What is the difference between an air-cooled and water-cooled rectifier? | KraftPowercon



Posted By
Göran Stenmark



It works almost everywhere as long as you have sufficient airflow in the space you are placing the rectifier in.

It is easier to install as it does not have to be connected to the ship’s existing water-cooling system.

As there is no water in the appliance, an air-cooled rectifier does not run the risk of freezing if the temperature drops below zero degrees Celsius in the space it is placed in.

No risk for condensation inside the appliance as no cold water is run through a heat sink. (In a water-cooled rectifier, the humidity in the air can cause condensation on the heat sink, which can lead to water leaking into the hardware.)


Air is not as efficient in transporting heat as water. Hence, to properly cool the rectifier, the airflow needs to be high. Especially if the ambient temperature is high. If the ambient temperature increases out of the specification – i.e., gets too high – the rectifier might stop due to overheating.

Bad air quality can have a negative impact on the performance of the rectifier and might result in the inlet air filter having to be changed more frequently. If the air quality is very poor, it can even cause the rectifier to break down.



Water-cooling is a more efficient cooling method since the thermal resistance is much lower between the heat sink and water tubes as opposed to the heat sink and forced air.

Water has a much higher energy density compared to air hence less volume is needed.

Cooling power is solely dependent on water temperature and water flow, which means that even if the ambient temperature around the rectifier is very high, the rectifier can still operate as normal.


Availability of cooling water circuit needed.

Water-cooled rectifiers run a risk of freezing if placed in a space where the temperature can fall below zero degrees Celsius.

Obvious risk for condensation issues if the heat sink in the rectifier is colder than the ambient temperature.

To avoid risk of freezing damage as well as condensation issues it is absolutely necessary to control the water flow. Let the water flow in case of risk for freezing damages and stop the flow in case of risk for condensation issues.

Since the LT system sometimes contains sediment that might clog the water tubes, a strainer might be needed, which must be cleaned regularly.


Regardless of whether you choose an air-cooled or a water-cooled rectifier, the environmental requirements for the rectifier’s performance are the same. They operate in the same environment and feed the same load. The only difference is that the heat generated inside the rectifier is removed by using either forced air or water as cooling media.

Making sure your rectifier has a modular design is also crucial, as it ensures easy troubleshooting and maintenance if anything were to go wrong. From an operational perspective, this is especially important. Because if one module malfunctions or breaks down, the remaining modules will compensate for the output lost from the malfunctioned component. If this were to occur, the rectifier will keep operating – albeit at a reduced capacity – thanks to the remaining modules’ built-in redundancy. This is of great help when troubleshooting the system. But more importantly: it is of great value for the ballast water management system owner, as they can continue to load and unload their cargo.

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