What Is An L.T.F.W. COOLER in A Ship?

Ships generally have a central cooling system that is crucial for maintaining the proper operating temperatures of various components. The use of one or two large plate heat exchangers is a key feature of this system. Plate heat exchangers are efficient in transferring heat between different fluids.
The three main subsystems within the central cooling system, namely the seawater cooling system, the freshwater low - temperature (FW - LT) system, and the freshwater high - temperature (FW - HT) system, work together to manage heat transfer effectively.

Function of LT and HT Circuits
In the LT circuit, fresh water is used to cool the engine directly. Fresh water is a suitable coolant for the engine because it has good heat transfer properties and is less likely to cause corrosion or other damage to the engine components compared to seawater. The LT water absorbs the heat from the engine and its temperature rises as a result.
The HT circuit, on the other hand, uses seawater to cool the LT water. Seawater is abundant and has a relatively stable temperature in the marine environment. The heat exchanger between the HT (seawater) and LT (freshwater) circuits allows the transfer of heat from the warmer LT water to the cooler seawater. This way, the LT water is cooled down and can be recirculated to continue cooling the engine.

Advantages of the System
Using a combination of fresh and seawater in this way provides several benefits. The use of fresh water for direct engine cooling helps protect the engine from the corrosive effects of seawater. At the same time, the availability of seawater as a coolant for the LT water allows for efficient heat dissipation into the surrounding ocean environment.
The central cooling system with its multiple circuits and heat exchangers also provides better temperature control. It can handle the variable heat loads of the engine and other components more effectively than a simpler cooling system. For example, during periods of high engine load, the system can adjust the flow rates of the different fluids and the heat transfer rates in the heat exchangers to maintain the proper operating temperatures.