Mixing of newtonian and non-newtonian liquids: Screw agitator and draft coil system

Mixing efficiency and power consumption have been investigated for several Newtonian and non-Newtonian liquids in a novel system consisting of a screw agitator rotating in a draft coil. For Reynolds numbers larger than 50, the inertial forces increase the pumping capacity of the screw impeller and hence its mixing efficiency. Shear-thinning effects can be accounted for by taking the effective rate of deformation to be proportional to the impeller rotational speed. Elasticity effects could be satisfactorily correlated with the Weissenberg number. The ratio of the mixing time to the average circulation time is constant. The power number could not be correlated with the Reynolds number; however, the ratio of the power number to the circulation number is inversely proportional to the Reynolds number for Newtonian as well as for shear-thinning inelastic fluids. The power consumption for elastic fluids is much larger.     

Heat transfer to newtonian and non-newtonian liquids in a screw agitator and draft coil system

Heat transfer has been investigated for several Newtonian and non-Newtonian liquids mixed in a flat bottomed vessel equipped with a screw agitator and a coil acting simultaneously as draft tube and heat exchanger. Heat transfer rates from coil to liquid were determined for different coil designs, rheological properties and operating conditions in the heating and cooling modes. A circulation Reynolds number is defined, the characteristic length being the effective height of the heat exchanger (the coil) and the characteristic velocity being the circulation velocity of the fluid which was determined experimentally. Using this Reynolds number, it was possible to establish a single correlation for the Nusselt number as a function of Reynolds and Prandtl numbers. Geometric ratios do not appear in this correlation which could adequately represent more than 200 experimental data. A similar single correlation could not be obtained when using the conventional mixing Reynolds number. This novel system is shown to be very efficient for handling rheologically complex fluids.     

Electrostatic Drop Formation in Liquid/Liquid Systems

Electrostatic drop formation in liquid/liquid systems was studied, using high frequency AC fields (45 kHz). The dispersion of nonconductive into conductive fluids was investigated under various conditions, as are the effect of aqueous phase conductivity, capillary geometry and organic phase viscosity on the resulting drop size. The experimentally determined drop sizes and literature data, were correlated with a model equation, which was derived from a simple force balance, with an empirical term for the electric force. The model parameters were obtained in a toluene/water system and the model allows the prediction of the drop sizes of other organic solvents, if the capillary geometry is kept constant.     

Drop Detachment from a Micro‐Engineered Membrane Surface in a Dynamic Membrane Emulsification Process

Drop size distribution is an important characteristic of emulsions, probably the most crucial one for their use in various applications. Here, a pilot‐scale apparatus with a cone‐shaped flow geometry is introduced. The plate contains a micro‐engineered membrane manufactured from silicon allowing for the production of emulsions with narrow drop size distributions. The process is characterized by producing model emulsions of the oil‐in‐water type under laminar rheometric flow conditions and by accessing the regime of drop detachment as a function of the wall shear stress applied, by means of high‐speed imaging in a separate flow cell. Furthermore, clear evidence is given of the crucial influence of the membrane wetting properties on the emulsification results, by comparing the performance of micro‐engineered membranes composed either of silicon, silicon nitride, or nickel, for pore diameters from 1 to 12 μm, in the flow cell.     

Bubble formation in quiescent liquids under constant flow conditions

In this investigation, a simple equation has been theoretically developed to predict the bubble detachment diameter in quiescent liquids under constant volumetric gas flow conditions. The equation is valid in the bubbling regime up to transition to the jetting regime and for liquids with very low up to very high viscosities. Known experimental measurements were used to examine the validity of the developed equation. The present measurements cover gas Weber numbers from about 0 up to 4, liquid dynamic viscosities from 10⁻³ up to 1 Pa s, and nozzle diameters from 0.2 up to 6 mm. The comparison between the theoretical predictions and the experimental measurements is satisfactory; the deviations lie in most cases within ± 10%.     

Bubble formation in viscous liquids under constant flow conditions

Bubble formation from single nozzles has been studied in liquids of different viscosities. The viscosity is varied in the range 50 to 500 c.p., whereas flow rates up to 100 cm³/second have been investigated. A model based on a two step (viz. expansion and detachment) mechanism has been proposed for bubble formation. The model explains the results of the present investigation as well as those reported in the literature for similar systems. As an extreme case, the model is tested on liquids of very low viscosity after dropping the viscosity terms from the equations and is found to explain even these data quite well.     

Bubble drag in contaminated non-newtonian solutions

The motion of a bubble in an infinite fluid is examined in the case where the surrounding fluid is non-Newtonian and contains impurities. An expression is developed for the drag force as a function of the shear-thinning character as well as of the concentration of surfactant of the fluid. The obtained expression for the drag force correlates quite nicely with experimental data for small bubbles.     

