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The mass transfer between a single droplet and a surrounding fluid can be described mathematically solving the momentum and mass balances in both phases (conjugate problem). This study of dimensionless parameters shows how the process is influenced by changes in material properties and operating conditions. The influence of the Reynolds number Re on the mass transfer is found to be small and to vanish for creeping flows. A sensitivity to the viscosity ratio μ * exists only in a limited range. The influence of the Peclet number Pe can be approximated for small Pe by considering only the...
It has recently been reported that noise generated in screw compressors can by reduced by modifying the shape of the high pressure port to minimize gas pulsations in the discharge chamber. This paper describes a simulation mode developed to predict the optimum form of this. The procedure used was to simulate the flow in three dimensions within the discharge chamber, using CFD, and to couple this with flow simulations in the working chamber and outlet reservoir, based on one dimensional models. The model takes into account the real shape of the discharge port. By its use it is possible to...
Computer simulations of two-phase gas-liquid pipe flow cases have been performed with the commercial code STAR-CD using the VOF method and the results are illustrated in this paper. Computed pressure losses for stratified flow and stratified-wavy flow and time-averaged liquid levels are compared against measured data, showing good agreement with the experimental data. To achieve these results, turbulence in the region close to the interface required the introduction of a law-of-the-wall based correction term in the turbulent energy dissipation equation. Two approaches for the turbulence...
A numerical study of a racecar front wing is presented. The focus of the study is to investigate the aerodynamics characteristics of a wing operating in a small ground clearance. A finite-span wing with a symmetric airfoil section is used. It was found that as the wing gets closer to the ground it generates more downforce and more drag. As the wing gets very close to the ground, the downforce reaches a maximum value and after that the wing generated less downforce as it gets closer to the ground. The drag force follows a similar trend of dependency on the ground clearance. The lower surface...
Abnormalities of the aortic arch , as the most proximal site of the cardiaovascular system , are of the great interest due to its major role in blood distribution to all downstream members. Wall dissection is one of the disorders that an aorta mau suffer due to hypertension or degaration of aortic wall properties. A geometrical change of the aortic ach caused by the dissected wal, and consequently the blood flow path ,makes the time varying flow curves to be different in comparison to the healthly aortic arch. This phenomenon modifies wall shear stres( WSS) history during the cardiac cycle...
This paper is devoted to premixed combustion modeling in turbulent flow. First, we briefly remind the main features of the Self-Similar Turbulent Flame model that was more extensively developed in a former paper. Then, we carefully describe some improvements of the model. The determination of the turbulent flame velocity is based on the observed self-similarity of the turbulent flame and uses the local flame brush width as a fundamental parameter, which must be retrieved. With respect to the former version, we now derive more rigorously how the density variation has to be taken into account...
Monitoring the real-time behavior of spatial arrays of single living bacteria cells is only achieved with much experimental difficulty due to the small size and mobility of the cells. To address this problem, we have designed and constructed a simple microfluidic device capable of trapping single bacteria cells in spatially well-defined locations without the use of chemical surface treatments. The device exploits hydrodynamics to slow down and trap cells flowing near a narrow aperture. We have modeled this system numerically by approximating the motion of Escherichia coli cells as rigid 3-D...
The applicability of the commercial CFD-Program STAR-CD for hydraulic problems was evaluated by the pressure distribution downstream of an opening lock valve.Various valve operation speeds were modeled. This gave information about the possibility to simulate the flow around and induced by moving structures. Results of the numerical simulations were compared with results of physical model tests. Differences between measured and computed pressures in the unsteady flow were in a range of 1-2 percent, although the maximum differences in flow rates were about 15 percent.
A time dependence of three-dimensional simulation including water phase change and heat transfer of a PEMFC model has been studied. The overshoot behavior has been observed during a change in the electrical load during operation with fixed flow rates of hydrogen and air. The simulation of 25-cm2 active area with a serpentine flow path shows the interactions of the anode and cathode flow streams, the flow through the gas diffusion media, and the movement of water through the MEA by electroosmotic and back diffusion forces. The simulation used a commercial computational fluid dynamics (CFD)...

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