Mujeeb Smith | University College London (original) (raw)
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Papers by Mujeeb Smith
Chemical Engineering Science, 2007
The characteristics of waves at the interface of oil-water stratified flow and at the onset of en... more The characteristics of waves at the interface of oil-water stratified flow and at the onset of entrainment, where drops of one phase appear into the other, were studied. Theoretically a model was developed based on Kelvin-Helmholtz instability to predict the critical wave amplitude at which the waves become unstable for a specific wavelength. According to the model, waves become unstable in stratified flow when at a particular wavelength they exceed a critical amplitude, which decreases with increasing wavelength until it acquires an almost constant value. The model predictions showed that for low-viscosity oils the maximum critical amplitude appears at slip velocity close to zero, while for high-viscosity oils, the maximum amplitude appears for water velocity higher than that of the oil. Also the required entrainment wavelength over the pipe diameter, calculated using literature experimental onset conditions, was found to decrease as the viscosity of the oil increased. Experimentally, wave characteristics before and at the onset of entrainment were investigated by measuring the instantaneous fluctuations of the interface between oil (5.5 mPa s, 828 kg/m 3 ) and water in a 0.038 m ID stainless steel horizontal pipe using a conductivity probe. The formation of drops and the onset of entrainment were identified using a high-speed video camera. At the onset of entrainment, wave characteristics were above the stability lines predicted by the model. Using a semi-empirical characteristic amplitude and wavelength in the model, it was possible to predict the onset of entrainment and transition from stratified to other mixed flow patterns reported in a number of studies. ᭧
Journal of Petroleum Science and Engineering, 2007
The effect of a drag-reducing polymer (DRP) in the water phase during horizontal oil-water flow w... more The effect of a drag-reducing polymer (DRP) in the water phase during horizontal oil-water flow was investigated in a 14 mm ID acrylic pipe. Oil (5.5 mPa s, 828 kg/m 3 ) and a co-polymer (Magnafloc 1011) of polyacrylamide and sodium acrylate were used. Two polymer concentrations were tested, 20 ppm and 50 ppm, made from a 1000 ppm master solution. The results showed a strong effect of DRP on flow patterns. The presence of DRP extended the region of stratified flow and delayed transition to slug flow. The addition of the polymer clearly damped interfacial waves. Annular flow changed in all cases investigated to stratified or dual continuous flow, while slug flow changed in most cases to stratified flow. In the cases where the slug and bubble flow patterns still appeared after the addition of the polymer, the oil slugs and bubbles were seen to flow closer together than in the flow without the polymer. The DRP caused a decrease in pressure gradient and a maximum drag reduction of about 50% was found when the polymer was introduced into annular flow. The height of the interface and the water hold up increased with DRP. There were no large differences on pressure gradient and hold up between the two DRP concentrations. Using a two-fluid model it was found that the addition of the polymer results in a decrease in both the interfacial and the water wall shear stresses.
Chemical Engineering Science, 2007
The characteristics of waves at the interface of oil-water stratified flow and at the onset of en... more The characteristics of waves at the interface of oil-water stratified flow and at the onset of entrainment, where drops of one phase appear into the other, were studied. Theoretically a model was developed based on Kelvin-Helmholtz instability to predict the critical wave amplitude at which the waves become unstable for a specific wavelength. According to the model, waves become unstable in stratified flow when at a particular wavelength they exceed a critical amplitude, which decreases with increasing wavelength until it acquires an almost constant value. The model predictions showed that for low-viscosity oils the maximum critical amplitude appears at slip velocity close to zero, while for high-viscosity oils, the maximum amplitude appears for water velocity higher than that of the oil. Also the required entrainment wavelength over the pipe diameter, calculated using literature experimental onset conditions, was found to decrease as the viscosity of the oil increased. Experimentally, wave characteristics before and at the onset of entrainment were investigated by measuring the instantaneous fluctuations of the interface between oil (5.5 mPa s, 828 kg/m 3 ) and water in a 0.038 m ID stainless steel horizontal pipe using a conductivity probe. The formation of drops and the onset of entrainment were identified using a high-speed video camera. At the onset of entrainment, wave characteristics were above the stability lines predicted by the model. Using a semi-empirical characteristic amplitude and wavelength in the model, it was possible to predict the onset of entrainment and transition from stratified to other mixed flow patterns reported in a number of studies. ᭧
Journal of Petroleum Science and Engineering, 2007
The effect of a drag-reducing polymer (DRP) in the water phase during horizontal oil-water flow w... more The effect of a drag-reducing polymer (DRP) in the water phase during horizontal oil-water flow was investigated in a 14 mm ID acrylic pipe. Oil (5.5 mPa s, 828 kg/m 3 ) and a co-polymer (Magnafloc 1011) of polyacrylamide and sodium acrylate were used. Two polymer concentrations were tested, 20 ppm and 50 ppm, made from a 1000 ppm master solution. The results showed a strong effect of DRP on flow patterns. The presence of DRP extended the region of stratified flow and delayed transition to slug flow. The addition of the polymer clearly damped interfacial waves. Annular flow changed in all cases investigated to stratified or dual continuous flow, while slug flow changed in most cases to stratified flow. In the cases where the slug and bubble flow patterns still appeared after the addition of the polymer, the oil slugs and bubbles were seen to flow closer together than in the flow without the polymer. The DRP caused a decrease in pressure gradient and a maximum drag reduction of about 50% was found when the polymer was introduced into annular flow. The height of the interface and the water hold up increased with DRP. There were no large differences on pressure gradient and hold up between the two DRP concentrations. Using a two-fluid model it was found that the addition of the polymer results in a decrease in both the interfacial and the water wall shear stresses.