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Semiconductor diodes, in conjunction with a constant current source, are sometimes used as thermometers. It has been observed experimentally that, within a certain temperature range, the relation between temperature and voltage is almost linear. We show that this linearity is a direct consequence of the constancy of the current flowing through the diode, and that the parameters resulting from a least-squares fit to the experimental data can be used to determine the band gap energy of the semiconductor. We test the validity of our model by comparing our results to measurements on diodes made of germanium and silicon. If we take into account the simplifications used in our model, the results agree well with known values of the energy gaps.

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This article aims at determining thin-layer drying curves for grains of lima bean, variety olho-de-peixe and to predict them using diffusion models. Samples of lima bean (110.0 g) with initial moisture content of 66.0% (wet basis, wb) were dried at temperatures of 40.0, 50.0 and 60.0°C. The effective diffusivity of moisture was determined by analytical solutions of the mass diffusion equation (Fick’s second law) with prescribed boundary condition for spherical, cylindrical, and infinite slab at each temperature. Comparison with the experimental data showed that the infinite slab with constant diffusivity predicted more accurately, but statistical indicators of the goodness of fit were not completely satisfactory. Thus, a model for the infinite slab with constant volume, moisture-dependent diffusivity and convective boundary condition was numerically integrated. This model was solved by the numerical method of finite volumes with fully implicit formulation. The values obtained for the diffusivity were between 5.58 x 10-9 and 6.39 x 10-8 m2 min-1, being the activation energy 28.4 kJ mol-1. The model satisfactorily describes the drying process of this lima bean cultivar under all conditions investigated.