Heat transfer in spouted beds.

Abstract

The transfer of heat from spouted beds to verticle 6-in. and 3-in. columns was investigated. The bed materials consisted of polyethylene, polystyrene, wheat, rice, millet, Timothy seeds and Ottowa sands. The effect of bed temperature, particle diameter, density and heat capacity, bed height, mass velocity of air and orifice diameter were investigated and correlated. The value of the heat transfer codfficient varied fron 10-24 Btu/(hr.) (sq.ft.)(°F). During spouting, the heat transfer coefficient was found to be independent of mass velocity, cloumn diameter and orifice diameter, but increased with particle diameter and heat capacity, and decreased with bed height. Heat transfer data in the 6-in. column were collected from the transition bed for polythylene, and wheat with a 13-in. bed height, and 3/4-in. orifice diameter and the results were correlated. The heat transfer codffficient was found to increase with increase in mass celocity up to the point of spouting and at a fixed mass velocity it was found to decrease with increase in bed level. Experiments were also conducted to collect heat transfer data from a fluidized bed in the 6-in. column with wheat as bed material. It was found that the heat transfer coefficient was from 10-66% lower for a spouted bed than for a fluidized bed and the correspoinding mass velocity for spouting varied from 35-55% of that required for obtaining the maximum heat transfer in a fluidized bed under similar flow conditions. A generalized correlation is proposed to estimate the spout diameter in a spouted bed from literature data as well as from the data collected with the aid of a 6-in. and a 4-in. semicircular column. An attempt is made to predict the pressure drop for the transition bed and the spouted bed.