Mass transfer coefficient

About: Mass transfer coefficient is a research topic. Over the lifetime, 7827 publications have been published within this topic receiving 168354 citations.

Effect of organic substances on mass transfer in bubble aeration

Abstract: Dispersion of gas bubbles in water has a wide application in aeration and ozonation processes. The rate of mass transfer in such systems depends strongly on the wastewater quality as well as on the design and operational characteristics of gas liquid contact units. Small amounts of surface active compounds in water were shown to reduce the overall mass transfer coefficient, kLa, in single bubble systems1,2,3 and in swarms of bubbles.4 This effect was attributed to the decrease in the liquid-phase mass transfer coefficient, kL.l~5 The adsorption of the large molecules of surfactants reduced the surface tension of water,1,467 reduced the bubble size,1,3,4,8 lowered the terminal velocity of bub bles,9-11 and increased the drag coefficient.5,10 Accordingly, surfactants were believed to reduce the kL by depressing the hydrodynamic activity, and by offering additional barriers for the passage of gas molecules at the gas-liquid interface. Higher concentrations of the surfactants improved kLa\ this was attributed to the increase in the interfacial area caused by the formation of smaller bubbles.1,4 On the other hand, Zieminski and his co-workers8,12"14 reported a definite improvement in kLa in the presence of various alcohols and carboxylic acids. The authors stated the principle action of such substances to be prevention of bubble coalescence. This study was undertaken to investigate the effects of various organic substances on the characteristics of oxygen transfer from air bubbles to water. The compounds listed in Table 1 were chosen to represent various groups of water contaminants. To elucidate the effective mechanisms, experi ments were conducted by using either a fritted glass diffuser or a capillary for gas dispersion. The effects of gas flow rate, pH, and ionic strength were also examined.

The Rate of the Phosphorous Reaction Between Liquid Iron and Slag

Abstract: In the current study, the rates of dephosphorization and rephosphorization of liquid iron with simulated steelmaking slags were investigated at 1873 K (1600° C). The experiments were conducted in an induction furnace with supplemental heating to maintain a consistent temperature within both the metal and slag phases. An integrated form of the rate equation was used to evaluate the results, assuming mass transfer in both the slag and metal was rate controlling. The results of the current and previous studies indicate that the mass transfer parameter, the slag-metal surface area, and the overall mass transfer coefficient (A*k0), decreased as the reaction proceeded. It is proposed that initially when the rate and oxygen flux are high, the interfacial energy decreases, and the interfacial fluid velocity increases causing disruption of the slag metal interface. The consequent increases in interfacial area and interfacial fluid flow cause A*k0 to be high initially and then decrease as the oxygen flux decreases.