The ongoing miniaturization of electronic devices imposes design limitations on the placement of cooling fans in active heat sinks. This work investigates thermal and hydrodynamic performance in different flow configurations of impinging, parallel, and induced flow for three distinct heat sinks, including plate-fin, metal foam, and hybrid. Numerical modeling of the flow field with computational fluid dynamics employed the local thermal non-equilibrium (LTNE) approach and the standard k-ε model for heat transfer and turbulence. The results indicate that flow directionality significantly influences both heat transfer and pressure characteristics. Specifically, the Nusselt number increased by 62.86% and 46.51% for the plate-fin, 35.6% and 37.6% for the metal foam, and 42.59% and 31.17% for the hybrid model under induced and impinging flow conditions, respectively, when compared to parallel flow. Impinging flow resulted in the highest pressure drop in all cases, whereas parallel flow exhibited the lowest pressure drop. Evaluation based on the Figure of Merit (FOM) revealed that impinging flow significantly degraded overall performance, reducing FOM by 40.44% (plate-fin), 36.7% (metal foam), and 41.51% (hybrid). In contrast, induced flow consistently improved thermo-hydraulic efficiency, increasing the FOM by 17.38%, 15.95%, and 76.6%, respectively. Overall, the comparative analysis highlights that flow directionality plays a decisive role in determining the balance between heat transfer enhancement and hydraulic penalty in compact heat sink systems. While impinging flow promotes strong local convection, the associated pressure drop can compromise overall efficiency. In contrast, induced flow provides a more favorable trade-off between thermal improvement and pumping power requirements, particularly in hybrid configurations. These findings offer practical design guidance for airflow arrangement in space-constrained electronic cooling applications and emphasize the importance of simultaneously evaluating thermal and hydraulic metrics when selecting optimal heat sink configurations.

Maintaining optimal air quality in cleanrooms is critical for contamination control in sensitive industries, such as pharmaceuticals, electronics, and healthcare. Among the factors affecting cleanroom integrity, door movement plays a significant role in disturbing airflow and enabling contaminant intrusion. This study analyzed the hinged door motion effect on airflow dynamics and particle distribution employing computational fluid dynamics, discrete phase method and dynamic mesh approach. A novel index was proposed to quantitatively assess contamination transfer under varying operational scenarios. The simulation setup modeled a cleanroom connected to an airlock, with door opening and closing speeds ranging from π/8 to π/4 rad/s. Obtained numerical results were verified with literature experimental data to ensure the accuracy of the velocity field and particle concentration. The findings reveal that both the door speed and direction substantially influence contaminant transport. Based on these results, this study suggests optimal door operation strategies to minimize contamination risks, offering practical guidance for improved cleanroom design and protocols. A variable-speed door operation opening slowly and closing at twice the opening speed was shown to reduce the contaminant levels by 21%. Additionally, a new parameter, Normalized Particle Exposure Index (NPEI), was introduced to quantify contamination persistence, revealing that phased door movement improved performance by 17% compared to a 3-second opening and by 15% compared to a 2-second opening.

A numerical erosion study was performed using Computational Fluid Dynamics (CFD) integrated with a Discrete Phase Model (DPM) on a standard 90 degrees elbow, branch pipe elbow, and the effects of using a butterfly valve and orifice to control the flow. The butterfly control valve was studied at 20 degrees, 40 degrees, 60 degrees, and 80 degrees rotation angles around its axis, as well as at an orifice with a hole plate diameter of 20 %, 40 %, 60 %, and 80 % of the pipe diameter. In this study, the Euler-Lagrange approach was used to model two-phase flow with one-way coupling. After the fluid phase and non-spherical solid particles entered the pipe, the geometry erosion was calculated using the confirmed particle restitution model and erosion model. The numerical results showed that the branching pipe passes 30.9 % of the flow through the branching part, which reduces elbow erosion by 4.7 %. For this purpose, the use of the control valve and the orifice before the elbow increases the passage of the maximum two-phase flow of gas-particles up to 89.7 % and 96.4 %, respectively, in the branching path of the straight pipe. This leads to less impact of particles on the wall of the elbow compared to the complete passage of the flow in the path of the elbow. Therefore, the erosion damage in the elbow part of the branch pipe with 4 cases of the butterfly control valve is 61.1 %, 56.2 %, 24.7 %, and 4.5 % and the branch pipe with orifice 4 cases is 64.8 %, 54.9 %, 46.4 %, and 19.9 % compared to the normal state is reduced, which led to the improvement and replacement of the branching straight pipe path with only the elbow path.

