Cs. Mészáros

Analytical and experimental study of a modular solar dryer

A plenty of recently established small Hungarian farms need new small scale agricultural equipment to expand the productivity and to fulfil the increasing quality control demand. As a response for this demand a modular solar dryer was developed and built which can help the quality saving with renewable energy. In this paper the features and the operation of the dryer is presented first. The effect of the solar air collector module for the physical properties of drying air was studied along with the calculation of efficiency, too. The mass flow of the drying air through the system is one of the most important factor concerning to the whole process, for that reason the velocity distribution is also presented. Finally some measuring results are presented for drying of apple.

A new application of percolation theory for coupled transport phenomena through porous media

A new application of the percolation theory for describing the coupled heat and mass transport phenomena through porous media is given. The space and time dependence of the temperature and moisture level functions are calculated by taking into account the discrete, sudden changes of the diffusion coefficient in the vicinity of the critical points. A further possible application of the method leading to exact treatment of the thermodynamic state dependence of the conductivity and coupling coefficients is also indicated.

Surface changes of temperature and matter due to coupled transport processes through porous media

A new calculation is elaborated for the description of surface changes of temperature and matter due to coupled transport through a porous medium. It is based on a finite-size supposition (Neumanns type boundary condition) and on the solutions of parabolic type partial differential equations combined with Lamberts W-function. The boundary layer phenomena are also incorporated into the description of the general transport. The procedure leads to a direct computer simulation, providing concrete results on the real physical picture of the given problem in good agreement with some experiments analysed.

Modeling Condensation and Evaporation on Fruit Surface

Rewarming of fruits and vegetables after cooling is characterized by heat and mass transfer processes, which leads commonly to condensation of water on the produce surface at temperatures below the dew point. This effect may affect the produce quality due to microbial growth at unfavorable environmental conditions. The amount of condensed water is a function of the produce surface temperature and of the surrounding conditions as air temperature, air humidity, and air flow. Under practical conditions, both the warming and the condensation are strongly affected by the packaging system used. Depending on the flow conditions close to the produce surface, parameters of heat and mass transfer under laboratory conditions were measured. A mathematical model was developed for the determination of the amount of condensed water on fruit surfaces, its reevaporation, and its total dwell time dependent on the environment air conditions. The model describes the heat and mass transfer processes on single fruits. The process of diffusion of humidity in air and proceed of surface temperature is the basis for the model.

Modeling of the coupled heat and mass transfer through porous media on the base of the wave approach

Abstract A new method is given for mathematical modeling of the coupled heat and mass transfer through porous media. The behavior of the moisture level function in the vicinity of the critical value of the conductivity probability is discussed, at general initial-, and boundary conditions. Instead of the usually applied two coupled partial differential equations of parabolic type, a coupled system of hyperbolic partial differential equations containing also explicitly the relaxation time constants is used. A general solution is presented for the moisture level function, when the relaxation time constant relevant for temperature changes tends to value zero. This description is combined with scaling relations following from the contemporary statistical physical theory of percolation phenomena.

Transient transport processes in deformable porous media

The basic partial differential equations relevant for convection-diffusion and convection-diffusion-wave phenomena are presented and solved analytically by using the MAPLE symbolic computer algebra system. The possible general nonlinear character of the constitutive equation of the convection-discussion process is replaced by a direct posteriori stochastic refinement of its solution represented for Dirichlet-type boundary conditions. A thermodynamic analysis is performed for connecting the relaxation time constants and Jacobi-determinants of deformations at transient transport processes. Finally, a new procedure for general description of coupled transport processes on the basis of the formalism originally developed for convection-free phenomena is presented by matrix analysis methods in the Fourier space.

Mathematical Modeling of Drying Processes Using Methods of the Nonequilibrium Thermodynamics and Percolation Theory

A twofold refinement of the basic mathematical model for describing a coupled heat and mass transfer taking place in porous media is presented. The common application of irreversible thermodynamics and fluctuation theory of phase transitions is proposed for calculating the moisture level and temperature. Instead of parabolic partial differential equations, hyperbolic type partial differential equations are used. The relaxation time constants, whose percolation state-dependence is also taken into account, are incorporated into this formalism. Some possible new research domains in mathematical and statistical physics are also indicated.

Development of the Heat and Mass Transfer Model for Mixed-Flow Grain Dryer

Abstract A mathematical model of the coupled heat and mass transfer has been developed to calculate the drying process in a mixed-flow grain dryer. Periodical discharge operation of the dryer causes strong variations of temperature and moisture of the material. A series of quasi-stationary drying experiments have been carried out. These results are used to test and to improve the dryer model. The calculated results are in relative good agreement in the stationary operation period which is relevant for practice.

Mathematical modeling of the simultaneous convection–anomalous diffusion processes in porous media

ABSTRACT After a brief overview of most important general features of the nonclassical diffusion on the base of the extended irreversible thermodynamics, the relevant mathematical formulae are incorporated into general formalism of the simultaneous convection–diffusion processes taking place in porous media. Then, using the simplest variant of the convection–diffusion equation, novel-type analytic solutions are derived for transport processes with both subdiffusion and superdiffusion characters in Lagrangian representation.

ANALYSIS OF GRAIN MASS FLOW EXPERIMENTS IN A MIXED-FLOW DRYER

Abstract In Central Europe approximately 30% of the grain must be dried after harvest. The most popular continuous crop dryers are mixed-flow dryers. Although this type of dryer is widely used it is still necessary to optimize many segment processes during the drying. For example there are big differences in the vertical grain particle velocity causing differences in the residence time. The aim of the work was to carry out experiments for the grain mass flow measurements in a semi technical dryer. Based on the results a mathematical and 3D computer model for the grain mass flow will be developed in the future enabling improvements in the prediction of the drying process which does not form part of present study.