Boiling enhancement in a mini-channel of a three-phase circulating fluidised bed

In fouling, the accumulation of poorly conducting materials on the surface of process equipment, results in an increased resistance to heat transfer and hence reduces heat exchanger effectiveness. Under most conditions fouling is more severe during boiling heat transfer, due to the mechanisms of bubble formation and detachment. Thus, in order to enhance heat transfer and mitigate fouling in boiling processes, a new type of vapour-liquid-solid (three-phase) circulating fluidised bed boiling system has been designed, combining circulating fluidised bed technology with boiling heat transfer. Experiments are conducted in a glass mini-channel of square cross sectional area 21.5 mm x 11mm, height 1000mm, and fitted with an electrically heated cartridge heater rod of 8mm diameter x 730mm length. The set-up uses stainless steel balls to investigate the effect of particle properties (specifically particle size) on three-phase boiling heat transfer enhancement. Experimental results show that overall, compared with two-phase flow boiling, the presence of solid particles in the three-phase boiling system augments the heat transfer coefficient. Results are presented and discussed.