Lionel Boillereaux

Numerical modeling of high pressure thawing: Application to water thawing

A finite difference scheme model which performs both atmospheric and high pressure thawing simulation is presented. The comparison between numerical simulation and experimental data shows a good level of agreement. This model has been used to predict the performance of the thawing process under a wide range of operation conditions. It clearly shows that high pressure thawing reduces the thawing time.

Thermal properties estimation during thawing via real-time neural network learning

Predicting time duration of food thawing operations has a major importance in controlling the product safety and quality, as well as in optimizing and controlling the process in food industries. However this prediction, based on a model represented by a nonlinear distributed parameter system, depends essentially on a good knowledge of the thermal properties of the foodstuff. Instead of using classical differential scanning calorimetry or high order polynomial approximations, we propose in this paper to replace the estimation of these properties by real-time learning using simple neural networks. This network refinement is based on the Moving Horizon State Estimation and the reverse techniques. Experimental results were carried out during gelatin thawing, and are sufficiently good to now look forward to applying this method to real food, and to contribute further to the on-line control of thawing operations.

A 2D non-linear grey-box model dedicated to microwave thawing : Theoretical and experimental investigation

Abstract A grey-box model, based on a priori knowledge about heat transfer with phase change and on microwave effects approached by a continuous function, is proposed to simulate the thawing of food in a microwave guide in fundamental TE1,0 mode. The partial differential equation describing heat transfer with phase change is reduced into a lumped parameters system using a 2D finite volumes scheme. The heating due to the microwaves is considered in the heat equation as the spatial variation of the microwave power flux. Flux variation is approached by a continuous function of temperature and of the wave power, whose coefficients are estimated via reverse techniques. Finally, the model is validated during the thawing of a block of tylose filling the section of the wave guide.

Nonlinear trajectory control of high pressure thawing

Abstract This paper deals with the control of the thawing front propagation in a foodstuff. Recently, many results were obtained about the large influence of the pressure on the thawing time. However, such a technology is used without any control of the thawing kinetics, which seems to affect the quality of the foodstuff. With a view to improving it and to choosing the thawing time, the melting front propagation rate has to be mastered. To achieve this objective, we propose here to use a nonlinear control methodology. This methodology is carried out on water thawing.

Conjugate Heat and Moisture Transfer During a Dynamic Thermal Treatment of Food

This work concerns the thermal decontamination of the surface of a food by hot air with the objective of inactivating the bacteria located at the surface. This heat treatment is considered to be intense and short, compared to more conventional drying processes. In order to predict the surface temperature, a coupled heat and mass transfer model was developed taking into account convective and diffusive mechanisms, evaporation, and shrinkage. A pragmatic alternative between Eulerian and Lagrangian formalisms was used in order to perform an efficient model. It was shown that this thermal decontamination process was governed by convection in a first stage, whereas mass diffusion was the limiting phenomenon in the second period. An inverse method was carried out in order to optimize the parameters of the mass diffusivity law.

Further Investigations on Energy Saving by Jet Impingement in Bread Baking Process

This paper presents a study of the estimation of potential energy saving in bread baking process using the jet impingement technology. This new technology is developed to increase the heat transfer efficiency during the baking process. Based on a mechanistic heat exchange model identified in the past work, a non convex optimization problem is formulated taking account of a non zero energy cost related to the new technology. The simulation result shows that one can expect to obtain up to 12% of energy saving under some reasonable assumptions.

Reference Trajectory Tracking of Superficial Temperature in Food Decontamination

Abstract This paper proposes a preliminary study, for the tracking control of the superficial temperature in rapid decontamination of foods surface. The data are issued from a heat and mass transfer simulator, taking into account all the specificities of the process and of the product. This study, supported by a on-going European project, aims at imposing an increasing and decreasing ramp-type temperature profile to the surface of foods, to achieve a complete or partial destruction of microorganisms. A complete model including water activity, food desiccation and heat transfer is proposed to describe the phenomena induced by the process. A simplified model, based only on heat transfer, is finally proposed to design a tracking control of a superficial temperature reference profile. The robustness of the solution is discussed through different conditions of use.

Model-Based Settings of a Conveyorized Microwave Oven for Minced Beef Simultaneous Cooking and Pasteurization

Abstract A major drawback of microwave processing is the heterogeneity of treatment, which prevents from a plenty benefit of its flexibility and rapidity. Most of time, this operation is realized in continuous processes, composed of a series of microwave generators with adjustable power. In this paper is proposed a methodology leading to an optimal setting of these powers in order to warrant the expected microorganisms’ inactivation during simultaneous cooking and pasteurization, while preserving quality. It consists in minimizing a multicriteria formulation including hottest and coldest points on the first hand, and final logarithmic inactivation on the other one. The simulation model is composed of a reduction of the heat equation via a finite volume scheme with a source term deduced from appropriate closed-form solutions of the Maxwells equations, whereas the non-isothermal inactivation is described by the Geeraerd model. The methodology is carried out by considering treatment of minced beef.

Robust Estimation of temperature field during microwave tempering under unknown dielectric properties

Abstract In this paper, a framework is proposed for the estimation of internal temperatures within a foodstuff during microwave tempering under unknown dielectric properties. The solution is based on a partially known model issued from the closed form solutions of Maxwells equations coupled with the conduction heat equation solved by finite differences. The algorithm converges towards acceptable dielectric properties functions whereas 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 allowing to consider a fundamental mode with perfectly known electromagnetic conditions.

Towards an all-terrain identification method for models of industrial processes

Abstract In this paper, a new strategy of identification, based on Predictive Control, is presented. This method has already been developed for two years (Shook et al., 1991 & 1992). However, in this paper is shown how to identify a process when the output is disturbed by an offset plus a drift plus a white noise. This case is interesting to study because, most of the time, disturbances can be modelled both as deterministic and stochastic signals. The prediction calculation used for the minimisation criterion take drifts, offsets and white noise into account. Concerning the drift, the slope is estimated at the same time as the model parameters.