A model for simultaneous heat, water and vapour diffusion

A model for simultaneous heat, water and vapour diffusion was developed to use for prediction of the diffusion of water inside foods during heat proce ssing. The model is based on Fourier's and Fick's Laws. The diffusion of li quid water is separated from the diffusion of water vapour. The model was e valuated in a drying process. Slabs of bread crumbs, 12 x 12 x 2 cm(3) in s ize, were dried in a conventional oven at 210 degrees C and the local water content and temperatures were measured during the drying in the centre, ha lfway to the centre and at the surface. From the measurements, the diffusio n coefficient as a function of temperature and concentration and several ot her material parameters were estimated. The results show that the measured water content slowly increases in the ce ntre of the sample. During the increase, the temperature remains on a plate au. When the centre starts to dry the temperature increases. Halfway to the centre the water content also increases slightly before it starts to dry o ut, while the surface starts drying immediately. The simulated water conten t levels and temperatures conform well to the experimental values and show that the evaporation and condensation model describes well the diffusion me chanisms in a porous food. (C) 1999 Elsevier Science Ltd. All rights reserv ed.