Measurements of Heat Transfer in Flowing Granular Media

Abstract In recent years, there has been an increased interest in the thermal behavior of granular solids because of many relatively new industrial applications. Process industries involving particulate solids being immersed or carried in a “continuous” fluid phase include chemical, petroleum, metallurgical, food, and pharmaceuticals, as well as many fluidized bed operations. An investigation was conducted of the heat transfer characteristics of a variety of flowing particulate solid media. Five different granular materials were studied in a vertical gravity-driven flow through an electrically-heated circular stainless steel tube test section. From measurements of wall temperature distribution, particle bulk inlet temperature, radial temperature distribution of the particle flow at the test section exit, and mass flow rate determination of local and average heat transfer coefficients along the test section were made. The key to this proposed approach lies in the use of proper equations to evaluate the thermophysical properties of the medium in the critical region adjacent to the heat transfer surface, i.e., voidage, density, thermal conductivity, thermal diffusivity, and specific heat. The design and construction of the thermal loop test facility used in this study is described in this paper. Comparison of the experimental results with available experimental data and predictions of various models appearing in the literature were made. Agreement existed with the modified versions of the packet model. However, for correlations based upon and compared with only limited data, agreement was not satisfactory.