The rise in power density and the shrinking size of electronic components have made efficient thermal management an essential aspect of design. Present study uniquely explores the thermal and hydraulic performance of three different heat sink designs: plate-fin, porous metal foam, and hybrid of finned metal foam, using both experimental and numerical methods under the same impingement cooling conditions. The innovation of this study is its thorough evaluation of these designs using the Local Thermal Non-Equilibrium (LTNE) method to precisely simulate heat transfer within porous materials. Key metrics such as Nusselt number, and pressure drop were assessed. The findings reveal that both porous and hybrid heat sinks surpass the traditional plate-fin design, with the hybrid model showing the highest thermal efficiency due to its larger effective surface area and improved flow disruption. Experimental results indicate that utilizing a hybrid heat sink and metal foam at an input power of 30 W increases the average Nusselt number by 35.82 % and 24.79 %, respectively, compared to the plate-fin heat sink, which, according to the numerical results, these values are 34.76 % and 20.65 %, respectively. These results provide valuable insights for designing advanced thermal management systems for compact electronic devices. The Figure of Merit (FOM) is determined by simultaneously considering both thermal and hydraulic performance. the average FOM for the hybrid and metal foam heat sinks increases by 32.62 % and 19.47 %, respectively, relative to the plate-fin configuration. An increase in the Nusselt number and enhancement of the FOM in heat sinks lead to improved heat transfer efficiency and better protection of electronic components against thermal stress. The effects of input power, interfacial area density, and interfacial heat transfer coefficient are also examined.

Gas–particle flow in a spouted fluidized bed with rectangular geometry and pulsed inflow was numerically studied using a coupled CFD–DEM approach. The study investigated pulsed spouting at frequencies of 1, 4, and 10 Hz under different combinations of spout and background gas velocities. When background gas was present, pulsed inlet flow effectively reduced dead zones and improved particle circulation across all frequencies. At 10 Hz, the spouted fluidized bed showed a 12.81% increase in particle travel distance and a 55% reduction in dead zones. On the other hand, the removal of background gas created a poor performance with dead zones increasing from 0.5% to 7.7% of the particles. The effect of varying inlet velocity ratios of gases was also studied and revealed that appropriate gas distribution could improve the bed performance. The results generally demonstrate that pulsed flow in combination with suitable inlet velocity distribution is capable of improving the hydrodynamics of spouted fluidized beds without altering any geometry or total flow rate.

This study aims to determine the effect of a square cyclone body shape on the performance of a square cyclone separator. To achieve this goal, four square cyclone separators with square lengths 0, 1, 2, and 3 times the hydraulic diameter of the cyclone body were considered. The simulation of the gas-solid flow was carried out using the Euler-Lagrange approach, while the gas flow was modeled by Navier-Stokes equations and the Reynolds stress turbulent model (RSTM), and the injected solid particle was solved using the Newton equation. The pressure drop, separation efficiency, and flow pattern were investigated to evaluate the performance of square cyclone separators. The results revealed that the pressure drop and separation efficiency decreased as the relative square length increased. In the case with a lower relative square length, the vortex core penetration is less than that in the other cases, which leads to a decrease in the entrainment phenomena and separation efficiency enhancement. At an inlet velocity of 16 m/s, an increase in the relative square length from 0 to 3 reduced the pressure drop by approximately 35%. At an inlet velocity of 24 m/s and a particle diameter of 8 & mu;m, with an increase in the relative square length from 0 to 3, the efficiency decreased from 88.7 to 77.4%.

This paper examines and compares two different block geometries to fit in the oxygen channel. A fuel cell is a device that produces electricity from the chemical energy resulting from the reaction of hydrogen with oxygen. This type of energy has been of interest to researchers due to its cleanliness. It was determined that a block is a useful tool placed in the path of oxygen flow in a fuel cell. By diverting the oxygen fluid flow towards the membrane and gas diffusion layers, it increases the contact surface between the two oxygen and hydrogen fluids in a fuel cell. Computational fluid dynamics method was used to investigate the performance of these channels. This method is based on predicting the behavior of fluids by solving equations governing them using a computer. The modeling and analysis stages of these channels are explained. In this study, blocks were designed in two forms, rectangular and triangular blocks. The triangular block is actually a rectangular cube that has been cut along the diagonal of its cross-sectional area.