Drag on non-spherical particles in non-newtonian fluids

Extensive experimental results on the free fall of a range of non-spherical particles such as square bars, cylinders, spheres and crushed rock chips in Newtonian, inelastic, viscoelastic and Boger fluids are presented. It is demonstrated that the use of a volume equivalent sphere diameter in addition to a shape factor provides an adequate approximation for the non-sphericity of particles used in this study. The applicability of two rheological models, namely, the power-law and the Carreau viscosity model has been examined in representing the drag coefficient results. Appropriate predictive expressions of the drag coefficient as a function of the particle Reynolds number and the Deborah number, encompassing wide ranges of rheological and kinematic conditions, are presented.     

Calcium carbonate deposit formation under isothermal conditions

Scale formation of calcium carbonate on tube walls is studied in a once-through flow system under isothermal conditions. The effects of supersaturation ratio, flow velocity and liquid temperature on the deposition rates are investigated. For relatively small supersaturation ratios (in the range 3.5 to 8) the deposition rate tends to increase with increasing supersaturation. For higher fluid supersaturations with respect to calcium carbonate, the deposition rates remain roughly constant but they are influenced strongly by the fluid velocity. This dependence of the deposition rate on fluid flow suggests a mass transfer-controlled process.     

Drop mixing in suspension polymerisation

In suspension polymerisation, monomer is suspended as liquid droplets in a continuous water phase by means of strong agitation and the presence of a suspending agent. As the suspension polymerisation proceeds, the viscosity of a monomer-polymer droplet increases with conversion. Hence, the physical behaviour of the droplet changes during the process. When new dispersible material is added to the existing suspension drops, the new material and existing drops can remain segregated for significant amounts of time. The aim of this project was to study the behaviour of drop mixing when new material is added to the existing suspension polymerisation. This study concentrated on the effect of the dispersed phase viscosity on drop mixing. The results show that viscosity affects drop size and that may then affect the rate of coalescence between drops. A critical drop size exists which determines the coalescence efficiency effect. Above the critical drop size, mixing rate increases as the drop viscosity decreases. While below the critical drop size, drop size of the dispersion determines the coalescence rate; as the drop size increases, coalescence rate also increases. The investigation of the effect of suspending agent shows that Tween 20 is more efficient in stabilising and protecting the drops, based on a weight basis, than PVA as the coalescence rate is lower with Tween 20.     

Drop size distribution and mean drop size in a pulsed packed extraction column

Drop size distribution and mean drop size are used for calculation of interfacial area available for mass transfer. In this study, the drop size distribution and Sauter mean drop diameter (d₃₂) have been investigated using three different liquid systems in the absence of mass transfer in a pilot plant pulsed packed column. The drop size was measured at four different points along the active column height. Three operating variables have been studied including the pulse intensity (af) and flow rates of both liquid phases. The effect of liquid properties and height of the active column were also investigated. A combination of the pulse intensity and interfacial tension had the largest effect on the drop size distribution while none of the flow rates were of significance. The height of the column played an important role at the bottom of the active column, but the associated effect was reduced with increase of the height. Finally, a normal probability function of number density was proposed for prediction of the drop size distribution with an Average Absolute Relative Error (AARE) of 8.8% for their optimized constant. Furthermore, two correlations were presented involving height or flow rates of the two phases along with operating variables and physical properties of the liquids. These correlations had AARE values of about 8.5 and 7.8%, respectively.     

Drainage in thin planar non-newtonian fluid films

Equations for the radial and linear drainage of non-Newtonian fluids in horizontal and inclined films are presented. For a power law fluid with index m, the variation in dimensionless film thickness Δ with dimensionless time T is given by: where Δ and T are appropriately defined for drainage in radial horizontal and linear inclined films. The corresponding approximate expression for a Bingham plastic fluid is: in which A is the minimum film thickness defined appropriately at the asymptotic limits when Δ » A and Δ ? A.     

Drop formation in a co-flowing ambient fluid

Drop formation at a capillary tip in laminar flow is investigated experimentally. The disperse phase is injected via a needle into another co-flowing immiscible fluid. Two different drop formation mechanisms are distinguished: Either the drops are formed close to the capillary tip—dripping—or they break up from an extended liquid jet—jetting. The effect of the process and material parameters on the drop formation depends on the breakup mechanism and has to be investigated for each flow domain separately. In this study, we focus on dripping. The drop breakup is affected by the flow dynamics of both the disperse and the continuous phase. Consequently, we investigate the effect of flow rates, fluid viscosities and interfacial tension on the droplet size and observe the dynamics of satellite drop generation. Whereas the fundamentals of disperse fluid injection via a capillary into an ambient fluid have been investigated extensively, the focus of this article is on providing a comprehensive experimental data set for proving the applicability of this technique as a dispersing tool. It is shown that drop formation at a capillary tip into a co-flowing ambient liquid represents a promising technique for the production of monodisperse droplets where the droplet size is controlled externally by the flow strength of the continuous phase. The breakup dynamics changes significantly at the transition point from dripping to jetting. Consequently, the transition point between the flow domains represents an important operating point. In this article, dripping is demarcated from jetting by studying the influence of the various material and process parameters on the transition point.     

