Heater tube nest for heating fuel oil

Heater tube nest for heating fuel oil

Heat exchangers is a term used for transferring heat from one medium to another. Seawater is used to cool another medium. The other medium may be fresh water, for engine cooling or oil for engine lubrication. Steam is used to heat up fuel oils.

Shell and tube cooler on the left

Shell and tube cooler on the left

For a tubular heat exchanger, seawater is passed through tubes internally, while fresh water or oil is led through the tubes externally. The heat from the fresh water or oil is conducted through the walls of the tubes to the seawater and is discharged overboard. 

Plate heat exchanger fluid flow

Plate heat exchanger fluid flow

In winter months, it is usual to re-circulate back some of the seawater instead of discharging it. This ensures a better control on the temperatures in the systems.

Other designs make use of plates instead of tubes, but the principle of the heat exchanger remains the same.

Boiler tubes used for producing steam

Boiler tubes used for producing steam

Despite the use of seawater strainers, after a period of use, the tubes or plates tend to choke up with barnacles, scales and other marine growth. Periodic cleaning of the tubes is necessary to improve on the cooling effect.

The purpose of the heat exchangers is to cool. However, the sea waters temperature changes in different climatic regions and the engine load can also change. The heat exchangers have to work together with temperature controllers in order to be effective.

There is another type of heat exchanger – the electrical tankless heater. Mostly found in homes, they may be used in the galleys for hot water. They are very economical and saves energy.