Estimation of Average Void Fraction for Gas-Liquid, Two-Phase Flow in an Industrial Nozzle Assembly Using a Quick-Closing-Valve

Experimentally accurate void fraction measurements are a challenge in an air/water, two-phase flows through an industrial nozzle assembly, as a highly non-uniform void fraction exists in the feeding conduit prior to the nozzle. In this study, average void fractions were measured by isolating a section in the feeding conduit of a horizontal nozzle assembly, termed as the quick-closing-valve (QCV) technique. A high-speed video camera was utilized to capture the asynchronization closing time, tac. The average closing time and asynchronization for the pneumatically controlled valves were 200 ms and 2 ms, respectively. Based on the equation of 100umtac (1−α)/αlc, the synchronization error between the two valves was 1.12%, 1.26%, and 1.79% for the 1%, 2% and 4% ALR cases, respectively; here um is the mixture velocity, α is the void faction, and lc is the closing length. Higher synchronization error at 4% ALR occurs due to enhanced momentum in the flow regime. Experimental results indicate that the average α over the 33.4 cm feeding conduit (6.25 mm ID) was 76% (αtheoretical = 75%) for the 2% ALR, and 85% (αtheoretical = 83%) for the 3.3% ALR. In the two-phase, two-component flow the α affects the drop size and stability of the spray produced from an industrial nozzle assembly. Learning from this study will yield insights and conceptual understanding of two-phase flow phenomena in conduit, which would affect stability, pulsation tendency, and possibly atomization performance of the nozzle downstream. Two-phase flow nozzles have wide applications in the industries, e.g. petrochemical, pharmaceutical, and others.

Optimization of Stacking Line and Blade Profile for Design of Axial Flow Fan Blade

This work presents a numerical optimization procedure for a low-speed axial flow fan blade with weighted average surrogate model. Reynolds-averaged Navier-Stokes equations with SST turbulence model are discretized by finite volume approximations and solved on hexahedral grids for flow analyses. The blade profile as well as stacking line is modified to enhance blade total efficiency, i.e., the objective function. Six design variables related to blade lean and blade profile are selected, and a design of experiments technique produces design points where flow analyses are performed to obtain values of the objective function. PBA model is employed as a surrogate model for optimization. A search algorithm is used to find the optimal design in the design space from the constructed surrogate model for the objective function. As a main result, the efficiency is increased effectively by the present optimization procedure.

Optimized High-Aspect-Ratio Diffusional Micromixers

This part of our work has been aimed at designing, manufacturing and characterizing effective micro-mixers which are cheap, durable and easily integrated on a variety of bio-chips with emphasis on those performing Polymerese Chain Reactions (PCR) and Ligase Detection Reactions (LDR). A key contribution is the development of an optimization procedure for the design of passive micro-mixers utilizing high-aspect-ratio micro-channels (HARMC). The optimization procedure identifies the optimum type of mixer on the basis of the flow rate proportions of the mixture constituents and provides for two optimum designs of the selected mixer type for an aspect ratio of choice in two ways: (a) for specified mixture volume and mixer pressure drop the optimum mixer dimensions and operating condition minimize the total production time and (b) for specified mixture volume and a total production time the optimum mixer dimensions and operating condition minimize the mixer pressure drop. The simplest and easiest to manufacture layout of an optimized mixer configuration (X2JC) with two inlet ports and three layers is shown in Figure 1. The injection of compound 1 into the compound 2 main stream is performed through two side-jets in a wider channel to further reduce the pressure loss overhead followed by a contraction into the main mixing channel.

Application of Pressure Regulating Valve in the Hydraulic Transients of Hydropower Plant

In the operation of the hydropower station, the sudden change of load in the large range often happen, the emergency closing law of turbine guide vane is difficult to control speed-rise and pressure-rise to the extent permitted for the length of pressure pipeline longer and discharge larger. With the development of the surge chamber of alternative technique, the pressure regulating valve is used to reduce the large pressure and speed-rise of the unit in hydraulic transients as the effective measure to saving investments. The layout of water conveyance system and process of hydraulic transients of a certain hydropower in China are analyzed, and the pressure regulating valve is installed in the spiral case inlet to meet the hydraulic regulation calculation guarantee after technical and economic comparison, for the joint action of valve and turbine guide vane, the pipeline water hammer pressure and unit speed-rise are reduced effectively. The pressure regulating valve diameter and opening and closing law in combination with the turbine guide vane are discussed in the power station, as well as the possible problems may be caused by the using of the pressure regulating valve is pointed out in theory. The achievements to scheme decision of adopting the pressure regulating valve to replace the surge chamber in high-head hydropower station with longer pressure water conveyance system can be for reference and provide the certain technological supply.

Microfluidic Device for Synthesis of Lipid Bi-Layers

Lipid bi-layers are ubiquitous components of biological cells — and are found in variety of cell components ranging from cell membranes to membranes of organelles inside the cells. In biological membranes, lipid bi-layer membranes carry membrane proteins, which serve as single channel nanopores that are used to study transport of proteins and characterize the properties of proteins. However, lipid bi-layers have very short half lives, which are usually less than an hour. The lipid bi-layers are usually obtained by physico-chemical interactions between a lipid containing organic solvent, an aqueous buffer solution and a hydrophobic surface. We have developed a continuous flow through microfluidic device using pressure driven flow (by means of a tandem syringe pump system) for synthesis of lipid bi-layers. The microfluidic device consists of two glass substrates with micro-channels and microchambers microfabricated using photolithography and wet glass etching. The microchannels in each substrate is in the form of “+” shape and form a mirror image of each other. A Teflon sheet (∼200 microns thickness) is sandwiched between the glass substrates with a ∼200 microns diameter hole etched in the center to communicate with the two sets of microchannels. A lipid solution in an organic solvent (Pentane) and KCl buffer solution are alternately flown through the legs of the microchannel. The conductivity of the buffer is monitored using a current amplifier. The formation of the lipid bi-layer is confirmed by monitoring the resistivity and the impedance to high frequency electrical oscillations. The flow rate in the microfluidic device is optimized to obtain the lipid bi-layer.

