Homogeneous swarm of high-Reynolds-number bubbles rising within a thin gap. Part 1. Bubble dynamics

The spatial distribution, the velocity statistics and the dispersion of the gas phase have been investigated experimentally in a homogeneous swarm of bubbles confined within a thin gap. In the considered flow regime, the bubbles rise on oscillatory paths while keeping a constant shape. They are followed by unstable wakes which are strongly attenuated due to wall friction. According to the direction that is considered, the physical mechanisms are totally different. In the vertical direction, the entrainment by the wakes controls the bubble agitation, causing the velocity variance and the dispersion coefficient to increase almost linearly with the gas volume fraction. In the horizontal direction, path oscillations are the major cause of bubble agitation, leading to a constant velocity variance. The horizontal dispersion, which is lower than that in the vertical direction, is again observed to increase almost linearly with the gas volume fraction. It is however not directly due to regular path oscillations, which are unable to generate a net deviation over a whole period, but results from bubble interactions which cause a loss of the bubble velocity time correlation.

Flow Morphology and Heat Transfer During Subcooled Flow Nucleate Boiling of HFE-7000 in Microchannels

Flow boiling was experimentally studied in parallel microchannels using coolant HFE-7000. Subcooled nucleate boiling was achieved under various thermal-hydraulic conditions for mass velocities ranging from G = 164 kg/m2·s to G = 3025 kg/m2·s. Local surface temperatures were measured and flow visualizations were conducted to obtain flow morphologies, boiling curves, and heat transfer coefficients during boiling process. It was found that heat transfer was significantly enhanced during subcooled flow boiling by bubble agitation of the liquid.

DECOMPOSING ORGANIC CHLORINE COMPOUNDS IN DRY CLEANING WASTEWATER BY FENTON'S REACTION ON RETICULATED IRON

Decomposition of tetrachloroethylene which is used in dry cleaning was studied. Static (vial bottle) and dynamic (circulating apparatus) experiments were performed. The comparison of effectiveness as an iron source for Fenton's reaction was made among several kinds of iron and reticulated iron was chosen as the best material. While organic chlorine compounds added in pure water were easily decomposed by Fenton's reaction on porous (reticulated) iron in aqueous phase, it was found difficult to achieve high efficiency in the case of wastewater from the actual laundry process. The reason was estimated to be the coexistence of high COD residuals, such as dirt and organic acids. The combination of circulation and air bubble agitation have even led to the total removal of99.8% of the tetrachloroethylene.