This paper presents a mathematical model and numerical analysis of the convective drying process of small particles of potatoes slowly moving through the flow of a drying agent - hot moist air. The drying process was analyzed in the form of a one-dimensional thin layer. The mathematical model of the drying process is a system of two ordinary nonlinear differential equations with constant coefficients and an equation with a transcendent character. The appropriate boundary conditions of the mathematical model were given. The presented model is suitable in the automated control. The presented system of differential equations was solved numerically. The analysis presented here and the obtained results could be useful in predicting the drying kinetics of potatoes and similar natural products in a conveyor-belt dryer. [Projekat Ministarstva nauke Republike, br. TR-33049, br. TR-37002 i br. TR-37008]

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Influence of local loads on the stress state of the shell appears as the consequence of pressure, external forces, and moment influence. Loads which act directly upon the shell surface or the parts (nozzles) connected to the shell appear in their proximity, especially in the welded joint influence zones.The influence of the torque moment affecting the free end of a slanted branch on the pressure vessel cylindrical shell is considered in this article. The stress on the cylindrical shell was analysed on 245 models of different geometrical characteristics. Stress calculated by applying the finite element method was classified by maximum stress criteria. For every considered model, maximum stress envelope has been prepared. The regressive analysis enabled the determination of correlation functions, which allow calculation of stress maximum values on the cylindrical shell according to which the shell dimensions may be determined. Result analysis shows that the percentual error is within limits as follows: from À13.4 per cent to þ12.7 per cent.

This paper presents an analytical solution of a mathematical model which treats fluid flow suspension in a cylindrical channel. The model is the application of the theory of micropolar continuum on the flow of suspension and it consists of coupled linear differential equations with variable coefficients. The cylindrical channel consists of two cylinders: the internal cylinder was still and the external one rotated with constant velocity. This model enabled us to analyze the motion of a suspension, as heterogeneous mixture of a liquid with solid particles. The solution was found in the form of special Bessel's functions of the zero and the first order. The results were shown on diagrams for some characteristic values, and the good agreement was achieved between the calculated and expected results.

The paper describes a three-dimensional model with non-constant coefficients for the heat and mass transport process in desorption of water in wood. The model is based on conservation of mass and energy and uses various parameters obtained by comparing experimental data with numerical results. In this way, the relations between some parameters and average temperature and moisture content are obtained in the form of analytical expressions. Experimental results obtained for temperature profiles during drying of oak wood samples are compared with the model results. Satisfactory agreement is obtained over a range of drying air temperatures and velocities.