In this study, a realistic model of the respiratory tract obtained from CT medical images was used to solve the flow field and particle motion using the Eulerian-Lagrangian approach to obtain the maximum particle deposition in the bronchial tree for the main purpose of optimizing the performance of drug delivery devices. The effects of different parameters, including particle diameter, particle shape factor, and air velocity, on the airflow field and particle deposition pattern in different zones of the lung were investigated. In addition, a genetic algorithm was employed to obtain the maximum particle deposition in the bronchial tree and the effect of the aforementioned parameters on particle deposition. Reverse flow, vortex formation, and laryngeal jet all affect the airflow structure and particle deposition pattern. The mouth-throat region had the highest deposition fraction at various flow rates. A change in the deposition pattern with an increased deposition fraction in the throat was observed owing to the increased diameter and shape factor of the particles, resulting from the higher inertia and drag force, respectively. The particle deposition analysis showed that three parameters, shape factor, diameter, and velocity, are directly related to particle deposition, and the diameter is the most effective parameter for particle deposition, with an effect of 60% compared to the shape factor and velocity. Finally, the prediction of the genetic algorithm reported a maximum particle deposition in the bronchial tree of 17%, whereas, based on the numerical results, the maximum particle deposition was reported to be 16%. Therefore, there is a 1% difference between the prediction of the genetic algorithm and the numerical results, which indicates the high accuracy of the prediction of the genetic algorithm.

This study was conducted with the aim of replacing different geometric fittings instead of the standard 90 degrees elbow and trying to change the flow pattern to reduce erosion damage. Among fittings, the elbows are at a more serious risk. Numerical investigation of the present erosion with the novelty of research on non-spherical particles and changes in the impact angle of particles along with fluid flow using eight new proposed fittings, including two miter fittings, three blinded fittings, one reducer elbow fitting, and two spherical elbows fittings in comparison with the standard 90 degrees elbow was controlled. The numerical simulation of the gas-solid two-phase flow of nonspherical particles was studied using the Euler-Lagrange approach. To carry out the study numerical, first, the gas flow was modeled by the Navier-Stokes equations and the turbulent Reynolds stress model, and then the solid particles were injected using Newton's equation. Finally, the erosion was calculated using Grant and Tabakoff model of the restitution of particles of after hitting the wall and the erosion model of Oka. The amount of erosion caused by changes in the flow pattern was investigated to evaluate the performance of the new proposed fittings. Numerical results for the most critical mode (Vin = 27 m/s and DP = 300 mu m) showed that the new proposed fittings increase the erosion resistance by 22.5 % to 39.6 % compared to the standard 90 degrees elbow. Also, in this research, the effect of different parameters including flow velocity, particle diameter size, particle input rate, and particle rotation on erosion were investigated.

This study aims to analyze two-phase flow patterns of water and air in a vertical column using experimental tests, and investigate the effect of pulsed gas flow on the characteristics of the Taylor bubble under different inlet conditions. First, three patterns of bubble, slug, and churn were observed with above hundred tests and a flow patterns map was drawn. Then, the effect of the pulsed gas flow on the length of the Taylor bubble was investigated in 150 different experiments. The ranges of superficial velocity of liquid and gas phases were 0.12–0.28 m/s and 0.05–0.25 m/s, respectively. The frequency of pulsed gas feed was 0.25–4 Hz. The results of this study showed that the length of the Taylor bubble in pulsed gas feed decreases with increasing the frequency. In addition, at a fixed gas frequency, the bubble length increases with increasing gas velocity. Present study prove that the pulsed gas flow technique can reduce the length of Taylor bubbles, which will be useful for future industrial applications in two-phase gas-liquid columns.

The motion effect on the contaminant dispersion is a key parameter in cleanrooms. This parameter is ignored in many experimental and numerical studies because of its complexities but could cause errors in the obtained results. In real situations, particularly in isolating rooms and cleanrooms, the motion that is usually caused by the human moving and doors opening and closing leads to considerable flow changes that require attention. The present study aimed to explore studies that noticed and studied different aspects of the subject and to summarize the areas with priority for further investigation. Modeling the problem using experimental and numerical approaches requires steps and settings that are described in the experimental and numerical sections. The motion analysis is divided into two sections of human and door motions, covering the key findings of previous and recent publications, and concluding the required future studies. The results of approximately fifty published studies have revealed important findings related to cleanroom class degradation, temperature gradient reduction, increased contamination and secondary flow depth, and particle settlement in patients. These studies have shown that the ventilation system may need to be redesigned. Furthermore, it is crucial to consider the motion in both experimental and numerical studies based on the application. Additional research is necessary to further understand these findings.

