MECHANICAL/SOLAR - ASSISTED DRYING PROCESSES AND SYSTEMS

Research in this field focuses on the analysis of heat and mass transport phenomena, the investigation of optimal drying conditions for various agricultural products (drying curves) and the development of drying process models aiming at the optimal design of hot air mechanical dryers. Both experimental methods and numerical simulation are employed and the main activities so far comprised :

Experimental Investigation

• Measurements on a series of agricultural product aiming at the characterization of porosity after drying (size and distribution of pores etc.) and its relation to the quality and thermophysical properties of products.
• Drying Kinetics : comparison between natural processes (sun drying) and industrial-type drying. Criteria for optimal dryer operation.
• Determination of the influence of drying air parameters (speed, temperature), heat transfer correlations. Representative product : Figs (figus carica) (Fig.1)



• Effect of alternating air flow direction
• Measurements on a solar-assisted dryer heated by an air collector with evacuated tubes (Fig. 2). Determination of process efficiency factors, drying curves, drying rates, diffusion coefficients for drying of apples, carrots, apricots.

Numerical Simulation

• Effect of air velocity distributions in industrial-type drying chambers (Fig. 3). Detection of regions of non-uniformity. Correlation of air speed-drying quality, based on comparisons of air speed measurements and moisture content.
• Development of coupled flow and transport numerical models (conjugate heat and mass transfer) for convective drying. Macroscopic treatment by formulating and solving drying problems on bodies of rectangular geometry, e.g., blunt plates representing layers of the drying product. Study of the effect of product thickness, multiple plate interactions in alternative placements within the drying chamber (Fig. 4).
• Effect of fluid-dynamical phenomena such as flow separations, unsteadiness due to vortex shedding downstream of the plates, flow acceleration due to blockage and bluff body effects in general, on the heat-mass transfer coefficients of the drying process.