Papers by Keyword: Flow Field

Abstract: . Electrochemical etching is widely used to process refractory metals such as tungsten and molybdenum. Flow field is one of the crucial factors that influence the surface quality in electrochemical etching. In this paper, the electrochemical etching flow field was analyzed via FLUENT, the characteristics of flow field in electrochemical etching are studied, furthermore, the effects of four different outlet forms of electrolyte on flow field uniformity, electrolyte velocity and pressure distribution are investigated. Under the same electrolyte flow rate, the flow field characteristics of different outlet forms are analyzed by velocity vector diagram, pressure distribution nephogram, velocity and pressure curve diagram. The simulation results indicate that stable electrolyte velocity and uniform pressure distribution of flow field are obtained when the outlet form of electrolyte adopts the optimized flat. Finally, the fixture for this outlet form is designed and fabricated, and experimental verification is carried out, which shown that the flow field is uniform and the crystal plane of the workpiece is well-distributed which according with the process requirements.

Abstract: . The flow pattern on the combined effect of a horizontal cylinder and a vertical plate is observed and analysed in this experimental study. The experiment was conducted with a 4 cm outer diameter cylinder arranged horizontally across flow above 2 cm from the bed and a vertical plate of 5 cm placed 9 cm downstream from cylinder surface reference as tilting flume bed surface. The water depth was maintained at 17 cm through a constant discharge of 35 lps in a re-circulating flume. Acoustic Doppler Velocimeter (ADV) was used to store the velocity fluctuation of velocity components and further used as a pictorial frame to understand the turbulence and the turbulent kinetic energy around the cylinder, plate and in between the cylinder - vertical plate. From the pictorial contour diagrams drawn, the velocity vector represents the flow feature over the cylinder and it is found that a horseshoe vortex, developed upstream of the plate, does effect on turbulent kinetic energy formed in between cylinder and vertical plate. The observation and obtained results from present study is compared with a 5 cm horizontal cylinder above 2 cm from the bed and a plate situated on 5.5 cm from cylinder curvature towards downstream.

Abstract: The transient electromagnetic phenomena and solidification of Al-Cu alloy under a typical pulsed magnetic field (PMF) are numerically studied by a two-dimensional (2D) axisymmetric model. The results show that the magnetic flux density, eddy current density, Lorentz force and Joule heat all inherit the instantaneous and intermittent feature of the PMF, and their amplitudes and phases decrease with the increasing distance to the side surface of the ingot. The Lorentz force appears alternatively as pressure force and pull force mainly in the radial direction. Forced convection is induced in the liquid metal, and the flow field is composed of a clockwise vortex and a counter-clockwise vortex in the meridian plane of the ingot. The melt velocity is accompanied with a dramatic periodic oscillation. The temperature field in the ingot with the PMF tends uniform due to the mixing effect of the melt flow. However, the convection is damped soon after the solidification starts due to the increasing penetration resistance, and the temperature field gradually approximates that in the case without the PMF.

Abstract: Bipolar plates in Proton Exchange Membrane fuel cells (PEMFC) distribute fuel and oxidant over the reactive sites of the membrane electrode assembly. In a stack, bipolar plates collect current, remove reaction products and manage water. They also separate neighboring cells and keep the oxidant and the fuel from mixing; they provide structural support to the stack. The plates are typically graphite with parallel or serpentine channels. The efficiency of a stack depends on the performance of the bipolar plates, which depends on the material and flow field design. The drawbacks of graphite include weight, fabrication inaccuracy, cost, porosity, and brittleness. Open-cell metal foam is investigated as a flow field/bipolar plate and compared to conventional graphite bipolar plates. The complex internal structure of the foam was modeled using an idealized unit cell based on a body center cube. This cell maintained the actual structural features of the foam. Clones of the idealized cell were virtually connected to each other to form the new bipolar plate. SolidWorks, and Auto-CAD were used to generate the unit cell and the computational domain, which was imported into ANSYS. Meshing of the domain produced than 350,000 elements, and 70,000 nodes. Appropriate boundary and operating conditions for PEMFC were applied, and the PEMFC module within ANSYS was used to obtain the temperature and flow distribution as well as the fuel cell performance. In comparison to conventional bipolar plates, results show that the cell current and voltage densities were improved, and temperature distribution on the membrane was even, and within the allowable limit. As importantly, there was a weight reduction of about 40% as a result of using metal foam as a bipolar plate.

Abstract: The objective of this study is to analyze the flow filed in the intake manifold using Computational Fluid Dynamics (CFD). The main function of the intake manifold flap is to regulate the air flow and to uniformly distribute in the cylinders. If the air is distributed uneven to the engine the volumetric efficiency, power and fuel consumption is reduced. The finite element method can be used to optimize the throttle flap. The results in the simulation offer valuable information’s of the flow field in the throttle assembly. The results show that the CFD model can be used as a tool for improve and optimize various part of the intake manifold flap.

