Effect of liquid addition on heat transfer in gas-fluidized beds of large light particles

Abstract

When liquid is added to large-particle gas-uidized beds where the liquid density is similar to the particle density, the liquid addition can cause a dramatic increase in the velocity range and intensity of uidization. In this paper it is shown that this also leads to strong enhancement of the heat transfer between the bed and an immersed tube. Experiments were carried out using a heated tube of outer diameter 25 mm in air-uidized beds of polystyrene particles or glass beads to which small quantities of water (typically equivalent to 10 per cent of the bed volume) were added. The results from the heat transfer experiments are explained with the aid of observations of the tube surface using an industrial endoscope located inside the tube. The key factors underlying the enhancement of heat transfer are identi ed to be heat conduction to liquid-solid aggregates, convection to the liquid phase, convection to the gas phase and vaporization.

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

“…The validity of the force sensor tube and heat transfer tube have already been confirmed in work reported previously [6,7] .…”

Fundamental Study on Washing Characteristics of a Novel Multi-Phase Flow System

“…To discuss the washing characteristics of this multiphase system, the authors' earlier experimental results [2] of liquid distribution on the tube surface immersed in the wetted fluidized bed is introduced here in relation to the results of this article.…”

“…When a little water (typically one-tenth of the dense bed total volume) is added to a gas-fluidized bed of relatively large non-wettable particles, such as 6 mm polystyrene (PLST) spheres, the added water can cause a dramatic improvement in the extent of fluidization [1][2][3], contrary to most conventional gas-solid fluidized beds where liquid causes immobilization. The resulting unique fluidized bed is suitable for washing of objects, due to the motion of light rounded particles, with a major reduction in the amount of water needed compared to conventional washing techniques.…”

“…In this article, the fundamental washing properties and mechanisms of this novel multi-phase flow system are investigated based on relatively simple experiments. Improved understanding is achieved based on results, presented below, of three kinds of experiments related to particle collision forces on the surface of an immersed cylinder, attrition of a plaster cylinder, and whitening of a cloth covering a cylinder, combined with earlier results [2] on the distribution of liquid on a cylinder surface. The effect of the addition of small particles is also discussed.…”

Spouting Enhancement by Addition of Small Quantities of Liquid to Gas-Spouted Beds

“…The fl uidization enhancement manifests itself by a substantial decrease of minimum fl uidization velocity and therefore by a higher voidage, greater particle mobility and improved heat transfer between the bed and an immersed surface (Nagahashi et al, 2003b), for any given fl uidization velocity. It was explained by assuming that the added liquid, the occupied volume of which caused a gas velocity increase, coated the particles throughout the bed but without causing bridging between the particles.…”