Natural convection heat transfer of water/Ag nanofluid inside an elliptical enclosure with different attack angles Seyed Alireza Rozati, Farnaz Montazerifar, Omid Ali Akbari, Siamak Hoseinzadeh, Vahid Nikkhah, Ali Marzban, Hadi Abdolvand, Marjan Goodarzi Mathematical Methods in the Applied Sciences, 2026 In this presentation, flow physics and natural heat transfer of water/Ag nanofluid are implemented by utilizing finite volume method (FVM) considering 0–6% of solid nanoparticles in volume fraction in an elliptical‐shaped enclosure affected by different attack angles range from 45° to 135°. This survey's foremost objective is to find the optimum attack angle for the highest heat transfer performance in the studied geometry. The attained results demonstrated that the Rayleigh number's augmentation leads to buoyancy force amplification and intensification of velocity components in the enclosure. Hence, the shapes of streamlines for each attack angle are different from the other states. The enhancement of the Rayleigh number causes better temperature distribution between cold and hot sources. The attack angle changes are the other factor for creating and intensity of the temperature gradients. By increasing the attack angle when the heat is transferred from the hot source to the top of the enclosure, the thermal distribution effects come with high gradients due to the flow balance disturbance and the changes in two sources' location. As the fluid moves, velocity components always change. In Rayleigh number of Ra = 1 × 10 3 due to a decrease of buoyancy force and negligible density changes in the enclosure, the average friction coefficient (C fave ) is not considerable, and for everyone studied attack angles, these changes are negligible. By augmenting attack angle (attack angles of 90° and 135°), because the tangential velocity component is weakened by gravity force, the values of created surface stress and fluid adhesion to the hot surface are less.
“Multi-optimization of nanofluid and fractal fin in the plate heat exchanger using RSM and TOPSIS” Farnaz Montazerifar, Omid Ali Akbari, Seyed Morteza Javadpour Energy Conversion and Management X, 2026 • A novel heat exchanger design integrating fractal fins and Oil/MWCNT nanofluids is optimized for superior thermal–hydraulic performance. • Multi-objective optimization reveals a Pareto-optimal solution that increases the Nusselt number by 50% and the Colburn coefficient by 260%, while simultaneously reducing pumping power by 93%. • The fin attack angle is identified as a dominant geometric parameter, with a critical threshold of 60 degrees for significant heat transfer enhancement. • A synergistic effect is demonstrated: combining a high attack angle with a 4% nanoparticle concentration boosts heat transfer performance by up to 60%. This study employs a three-step methodology to conduct a multi-objective optimization of a novel three-stream plate-fin heat exchanger design. The analysis evaluates the thermal performance of the system across attack angles of 30°, 60°, and 100° while integrating an Oil/multi-walled carbon nanotube (MWCNT) nanofluid to enhance heat transfer efficiency. Numerical simulations are conducted using the finite volume method (FVM) to analyze the thermal-fluid performance of a three-layer heat exchanger incorporating fractal fins in its mid-layer. The study spans Reynolds numbers ranging from 10,000 to 40,000, with the pressure–velocity coupling resolved via the SIMPLE algorithm. Subsequently, a multi-objective optimization framework is implemented, combining the Non-dominated Sorting Genetic Algorithm (NSGA-II) with the Technique for Order Preference by Similarity to Ideal Solution (TOPSIS) for Pareto-front analysis and optimal design selection. The results of this research show that the fractal fin attack corner increases cause more flow deviation from the direct route and better fluid mixing arising from collisions to the internal surfaces of the exchanger. With the flow velocity increase, the thermal boundary layer forms and disappears by collision with the fin surfaces. The temperature distribution is more uniform in the exchanger due to the flow collision with the fractal fins, which have more attack corners. A Reynolds number of 40,000 can improve the heat transfer on average to about 63 percent. Also, adding volume fractions of solid particles to a similar Reynolds number for different attack corners can increase heat transfer by about 48 percent. An increase of the fractal fin’s attack angle to 100 degrees increases the amount of pumping power to about 50 percent in comparison to the fin with a 30-degree attack corner. The fractal fins attack corner increases to 100 degrees, increasing the coefficient of friction to about 45 to 85 percent in comparison to the lower attack corner. The Colburn factor exhibited limited sensitivity to variations in angular orientation and nanoparticle concentration. However, it demonstrated a significant nonlinear decrease of about 1.2 times as the Reynolds number increased to 11,000. In the multi-objective optimization analysis, significant enhancements were observed in the Nusselt number and the Colburn coefficient, which increased by approximately 50 % and 260 %, respectively, compared to the initial state. Conversely, the pumping power was sharply reduced by 93 %, while the Friction factor saw a 43 % increase.
