Drying of foam under microgravity conditions

Foams have recently been characterised as ideal products for pharmaceutical and topical use applications for the delivery of topical active agents. Foams are usually produced in a wet form but in a number of applications moderately dry foams are required. Drying of foam under terrestrial conditions proceeds under the action of gravity, which is impossible under microgravity condition. Below a new method of drying foams under microgravity condition is suggested. According to this method foam should be placed on a porous support, which will absorb the liquid from foam based on capillary forces only. The final liquid content inside the foam can be achieved by a proper selection of the porous support. The suggested method allows drying foams under microgravity conditions. Interaction of foams with porous support under terrestrial conditions was developed only recently and theoretically investigated (Arjmandi-Tash, O.; Kovalchuk, N.; Trybala, A.; Starov, V. Foam Drainage Placed on a Porous Substrate. Soft Matter2015, 11 (18), 3643–3652) followed by a theory of foam drainage on thin porous substrates (Koursari, N.; Arjmandi-Tash, O.; Johnson, P.; Trybala, A.; Starov, M. V. Foam Drainage Placed on Thin Porous Substrate. Soft Matter, 2019, (submitted)), where rate of drainage, radius of the wetted area inside the porous layer and other characteristics of the process were predicted. The latter model is modified below to investigate foam drying under microgravity conditions. Model predictions are compared with experimental observations for foam created using Triton X-100 at concentrations above CMC. Wetted radius inside the porous substrate was measured and results were compered to model predictions. Experimental observations for spreading area versus time show reasonable agreement with theoretical predictions for all investigated systems

Removal of micrometer size particles from surfaces using laser-induced thermocapillary flow: Experimental results

© 2016 Published by Elsevier Inc.Hypothesis: Reducing particle contaminations on solid and delicate surfaces is of great importance in a number of industries. A new non-destructive method is proposed, which is based on the laser-induced thermocapillary effect for the removal of micron size particles from surfaces. The cleaning mechanism is related to the surface-tension-driven flows produced by the laser heating of thin layer of a cleaning liquid deposited onto a surface contaminated with particles. Experiments: Focusing the laser irradiation into the line laser beam allowed using this method for a large-scale cleaning of surfaces. Hexadecane was used as a cleaning liquid to remove micron-sized polyethylene, Teflon, talc and Al2O3 particles from surfaces of welding glass, carbolite and soft magnetic disc using the line beam of the IR laser. Findings: A good cleaning efficiency was achieved for cases of polyethylene and Teflon particles on both the complete wettable welding glass and the low-wettable soft magnetic disc, while in case of oleophilic talc and Al2O3 particles the effectiveness of the cleaning method was lower on all three substrates investigated. The thermal influence of the laser irradiation on substrates used was measured with infrared camera. It was shown that temperature in the irradiated area during the long-time heating increases insignificantly and cannot cause any damage of the substrate

Stability and deformation of oil droplets during microfiltration on a slotted pore membrane

This article was published in the Journal of Membrane Science [© Elsevier] and the definitive version is available at: http://dx.doi.org/10.1016/j.memsci.2012.01.034The effect of interfacial tension between two fluids, on the passage and rejection of oil droplets through slotted pore membranes is reported. A mathematical model was developed in order to predict conditions for 100% cut-off of oil droplets through the membrane as a function of permeate flux rate. Good agreement of theoretical predictions with experimental data shows that the model can be applied to the filtration of deformable droplets through slotted pore membranes. At high interfacial tension (40 mN/m) with lower flux (200 l m−2 hr−1)droplets of crude oil (27 API) were 100% rejected at droplet diameter 4.3 μm using a 4 μm slotted pore membrane. At lower interfacial tension (5 mN/m), with the same flux rate, 100% rejection occurred at 10 μm droplet diameter using the same membrane. It was also found that the droplet rejection efficiency below the 100% cut-off was roughly linear with drop size, down to zero rejection at zero drop diameter. Hence, the model, coupled with this approximate correlation, can be used to predict dispersed oil drop concentration from a known feed drop size distribution

Prediction of size distribution of crude oil drops in the permeate using a slotted pore membrane