Abstract: In wire EDM process, it is important to smoothly exclude debris and bubbles generated in the working gap for keeping stable performance. Much debris stagnation in the gap would cause frequent occurrence of discharge concentration and secondary discharge, which results in unstable machining performance, such as frequent wire breakage, low removal rate, and low shape accuracy. Therefore, a jet flushing of working fluid using upper and lower jet nozzles has been conventionally applied for excluding the debris and bubbles from the machined kerf. Nevertheless, it is well known that the wire often breaks when the machined kerf length is a few mm from the start hole in 1st-cut wire EDM. The influence of machined kerf length on the flow field, the debris exclusion, and the wire behavier caused with hydrodyanamic force by the jet flushing should be made clear.In this study, variations of flow field in the kerf, the debris accumulation state and the wire deflection caused jet flushing with machined length were analytically investigated by CFD (computational fluid dynamics) and structural analysis when 1st-cut wire EDM was done from a small start hole. Moreover, the effects of machined kerf length on the wire deflection and wire breakage were discussed. Wire breakage frequency experiments showed that wire tended to frequently break at a certain machined kerf length, where the wire deflection rapidly increased and the debris particle residence time in the gap became long.

Abstract: In order to reduce the required manpower and biosecurity control risk for waterfowl breeding eggs, this study developed waterfowl automatic eggs cooling incubator which using the concept of pre-heating and pre-wetting type front control thermal system and add the automatic watering eggs cooling system, trolley egg rack, pneumatic eggs overturning system and monitoring system. The front control thermal system preheats and pre-wet the air to the required environment for hatching and import into incubator for the hatching test. The test results show that the hatching environment uniformity of automatic eggs cooling incubator developed by this study is better than the traditional incubator’s environment. The monitoring system can stable control the variation for three hatching parameters of temperature, humidity and carbon dioxide concentration. Besides the combination of automatic watering eggs cooling system for hatching process can significantly reduce the required manpower for watering eggs cooling and biosecurity control risk, the average hatching ratio is 82.06% that can satisfy the requirement of general professional goose breeding eggs incubator. The test using computational fluid dynamics simulation software (CFD) to simulate the variable turbulent wind speed. On the premise of using temperature as the respondence to conduct the optimization design of response surface methodology. The results shows that the incubator temperature standard deviation decreased from 0.26°C to 0.14°C when three turbulent wind speed changed from 4.25 m/s, 3.50 m/s and 4.63 m/s to 2 .00m/s, 5 .00m/s and 3.81 m/s. There is a further increase for the uniformity of the temperature field.

Abstract: In the present numerical investigation, the flow field of confined slot air jet in a rectangular computational domain is reported. In the present work the flow field parameters like reattachment length, vortex center and horizontal velocity profiles for various Reynolds numbers and for various aspect ratios are presented .The present study reveals that the vortex centers are moving in a downstream direction with increase in Reynolds number. The reattachment length is directly dependent on the Reynolds numbers. In case of vortex dynamics, the vortex size is indirectly dependent on the inlet jet width. In the present investigation, SIMPLE algorithm is used to solve the governing equations. It is concluded that the aspect ratio and the Reynolds number are playing dominant roles in flow field of the present computational domain.

Abstract: Fiber air dispersion system (FADS) is an advanced flexible ventilation terminal in ventilated areas. Its benefits are numerous, which are air diffusion without feeling, anti-condensation, easy cleaning and low cost etc. The technology of computational fluid dynamics (CFD) was used in this paper. At first, a physical model of the environment conditioned by FADS was built. Then, the both field of temperature and flow in the environment was simulated. The boundary conditions and parameters was measured and calculated. Finally, the numerical results were verified by comparing with the experiment data to confirm the reliability of the model. Meanwhile, by using the indoor air evaluation standard, FADS was confirmed to provide a more comfortable environment and better air quality.

Abstract: Valve orifice is the common place that the cavitation easily occurs in the hydraulic systems. This paper introduces a criteria to estimate the inception of the cavitation of the V-type valve orifice with the stress state. Based on this criteria, a cavitation model which considers the dynamics of the cavity and incompressible gas is proposed to analyze the pressure, stress and the cavitation distribution of the phase in the V-type orifice. The distributions of the cavitation along the axis and the cross section are analyzed. The simulation results show that the cavitation is easily occurred in the downstream just after the orifice and the bubbles are mostly gathered in the top of the cross section which is vertical to the axis of the flow field. The simulation results is reasonable according to the facts. Accordingly, the cavitation of the V-type orifice is predicted reasonably. The research and results of this paper are useful for the design of the hydraulic valves.