This chapter contains examples demonstrating the importance of metal temperature. Not all apply to heat exchangers, but all are heat-related problems that can affect the operation of process, air-conditioning, or electronics cooling facilities. The metal temperature is calculated much the same way in all cases.
In heat exchangers the tube metal temperature will be between the hot- and cold-side fluid temperatures. Its reading at any point will depend on the film and fouling resistances of one stream relative to the comparable resistance(s) in the other stream. If one fluid is steam with a low film resistance and the other is asphalt with a high film resistance, the tube temperature will be nearer the steam temperature. On the other hand, if one stream is cold water, with a minimum film temperature, the metal temperature will be nearer the water temperature. Knowing the metal temperature is necessary in many applications. Here are some of them.