Analysis of the unsteady behavior of an electrical heater using the lock-in technique: Comparison of theory and experiments
Résumé
In the recent years, the lock-in technique has been tested in thermal engineering. Due to its high sensitivity for signal analysis, it has great potentialities for drift detection. Here the aim is more particularly fouling detection. The key point for this technique is the choice of the angular frequency of the exciting signal. It is a tradeoff between getting a high value of the modulus of a complex number, getting a stable value of this modulus in a time as short as possible, and leading to low variations of the temperature of the product passing through the thermal device. The aim of the present study is to show that experimental results obtained using a specialized measurement apparatus are in a good agreement with the theoretical developments for an electrical heater. The first part of the paper is dedicated to a brief presentation of the theory of the lock-in technique for lumped systems. The second part presents the developments for an electrical heater. The third part is dedicated to the presentation of the test rig. Then experimental results are given in the way they have been presented for the theoretical electrical heater. Even if some simplifications have been necessary for the theoretical developments, these experimental results show that the evolution of the modulus is similar to what is expected according to the angular frequency and to the mass flow. A final comparison between experimental results and theoretical computations shows a reasonable agreement for a particular set of parameters.