This paper was accepted for publication in the journal Chemical Engineering Research and Design and the definitive published version is available at http://dx.doi.org/10.1016/j.cherd.2014.02.017Permeate size distribution of various crude oil drops with, and without, oscillating the membrane has been predicted using the 'Linear Fit' approach. Drops pass through the membrane due to drag force created by the flow of fluid around the drops. Static force is the force responsible for the rejection of drops through the membrane and is directly proportional to the interfacial tension between dispersed and continuous phases. Without applied shear, 100% cut-off of drops though the membrane is assumed when the drag force and the static force balances each other. With the applied shear, 100% cut-off of drops through the membrane is when drops moves away from the membrane surface due to migration velocities and do not pass the membrane into the permeate. Extrapolating 100% cut-off to the origin of the rejection graphs gives a straight line that is referred as 'Linear Fit' and can be used for predicting rejection below 100% cut-off. Linear fit can be used for predicting drop rejection below 100% cut-off. The portion of oil that would not be rejected by the membrane and would pass through the membrane into the permeate can be calculated using this approach. For a given size of drops in a feed suspension, permeate size distribution can be predicted by multiplying the fraction of oil passing through the membrane and the feed size distribution data. Overall concentration of oil in the permeate can be calculated by knowing size distribution of drops in the permeate, and that provides an idea whether the concentration of oil in the permeate is below the standard set by international regulatory authorities

Shear enhanced microfiltration and rejection of crude oil drops through a slotted pore membrane including migration velocities

This article was published in the Journal of Membrane Science [© Elsevier] and the definitive version is available at: http://www.sciencedirect.com/science/article/pii/S0376738812004991Shear enhanced microfiltration of crude oil/water emulsion is investigated and the effect of an applied shear rate on the rejection of droplets by the membrane is reported. Applying vibration provides shear rate at the membrane surface leading to shear-induced migration and an inertial lift of drops/particles. Both phenomena tend to move the droplets away from the membrane surface. The shear-induced migration and inertial lift increase with increasing of the shear rate. A mathematical model is presented to account for the presence of both phenomena. The developed model is used for theoretical prediction of 100% cut-off of crude oil droplets by the membrane with, and with-out, vibration applied. A satisfactory agreement of the model predictions with experimental data shows that the model can be successfully used for a theoretical prediction of 100% cut-off of droplets by slotted pore membranes. Rejection of droplets increased with applying shear rate: at 8000 s-1 shear rate and 200 l m-2 hr-1 flux rate 3 to 4 μm radius droplets were almost completely rejected reducing 400 ppm of crude in the feed to 7 ppm in the permeate

Droplet Actuation by Electrowetting-on-Dielectric (EWOD): A Review

This paper reviews publications that have fortified our understanding of the electrowetting-on-dielectric (EWOD) actuation mechanism. Over the last decade, growing interest in EWOD has led to a wide range of scientific and technological investigations motivated by its applicability in microfluidics, especially for droplet-based optical and lab-on-a-chip systems. At this point in time, we believe that it is helpful to summarize the observations, insights, and modeling techniques that have led to the current picture showing how forces act on liquid droplets and how droplets respond in EWOD microfluidic devices. We discuss the basic physics of EWOD and explain the mechanical response of a droplet using free-body diagrams. It is our hope that this review will inspire new research approaches and help design useful devices. © 2012 Copyright Taylor and Francis Group, LLC

Droplets evaporation: Problems and solutions

The evaporation of single droplets and sprays into gaseous atmosphere and the evaporation of sessile liquid droplets on solid substrates are here considered. We argue that if thermodynamics is augmented with Derjaguin’s (disjoining/conjoining) pressure to handle phenomena in a vicinity of the three-phase contact line, problems like the singularity of the evaporation flux and of the viscous stress at the three-phase contact line of a sessile droplet are ruled out

Evaporation of Sessile Water Droplets in Presence of Contact Angle Hysteresis

In this paper we present a theory describing the diffusion limited evaporation of sessile water droplets in presence of contact angle hysteresis. Theory describes two stages of evaporation process: (I) evaporation with a constant radius of the droplet base; and (II) evaporation with constant contact angle. During stage (I) the contact angle decreases from static advancing contact angle to static receding contact angle, during stage (II) the contact angle remains equal to the static receding contact angle. Universal dependences are deduced for both evaporation stages. Obtained universal curves are validated against available in the literature experimental data