Computational Fluid Dynamics Simulation Study Research Articles

CFD simulation and experimental study on vapour splitter in packed Divided Wall Column

AbstractA Divided Wall Column (DWC) with an optimal vapour split offers much greater potential for energy savings compared to conventional column sequences. To realize the adjustment of the vapour split as well as uniform vapour distribution, a vapour splitter which had been applied for an invention patent was put forward. The effects on performance of adjusting the vapour split and gas nonuniformities under different factors were investigated using numerical simulation and experimental research. The simulation study was carried out using the Computational Fluid Dynamics (CFD) software STAR‐CCM+. The simulation results were compared with experimental data, and they showed close agreement with each other. All the results revealed that the device can flexibly adjust the vapour split and achieve a uniform vapour distribution.

Computational fluid dynamics simulation study of gas flow in dry scroll vacuum pump

Based on CFD method and dynamics mesh method, the transient flow simulation model of dry scroll vacuum pump was established. Numerical calculation was carried out under three kinds of typical working conditions of viscous flow state including under-compression, slightly over-compression and over-compression. Simulation results are in line with the results of experiment or theoretical calculation on the whole. The maximum error of pumping speed between the simulation and the experiment is about 30%, and the minimum is close to 10%. The predicted compression power accords with the theoretical prediction of approximate polytropic process. The simulation pressure inside the pump also has a consistent change process with experimental results. The contrast and analysis of the simulation model and the physical experiments suggest that the further correctly modified geometric parameters and boundary conditions according to practical situations can significantly improve the accuracy of the numerical calculation. Further analysis of the main flow phenomena and characteristics of scroll compression chamber at the discharge side during the discharge process confirms that under-compression and over-compression lead to the large variation of gas pressure and dramatic fluctuation of compression torque.

Air and air contaminant flows in office cubicles with and without personal ventilation: A CFD modeling and simulation study

The paper is aimed at building an appropriate computational fluid dynamics (CFD) model for simulating the flow field in the office cubicle with and without personalized ventilation (PV) and using it to investigate the flow field in the cubicle. A computational model was first constructed by using a commercial CFD code (STAR-CCM). In this process, different approaches to represent manikins, boundary conditions, geometries, and gridding were tested, and a proper approach was selected for simulating the air and contaminant movement in the cubicles and their interactions with the remaining room space. A comparison between the simulation and the experimental results are made to show how accurate the CFD model can be. A brief evaluation of the environmental quality was conducted for both cases with PV and underfloor air diffuser (UFAD). This comparison showed a significant advantage in the PV system, indicating how the PV system performed under different airflow rates. This verified CFD model will be utilized in the future to investigate the performance of the partitioned cubicle collaborating with personalized ventilation systems.

Temperature distribution measurement of Au micro-heater in microfluidic channel using IR microscope

The temperature control and measurement of micro-heater in microfluidic devices are very essential in various application fields such as gas sensors, flow sensors and bio-sensors. In this study, the temperature of a micro-heater was measured while applying voltages to micro-heaters with 100 μm width in microfluidic devices using infrared microscope. The Au micro-heater was fabricated onto a sapphire substrate with good infrared transmission. In order to measure the temperature of Au micro-heater from the back side of sapphire substrate using infrared microscope, the adhesion layer was not used during e-beam evaporation. To overcome the poor adhesion force between sapphire substrate and Au thin-film, thermal annealing was carried out at 400°C. This measurement method enables us directly to measure the IR emissivity of Au micro-heater in aqueous media without infrared diffraction, absolution and reflection. Based on the calibration curve, we could measure the real temperature of Au micro-heater with 100 μm width at atmospheric environment and in aqueous media. Consequently, we could measure the temperature range at atmosphere and in DI water. The companion computational fluid dynamics simulation studies showed that the measured temperature of Au micro-heater was in accordance with the simulated results within 5 K in average sense.

Validation of CFD Modeling and Simulation of a Simplified Automotive Model

In the early design phase of automotive sector, the flow field around the vehicle is important in decision making on design changes. It would consume a lot of money and time for multiple prototypes development if adopt traditional testing method which is wind tunnel test. Thus, numerical method such as Computational Fluid Dynamics (CFD) simulation plays an important role here. It is very often simulation results been compared with wind tunnel data. However, with various mesh types, meshing methodology, discretization methods and different solver control options in CFD simulation, users may feel low confidence level with the generated simulation results. Thus, a robust modeling and simulation guideline which would help in accurate prediction should be developed due to the industry’s demand for accuracy when comparing CFD to wind tunnel results within short turnaround time. In this paper, a CFD modeling and simulation study was conducted on a simplified automotive model to validate with wind tunnel test results. The wind tunnel environment was reproduced in the simulation setup to include same boundary conditions. Meshing guidelines, turbulence model comparisons and also the best practice for solver setup with respect to accuracy will be presented. Overall, CFD modeling and simulation methods applied in this paper are able to validate the results from experiment accurately within small yaw ranges.