An Exploratory Investigation of Cavitation Inception on the Pressure Side of Propellers

Delayed sheet cavitation inception has occasionally been observed in the MARIN Depressurized Towing Tank (DTT). The problems are specifically related to the pressure side of model ship propellers, and occur despite the application of leading-edge roughness. As a consequence, no cavitation at all or cavitation on parts of the propeller blades is observed, in cases where cavitation in the cavitation tunnel or at full scale is present. In an exploratory investigation, the effect of several parameters that may influence cavitation inception is studied in the DTT. In particular, the influences of Reynolds number, free-stream turbulence and additional gas nuclei are investigated. It is concluded that the presence of sufficient gas nuclei is crucial for sheet cavitation inception, even if leading-edge roughness is applied. With additional nuclei in the propeller inflow, sheet cavitation inception in the DTT is no longer delayed with respect to the cavitation tunnel.

Development of Microcapsules Including a Gas Bubble for Shock Wave Based Drug Delivery

This paper describes the trial of making microcapsules including a bubble for shock wave drug delivery systems, evaluation of their mechanical properties and development of new driving mechanics of the microcapsules.

Computer Simulation of the Hydropower Stations With Long Pressurized Pipelines and Far Transmission Line

With the rapid development of automatic technology and computer science in the hydropower stations, the computer simulation system named as simulator is developed quickly and applied widely especially as a modern training tool for field operators. In the project of power transmission from west to east in Southwest China, there are lots of hydropower stations with long pressurized pipelines and far transmission line, so their simulators are more complex to be built correctly to show the characteristic of hydraulic-mechanical-electrical system and its dynamic procedure distinctly in real time. Based on the characteristic analysis of hydraulic system and long transmission system, a new easily-decoupled elastic model of water flow in pressurized pipelines is given and recommended, and its application and the choice of appropriate model order are analyzed considering the effect of power system, furthermore, how to build the model of far transmission line is discussed in detail based on its state equations. The results indicate that, in order to realize the truthfulness and robustness of the simulator, the higher order oscillation mode of water flow in long pressurized pipelines should be introduced and the frequency property of far transmission line should be analyzed.

Gas-Liquid Flows in Flow Cells and Fracture Models

Gas-liquid multiphase flows in porous media and fractured rock is of importance when carbon-dioxide displaces brine within geological reservoirs during CO2 sequestration activities. In this paper, experimental and computational modeling of multiphase flows in a porous flow cell and a modeled fracture are described. The experiments performed with the laboratory-scale flow models are described in detail. Experimental data concerning the displacement of two immiscible fluids in the lattice-like flow cell are presented. The flow pattern and the residual saturation of the displaced fluid during the displacement are discussed. It was shown that the gas-liquid flows generate fractal interfaces, with lower fractal dimensions and higher residual saturations at low injection rates. This phenomenon corresponds to viscous and capillary fingering, and is discussed. Numerical simulations of the experimental flow cell are also presented. These are shown to be similar to the experimental results, and then varied to included different surface-fluid interactions not easily studied with the experimental equipment. Numerical simulation results for single and multiphase flows through rock fractures are also presented. A fracture geometry was obtained from a series of CT scans of fractured sandstone and used to construct a laboratory scale model and a computational domain. Computational results showed that the major losses occur in the regions with smallest apertures. These computational results are compared to flows through the experimental model. An empirical expression for the fracture friction factor was also described.

Quantification of Discretization Error in Wall Shear Stress Calculations for Aneurismal Flows Using CFD

Many recent studies suggest that hemodynamic factors such as wall shear stress (WSS) and pressure contribute to the genesis and growth of intracranial aneurysms. Recently there have been a number of computational hemodynamics studies that calculate the values of wall shear stress in arterial and aneurismal flows. However there is a lack of comprehensive error analysis in many of the computational hemodynamics studies. This is perhaps the reason for speculative and ambiguous conclusions drawn by various studies as to the nature of wall shear stress responsible for aneurysm growth. In the current study, geometry involving an actual aneurysm is built from angiogram images. Another geometry consisting of the primary artery where the aneurysm formed is also built by removing the aneurysm volume. The two geometries are meshed using three different grid densities. Second order schemes are used to simulate the pulsatile hemodynamics through each of the geometries. Various representative planes along the geometries are considered and the major flow variables and WSS are plotted as a function of grid densities. The procedure for estimation of discretization error, suggested by ASME Journal of Fluids Engineering, is applied at various representative locations along the aneurysm and arterial geometry. The results suggest high dependence of calculated WSS on local grid density. The contours of WSS in the arterial geometry suggest that high WSS does not necessarily occur at the location where the aneurysm originated. Possible remedies are suggested so that this uncertainty could be eliminated from future studies.