This research paper delves into the analysis and comparison of two distinct geometries that can be employed to accommodate blocks in the oxygen channel. A fuel cell is an apparatus that generates electricity through the chemical reaction between hydrogen and oxygen, and this form of energy has garnered significant interest from scientists due to its eco-friendliness. The research team discovered that blocks can be strategically placed in the path of oxygen flow within a fuel cell to enhance its performance. By directing the oxygen fluid towards the membrane and gas diffusion layers, the contact surface between the hydrogen and oxygen fluids is augmented. The computational fluid dynamics technique was utilized to evaluate the efficacy of these channels. This approach relies on predicting fluid behavior by solving equations governing them using a computer. The study outlines the modeling and analysis stages of these channels. The team designed blocks in two different quantities, namely three blocks and ten blocks, with each block being triangular in shape.

In this study, an additional inlet was added to the gas-solid cyclone separator to enhance the separation efficiency. Four different heights were tested, including 0.95D, 1.4D, 1.5D, and 1.95D (D is the diameter of the cylindrical section). The investigation involved two inlet flow conditions: increasing and dividing the inlet flow rate. The finite volume method and Reynolds stress turbulence model were used to solve the averaged Navier-Stokes equations, whereas the Eulerian-Lagrangian approach and discrete phase model (DPM) were applied to track particles with a uniform diameter of 0.5-1.8 microns as the discrete phase. Owing to the low Stokes number and small and low-volume-fraction particles, a one-way coupling method was employed between air and the particles. The addition of an additional inlet reduced the static pressure in the center and downstream areas and increased the reverse flow velocity at the end of the cyclone. The installation of an additional inlet at 0.95D had the most positive effect on the separation efficiency, with an increase of 28.8% in the increasing flow rate case and 19.6% in the dividing flow rate case compared with the cyclone without an additional inlet. Furthermore, the increase in the separation efficiency of the submicron particles was greater than that of the larger particles in both flow distribution cases.

This paper explores the effect of curved shape fin heights on open microchannel heat sink performance. Different geometries of rectangular, plano-convex, and plano-concave fins have been investigated by employing three-dimensional simulation. A variety of parameters including fin height, curve range coefficient, Reynolds num-ber, and heat flux have been examined. At the same heat flux, Reynolds number, and fin height, the Nusselt number of the rectangular fin is lower than the two shapes of plano-convex and plano-concave. In Comparison of the two curved shapes, due to their geometries and fluid flow behavior, in the lower fin heights, the Nusselt number of the plano-concave is greater than the plano-convex. In the higher fin heights, the Nusselt number of the plano-convex is greater than the plano-concave. Even though at higher fins, where the Nusselt number of the plano-convex fins is greater than the rectangular and plano-concave shape, the plano-convex pressure drop is less than these two shapes. In a heat flux of 450 kW/m2, Reynolds number of 600, and a fins equivalent height of 0.6 mm, that the volume and mass of the fins are the same, there is an 18% difference between the maximum and minimum Nusselt number of plano-convex and plano-concave, by different curve coefficients. The obtained results are beneficial in designing novel shape fins in enhanced open microchannel heat sinks.

A numerical study on the flow field and particle mixing behavior in spouted beds with the aim of considering different base shapes was carried out using CFD-DEM modeling. Four spouted beds with different base angles of 180, 120, 90 and 60 degrees were compared. In order to have a qualitative and quantitative analysis on the mixing behavior, particle tracing and Lacey mixing index calculation were executed for the models. Rectangular spouted beds generate dead-zones in the corners of the system that causes less ultimate mixing index value. As the base angle decreases, the mixing index tends to increase. A mixing degree of the case with 180 degrees base angle reaches no more than 79% at the end of the simulation, which is the lowest, whereas a mixing degree of the 60 degrees base angle reaches the maximum value of 97%, which is the highest. Particle tracing conducted in these models indicates that this matter is due to the observed fact that with more incline of the base walls, particles slip more into the spout, thus entering the circulating flow. The results also indicate this increase in the slope has almost no effect on the rate which the mixing index reaches its maximum value.