CFD Simulation Study on Particle Arrangements at the Entrance to a Swirling Flow Field for Improving the Separation Efficiency of Cyclones

Based on the concept of particle arrangements at the entrance of a swirling flow field, this paper designs common cyclone (C-cyclone), positive rotation cyclone (PR-cyclone), and reverse rotation cyclone (RR-cyclone). FLUENT software is used to perform CFD (computational fluid dynamics) simulation study on these three cyclones. The study result shows that particles are more easily separated if they are closer to the lower part of the outer wall of the entrance to the swirling flow field, whereas particles access the short circuit current more easily if they are closer to the upper part of the inner wall, thereby generating particles escape. The RR-cyclone helps particles to avoid regions of short-circuiting flow, and thus improves the separation performance. In each part of the separator, the particle concentration within the RR-cyclone is lower than that in the C-cyclone and in the PR-cyclone. Moreover, the separation efficiency of the RR-cyclone is higher than that of the C-cyclone and the PR-cyclone in different inlet flows.

A computational fluid dynamics simulation study of coronary blood flow affected by graft placement†.

To determine the effect of graft placement and orientation on flow rates through a partially obstructed coronary artery. A numerical, parametric study of blood flow in the human coronary artery was conducted using computational fluid dynamics simulation. A cylindrical approximation of the coronary artery with varying degrees of stenosis, with and without a bypass graft, was modelled to determine trends in volumetric flow rates. Steady and transient simulations were conducted for geometric variations of percentage of blockage, length and shape of stenosis, graft position relative to the coronary blockage and graft orientation. Accurate simulations were performed using a non-Newtonian fluid model and pressure-driven viscous flow. Simulations demonstrate, as expected, that total outlet flow rates of grafted arteries are consistently improved for upstream stenosis varying between 0 and 90% blockage. Grafts angled towards the artery provided increased total outflow. However, flow rates in the coronary artery upstream of the graft are substantially reduced in comparison with the non-grafted configuration due to competing flows. For some configurations (reduced blockage, graft placed close to long grafts), flow rates in the graft are below that of the flow rate through the stenosis. In general, a graft angled more towards the artery increased flow rates upstream of the graft. Placement and orientation of a graft may adversely affect upstream flow, with the degree of effect dependent on geometric factors of downstream position and graft angle.

CFD Simulation Study of Gas-Liquid Flow Regimes in Inclined Wellbore

Computational Fluid Dynamic (CFD) was used to investigate gas-liquid two phase flow regimes for the inclined wells. The simulation results were compared with the Taitel chart. A good agreement between the prediction and the Taitel flow regimes shows that CFD method can reasonably predict flow regimes in the inclined well. Another further study was conducted to explore the influence of flow rates and inclination angle on flow regimes. The results show both of flow rates and inclination angle have a significant effect on flow regime transition.

Flow disturbances in stent-related coronary evaginations: a computational fluid-dynamic simulation study

Angiographic ectasias and aneurysms in stented segments have been associated with late stent thrombosis. Using optical coherence tomography (OCT), some stented segments show coronary evaginations reminiscent of ectasias. The purpose of this study was to explore, using computational fluid-dynamic (CFD) simulations, whether OCT-detected coronary evaginations can induce local changes in blood flow. OCT-detected evaginations are defined as outward bulges in the luminal vessel contour between struts, with the depth of the bulge exceeding the actual strut thickness. Evaginations can be characterised cross-sectionally by depth and along the stented segment by total length. Assuming an ellipsoid shape, we modelled 3-D evaginations with different sizes by varying the depth from 0.2-1.0 mm, and the length from 1-9 mm. For the flow simulation we used average flow velocity data from non-diseased coronary arteries. The change in flow with varying evagination sizes was assessed using a particle tracing test where the particle transit time within the segment with evagination was compared with that of a control vessel. The presence of the evagination caused a delayed particle transit time which increased with the evagination size. The change in flow consisted locally of recirculation within the evagination, as well as flow deceleration due to a larger lumen - seen as a deflection of flow towards the evagination. CFD simulation of 3-D evaginations and blood flow suggests that evaginations affect flow locally, with a flow disturbance that increases with increasing evagination size.

