Estimation of temperature field during microwave tempering with unknown dielectric properties using CLPP: A generic user-friendly software sensor

The present study is dedicated to the estimation of internal temperatures within a foodstuff during microwave tempering, in the presence of unknown dielectric properties. The solution consists of a software sensor based on a model originating from the closed-form solutions of Maxwell's equations coupled with the conduction heat equation solved by finite differences. The algorithm implemented enables convergence towards acceptable dielectric property functions while the temperature field is estimated simultaneously. This approach is carried out in simulation by considering the tempering of a block of raw beef located in a rectangular wave guide in order to consider a fundamental mode with perfectly known electromagnetic conditions. In the industrial processes, the lack of sensors constitutes a brake to the design of relevant control strategies. One well-known solution is to implement software sensors (also called observers) to estimate online the lacking data. However, such a solution requires a good knowledge of the dynamical model structure and the model parameters. The development of software sensors remains nevertheless a difficult task for non specialist in process control. CLPP presented in this submission is particularly well suited to industrial cases, because it permits to estimate with a good accuracy the lacking state variables in the presence of large uncertainties on the parameters' vector. The interest is illustrated on a microwave food tempering process, where dielectric parameters are unknown, and where the available measurements are only surface temperatures. ► A real-time estimation of temperature field during microwave treatment is proposed. ► The estimation is performed with a priori unknown dielectric properties. ► Parameter and state estimation are performed simultaneously. ► A user-friendly software sensor is presented and carried out.