In this study, the influence of a vortex finder shape with different hydraulic diameters on the pressure drop, flow pattern, and separation efficiency of a square cyclone separator was analyzed using Computational Fluid Dynamics (CFD). The considered vortex finders included square and cylindrical shapes with hydraulic diameters of 0.25, 0.5, and 0.75 times the square part hydraulic diameter of the cyclone separator. In this study, the Euler-Lagrange approach was applied to model two-phase flow inside square cyclone separators. The results demonstrated that the use of a cylindrical vortex finder increased the pressure drop and separation efficiency. Moreover, as the relative hydraulic diameter changed from 0.5 to 0.25, the pressure drop increased ten-fold, and the separation efficiency increased from 34.2 % to 83.1 % at an inlet velocity of 20 m/s and a particle diameter of 8 mu m. In the cyclone separator with De/D= 0.75, employing the square vortex finder led to a decrease in the separation efficiency and an increase in the pressure drop compared to the cylindrical vortex finder because of dividing the inlet flow into two branches. (c) 2023 Institution of Chemical Engineers. Published by Elsevier Ltd. All rights reserved.

The main purpose of the present numerical study is to evaluate the influences of aneurysm geometric features on the hemodynamic conditions within the left coronary arteries (LCA). Simulations have been conducted in two major parts: Section (I) encompassing three different cases (case 1, case 2, and case 3), in which three various sizes of the bifurcation region ( V/V_0=1 , V/V_0=0.8 , and V/V_0=0.6 ) were considered for each case, and Section (II) also consists of three distinct cases (case 4, case 5, and case 6) which two different positions (P1 and P2; proximal and distal to the main bifurcation, respectively) were taken into account for a fusiform aneurysm located on their left circumflex branch. Prediction and assessment of the correlation between morphological characteristics of an aneurysm with atherosclerosis and thrombosis were performed using quantitative and qualitative results including streamline and velocity contours, wall shear stress, oscillatory shear index, and relative residence time. Depending on the various cases, the time-averaged wall shear stress (TAWSS) of the bifurcation region for models of V/V_0=1 was nearly 18–24 V/V_0=0.8 , and around 74–81

A comprehensive study using computational fluid dynamics integrated with discrete element method was carried out on spouted beds with different geometries to investigate effects of employing secondary jet inlets with lateral injection to eliminate particle accumulation. Spouted beds with various base angles of 180, 120, 90 and 60 degrees were modelled and studied. In order to quantify the influences of utilizing secondary jet inlets, the hydrodynamics including particle flux, bed circulation time, air volume fraction and active particles in the cyclic flow were analyzed. Plus, qualitative and quantitative analysis on mixing characteristics of the beds was executed. Results indicated that addition of jets decreases the air volume fraction in the spout channel by a significant margin and therefore, more solids mass flow rate in the spout. This ensues a reduction in the bed circulation time and a promotion in the particle flux. Mixing characteristics were also developed in all geometries and the maximum value of mixing was intensified in higher velocity of the lateral aeration.

This work studies the effect of cardiac function parameters on ventricular flow pattern in a stenosed mitral.A three-dimensional simulation is performed employing dynamic mesh based on a geometry and valve flow rates extracted from medical images. Different mitral areas from 6 to 2 cm2 then different parameters for stenosed 2 cm2 case are investigated. Special attention has been drawn to compare wall shear stress, blood velocity and pressure distribution, while the power used by ventricle and atrium to pump the blood are also highlighted. Computing the power used by the heart walls to move the blood shows that the stenosed mitral increases the needed force and the energy for the blood flow suction during the early diastole (from 0.06 W for mitral area of 6 cm2 to 1.28 W for mitral area of 2 cm2). For the stenosed mitral area of 2 cm2, in the systole, decreasing the ejection fraction to half decreased the maximum ventricle power to around half. In the diastole, decreasing the E/A which is the ratio of early diastole (E wave) and late diastole (A wave) ratio from 4.8 to 1 decreased the maximum ventricle power to one-third. The numerical results confirmed that the compensation mechanism to afford the pumping power could be changing the E/A ratio which leads to enlarged atrium.