Corrosion can cause problems two different ways. Not only can material corrode away, which leads to leaks, but the corroded material can be deposited elsewhere in the system and block fluid passages or filters. This can produce a pressure drop that causes reduced coolant flow. In addition, if the deposition occurs on active heat transfer surfaces, the extra thermal resistance caused by fouling can make temperatures rise.
Both galvanic corrosion and erosion-corrosion should be minimized in the liquid cooling loop. Galvanic corrosion occurs when dissimilar metals are in electrical contact with each other in the presence of an electrolyte such as a conductive liquid. Most water-based coolants are electrolytic to some degree. To prevent galvanic corrosion, either the loop should be designed with similar materials throughout the system, ideally with just one metal, or a non-conductive fluid should be used. The galvanic potentials of all materials in the system should be considered. This includes not only the primary thermal components, but also all connectors, fittings, valves, and junctions in the fluid path.
Erosion-corrosion is the acceleration in the rate of corrosion in metal due to the relative motion of a fluid and a metal surface. It is most often found in pipe bends & elbows, tube constrictions, and other structures that alter flow direction or velocity. Erosion-corrosion is most prevalent in soft alloys, such as copper and aluminum.
Some methods for minimizing erosion-corrosion include allowing bends to have larger angles, changing pipe diameters gradually rather than abruptly, and improving flow lines within the pipe by deburring, i.e., smoothing out irregularities. Other methods include reducing the amount of dissolved oxygen, changing the pH, and switching the pipe material to a different metal or alloy. See our application notes "Erosion-Corrosion in Cooling Systems" and "Avoiding Galvanic Corrosion" for more information on corrosion.