sajadollah rezazadeh

This article presents a comprehensive approach to enhance heat transfer rates in a 3D channel using Ferrofluids. The study investigates the individual and combined impacts of rectangular winglet vortex generators and magnetic fields on flow characteristics, heat transfer enhancement, and entropy generation. Numerical solutions are derived for the governing partial differential equations using the finite volume technique and the SIMPLE algorithm. The investigation assesses the influence of key parameters, including the type of rectangular winglet vortex generator (simple, concave, and convex), Reynolds number, and magnetic field strength. Optimal operational conditions are identified based on thermodynamics' first and second laws. This study has been conducted in three steps, and the interaction of created vortices and their effect on heat transfer, pressure drop, and entropy production were investigated. In the first step, the effect of the vortex generator in different Reynolds has been investigated. In the next step, the impact of applying a magnetic field at different intensities by a current-carrying wire has been studied in a channel without vortex generators. Finally, the application of vortex generators and magnetic fields has been investigated simultaneously. The results showed that using the concave vortex generator in the absence of a magnetic field increased the heat transfer by 50% and pressure drop by 60%. Applying a magnetic field in the channel without vortex generators has increased heat transfer and pressure drop by 70% and 118%, respectively. Moreover, it is observed that the magnetic field induces a greater pressure drop penalty than the vortex generator for achieving the same heat transfer augmentation. The simultaneous application of magnetic field and vortex generator has also increased the heat transfer and pressure drop by 200% and 269%, respectively, for simple vortex generators.

Numerical study of turbulent and laminar flow is investigated for an incompressible nanofluid flow in a 2D wavy channel by using the finite volume method (FVM). The results of the Nusselt number, pressure drop, and thermal performance has obtained for diameter ratios (a/b=0, 0.25, 0.5, 0.75, 1), volume concentration(FI = 0%, 2%, 4%) and nanoparticle diameters in four Reynolds number(Re=10000, 20000, 30000, 40000). The validation was compared with analytical and numerical studies. The results shown a good convergence between them . The results showed that using wavy parts caused to increasing in heat transfer rate and pressure drop by 1.78 and 8.1 times respectively. Additionally, augmentation of the volume concentration increased the heat transfer rate and pressure drop by 2.1 and 3 times respectively. The use of laminar flow also had a higher heat transfer rate, pressure drop and, thermal performance compared to turbulent flow within the Reynolds 1000 range.

Mixing different or identical fluids together plays an important role in many microstructures, so it is important to study the quality of mixing in microchannels. Numerical study of oxygen and nitrogen mixing in passive three-dimensional micromixer was performed by finite element method and the effect of Reynolds number, type, number and width of mixing units and obstruction in the flow path on mixing quality and pressure drop was investigated. While most previous studies have been on the mixing of liquids, in this study the mixing of gases in simple micromixers, as well as micromixers with mixing units, has been investigated. For this purpose, two new types of micromixers named A and B with new and multiple mixing units have been introduced. Mass performance evaluation of the new model's A and B with helical mixing units, compared to the base model without the mixing unit shows that the new models have a higher performance than the base model as micromixer A with five mixing units, in Reynolds 110, compared to the base model. Improves mixing quality 2 times and 1.25 times better than Model B. Also, the effect of the depth of cubic barriers in micromixer B with five mixing units indicates the improvement of mixing quality compared to the unobstructed model in higher Reynolds. As in Reynolds 110 model B with five mixing units, the mixing quality is about 95%.

In this paper, the fin profile of heat exchangers change effect on the heat transfer and fluid flow pattern has been investigated. In order to best model presentation to the user by comparing the various models results. For numerical simulation and discretization of governing equations, the finite volume method and for coupling the velocity and pressure fields, the SIMPLEC method have been used. The inlet fluid to heat exchanger is Newtonian; the fluid is steady, incompressible and according to Reynolds number range, is turbulent; the no-slip condition has been applied on the walls.Also the inlet fluid temperature is 573K and the heat exchanger walls have constant temperature equal to 353K. The numerical results have been compared with valid data which illustrated good agreement. The average Nusselt number on the wall, pressure drop, output temperature, and velocity variation have been analyzed in different models with more details for two mass flow rates. The results show that the heat exchanger with 6 fins and m ̇=0.04 kg⁄s has best performance and presented the high nusselt and PI and also low pressure drop.

In this study a two-dimensional (2D) numerical simulation using two-phase level set method (LSM) have been carried out to investigate the influence of continuous phase entrance flow rate on the microdroplets generation process. The analysis of the breakup process of microdroplets in immiscible liquid/liquid two-phase flow in T-junction microchannel has been predicted. Governing equations on the flow field have been discretized and solved by using finite element method. Obtained numerical results have been validated by comparing the experimental data reported in literature which show acceptable agreement. The simulation results show that the continuous phase entrance flow rate has a major effect on the size of generated droplets. Studies have shown that pressure diagram of the junction point can reflect the number of formed droplets and the triple stages of droplet formation. Also, Examinations of the pressure and velocity gradient inside the main channel show that the pressure difference of the droplet’s tip and rear and shear force caused by viscosity dominates the droplet formation which the pressure difference between two side of droplet is more effective.

In the present work, a Proton-Exchange Membrane Fuel Cell (PEMFC) as a three-dimensional and single phase was studied. Computational fluid dynamics and finite volume technique were employed to discretize and solve a single set of flow fields and electricity governing equations. The obtained numerical results were validated with valid data in the literature and good agreement was observed between them. The main purpose of this paper is to investigate the effect of deformation of the geometric structure of a conventional cubic fuel cell into a cylindrical one. For this purpose, some important parameters indicating the operation of the fuel cell such as oxygen distribution, water, hydrogen, proton conductivity of the membrane, electric current density, and temperature distribution for two voltage differences between the anode and cathode and the proposed models were studied in detail. Numerical results showed that in the difference of voltages studied, the proposed new model had better performance than the conventional model and had a higher current density, in which at V = 0.4 [V], about a 10.35 % increase in the amount of electric current density was observed and the average increment in generated power was about 8 %, which could be a considerable value in a stack of cells. Finally, the discussion of critical parameters for both models was presented in more detail. The core idea of the results is that the Oxygen and Hydrogen utilization, water creation, and heat generation are greater in the new model.