Increasing Flow Rate Ratio Research Articles

EXPERIMENTAL INVESTIGATION OF SECONDARY FLOW DURING THE DROPLET FORMATION IN THE FLOW-FOCUSING CHANNEL

In this study, we have investigated the complex dynamics of droplet formation in a flow-focusing channel. Experiment has been performed under micro-particle image velocimetry (μPIV). The growth of droplets has been observed at four stages: lagging, filling, necking, and detachment. The interaction of two immiscible fluids, de-aerated water and silicon oil, is used. Characteristics of the droplet thread have been analyzed. Length of dispersed thread and tip size decrease with increased flow rate ratio. Furthermore, the flow characteristics of the dispersed phase, the velocity fields, contour plots of vorticity (ω<sub>z</sub>) swirl strength (λ<sub>1</sub>), and circulation strength (Г/U<sub>d</sub>W) have been investigated. Vortex flow region is identified during the droplet formation in such flow conditions (Re ~ 1 and Ca < 0.01). The vortex flow region shrinks with increasing flow rate ratio. Our experimental methodology and results have illustrated the presence of a temporal vortex pair during droplet formation in dispersed phase, a phenomenon with potential to amplify the chaotic mixing of multiphase fluids in a microchannel.

Comprehensive operational parameter analysis of cross-flow hollow fiber membrane humidifier for humidification dehumidification desalination

Experimental results show that the cross-flow hollow fiber membrane contactor is the controlling component of the humidification dehumidification desalination system performance. Three sets of main operating conditions sensitivity analyses are performed numerically, including solution conditions (temperature, salinity, flow rate), air conditions (temperature, relative humidity, flow rate) and dimensionless parameters (number of heat transfer units, flow rate ratio of solution to air). Increasing flow rate ratio can effectively promote freshwater production rate before flow rate ratio reaches a critical value of 6.0. It is useful to improve moisture effectiveness by increasing number of heat transfer units. Solution inlet temperature has an exponential promoting effect on membrane flux, which is consistent with the exponential upward trend of the solution phase equilibrium humidity. Membrane flux increases dramatically at first and then slowly after solution flow rate exceeds 228 kg/h and air flow rate exceeds 57 kg/h. Ambient air with high temperature and relative humidity as well as the high salinity of the solution will slightly degrade the membrane flux.

Effect of Flow Channel Configuration on Nano Fibril Alignment by Elongational Flow

Cellulose Nano-fibrils (CNFs) are the fundamental building blocks extracted from wood fibers and have gained great attentions as a novel biological material. It is known that the outstanding mechanical properties of cellulose filament made of CNFs can be obtained with their orientation inside the filament, the orientation control of CNFs is essential in the material fabrication. In this study, the effect of channel configuration on the orientation of CNFs by elongational flow are clarified both by numerical simulation and experiment. The higher CNF orientation parameter can be obtained for the channel with the focusing angle of 45 degrees compared to that with 90 degrees and also by increasing the flow rate ratio of downstream sheath flow to the upstream one. The ultimate tensile strength and toughness of cellulose filament increases by 11 % and 59 %, respectively by increasing flow rate ratio from 1.0 to 3.0 with 45 degrees focusing angle as predicted from the numerical simulation results.

A Numerical Investigation of the Onset of Flow Separation in Round-Edge Diverging Tees

The onset condition of flow separation in diverging tee junctions was investigated numerically. Flow separation and recirculation at the proximal region of a bypass graft can contribute to early phase graft failure in aortocoronary bypass (ACB) surgery. Rounding the inlet edge of the branch reduces the likelihood of flow separation and recirculation. The recirculating zone at the upstream end of the branch is fully eliminated when a threshold value of mass flow rate ratio is reached. The corresponding flow characteristics obtained from diverging tees with a diameter ratio ≤0.2 and a radius of curvature ≤ 0.25 for a Reynolds number ≤ 1817 indicate that an increasing flow rate ratio induces an exponential decrease in the recirculation length. An increase in the diameter ratio and Reynolds number increases both the onset condition of the flow separation and the recirculation length at the upstream end of the branch. However, a decrease in the diameter ratio reduces the onset condition of separation more effectively than a decrease in the radius of curvature at the junction.