Experimental, CFD simulation and parametric studies on modified solar chimney for building ventilation

The solar chimney is a passive solar system which can be used for enhance the natural ventilation and space conditioning of a building. A solar chimney design is modified and installed at CBRI Roorkee (29.87° N 77.88° E), India. A Computational fluid dynamics (CFD) software is used for prediction of velocity and temperature in Modified solar chimney (MSC) and evaluating the Air Change per hour (ACH), which is validated through experimental and theoretical counterpart and found a good agreement between them. From the result of thermal performance analysis, it is found that MSC generates 2.39–7.13 ACH in experimental room in month of May 2013, when outdoor solar radiation was in the range of 250–612 W/m2. Due to this ACH, the room temperature is dropped by 2–4°C as compared to reference room temperature. The parametric study shows that the optimum glass tilt angle estimated by 5 degree for highest performance consideration of MSC. The air gap is optimised by 60 mm and air gap to inlet opening height ratio is optimised by 0.2.

A CFD simulation study to evaluate the flow and catalytic hydrogenation of dimethyl oxalate in a packed bed, a two‐stage fluidized bed, and a circulating fluidized bed

ABSTRACTHydrogenation of dimethyl oxalate (DMO) can be operated in various reactors, such as the packed bed (PB), two‐stage fluidized bed (TSFB), and circulating fluidized bed (CFB) reactors. Fluid dynamic behaviors in these reactors are different and can lead to different transport and reaction behaviors. Recent advances in the computational fluid dynamics (CFD) technique show its great potential in advancing current understanding of fluid dynamics and its interactions with chemical reaction dynamics. In this study, CFD models for the simulations of flow and hydrogenation of Diethyl Oxalate (DEO) in PB, TSFB, and CFB reactors were developed. The CFD model for the PB reactor was validated using experimental data. The models were then used to predict flow and hydrogenation behaviors in the other two reactors. Various critical issues to be considered in choosing a reactor and how CFD modeling can be utilized to reduce uncertainties associated with this are discussed in details. The approach, models, and results presented here will be useful for understanding the complex flow dynamics and its interaction with the reaction dynamics of DMO hydrogenation in various types of reactors. © 2013 Curtin University of Technology and John Wiley & Sons, Ltd.

Particle image velocimetry studies on the swirling flow structure in the vortex gripper

In this article, particle image velocimetry was used to measure the two-dimensional flow field for vortex gripper. The vortex gripper was divided into two parts for respective research, including vortex cup and the gas film gap. In the part of vortex cup, the tangential velocity increases gradually, and the velocity decreases intensely in the vicinity of the vortex cup’s wall after it reaches maximum. In addition, the velocity decreases gradually with the increase of the gas film gap. In the part of gas film gap, the tangential velocity increases to maximum along the radial direction first; after the air flows into the gas film gap due to the viscous impedance, it decreases gradually. When the gas film gap’s thickness is smaller, the velocity almost decreases to zero at the external edge of the skirt. However, when the gas film gap increases to a certain thickness, the velocity does not decrease to zero, and the flow air still keeps a certain speed out of it. The velocity decreases gradually with the increase of the gas film gap. The radial velocity in the vortex cup and the gas film gap is of very small order of magnitude comparing with the average velocity and tangential velocity. The analysis of the Reynolds number shows that the flow in the vortex cup is the turbulent flow, and at the part of the gas film gap, the Reynolds number increases with the increase of the gas film gap, and the flow changes from the laminar flow to the turbulent flow. Through the particle image velocimetry experiment, the vortex gripper’s internal flow structure is studied. It is the theory support of the computational fluid dynamics simulation study for vortex gripper and the structure optimization in the future work.

Influence of hemodynamics on recanalization of totally occluded intracranial aneurysms: a patient-specific computational fluid dynamic simulation study

Some totally occluded intracranial aneurysms may recur. The role of hemodynamic mechanisms in this process remains to be elucidated. The authors used computational fluid dynamic analysis and investigated the local hemodynamic characteristics at the aneurysm neck before and after total embolization, attempting to identify hemodynamic risk factors leading to recurrence of totally embolized aneurysms. Between May 2008 and June 2010, the authors recruited 17 consecutive patients with totally occluded intracranial aneurysms (7 recanalized and 10 stable lesions). Using patient-specific 3D digital subtraction angiography data, the hemodynamic features before and after embolization were retrospectively characterized. The overall preembolization blood flow patterns were nearly the same in the recanalized and stable groups, with no significant difference in either the maximum wall shear stress (WSS) (p = 0.914) or the spatially averaged WSS (p = 0.322) at peak systole at the aneurysm neck. After occlusion, the overall flow pattern changed, and the WSS distribution at the treated aneurysm neck differed in the 2 groups. In all of the 7 recanalized cases, both the maximum WSS and spatially averaged WSS at peak systole at the treated aneurysm neck were higher than those at the aneurysm neck before embolization. In contrast, both parameters were decreased in 70%-80% of the stable cases. After embolization, both the maximum WSS (p = 0.021) and spatially averaged WSS (p = 0.041) at peak systole at the treated aneurysm neck were higher in the recanalized group than in the stable group. Higher WSS at the treated aneurysm neck after total embolization can be an important hemodynamic factor that contributes to aneurysm recurrence after endovascular treatment.

