When a heat exchanger generates little heat loss, it may seem that the device works in every way as intended; the heat received by the cold fluid corresponds very well to the heat delivered by the hot fluid. The efficiency approaches unity and the customer can be informed that the heat exchanger works in the desired manner. A closer look, however, shows that the performance evaluation of heat exchangers is not quite such a simplistic matter.
Often, heat exchanger functioning is monitored only for the rate of heat transfer. Furthermore, the heat transfer rate can be controlled by altering ow rates. An experienced process operator can see when a heat exchanger no longer transfers its typical thermal output under certain flow conditions. In such cases the operator has limited options available to handle the situation.