Hot Spot Formation in Mock Materials in Impact Sensitivity Testing by Drop Hammer

Powder and granulated sugars were exposed to the drop hammer impact test configured with 120‐ and 180‐grit Si/C sandpapers. The sugars were selected as mock materials for HMX (Octahydro‐1,3,5,7‐tetranitro‐1,3,5,7‐tetrazocine). The drop heights ranged from 24.2 to 40.7 cm. Samples were examined by visible microscopy before and after testing and the appearance of yellow and brown discolorations in the spent samples were assigned as hot spots. These discolorations were divided into two types; those collocated with grit particles and those that were not. Hot spots are found in the spent samples in almost every test condition. Powder sugar appears to be more active in producing hot spots than the granulated sugar based on comparisons at identical conditions. Drop height, within this specific range, has little effect on the formation of hot spots, except for 40.7 cm high‐end limit, which causes a dramatic increase in spot formation. The predominant hot spot type formed is collocated with grit particles, suggesting association of hot spot formation due to grit, something that has been discussed in previous treaties. Foreign objects were also observed, some imbedded and some not imbedded. Discoloration was not observed around these sites, suggesting these types of foreign materials are not responsible for hot spot formation, at least under these conditions. Grit associated with a visible tail was observed in some instances, suggesting that grit can be quite mobile through the sample when the pressure is applied by the drop weight (through the striker).     

天然气水合物生成条件的测定和计算

利用全透明蓝宝石水合物静力学实验装置,测定了4种塔里木油田天然气在纯水中的水合物生成条件.将Chen-Guo 水合物模型应用于天然气水合物生成条件的计算,实验测定的4种天然气水合物生成条件的计算结果和实验结果符合得很好.     

Hindered settling in non-newtonian power law liquids

New experimental results on the hindered settling of model glass bead suspensions in non-Newtonian suspending media are reported. The data presented encompass the following ranges of variables: 7.38 × 10^?4 ≤ Re_1∞ ≤ 2; 0.0083 ≤ d/D ≤ 0.0703; 0.13 ≤ C ≤ 0.43 and 1 ≥ n ≥ 0.8. In these ranges of conditions, the dependence of the hindered settling velocity on concentration is adequately represented by the corresponding Newtonian expressions available in the literature. The influence of the power law flow behaviour index is completely embodied in the modified definition of the Reynolds number used for power law liquids.     

Experimental study on drop formation in liquid-liquid fluidized bed

Drop formation in liquid-liquid fluidized bed was investigated experimentally. The normal water was injected via a fine-capillary spray nozzle into the co-flowing No. 25 transformer oil with jet directed upwards in a vertical fluidized bed. Experiments under a wide variety of conditions were conducted to investigate the instability dynamics of the jet, the size and size distribution of the drops. Details of drop formation, drop flow patterns and jet evolution were monitored in real-time by an ultra-high-speed digital CCD (charge couple device) camera. The Rosin-Rammler model was applied to characterize experimental drop size distributions. Final results demonstrate that drop formation in liquid-liquid system takes place on three absolutely different developing regimes: bubbling, laminar jetting and turbulent jetting, depending on the relative Reynolds number between the two phases. For different flow domains, dynamics of drop formation change significantly, involving mechanism of jet breakup, jet length pulsation, mean size and uniformity of the drops. The jet length fluctuates with time in variable and random amplitudes for a specified set of operated parameters. Good agreement is shown between the drop size and the Rosin-Rammler distribution function with the minimum correlation coefficient 0.9199. The mean drop diameter decreases all along with increasing jet flow rate. Especially after the relative Reynolds number exceeds a certain value about 3.5×10⁴, the jet disrupts intensely into multiple small drops with a diameter mainly ranging from 1.0 to and a more and more uniform size distribution. The turbulent jetting regime of drop formation is the most preferable to the dynamic ice slurry making system.     

Liquid circulation time in concentric-tube airlift columns with non-newtonian fermentation broths

Liquid circulation times were measured in a 40-dm³ concentric-tube airlift fermenter with simulated media over a wide range of rheological properties. Circulation times decreased with increasing shear-thinning, and the influence of draft-tube geometry on circulation time was found to depend on the shear-thinning of the media. A semi-theoretical correlation for both Newtonian and non-Newtonian fermentation media was developed.     

Size Distribution of Drops Formed from Nozzles in Air at Velocities below Jetting

The drop size distribution of drops formed from four nozzles (d = 0.5, 1.8, 2.7 and 3.6 mm) were measured for the flow rate range Q = 0.1–1.17 cm³/s and Reynolds number 56–448. Distilled water was used as the dispersed phase and air as the continuous one. The experimental drop size distributions were described satisfactorily by the theoretical upper limit number and volume distributions. The experimental data of minimum and maximum diameters versus the respective Sauter mean diameters gave straight lines with slopes of 0.81 and 1.18, respectively.     

Pressure losses in orifices for the flow of gas-non-newtonian liquids

An investigation has been carried out to evaluate the two-phase pressure drop for gas-non-Newtonian liquid flow across orifices. The method of dimensional analysis was used to correlate the experimental data. The correlation developed predicts the two-phase frictional pressure drop across the orifices with acceptable statistical accuracy.