Flow and Heat Transfer Characteristics Inside Packed and Fluidized Beds

Abstract

This paper investigates experimentally and theoretically the flow and heat transfer characteristics inside packed and fluidized beds. A single-blow transient technique combined with a thermal nonequilibrium two-equation model determined the heat transfer performances. Spherical particles were randomly packed in the test section for simulating the packed beds with porosity ε=0.38 and 0.39. Particles were strung with different spaces for fluidized beds with ε = 0.48 ~ 0.97. The ranges of dominant parameters are the Prandtl number Pr = 0.71, the particle Reynolds number Red = 200 ~ 7000, and ε = 0.38 ~ 0.97. The results show that the heat transfer coefficient increases with the decrease in the porosity and the increase in the particle Reynolds number. The friction coefficients of the fluidized beds with ε = 0.48 and 0.53 have significant deviations from that of the packed bed with ε = 0.38 and 0.39. Due to fewer interactions among particles for ε = 0.97, the friction coefficient approaches the value of a single particle.

Continuous time random walks and heat transfer in porous media

“…However, many other studies, which have examined systems far from thermal equilibrium, have reported breakthrough curves that are highly non-Fourier in nature (e.g., Liang and Yang 1975;Vafai et al 1985;Hwang and Chao 1994;Wu and Hwang 1998). Of these studies, we focus on the well-constrained data reported by Wu and Hwang (1998) for pseudo-1D experiments of forced convective flow through an artificial porous matrix.…”

“…A step increase in temperature was applied to the inlet, and the evolution of temperatures at the outlet were subsequently Table 2. Experimental data from Wu and Hwang (1998) recorded. The highly non-Fourier behavior that was observed, which combined rapid thermal breakthrough with extremely long-tailing, was attributed to disequilibrium between the fluid and the porous matrix (Wu and Hwang 1998).…”

“…Experimental data from Wu and Hwang (1998) recorded. The highly non-Fourier behavior that was observed, which combined rapid thermal breakthrough with extremely long-tailing, was attributed to disequilibrium between the fluid and the porous matrix (Wu and Hwang 1998). The data were fit reasonably well by a modified version of the LTNE theory (Wu and Hwang 1998), which neglected the effects of thermal dispersion in both fluid and solid.…”

“…In this section, we give only a brief description of the experimental setup; a more detailed account is provided by Wu and Hwang (1998). During the experiments, air was blown through a square channel of cross section 10 × 10 cm 2 and 30 cm in length, at velocities of up to 10 m s −1 ; in the series of experiments explored here, spherical synthetic polymer particles were suspended in the channel using nylon thread, producing a highly porous fluidized bed (n = 0.73).…”

“…A clear limitation of the equilibrium approach (Eq. 2) is that, at the pore scale, fluids are not always in equilibrium with the porous matrix through which they flow (e.g., Levec and Carbonell 1985;Wu and Hwang 1998). This lack of equilibrium stems from a delay in the interaction between fluid and solid.…”