INTERPARTICLE STRESS, FLUID PRESSURE, AND BUBBLE MOTION IN GAS-FLUIDIZED BEDS

Direct measurements of stresses transmitted between particles and surfaces in bubbling fluidised beds are reviewed, to show that they are only significant when gross bubble-induced motion transmits particle momentum to the surface. New measurements of gas pressure around a tube in a two-dimensional bed show that the motion of a bubble near a tube, in both two- and three-dimensional beds, results from the local gas pressure rather than from interparticle effects. The implications of these observations are explored, to identify the limits to the analogy between fluidised beds and Newtonian liquids. By a further extension of the Davies and Taylor analysis of the rise of spherical-cap bubbles in liquids, a result is derived which enables the bubbling behaviour of beds containing heat transfer tubes or other immersed bodies to be simulated.