Effect of cold air stream injection on cyclone performance at high temperature

Abstract A cold air stream was injected into a cyclone operating at a high temperature through slits created in the cylindrical part of the wall. The effects of the cold stream injection on the cyclone performance were investigated by experiment and CFD simulation. The particle deposition on the wall was observed to be closely related to the cyclone wall temperature distribution, with the particles mainly deposited on the high-temperature (>932 K) parts of the wall, and no particle deposition occurring on parts with temperatures lower than 873 K. However, the separation efficiency decreased with increasing flow rate ratio of the cold air stream. This was because the injection of the cold stream caused the bypassing of the hot stream through the vortex finder, thereby decreasing the tangential velocity of the hot gas. Hence, when particle deposition on the wall severely interferes with the operation of a cyclone, the injection of a cold stream can be used to significantly reduce the particle deposition, although this also decreases the separation efficiency and 50% cut size.

CFD study on effect of channel confluence angle on fluid flow pattern in asymmetrical shaped microchannels

Five asymmetrical shaped microchannels were used to investigate the effect of channel confluence angle, flow rate and flow rate ratio on the mixing performance in a passive mixing test. The flow characteristics for all geometries were studied experimentally and numerically using CFD technique. The results reveal that the mixing performance depends on the channel geometry, total flow rate and inlet flow rate ratios. The classical T-shape microchannel had the worst performance in the lower flow rate and in higher Re numbers its performance was placed between the other ones. Furthermore, the mixing effectiveness for all microchannels was defined and measured at various feed flow rates. The results indicate that the mixing effectiveness increases with increasing flow rate ratio and decrease of confluence angle. The reasons for the observed experimental results were analyzed by the predicted CFD flow patterns.

Membranes of epitaxial-like packed, super aligned electrospun micron hollow poly(l-lactic acid) (PLLA) fibers

Novel epitaxial-like packed, super aligned, mono-layered hollow fibrous membranes were prepared by co-axial electrospinning technology. PLLA pellets were dissolved in solvent mixture of dichloromethane and dimethyl formamide (DCM/DMF=9:1) to prepare sheath solution dope with various concentrations (from 8 to 19wt.%). Aqueous solution of poly-ethylene glycol (PEG) was used as core solution dope. During the electrospinning process, dope concentrations and feed rate ratios were adjusted, separately, to evaluate the formation of resulting membranes. With lower shell solution concentration (from 8 to 15wt.%), the collected, flattened film showed arrangement of lower order. A stood-up film was clearly seen when concentration increased to 17wt.% and higher. As the collecting time went longer, these fibers piled up and eventually, stood up as a thin film from the surface of collector. Increasing flow rate ratio (FRR) also resulted similar outcomes and verify the cause of this phenomenon. After washing with water, scanning electron microscopy (SEM) revealed sheets of mono-layered, micron-sized hollow fiber arrays which were well aligned and tightly packed, just like the epitaxial growth of some semiconducting materials. These perfectly aligned and tightly packed hollow fiber arrays can be considered as highly anisotropic scaffolds that mimic tissue structures, such as nerve tissue, vascular structure as well as other application.

The influence of H 2/Ar ratio on Ge content of the μc-SiGe:H films deposited by PECVD

An alternative approach of adjusting the Ge content in μc-SiGe:H films is explored by changing the H 2/Ar flow rate ratio. The results reveal that the Ge content and film deposition rate both decrease with the increasing flow rate ratio of H 2/Ar. Optical constants of the films are obtained by simulating the optical transmission spectrum using a modified envelope method. The dark conductivity and activation energy are investigated by measuring the temperature-dependent conductivity. The dependence of Ge content, deposition rate and optoelectronic properties on flow rate ratio of H 2/Ar is discussed.

Effects of CF4 Addition on the Growth of Amorphous CNx Films by Plasma Decomposition of CH4-N2 Gas Mixtures

ABSTRACTHydrogenated amorphous carbon nitride (α-CNx:H) films are deposited at 50–300°C by radio-frequency plasma decomposition of CH4-CF4-N2 gas mixtures. Effects of fluorine radicals on the deposition rate, composition, and on chemical bonding are investigated. When CF4 gas is added as partial replacement of CH4 gas, the deposition rate at 200°C steeply increases with increasing flow rate ratio RCF = [CF4]/([CH4]+[CF4]) up to ∼0.3, and then it decreases gradually. It is found that the nitrogen content, x, increases from 0.22 to 0.46 when RCF increases from 0 to 0.75. The inclusion of fluorine atoms into the films is less than 5 at%. The infrared absorption spectra shows strong enhancement of the absorption bands related to various forms of C—N bonding by the CF4 addition. It is found that the addition of CF4enhances the formation of C–N bonds in PECVD α-CNx:H films.