Experimental investigation of thermal conductivity coefficient and heat exchange between fluidized bed and inclined exchange surface

Abstract

-The paper presents experimental research of thermal conductivity coefficients of the siliceous sand bed fluidized by air and an experimental investigation of the particle size influence on the heat transfer coefficient between fluidized bed and inclined exchange surfaces. The measurements were performed for the specific fluidization velocity and sand particle diameters d p =0.3, 0.5, 0.9 mm. The industrial use of fluidized beds has been increasing rapidly in the past 20 years owing to their useful characteristics. One of the outstanding characteristics of a fluidized bed is that it tends to maintain a uniform temperature even with nonuniform heat release. On the basis of experimental research, the influence of the process's operational parameters on the obtained values of the bed's thermal conductivity has been analyzed. The results show direct dependence of thermal conductivity on the intensity of mixing, the degree of fluidization, and the size of particles. In the axial direction, the coefficients that have been treated have values a whole order higher than in the radial direction. Comparison of experimental research results with experimental results of other authors shows good agreement and the same tendency of thermal conductivity change. It is well known in the literature that the value of the heat transfer coefficient is the highest in the horizontal and the smallest in the vertical position of the heat exchange surface. Variation of heat transfer, depending on inclination angle is not examined in detail. The difference between the values of the relative heat transfer coefficient between vertical and horizontal heater position for all particle sizes reduces by approximately 15% with the increase of fluidization rate.

Two-Phase Liquid-Solid Hydrodynamics of Inclined Fluidized Beds

“…Stojanovic et al [73] explored how quickly fluidization affected the warm exchange between a rectangular fluidized bed and a cross-segment warm exchange tube. For all of the radiator particles, the warm exchange coefficients showed a comparative propensity to increase the fluidization speed.…”

Experimental research of the influence of particle size and fluidization velocity on zeolite drying in a two-component fluidized bed

“…As the mechanisms of heat exchange in a fluidized bed are very complex, it is necessary to analyze them separately: interphase heat transfer (gas-solids) and heat transfer between the fluidized bed and the walls of the apparatus or the surface immersed in the fluidized bed [7,8]. Also, a very important role in these processes is played by the effective thermal conductivity of the fluidized bed and the emulsion phase.…”

“…Experimental results of most previous research in mass transfer are given in the dimensionless form as a function of Sherwood's, Schmidt's, and Reynolds's number or directly as a function of operating characteristics such as gas velocity, particle diameter, etc. A quite reliable expression for the Sherwood number was provided by Stojanovic [8] and Kunii and Levenspiel [9] for the use in the particles with diameters of less than 1 mm:…”