Experimental and CFD simulation studies of wall shear stress for different impeller configurations and MBR activated sludge

Membrane bioreactors (MBRs) have been used successfully in biological wastewater treatment for effective solids-liquid separation. However, a common problem encountered with MBR systems is fouling of the membrane resulting in frequent membrane cleaning and replacement which makes the system less appealing for full-scale applications. It has been widely demonstrated that the filtration performances in MBRs can be improved by understanding the shear stress over the membrane surface. Modern tools such as computational fluid dynamics (CFD) can be used to diagnose and understand the shear stress in an MBR. Nevertheless, proper experimental validation is required to validate CFD simulation. In this work experimental measurements of shear stress induced by impellers at a membrane surface were made with an electrochemical approach and the results were used to validate CFD simulations. As good results were obtained with the CFD model (<9% error), it was extrapolated to include the non-Newtonian behaviour of activated sludge.

A CFD Simulation Study of VOC and Formaldehyde Indoor Air Pollution Dispersion in an Apartment as Part of an Indoor Pollution Management Plan

This paper is a preliminary report of an indoor pollution case study in a complex of apartments as a part of an Indoor Pollution Management Plan (IPMP). It describes the calculation by Computational Fluid Dynamics (CFD) techniques and presents the predicted air flow, Volatile Organic Compounds (VOCs) and formaldehyde contaminant distributions in an apartment comprised of a full-scale kitchen with open access to a living room, ventilated by an exhaust hood. The CFD Code PHOENICS®, which is based on solving the full 3-D Navier Stokes equations for turbulent flow and scalar conservation equations, was used. Major kitchen indoor pollution sources, VOCs and formaldehyde emitting materials and their emission characteristics were calculated through the use of emission factors. A typical apartment was used under case study and its detailed geometry was applied for the CFD model. To analyze the characteristics of the indoor environment, different mixing ventilation schemes (different locations of the cooker/oven and air inlets) were chosen as the parameters to investigate the indoor environment. The fields of VOCs and formaldehyde for several air inlets window positions, and ventilation parameters were calculated and compared. It was concluded that CFD methods can be used as a useful tool to assist the rational design of indoor spaces.

Computational fluid dynamics simulation studies on pasteurization of egg in stationary and rotation modes

Abstract Eggs contain many nutritive compounds and are consumed all over the world. Pasteurization is an important unit operation for inactivation of pathogenic bacteria and is widely used for inactivation of Salmonella enteritidis. Experimental studies and computational fluid dynamics (CFD) simulations were performed on thermal pasteurization of egg at 55.6 °C. In this study, CFD simulation of temperature predictions was validated with experimental measurements of the temperature in the egg without yolk. After validation, a whole egg (with yolk) was simulated in CFD at two different modes namely stationary and rotation (at 2.5 and 5 rpm). These results revealed that the stationary egg took about 30 min to reach the pasteurization temperature, whereas, rotating egg needed only 9.5 min. This reduction in processing time minimizes the thermal damage of the egg's nutrients. Hence, rotation of egg made the thermal pasteurization process more efficient. Moreover, prediction of inactivation of S. enteritidis based on the process value F (min) also reinforced the positive effect of rotation during thermal pasteurization. Industrial Relevance In recent years, a rapid development in the application of CFD in food processing operations has been witnessed. The main need for CFD analysis of pasteurization is to determine the uniform and effective heat distribution in the egg and to examine the position of slowest heating zone (SHZ). Relatively few works have been published related to applications of CFD in thermal processing of egg. However, all the studies were performed for a stationary position of egg during thermal process. So far, no works have been published on the pasteurization of egg in a rotation mode. Hence, the present study was aimed at investigating the effects of pasteurization of egg at 55.6 °C on pasteurization time. Rotation mode of pasteurization decreases the time of pasteurization by a large extent and makes more energy efficient process. Hence, it is advantageous for food industries to adopt rotation as an additional operation during pasteurization of eggs to produce high quality intact eggs without affecting its functional properties.

