IGBT Modules - Technologies, Driver and Application (Second Edition) - page 200

The ducts for the coolingmedium should be as short as possible.
Avoid bending theducts
for the coolingmedium.
Viscosity of the coolingmedium should beas lowas possible.
It is not always possible to achieve all of these points, asmechanical factors relating to
the design or applicationmaywork against them.
Corrosion is often an issuewhen liquid cooling is used. Corrosion can cause deposits in
the cooling circuit that cause the pressure drop in the system to rise by reducing the
cross sectional area. They also change the surface of the duct walls, which usually
increases the thermal transfer resistance. Both effects make the cooling system less
efficient. In extreme cases, the corrosion can cause the system to leak and the entire
system to fail. Corrosion is caused by dissolved oxygen particles in the coolingmedium,
which react with the metal in the cooling circuit. If it is a closed cooling circuit in which
the amount of oxygen is limited, the oxygen is used up relatively quickly and no further
corrosion is possible. In open systems, however, oxygen is fed in, and this contributes
to continual corrosion. To prevent corrosionanddeposits, pleasenote the following:
It is best touse closed cooling circuits.
Reduce the chloride content of the water, as chloride is highly corrosive. Avoid
Use deionised and demineralised water, in order to avoid constituents like
magnesiumand calcium, which can createdeposits in the cooling circuit.
Use corrosion inhibitors, especially for deionised and demineralised water.
Phosphate is recommended for metals such as aluminium and steel, while
tolyltriazole can be usedwith copper.
Ensure continuous flowof the coolingmedium.
When using liquid cooling at low temperatures, there is a risk that the water in the
cooling circuit may freeze. Mixtures of water and glycol are therefore used for such
applications as these have amuch lower freezing point of well below0
C, depending on
themixing ratio. It must be borne inmind, however, that glycol transfers heat much less
efficiently than water. For applications that do not have to operate and be stored below
freezingpoint, it is best not touseglycol.
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