Estimation of bed expansions in a freely‐bubbling three‐dimensional gas‐fluidized bed

Knowledge of bed expansions is important in the design and operation of gas–solid fluidized beds. This paper presents a study on the estimation of expanded bed height in a large three‐dimensional gas‐fluidized bed with a square section of 0·61×0·61 m 2 . All experiments were performed at the freely bubbling mode and the bed expansions were recorded by a video camera. Bed materials were used 593 μm raw perlite and 1233 μm sand falling within the categories of Geldart's Groups B and D, respectively. The bed height at minimum fluidization ranged from 0·0398 to 0·3176 m, while the excess air velocity from 0·034 m s −1 to 0·7453 m s −1 . Equations related to the bed expansion were given using a modified form of two‐phase theory of fluidization. A correlation for the average bed expansion (void fraction) was also presented that has been derived from the principal form found successful in gas–liquid systems as follows: R=0·5482 d −0·129 p (U o −U mf ) 0·111 with an average deviation of less than 1%. The experimental findings were compared with previously reported results and were discussed in the light of available correlations. © 1998 John Wiley & Sons, Ltd.