On the effect of particle size on heat transfer in vertical upflow of gas-solids suspension

The occurrence of a minimum in heat transfer coefficient with particle diameter in a vertical upflow transport column as reported by Jepson et al. (1963) is explained by the minimum in total surface area of solid particles per unit volume of column with particle diameter. The minimum in the external surface area of solids in the column is shown to be due to the counteracting effects of increasing solids holdup with particle diameter and decreasing specific surface area of solid particles with increasing particle diameter.