Experimental and numerical studies of forced convection and radiation heat transfer in packed beds

Karim Janan Nasr, Purdue University

Abstract

This dissertation reports experimental and numerical studies of heat transfer in porous media. The main objective of the experimental studies was to provide a data base which can be used for the quantification of the heat transfer mechanisms and the validation of numerical models. A numerical simulation was carried out to study fluid flow and heat transfer in porous media and evaluate the effects of thermal dispersion. The first experimental investigation focused on forced convection heat transfer from a cylinder embedded in a packed bed. The effects of particle diameter and particle thermal conductivity were examined. In the presence of particles, the measured convective heat transfer coefficients, associated with the embedded cylinder, were up to seven times higher than those for a bare tube in crossflow. Higher heat transfer coefficients were obtained with smaller particles and higher thermal conductivity packing materials. The experimental data were compared against the predictions of a theory based on Darcy's law in conjunction with the boundary layer approximations and resulted in improved correlating equations accounting for particle diameter and thermal conductivity variations. The second experimental study investigated combined conduction and radiation heat transfer in packed beds. Higher effective thermal conductivities were obtained with larger particles and higher thermal conductivity packing materials. The measured effective thermal conductivities were compared against the predictions of the Kunii-Smith and the Zehner-Bauer-Schlunder models. Quantification of the radiation contribution was accomplished by treating radiation as a diffusion process, for which a radiative conductivity was formulated, normalized, and compared with the findings of other investigators. Numerical studies for a cylinder embedded in a packed bed were carried out. The macroscopic volume-averaged equations were employed and non-dimensionalized. The effects of governing dimensionless parameters on heat transfer were studied. The numerical predictions were compared to the predictions of the boundary layer theory and to the experimental results. The comparison between experimental data and numerical predictions provided a means for quantifying thermal dispersion effects. The contribution of thermal dispersion was expressed in terms of a dispersive conductivity. A correlating equation, describing thermal dispersion of a cylinder-bed system, was obtained.

Degree

Ph.D.

Advisors

Ramadhyani, Purdue University.

Subject Area

Mechanical engineering

COinS