Rate of Bitumen Film Transfer from a Quartz Surface to an Air Bubble as Observed by Optical Microscopy
The rate of bitumen transfer from a bitumen-coated quartz plate to a gas bubble surface in aqueous alkaline solutions was recorded photographically. During bitumen spreading, a bulk layer followed the formation of thin bitumen films (precursor films). The bulk layer spread at the bubble surface with a velocity of about one order of magnitude less than the velocity of the precursor film. The energy of activation for spreading of the bulk layer varied from about 66 to 123 kJ/mol depending on the stage of bitumen spreading but remained constant at about 105 kJ/mol for the precursor film. Results are discussed with respect to fundamental issues associated with flo t a t i o n r e c o v e ry of heavy oils.
Oil recovery from oil in water emulsions using a flotation column
A flotation column was used to recover oil from oil in water emulsions. The feed oil concentrations investigated were relatively high, in the range of 0.25 to 8 percent by volume. Previous studies using conventional flotation cells dealt with very dilute systems where the oil concentration was less than 0.1 percent by volume. 
 
 
 
The oil recovery was found to decrease with an increase in the feed oil concentration. The addition of wash water to the froth zone of the column had little effect on the oil recovery. The oil recovery decreased with increasing feed flow rate and surfactant concentration. The effect of increasing the gas flow rate was to initially increase the oil recovery. The oil recovery data were analyzed using a kinetic model. The order of the flotation kinetics was found to be 0.6. 
 
 
 
The gas hold-up behaviour of the recovery and the froth zones of the flotation column is found to correlate well with the drift-flux model. 
 
 
 
On a utilise une colonne de flottation pour la recuperation d'huile a partir d'emulsions d'huile dans I'eau. Les concentrations d'huile d'alimentation etudiees etaient relativement elevees, dans la gamme de 0,25 a 8 pour cent par volume. Les etudes anterieures utilisant des cellules de flottation classiques utilisaient des systemes tres dilues avec une concentration d'huile inferieure a 0, l pour cent par volume. 
 
 
 
On a trouve que la recuperation d'huile diminuait avec I'augmentation de la concentration d'huile d'alimentation. L'ajout d'eau de lavage dans la zone de moussage de la colonne a peu d'effet sur la recuperation d'huile. La recuperation d'huile diminue avec l'augmentation du debit d'alimentation et la concentration de surfactant. L'effet de I'augmentation du debit du gaz est d'augmenter au depart la recuperation d'huile. Les donnees de rCcuperation d'huile ont ete analysees avec un modele cinetique. On a trouve que I'ordre de la cinttique etait de 0,6. 
 
 
 
On a trouve que le comportement de retention du gaz de la recuperation et les zones de rnoussage de la colonne de tlottation se correler de facon satisfaisante au modele de flux-derive.
Carrier dynamical issues for extending the operating wavelength of quantum cascade lasers
Electron-longitudinal optic phonon and electron-electron intersubband scattering rates are calculated for a variety of quantum well systems. It is demonstrated that the internal quantum efficiency of a Terahertz radiative intersubband transition can be greater than in the mid-IR at 4K, however by room temperature has fallen to around 20 percent. A study of the internal quantum efficiency of a Terahertz energy intersubband transition in double and single quantum wells, has shown that the vertical intrawell transition is more efficient than the diagonal interwell transition.