Study on particle-to-fluid convective heat transfer characteristics in randomly packed bed

In the present paper, particle-to-fluid convective heat transfer coefficients in randomly packed beds were experimentally investigated by the naphthalene sublimation technique and the heat-to-mass analogy. The influence of the entrance effect is first studied. It is found that, the Nusselt number in the entrance is lower than that in the bulk of the bed and when the flow passes through 6-8 particle diameters, the heat transfer enters the fully developed region where the Nusselt number remains almost unchanged. The Nusselt numbers in the fully developed region are then compared to that of the Wakao's equation. The average deviation of experimental points and the Wakao's equation is 11.83%. Further, the applicability of Wakao's equation is discussed when the porosity of the packed bed is taken into consideration.