Study on the Effect of Nanoparticle Used in Nano-Fluid Flooding on Droplet–Interface Electro-Coalescence

Nano-fluid flooding is a new method capable of improving oil recovery; however, nanoparticles (NPs) significantly affect electric dehydration, which has rarely been investigated. The effect of silica (SiO2) NPs on the droplet–interface coalescence was investigated using a high-speed digital camera under an electric field. The droplet experienced a fall, coalescence, and secondary droplet formation. The results revealed that the oil–water interfacial tension and water conductivity changed because of the SiO2 NPs. The decrease of interfacial tension facilitated droplet deformation during the falling process. However, with the increase of particle concentration, the formed particle film inhibited the droplet deformation degree. Droplet and interface are connected by a liquid bridge during coalescence, and the NP concentration also resulted in the shape of this liquid bridge changing. The increase of NP concentration inhibited the horizontal contraction of the liquid bridge while promoting vertical collapse. As a result, it did not facilitate secondary droplet formation. Moreover, the droplet falling velocity decreased, while the rising velocity of the secondary droplet increased. Additionally, the inverse calculation of the force balance equation showed that the charge of the secondary droplet also increased. This is attributed to nanoparticle accumulation, which resulted in charge accumulation on the top of the droplet.

STUDI PENGARUH DINAMIKA TUMBUKAN MULTIPLE DROPLETS TERHADAP NILAI SPREADING RATIO PADA PERMUKAAN BIDANG PANAS YANG MIRING

Spray cooling merupakan aplikasi dari droplets yang digunakan sebagai salah satu teknik pendinginan. Pemanfaatan dari multiple droplets ini banyak dikaji sebagai sistem pendinginan pada peralatan elektronik dan pembuatan material quenching. Dinamika tumbukan multiple droplets pada permukaan bidang miring yang dipanaskan akan dikaji pada penelitian ini. Material uji yang digunakan adalah stainless steel 304 . Temperatur permukaan yang diamati adalah 120 ºC, 180 ºC dan 220 ºC pada bilangan Weber medium 70 dengan variasi bidang kemiringan adalah sebesar 10º, 20º dan 30º. Dinamika droplet selama tumbukan diamati menggunakan high-speed camera dengan kecepatan 4000 fps kemudian hasilnya diolah menggunakan image processing. Telah diperoleh hasil bahwa spreading ratio tertinggi terjadi saat temperatur permukaan 180 ºC pada sudut kemiringan 30 º dan terendah pada temperatur 220 ºC. Fenomena secondary droplet dapat meningkatkan nilai spreading ratio. Adapun fenomena bounching terjadi pada temperatur 220 ºC

High-throughput measurements of intra-cellular and secreted cytokine from single spheroids using anchored microfluidic droplets

While many single-cell approaches have been developed to measure secretion from anchorage-independent cells, these protocols cannot be applied to adherent cells, especially when these cells requires to be cultured in 3D formats. Here we demonstrate a platform to measure the secretions from individual spheroids of human mesenchymal stem cells, cultured within microfluidic droplets. The platform allows us to quantify the secretion from hundreds of individual spheroids in each device, by using a secondary droplet to bring functionalized micro-beads into proximity with each spheroid. We focus on vascular endothelial growth factor (VEGF) and measure a distribution of secretion levels that presents broad heterogeneity within the population of spheroids. Moreover, the intra-cellular level of VEGF-A on each spheroid, measured through immuno-staining, correlates well with the extra-cellular measurement, indicating that the heterogeneities observed at the spheroids level result from variations at the scale of individual cells. Finally, we model the molecular accumulation within the droplets and find that physical confinement is crucial for measurements of protein secretions. The model predicts the time to achieve a measurement, which scales with droplet volume. Therefore these first measurements of secretions from individual spheroids provide several new biological insights.

Study of Morphology and Secondary Droplet Behaviors during Droplets Impacting on Static Hot Film

The phenomenon of droplet impacting on hot film exists widely in nature and engineering applications. Considering limitations in current researches, an experimental setup to record the process of droplets impacting on hot film was built in this paper. Lots of experiments have been done and then the transitional threshold was established to determine impingement outcomes. The number of secondary droplets and the temperature of the secondary droplet are investigated based on the experimental results. The results show that impingement outcomes can be determined by the splashing parameter provided in this paper. The number of secondary droplets increases with the splash parameter, the probability distribution function of secondary droplet diameters follows the Weibull distribution. The temperature of secondary droplets is close to the hot film and almost all secondary droplets' temperature is above 90% of the hot film.

Collisions of water drops in a gas-vapor environment at high temperatures and vapor concentrations

The study of the characteristics of secondary droplet atomization, leading to formation of an aerosol cloud of polydisperse child droplets appears to be promising. It is topical to assess the influence of properties of liquid and gas medium on the position of transition boundaries between the regimes of drop collisions and characteristics of the formed child droplets. This article presents the experimental results for the characteristics of drop collisions at various temperatures of the liquid and gas-vapor mixture and water vapor concentration in the latter with the aim of developing the prospective heat and mass transfer gas-vapor technologies. For this purpose, we have created the experimental setup that allows varying the relative humidity of gas-vapor mixture in the area of drop collisions from 20% to 100%, its temperature from 20?C to 100?C and the temperature of the liquid from 20?C to 90?C. The test fluid is water. The collisions are recorded by a high-speed video camera. The consequences of collision and the boundaries between them on the regime maps are determined in accordance using the approach, distinguishing: bounce, coalescence, separation, and disruption.