الفهرس Only 14 pages are availabe for public view
 |  | from | 137 |  |  |
| | | from | 137 | | |
Abstract
The effects of various parameters on the characteristics of stable and unstable oil¬in-water (o/w) emulsions are considered in the present study. The viscosity of the emulsions is measured at different holdup, temperature, and shear rate values. Medicinal white oil (Bayol-35) and tap water are mixed and stabilized using two different kinds of surfactant (emulsifier). These are Sodium Dodecyl Sulfate (SDS), and Fatty Acid ~nd Amine (FAA). The Laser Particle Size Analyzer (LPSA) is used to measure the drop size distribution for stable and unstable o/w emulsions. The effect of emulsion age on the viscosity is investigated. Empirical relations are deducted to describe o/w viscosity as function in holdup, shear rate, mean drop diameter, and temperature.
In addition, the present investigation is dealing with the overall as well as detailed experimental study of energy loss due to friction of oil-in-water emulsions flow through pipes. The friction factor of stable and unstable o/w emulsions were established for Poly Vinyl Chloride (PVe) and Galvanized Iron (G.I.) pipes of different diameters. The results are compared with Poiseuille’s relation in laminar region, and Blasius relation in turbulent region.
Further, the present study also includes an experimental investigation of the behavior of the flow of oil-in-water (o/w) emulsions through pipe fittings. The energy losses for the flow of stable and unstable oil-in-water (o/w) emulsions through 90° short elbow, sudden enlargement, sudden contraction, and gate valve, were determined. Correlations for resistance coefficients ,K, were established for all these elements.
Moreover, orifice coefficient of discharge was calculated from the measurements of orifice head difference and flow rate at different values of holdup for stable and unstable oil-in-water emulsion flow. Empirical relations are derived to describe the orifice coefficient of discharge.
Furthermore, the performance of a centrifugal pump pumping water as well as stable and unstable oil-in-water emulsions is determined experimentally. The head-flow rate is measured at different temperature and holdup values and represented by empirical relations. A comparison between head-flow curves for centrifugal pumps pumping water and emulsions flow results in coefficients relating the flow rate and head for water and emulsions. The hydraulic efficiency is calculated for stable and unstable emulsions and compared with water flow.
For in-depth study as well as to shed some lights on the internal behavior of the oil-in-water emulsions flow, the preceding study accompanied with a photographic and subsequent image analysis technique to determine upstream and downstream droplet size distribution in unstable oil-in-water emulsion flowing through 25 mm diameter and 3 m length PVC pipe, 90° short elbow, fully opened gate valve, and orifice flow meter at different holdup and velocities. The images were automatically treated, analyzed and several object descriptors obtained for each droplet using a Matlab program. The upstream and downstream mean droplet diameter, calculated from the droplet size distribution resulting from image analysis, at different velocities is presented.
The experimental results show increase in stable and unstable emulsions viscosity with the increase in holdup, and the decrease in temperature. The shear stress-shear rate results show that for holdup less than or equal 0.5 the oIw mixture is Newtonian. But, for holdup greater than 0.5, the o/w mixture is non-Newtonian of type Psuedoplastic (shear¬thinning). The viscosity of unstable o/w emulsions has nearly the same viscosity of the stable o/w up to holdup == 0.55, but at higher holdup the viscosity of the two systems differs significantly. However, the viscosity of the unstable o/w is lower than that of the stable o/w even at low holdup. For unstable o/w mixture, the mean drop diameter and
viscosity suddenly increase at holdup 0.55, due to o/w inversion. The surfactant type (FAA or SDS) has no pronounced effect on the results for fresh o/w mixture, and as emulsion age increase the surfactant type affects the results. However, the viscosity of stabilized o/w emulsion with SDS emulsifier is lower than stable o/w emulsion with FAA emulsifier. The mean drop diameter of stable o/w emulsion increases as holdup and age of emulsion increase. The viscosity of stable o/w decreases as emulsion age increase.
The obtained results for the friction factor follow Poiseuille’s relation in laminar regime, while in turbulent regime a disparity between Blasius relation and the results is revealed due to drag reduction. However, some drag reduction activity is noticed for unstable o/w emulsions in laminar regime as the temperature, pipe diameter, and holdup increased. The comparisons show that unstable o/w emulsions exhibit more drag reduction activity than stable o/w emulsions. The drag reduction activity increases as holdup increase, and pipe diameters decrease. The friction factor ofPVC pipes is lower than G.I. pipes. As the holdup increases, the friction factor increase and the rate of rise decreases as temperature increase. The surfactant type (FAA or SDS) has no pronounced effect on the results for fresh o/w mixture. However, the friction factor of stabilized o/w emulsion with SDS emulsifier is slightly lower than stable o/w emulsion with FAA emulsifier. For unstable o/w emulsion, the effect of pipe material on friction factor is more significant than in stable o/w emulsion.
For the emulsion flow through pipe fittings, the present study shows that, for sudden contraction, as the area ratio, AJ Au, increases the energy loss coefficient decreases. For sudden enlargement, as the area ratio, AulA.J, increases the energy loss coefficient decreases. The flow in 90° short elbow exhibit the higher values in energy loss coefficient, then the fully open gate valve comes in the second stage, and the energy loss coefficient in sudden enlargement comes in the third stage. The sudden contraction exhibits the lower values for energy loss coefficient. The resistance coefficients for stable and unstable o/w emulsions were lower than that for water. The unstable O/W exhibits lower values in loss coefficient compared with that for stable o/w. The stable o/w emulsion with SDS emulsifier shows lower values for loss coefficient than that for stable o/w emulsion with FAA emulsifier. The energy loss coefficient is found to be inversely proportional to the generalized Reynolds number for laminar flow, and to approach constant aSYmptotic values for turbulent flow, which is in agreement with literature. The energy loss coefficient increases as the holdup increases and the flow rate decreases.
For the emulsion flow through orifice flow meter, the present study reveals that the coefficient of discharge decreases and orifice head difference increases as the holdup increase. For stable o/w emulsion, the type of emulsifier has pronounced effect on coefficient of discharge and orifice head difference. The unstable o/w emulsion has greater value of coefficient of discharge and smaller orifice head difference compared with stable emulsion.
For the flow of emulsion through centrifugal pump the present results show that the oil-in-water emulsion flow reduces the head and flow rate of the centrifugal pumps. As the holdup increases and temperature decreases, the reduction in head and flow rate increase. The unstable oil-in-water emulsions show less decrease in head-flow rate, while stable emulsions show higher decrease in head-flow rate compared with water. The surfactant type affects the head-flow rate, where the stable emulsions with Sodium Dodecyl Sulfate (SDS) show less reduction in head-flow rate than stable emulsions with Fatty Acid and Amine (FAA). The pump hydraulic efficiency decreases as the holdup increases and temperature decreases.