Dynamic force reduction and heat transfer improvement for horizontal tubes in large-particle gas-fluidized beds

Abstract

The effects of tube bank configuration on forces and heat transfer were investigated for both two-dimensional and three-dimensional gas fluidized beds. Effective dynamic forces and heat transfer coefficients were measured for several tube bank configurations, and it was found that the average forces are smaller than for a single tube. The heat transfer coefficient can be increased by providing sufficient space for particles to descend around both sides of the tube bank. The results provide useful guidelines for optimizing the configuration of tube banks to achieve high heat transfer coefficients while reducing tube erosion due to dynamic forces.

Dynamic forces on a horizontal slat immersed in a fluidized bed of fine particles

“…Similar to previous studies (Grace and Hosny, 1985;Hosny and Grace, 1984;Kennedy et al, 1981;Nagahashi et al, 2008), the RMS stress…”

“…13(a)] shows that at three installation heights q RMS increases linearly with increasing velocity. This result is similar to those previously obtained from measured force characteristics on horizontal tubes immersed in fluidized beds (Hosny, 1982;Hosny and Grace, 1984;Kennedy et al, 1981;Nagahashi et al, 2008). These results can be attributed to the enhanced bubble motion and the stronger motion of solids induced in the bed at increasing superficial gas velocities.…”

“…Indeed, the averages of most measured stress signals in this study, except at  = 90 • , were positive indicating that the resultant force on the test slat in the fluidized bed is upward. In previous studies (Grace and Hosny, 1985;Hosny, 1982;Kennedy et al, 1981;Nagahashi et al, 2008), the vertical force acting on a round tube in a fluidized bed was also found to be positive on average with fluctuations similar to the measured stress signal acting on the test slat at  = 0 • in this study. However, the horizontal force acting on a round tube had a zero average as for the test slat at  = 90 • in this study.…”

“…The horizontal force components have significantly lower magnitude than the vertical force components. The intensity of the force exerted on a single tube in a tube bundle is found to be reduced significantly, which was also proved by a later study by Nagahashi et al (2008). Hosny and Grace (1984) also found that the upstream (lowermost) tubes in a bundle experienced the largest rootmean-square (RMS) forces, while tubes in the top row encountered the smallest RMS forces.…”