Measurements and analytical modeling of heat transfer in flowing granular media

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. Comparison of the experimental results with 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. Consequently a more physically realistic theoretical model was developed to improve the agreement between experimental results and analytical predictions. The packet theory of heat transfer of Mickley was modified by accounting for the presence of the wall in affecting the local voidage. A model of the heat transfer processes within the media adjacent to the wall was developed that takes into account the variation of the thermophysical properties of the media in that region. A simple numerical solution to the resulting energy equation was obtained. The theory was found to correctly predict the trend of the measurements of the present study as well as the experimental data of controlled residence time available in the literature. Comparing present experimental Ill measurements with predictions from the model ( in terms of Nusselt number versus Fourier number), the maximum difference observed was 39 percent, over a Fourier number range from 0.001 to 20. The average difference observed was estimated to be about 12.6 percent