A mathematical model of heat transfer between a fluidized bed and an immersed surface and a model of gas flow and porosity, both recently published, were combined and further modified in the area of low velocities where the particle convective component of heat transfer is low or neglectable. Experimental work consisted of measurements of both porosity and heat transfer in a cold fluidized bed of sand. Five samples of sand, each having a narrow size range, were investigated; the mean particle diameter varied from 0.43 to 1.55 mm. Also two mixtures of these samples, which yielded a wide particle size distribution, were tested. Experimental results showed good agreement with model predictions, for both porosity and heat transfer.