Methane steam reforming in a microchannel reactor for GTL intensification: A computational fluid dynamics simulation study

The integration of the steam reforming and combustion of methane in a catalytic microchannel reactor has been simulated by computational fluid dynamics (CFD). Two models including 4 or 20 square microchannels of 20 mm of length and 0.7 mm of side have been developed. It has been assumed that a thin and homogeneous layer of an appropriate catalyst has been uniformly deposited onto the channels walls. The kinetics of the steam reforming of methane (SRM), water-gas shift (WGS) and methane combustion in air have been incorporated into the models. This has allowed simulating the effect of the gas streams space velocities, catalyst load, steam-to-carbon (S/C) ratio and flow arrangement on the microreformer performance. The results obtained illustrate the potential of microreactors for process intensification: complete combustion of methane is achieved at gas hourly space velocities (GHSV) as high as 130,000 h −1. As concerns the SRM, methane conversions above 97% can be obtained at high GHSV of 30,000 h −1 and temperatures of 900–950 °C. Under these conditions selectivity for syngas is controlled by the WGS equilibrium.

Integration of methanol steam reforming and combustion in a microchannel reactor for H 2 production: A CFD simulation study

A computational fluid dynamics (CFD) study of the thermal integration of the steam reforming of methanol (SRM) and the combustion of methanol in a catalytic microchannel reactor is presented. This issue is of interest for in situ H 2 production for portable power units based on low-temperature PEM fuel cells. Three-dimensional simulations have been carried out under relevant conditions for the SRM reaction that have shown that microreactors allow achieving complete methanol reforming and combustion at space velocities as high as 50,000 h −1, with selectivities for H 2 above 99% at relatively low temperatures in the 270–290 °C range.

Total Cavopulmonary Connection Flow With Functional Left Pulmonary Artery Stenosis

In our multicenter study of the total cavopulmonary connection (TCPC), a cohort of patients with long-segment left pulmonary artery (LPA) stenosis was observed (35%). The clinically recognized detrimental effects of LPA stenosis motivated a computational fluid dynamic simulation study within 3-dimensional patient-specific and idealized TCPC pathways. The goal of this study was to quantify and evaluate the hemodynamic impact of LPA stenosis and to judge interventional strategies aimed at treating it. Simulations were conducted at equal vascular lung resistance, modeling both discrete stenosis (DS) and diffuse long-segment hypoplasia with varying degrees of obstruction (0% to 80%). Models having fenestrations of 2 to 6 mm and atrium pressures of 4 to 14 mm Hg were explored. A patient-specific, extracardiac TCPC with 85% DS was studied in its original configuration and after virtual surgery that dilated the LPA to 0% stenosis in the computer medium. Performance indices improved exponentially (R2>0.99) with decreasing obstruction. Diffuse long-segment hypoplasia was approximately 50% more severe with regard to lung perfusion and cardiac energy loss than DS. Virtual angioplasty performed on the 3-dimensional Fontan anatomy exhibiting an 85% DS stenosis produced a 61% increase in left lung perfusion and a 50% decrease in cardiac energy dissipation. After 4-mm fenestration, TCPC baffle pressure dropped by approximately 10% and left lung perfusion decreased by approximately 8% compared with the 80% DS case. DS <60% and diffuse long-segment hypoplasia <40% could be considered tolerable because both resulted in only a 12% decrease in left lung perfusion. In contrast to angioplasty, a fenestration (right-to-left shunt) reduced TCPC pressure at the cost of decreased left and right lung perfusion. These results suggest that pre-Fontan computational fluid dynamic simulation may be valuable for determining both the hemodynamic significance of LPA stenosis and the potential benefits of intervention.

Integrated CFD simulation of concentration polarization in narrow membrane channel

Numerous analyses on the mass transfer phenomena and hydrodynamics for the fluid adjacent to the membrane have been studied and visualized by computational fluid dynamics (CFD) mathematical modeling and simulation. The availability of CFD simulation study to reveal the concentration polarization profile in the membrane channel, which considering hydrodynamics and membrane transport properties is found to be limited. The main goal of this paper is targeted to the utilization of CFD simulation using commercial CFD package FLUENT to predict the concentration polarization profile, mass transfer coefficient and wall shear stress under different types of conditions in the empty narrow membrane channel. The permeation conditions such as permeation flux and mass fraction have been taken into account in the solution of the governing equations. Simulation results show that the concentration polarization phenomena can be reduced by increasing feed Reynolds number. The decrease of wall shear stress also contributes to the formation of the concentration polarization layer along the membrane surface. The simulated results were validated and compared with the literature data, showing a satisfactory agreement.