Simultaneous measurement of temperature dependent thermophysical properties by the BICOND method with genetic algorithm based evaluation


B. Czél1, G. Gróf1 and L. Kiss2

1Budapest University of Technology and Economics, Department of Energy Engineering, Hungary
2Université du Québec à Chicoutimi, Département des sciences appliquées, Canada

Keywords: inverse heat conduction, genetic algorithm
property: thermal conductivity, volumetric heat capacity
material: insulation, polymer

In connection with a transient heat conduction problem volumetric heat capacity (density multiplied by specific heat) and thermal conductivity should both be known. These material properties may be considered constant in case of certain materials and temperature range, in turn, however, there are numerous cases where they significantly vary with temperature. Over the last decades a large number of measurement methods have become available, however none of these may be considered universal.

The topic of this research is the elaboration of an evaluation procedure for the BICOND thermophysical property measurement method with numerical approach (for solid materials with low thermal conductivity) devised by László Kiss [1]. The evaluation of the BICOND measurement means the solution of an inverse heat conduction problem with known geometry, initial and boundary conditions and unknown material properties.

We solved the designated inverse problem (evaluation of BICOND measurement) by genetic algorithm. We sought thermal conductivity and volumetric heat capacity according to an arbitrary function of temperature. The generality of temperature dependence was ensured by defining the functions by chart. Estimating 42 parameters we identified the two material property functions simultaneously and accurately enough for engineering practice. We also used the evaluation procedure to evaluate real measurements. We compared the results with those of verification measurements and data from literature. Besides establishing satisfactory correspondence we also concluded that the evaluation procedure was also suited for detecting second order phase transition in solid material.

As a result of this research we succeeded in devising a universal and automated evaluation procedure for the BICOND measurement method. By this, a measurement method has become available to engineering practice that allows for significantly more information to be derived from a single measurement than has been the case with prevalent methods. In addition, the measuring device does not require any special measuring technology, so it may be constructed relatively cheaply, while the measurement procedure itself is also significantly less time consuming than has been the case with prevalent methods.

The work was supported by the grant OTKA K82024.

References
  1. L.I. Kiss,: Determination of Thermal Properties, CSc Thesis, HAS, 1983.

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