E. Papanicolaou

Conjugate Heat and Mass Transfer from a Drying Rectangular Cylinder in Confined Air Flow

Heat and mass transfer from a porous body subject to convective drying is investigated numerically based on Luikovs equations. The air flow is assumed incompressible, two-dimensional, laminar, confined in a channel, and parallel to the rectangular-shaped solid. The finite-volume method is used and the computed temporal and spatial variations of moisture content, temperature, concentration, and flow parameters for two different flow rates are analyzed. Two flow configurations are studied: with and without a flow divider upstream of the cylinder in an attempt to eliminate the presence of separation zones and study their effect on drying. It was found that such effects may greatly affect the drying process, along with frontal area stagnation and the thickness of the body.

Flow and Temperature Fields in Cooling Devices with Embedded Serpentine Tubes

The turbulent flow (Re = 5124) and conjugate heat transfer in heat-sink designs of the tube-on-plate type are numerically investigated. The cooling configurations employ a serpentine tube partially (or fully) embedded inside the plate. Two-and four-pass configurations are investigated. A constant heat flux is applied at the bottom surface of the heat-sink plate. The SST k-ω model is used for the prediction of the turbulent flow and heat transfer. Two pairs of longitudinal vortices, as well as secondary flow separation, have been found to set in at the tube curved section. The combined secondary flow pattern enhances heat transfer at the tube sections over a considerable distance downstream of the 180° bends. In the last part of the analysis, the overall performance of the two configurations is compared using a number of evaluation criteria suitable for heat exchanging devices. The four-pass configuration with fully embedded tubing exhibits the best thermal (energetic) and exergetic performance.

Fundamental Mathematical Relations of Solar Drying Systems

Drying of agricultural products is a widely spread method achieving a physiochemical stabilization of the material by removing part of the moisture content, producing therefore products with new qualitative properties and different nutritional and economical value. Significant amounts of agricultural crops are dried artificially in mechanical drying systems using heated air. Simulation models of the drying process are used either for designing new or improving existing drying systems or for the control of the drying process. All parameters (transfer coefficients, drying constants, etc.) used by the simulation models are directly related to the drying conditions, i.e., temperature and velocity of the drying medium inside the mechanical dryer. As a consequence, the drying conditions, as directly related to the drying time, are affecting the energy demands.