand high pressure.
3) Plate Fin Heat Exchanger
Plate and fin type heat exchanger is constructed similar to a plate type exchanger but also contains fins to increase the efficiency of the system. Aluminium alloy is used as it gives higher heat transfer efficiency and lowers the weight of the unit.
Fins can be fixed in perpendicular to the direction of flow and are known as offset fins. Fins fixed in parallel to the direction of flow are straight fins. Fins can be fixed in curvature form to increase the heat exchanging effect and are thus known as wavy fins. Efficiency of this heat exchanger is slightly higher than plate type unit but installation and maintenance cost is higher
4) Dynamic Scrapped Surface Heat Exchanger
In this heat exchanger because of the continuous scrapping of the surface long running time is achieved which helps in better heat transfer efficiency and decrease in the fouling of the system.
The scrapping is done by a blade unit operated by a motor driven shaft with timer moving inside the frame. This heat exchanger is normally used for heat transfer of highly viscous fluid by increasing the turbulence of the fluid. Maintenance cost is less as compare to other types because of the auto cleaning process.
5) Phase Change Heat Exchanger
As the name suggests, this type of heat exchanger is used to change the phase of a medium from solid to liquid or liquid to gas by principle of heat transfer. This type is normally operated in freeze cycle and melts cycle for change in phase to happen.
The heat exchanger is normally constructed like a shell and tube type exchanger, but consists of at least two divider walls to construct upper and lower annular space for flow passage. It also consists of fins in both passage ways for efficient heat transfer.
6) Spiral Heat Exchanger
This type of heat exchanger consists of concentric shape flow passages which help in creating a turbulence flow of a fluid which in turns increases the heat transfer efficiency. Initial installation cost is higher but highly efficient as compare to other types as space saving is much more because of the compact size. Maintenance cost is lowest as compare to other types for the same size of the unit.
The Flow of fluid in spiral type is rotary current flow which itself possesses the property of self cleaning of fouling inside the spiral body.
7) Direct Contact Heat Exchanger
In this type of heat exchanger, there is no separating wall inside the unit. Both the mediums are in direct contact for heat transfer process.
Direct contact type heat exchangers can be further classified as
1. Gas – liquid
2. Immiscible liquid- liquid
3. Solid- liquid or solid- gas
If you liked this article, you may also like to read Heat exchanger on a ship explained.
Marine aux machinery by H.D.McGeorge