THE EFFECT OF BUBBLE FORMATION AND DETACHMENT ON MAGNETITE DEPOSITION ON ALLOY-800 SURFACES DURING BOILING HEAT TRANSFER

摘要

Fouling of heat transfer surfaces leads to a decrease in efficiency of heat exchanger equipment. The mechanism of deposition of magnetite particles from suspension in water onto Alloy-800 heated surface can be described as five steps: initiation, transport, attachment, re-entrainment and ageing. How re-entrainment and ageing affect the overall deposition remains unclear. Nonetheless, it is believed that when the particle has been deposited, it will be either re-entrained or bonded to the surface. Experiments have been conducted in an atmospheric-pressure, recirculating water loop under isothermal, non-boiling and boiling conditions. The effect of bubbling at various heat fluxes, magnetite concentration and surface roughness on the magnetite deposition has been investigated using photographic technique. Particle trapping at the liquid-vapour interface is believed to play an important role on the magnetite deposition. The experimental results and postulated mechanisms will be presented.