Studies on Cooling and Cold Air Drying for Grain Storage (IV)

Aspects of Fluidizing Behavior and Heat Transfer in Fluidized Beds of Unhulled Rice

Abstract

Some basic experiments were performed on aspects of fluidizing behavior and heat transfer of fluidized beds of unhulled rice. A summary of the results is shown below.
1) Onset velocity of fluidization increased in proportion to initial bed height. Therefore theory of M. Leva was inapplicable to fluidized beds of unhulled rice, but the simplified equation (10), suggested by C. Y. Wen et al could be used.
2) Mode of fluidization was strongly influenced by the type of distributor used. Within the limits of this experiment, it became evident that the packed bed of steel ball was the most excellent distributor for fluidization.
3) Apparent coefficient of heat transfer between grain and air decreased in inverse proportion to initial bed height.
4) In general, apparent coefficent of heat transfer between grain and air increased in proportion to air velocity, but a cooling of grains in dense phase was the most efficient method.
5) The result of the above (4) was correlated by the following equation. The value of the Nusselt number for Pr=0.7, 500<R_ep<1200 approached the Nusselt number in heat convection for a single sphere.
h_pD_p/k_f=0.0137(D_pρfU/μ)^0.939, (r²=0.87)