Thermal diffusivity estimation of the olive oil during its high-pressure treatment

This contribution concerns cooling of olive oil under the conditions of its treatment with high pressure and the estimation of its thermal diffusivity by the means of numerical analysis of the experimental data of the temperature drop at the time of holding at the pressure. The oil was placed in a small container in the middle of a high-pressure device chamber. The device chamber was filled with pressured water. The numerical method of the finite elements in the programme environment COSMOS was used for modelling the oil cooling without considering the free convection in the oil. During the calculation, the input thermal diffusivity dependence on the temperature was being purposely varied for so long until the reasonable agreement of the computed and measured temperature decays of the olive oil on the time was reached. It proved that thus gained temperature dependences of the apparent thermal diffusivity are a function of the starting temperature of the experiment and are therefore influenced by the free convection in the oil and hence values gained are not values of the physical property of the material. The experiment to estimate the real thermal diffusivity of the oil for the steady state at the end of the experiment from these dependences when the free convection already disappears was done. This work shows that it is necessary to take into consideration not only the heat conduction, but also the free convection when modelling the temperature history of the viscous liquid foods during high-pressure treatment. (c) 2005 Elsevier Ltd. All rights reserved.