Detection of drifts in thermal systems based on a synchronous detection technique

This study deals with the application of a very sensitive discrimination technique to the detection of a drift in thermal systems. After having presented the basis of the technique, the application to a lumped system shows that a decrease by 0.25% of the convection heat transfer coefficient is easily detected. To do so, the number of samples and the length of the observation have to be adjusted. It is shown that the method is powerful even if the system is not in a steady state. Finally, the method is applied to an electrical heater, and it is shown that it is possible to discriminate a mass flow decrease from the effect of fouling.