Width Of Liquid Film Research Articles

Multicellular structures in thin free liquid films induced by thermocapillary effect

Hypothesis:Multicellular convective structures that are induced in a fluid exposed to temperature difference are commonly observed in nature and in daily life. Different types of basic flow patterns are induced in a free liquid film by thermocapillary effect, whereas the formation of such multicellular structures has not been hitherto unravelled. Experiments:A thin film of high-Prandtl-number liquid is prepared in a rectangular aperture of the order of 0.1 mm in thickness sustained by its surface tension. A designated temperature difference is imposed between the end surfaces of the aperture to generate a thermocapillary-driven convection in the free liquid film. We monitor the induced thermal flow patterns to evaluate the cell numbers and their wavelength by experimental and numerical approaches. Findings:The multicellular structure is established by the thermocapillary effect in the free liquid films. The cell number increases in a stepwise manner as the liquid-film width increases. When the cell number increases, another pair of the cells always newly emerges. We determine the wavelength in a non-dimensional manner, and present the variation of the wavelength against the aspect ratio corresponding to the liquid-film width. The results are compared to those of convectional Marangoni-Bénard convection.

Experimental study of wavy-annular flow in a rectangular microchannel using LIF method

This article aims at studying gas-liquid flow in a rectangular microchannel with a high aspect ratio (200 × 2045 μm). Liquid and gas phases were 95% ethanol and nitrogen mixture. Experimental flow characteristics are obtained using high-speed visualization and laser-induced fluorescence (LIF) methods. Using the LIF method for wavy-annular flow, the average film thickness, liquid film distribution, and liquid film width were measured. The dependences of the liquid film width and the average film thickness on gas superficial velocity are presented in graphical form and analyzed. An increase in gas superficial velocity causes growth of the liquid film width and thickness of the liquid film, which indicates the process of liquid transfer from the menisci area to the liquid film. For different liquid velocities and the same gas superficial velocities, close values of averaged liquid film thickness were observed for flow with 2D waves and 3D waves on liquid film.

Free surface lubrication of rotating cylinders by impacting Newtonian liquid jet

AbstractFree surface lubrication of rotating cylinders by Newtonian liquid jets was investigated at different impingement positions, jet‐ and circumferential velocities. The interaction between impinging round laminar jet and rotating surface was characterised by high‐speed imaging. Compared to flat surface impingement, the liquid deposition mechanism is more complex and often accompanied by phenomena such as splashing, jet deflection and formation of radial surface stripes. Liquid splashing initially develops in direct deposition regime due to hydraulic jump‐induced droplet shedding, transitioning to lamella instability splash at higher Reynolds numbers. The critical Reynolds number for splash onset is of same order of magnitude as for flat surface impingement and fairly constant at low relative jet impingement angles, but increases exponentially when angle approaches 90°. Liquid film width and thickness were both determined proportional to the square root of the jet/surface velocity ratio, with respective power law models in good agreement with measured values.

Effect of surface properties of corrugated packing of dehumidification tower on surface liquid phase distribution

Abstract The uniform distribution of liquid phase on the packing surface is necessary for the dehumidification tower to maintain high dehumidification performance and efficiency. In this study, the effect of the packing properties and operating parameters on the liquid distribution of the packing surface is studied using a VOF method, the wetting ratio and liquid holdup of the packing were used as the evaluation indexes for the liquid distribution. The results show that the surface structure and wettability of corrugated packing have influence on the liquid distribution. The flow pattern of the liquid on the flat slat is mainly film flow. The lateral spreading of the liquid flow and the overall wettability on the fine corrugated slat are more effective than that on the flat slat due to the presence of granule ripples on the fine corrugated slat which increases the wettability of the packing , and the results in a gradual increase of the wetted area . However, even under ideal conditions, the liquid cannot wet the packing surface completely. As the inlet velocity of the gas increases(i.e., 0.617—1.85 m/s), the disturbance from the gas to the liquid phase increases and hinders the overall flow of the liquid which further increases the wetting ratio and liquid holdup. As the inlet velocity of the liquid increases (i.e., 0.057 m/s—0.11 m/s), the liquid film width of the filler surface gradually increases, the wetting ratio and liquid holdup increases significantly. The study provides guidance for the optimal design of the dehumidification tower and the design as well as selection of the packing in the tower.

