Study of a simple transient non-intrusive sensor for internal temperature estimation during food product freezing

It is first recalled that the temperature profile in a freezing product is almost linear. To estimate the freezing level of a food product, a non-intrusive sensor is proposed which may estimate the surface temperature and the slope of the internal temperature profile. It consists in analysing transient response when the sensor is set in contact with the product to characterise. The sensor is made of a thermopile (Peltier element) fixed on an isothermal medium made of a high effusivity material (copper). A modelling of the transient response of the sensor using the quadrupoles method is presented. Then, the results of the characterisation of the sensor by experimental determination of the transfer functions between fluxes and temperatures are given. A theoretical sensitivity analysis enables to study of the potential limits of this sensor. Finally, the influence of internal temperature profile slope on the sensor response is evidenced by the results of an experimental study. The main interests of this sensor are its simplicity and low cost and a flux measurement independent of thermal contact resistance to estimate a temperature.