As a fundamental study of sieve tray, the weeping phenomena at submerged orifices were examined in detail based on the pictures taken by a high-speed camera and on the data of pressure fluctuation in the gas chamber. The chamber pressure decreases excessively because of the formation of the larger bubble. Therefore, the liquid weeps immediately after the detachment of a bubble from the orifice. The effects of the orifice diameter, the orifice number, the pitch of orifices, the chamber volume, the gas flow rates, and the physical properties of liquid on the liquid weeping rates were

The adhesion of fine particles onto bubbles in flotation was studied on the basis of surface charge measurement3 of the bubbles and particles.The surface charges of the bubbles were measured by the use of a micro-electropheresis apparatus devised in our previous study and the mechanism of the bubble charging was studied under various experimental conditions. In distilled water, the bubbles were negatively charged and the iso-electric point appeared at pH = 2.5. The surface charges of the bubbles in the surfactant solution were determined by the surfactant molecules adsorbed at the surface and depend strongly on the values of pH.The flotation efficiency of latex particles (0.923 pin) was found to be strongly influenced by the surface charges of both the particles and the bubbles. The force between the particle and the bubble was estimated from the observation of the particle attachment to the bubble surface, and a simple equation including the effects of the hydrodynamic and surface charge interactions was proposed to determine the floatability limit.L'adhCsion de particules fines dans des bulles en tlottation a Ct C etudiee sur la base de mesures de charge de surface des bulles et des particules.Les charges de surface des bulles ont kte mesurees au nroyen d'un appareillage de micro-dectrophorese c o n y danr nos etudes anterieures, et on a Ctudit le mecanisme de chargement des bulles dans des conditions experimentales variees. Dans de I'eau distillte, les bulles ont CtC chargees negativement et le point iso-blectrique est apparu au pH de 2.5. Les charges de surface de bulles dans la solution de surfactant ont ttC dkterminees par les molkcules de surfactant adsorbkes B la surface et elles dCpendent fortement des valeurs du pH. On a trouve que I'effcacitC de flottaison des particules de latex (0,923 pm) Ctaient fortenient influencee par les charges de surface a la fois des particules et des bulles. La force entre les particules et les bulles a cte estimee 2 partir de I'observation de la liaison des particules a la surface des bulles, et on propose une equation simple incluant les effets des interactions des charges de surface et de I'hydrodynamique pour determiner la limite de flottabilitk.

A method and an apparatus to measure the^-potential of bubbles has been developed. The apparatus is of microelectrophoresis type. Small bubbles of 20-40/im in diameter are generated by pressure reduction of a solution containing dissolved air and are introduced into an electrophoresis cell of 0.972 mmthickness. As the movementof the bubbles is followed over 4 seconds in this arrangement, the measurement error due to the rapid rising of the bubbles can be considerably decreased. The bubbles were positively charged in a cationic surfactant solution of cetyltrimethylammonium bromide (CTAB)and the charge decreased with increasing electrolyte concentration in the solution. In an anionic surfactant solution of sodium dodecyl sulfate (SDS), both the bubbles and oil particles were negatively charged. But, by the addition of A12(SO4)3, the oil particles maintained their negative charge while the charge of the bubbles was changed to positive. The situation of the attaching of oil particles to bubbles was observed photographically.

The trajectory of a small particle moving to a bubble surface was analyzed by taking into account the effects of surface charges of the bubble and particle and the short range hydrodynamic interaction near the bubble surface, in a flotation process. The particle trajectories obtained theoretically were in good agreement with those obtained by direct observation. Even if the signs of the surface charges of the bubble and particle were the same, the particle adhered to the bubble surface when the net surface force, that is, the sum of the electrostatic force and the van der Waals force, was attractive. Particle capture efficiency, vs, per bubble was estimated by trajectory analysis and the flotation efficiency, qT, was calculated. The values of q calculated by the particle trajectory analysis were in reasonable agreement with those obtained experimentally. The dependence of particle diameter on q T was also examined by the particle trajectory analysis.~~ ~~~~ ~. . . ~~ ~~~~ On a analyse la trajectoire d'une petite particule se dtplaFant vers la surface d'une bulle en tenant compte des effets des charges de surface de la bulle et de la particule ainsi que de I'interaction hydrodynamique h courte distance pres de la surface de la bulle, dans un processus de flottaison. Les trajectoires de particules obtenues de maniere thdorique montrent un bon accord avec celles obtenues par observation directe. M&me si les signes des charges de surface de la bulle et de la particule sont identiques, la particule adhere B la surface de la bulle lorsque la force de surface nette, a savoir la somrne de la force Clectrostatique et la force de van der Waals, est attractive. L'efficacitt de capture des particules, q5, par bulle, a CtC estimCe par l'analyse de la trajectoire et I'efticacite de la tlottaison, v T , a CtC calculee.Les valeurs de q r , calculee par I'analyse de la trajectoire des particules, concordent raisonnablement avec celles obtenues expkrimentalement. La dipendance du diametre de particule sur q a Cgalement Ctt examinCe par l'analyse de la trajectoire des particules.

Bythe use of the experimental data of manyprevious studies, a newcorrelation for the pressure drop of a packed column was obtained in this work. The total pressure drop is expressed as the sum of the dry pressure drop and the wet pressure drop. The dry pressure drop originates mainly from the friction of gas rising through the void of the packed bed, and is expressed by the Fanning equation. The wet pressure drop originates from the increase in net gas velocity because of the smaller void of the packed bed owing to the liquid holdup, and therefore it is expressed as a function of liquid holdup, gas velocity, etc. The liquid holdup consists of static and dynamic holdups, and is correlated separately. Intr o du cti onIn previous studies, the method of dimensional analysis has been frequently used to correlate experimental values of the pressure drop of a packed column.Moreover, correlations of the pressure drop for dry packing (dry pressure drop) and for irrigated packing (total pressure drop) have been carried out separately, and no report expressing the total pressure drop consisting of the drop for dry packing and the residuals has apparently been published to date.Because of the smaller void of the packed bed in an operation with irrigation, the net gas velocity through the void becomes larger than that for dry packing. It is inferred that the difference between the total and dry pressure drops (wet pressure drop) is influenced strongly by the liquid holdup in the packed bed, because of the increase in the net gas velocity.However, there is a lack of studies referring to the relation of wet pressure drop and liquid holdup. In this paper, the experimental values of the many previous studies of the total pressure drop of a packed columnare correlated as the sumof the dry pressure drop and the wet pressure drop which is a function of liquid holdup, etc.