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Optimization of the temperature sensor position in a hot wire probe set up for estimation of the thermal properties of foods

Published by the American Society of Agricultural and Biological Engineers, St. Joseph, Michigan

Citation:  Paper number  016089,  2001 ASAE Annual Meeting. (doi: 10.13031/2013.4216) @2001
Authors:   H.B. Nahor, N. Scheerlinck, J.F. Van Impe, B.M. Nicolaï
Keywords:   Heat transfer, Finite element, Parameter estimation, Optimal experimental design, Hot wire probe, Modified E-Criterion

For successful design and simulation, accurate knowledge of thermophysical properties of food products is essential. When considering conduction heat transfer, the involved thermophysical properties are the thermal conductivity and the volumetric heat capacity. Recent interests are directed towards simultaneous determination of the thermophysical properties. In this context, the quality of the experimental data is crucial in order to estimate the parameters accurately and uniquely.

The objective of this paper is to determine the optimal measurement position with respect to the information content of an experiment in a hot wire probe set up given an input heat generation. Moreover, the influences of different parameters of the input heat generation profile such as the magnitude of the heat generation and final time with respect to the optimal sensor location were investigated.

To achieve this objective, a simple experimental set up has been developed using the line heat source method. A constantan heating wire is impeded in a stainless steel hypodermic needle and a thermocouple is placed at some point in the model food substances (Tylose and Agar gel) to measure the temperature. The heat conduction in the probe and its environment was modeled by means of the finite element method and the model has been validated using experimental data. For a given type of heat generation profile, the influence of the sensor location with respect to the information content of the experiment has been investigated by using an optimal design criterion based on the Fisher information matrix.

Simulations indicated that there is an optimal position where the time-temperature measurement should be recorded in order to have an informative experiment such that the parameters are estimated accurately and uniquely. Moreover, it was observed that the choice of magnitude of heat generation and final time have no significant influence on the information content. Implementation results confirmed that by using the time-temperature data measured around the optimal position, unique and accurate estimates could be obtained.

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