Phase Field Crystal Study for the Effect of Heating Rate on the Premelting of Grain Boundary

The effect of heating rates on the premelting of grain boundary (GB) is investigated by the phase field crystal method. The microstructure evolution of premelting under different heating rates are discussed, and the film width of GB is quantitatively calculated in terms of the excess mass method. Results show that the liquid film appears as the melting point () is approached from below and that the film thickness is affected by heating rate. In heating process, at the same temperature (close to), the liquid film width is larger when the temperature increases with lower rate. In insulation process, the liquid film thickness increase until to its equilibrium value with holding time prolonging. For low-angle GBs, the higher heating rate the system has during heating stage, the lager equilibrium value of liquid film will be reached during insulation stage. For high-angle GBs, the liquid film thickness has the same equilibrium value during the insulation process although the heating rate is different during heating process.

Effect of counter current gas phase on liquid film

Liquid film flow is very important in many industrial applications. However, there are few reports about its characteristics on structured packings. Therefore, in this paper, liquid film phenomena were investigated experimentally to exploit new approaches for intensifying the performance of the structured packings. All experiments were performed at room temperature. Water and air were the working fluids. The effect of counter current gas phase on the liquid film was taken into consideration. A high speed camera, a non-intrusive measurement technique, was used. It is shown that both liquid and gas phases have strong effects on film characteristics. In the present work, liquid film width increased by 57% because of increasing liquid flow rate, while it decreased by 25% resulting from the counter current gas phase.

Liquid Film Characteristics on Surface of Structured Packing

Structured packing is a good candidate for CO 2 capture process because of its higher mass transfer efficiency and lower pressure drop. Now, the challenging problem of CO 2 capture and storage demands more and more efficiency equipment. The aim of the present study is to investigate the liquid film characteristics under countercurrent gas phase and throw some insight into the enhancing mechanism of mass transfer performance in structuredpacking. A high speed digital camera, non-intrusive measurement technique, was used. Water and air were working fluids. Experiments were carried out for different gas/liquid flow rates and different inclination angles. Thetime-average and instantaneous film widths for each set of flow parameters were calculated. It is shown that the effects of gas phase could be neglected for lower flow rate, and then, become more pronounced at higher flow rate. According to instantaneous film width, three different stages can be distinguished. One is the constant width of liquid film. The second is the slight decrease of film width and the smooth surface. This kind of character will lead toless interfacial area and deteriorate the packing mass transfer performance. For the third stage, the variation of filmwidth shows clearly chaotic behavior. The prediction model was also developed in present work. The predicted and experimental results are in good agreement.

Liquid film flow and area generation in structured packed columns

Several correlations are available in the literature for the prediction of wetted area or the effective interfacial area in packed columns. A careful examination shows considerable discrepancies in the calculated areas and conflicting predictions concerning the influence of viscosity on the interfacial areas. In this work, the effect of physical properties of liquids and of surface treatment on wetted area of structured packings was experimentally studied. Several wetting tests were performed on metallic and ceramic plates with flat, smooth or textured surfaces, using a circulation system, specially designed for this purpose. The liquid film width and thickness were measured for solutions with different surface tension and viscosities in a wide range (1 to 200 cP). The experimental results show that the liquid film width, and hence the wetted area, decreased with liquid viscosity, contrary to earlier correlations in the literature. Also the influence of contact angle is not so strong as stated in the literature for random packings. In this study, a new statistical correlation for the estimation of the wetted area and for the liquid film thickness is proposed, reflecting the measured variations with viscosity and advancing contact angles.

Heat Removal Characteristics of a Primary Containment Vessel External Spray

To evaluate the heat release characteristics of a primary containment vessel (PCV) external spray (one of the PCV cooling systems utilizing the steel PCV wall as the heat transfer medium), the thermal-hydraulic characteristics of the falling liquid film on the PCV surface have been investigated experimentally. Then, the performance of the PCV external spray cooling system was evaluated using the experimental findings. The following results were obtained: (1) Heat transfer coefficients of the falling liquid film under steady-state conditions were increased as the film flow rate per unit length of the liquid film width increased, and they agreed with Wilke`s correlation within about {+-}15%. (2) The PCV surface temperature, when preheated up to 150 C, which is the supposed PCV temperature under a severe accident, decreased below 100 C within a few seconds when the PCV external spray was initiated, and boiling on the PCV surface could not be maintained. (3) Heat transfer coefficients of the falling liquid film under transient conditions were higher initially due to the boiling effect; however, they decreased rapidly and approached those under steady-state conditions. (4) The PCV external spray for the conceptually designed PCV could suppress the PCV pressure below the design goal undermore » a severe accident.« less