Numerical simulation of laminar and two-phase flow and heat transfer of water-aluminum oxide nanofluid in microchannel with V-shaped ribs Ali Koveiti, Ali B.M. Ali, Sabah F.H. Alhamdi, Omid Ali Akbari, Gholamreza Ahmadi, Soheil Salahshour, Sh. Baghaei Results in Engineering, 2025 • A rectangular microchannel equipped with V-shaped ribs at the bottom, filled with a solid-liquid suspension of water-aluminum oxide, is evaluated. • The two-phase mixture method is used to simulate the incompressible water-aluminum oxide nanofluid. • Fluid in the areas after the ribs has reverse velocity gradients and by increasing α , the wake area increases. • By increasing α , the vortices and velocity gradients separated from the ribs’ surfaces penetrate the central core of the flow. • In the ribbed region and for α =40° to α =50°, the changes in local Nusselt number are similar. In this study, a rectangular microchannel equipped with V-shaped ribs at the bottom filled with a solid-liquid suspension of water-aluminum oxide is evaluated. To better estimate the movement of solid-liquid phases, the two-phase mixture method simulates the incompressible water-aluminum oxide nanofluid (NF). The results are obtained for different hydrodynamic and heat transfer values and volume fraction of solid nanoparticles (φ) = 0, 2, and 4% and Reynolds number (Re) = 400-1200. The finite volume method (FVM) in three-dimensional (3D) space is used for simulations. The results show that the fluid in the areas after the ribs has reverse velocity gradients and by increasing α, the wake area increases. By increasing α, the vortices and velocity gradients separated from the ribs’ surfaces penetrate the central core of the flow. At α = 50°, because the fluid collides with the ribs, it is associated with a greater velocity drop and the creation of stronger vortices, so C f has the highest value. In the ribbed region and for α = 40° to α = 50°, the changes in local Nusselt number are similar. By increasing φ, the penetration of fluid to the back of the ribs becomes possible; In these diagrams, the minimum amount of S gen is for α = 40° and 50°. In general, the behavior of S gen is the same as the growth of dimensionless temperature, and at Re= 400, the maximum amount of S gen is related to α = 20°.
Optimization of the flow guiding fins configuration and tube arrangements in a shell and tube heat exchanger: Coupling response surface methodology and CFD Xiangmin Shao, Ali Marzban, Farzad Pourfattah, Omid Ali Akbari, Gholamreza Ahmadi, Nafiseh Emami, Soheil Salahshour Case Studies in Thermal Engineering, 2025 In the present study, the flow and heat transfer characteristics around a bundle of cam-shaped tubes have been numerically investigated using the finite volume method (FVM) in laminar and turbulent flows at different Reynolds numbers ( Re ). To increase heat transfer, flow guide fins have been used in the vicinity of each tube. The design variables include the vertical and horizontal spacing of the tubes, the major and minor diameters of the cam-shaped tube, the distance between the tube and the guide fin, and the angle covered by the guide fin. In both laminar and turbulent flow regimes, the objective functions include the maximum heat transfer and the minimum pressure drop. To optimize the tube layout and the arrangement of the guide fins, the methods of experiment design, the response surface methodology, and the genetic algorithm have been used. The results of this study show that the horizontal spacing between the tube bundles has no significant effect on heat transfer and the objective functions are most sensitive to Re and the angle of the guide fins. Based on the results, the conducting fins in the turbulent flow regime have performed better in increasing heat transfer. In this case, they have improved heat transfer by 20%, although they have also caused a significant increase in pressure drop. The simulation results of the two-phase flow of water-MWCNT nanofluid in the optimal arrangement of conducting fins show that the heat transfer is improved and the coefficient of performance is greater than 1.
A computational analysis of hybrid nanofluids on heat transfer amelioration through a conical helical shell-and-tube heat exchanger under turbulent flow conditions Mehdi Miansari, Fardin Nurpasand, Omid Ali Akbari, Hesam Moghadasi, Soheil Salahshour, Sh Baghaei Case Studies in Thermal Engineering, 2025 This research work examines the pressure drop and heat transfer trends within a conical helical tube heat exchanger utilizing pure water and hybrid nanofluids, namely Water/ A g − H E G and Water/ M O S 2 − F e 3 O 4 . The numerical simulation is performed using a Computational Fluids Dynamics (CFD) code in three-dimensional space according to the Finite Volume Method (FVM) for all examined cases. Also, turbulent flow regimes are conducted in this analysis employing the standard k–ε turbulence model, within the Dean Number (De) range of 2200 < De < 4250. In this regard, the proposed thermo fluids are evaluated under the same geometric and thermal conditions to assess their thermal performance parameters. Subsequently, the fluid exhibiting superior thermal performance is further analyzed at specific volume fractions. Results revealed that Water/ M O S 2 − F e 3 O 4 outperforms the other two fluids in terms of thermal performance, and the Nusselt Number for the hybrid nanofluid of Water/ M O S 2 − F e 3 O 4 is superior to that of water at diverse volume fractions of the nanofluids. Moreover, according to the outcomes, it was found that the pressure drop caused by the presence of the M O S 2 − F e 3 O 4 nanoparticles at volume fractions of 0.1 %, 0.3 %, and 0.5 % are 11 %, 19 %, and 20 % more than that of water, respectively. Thereby, the hybrid nanofluid of Water/ M O S 2 − F e 3 O 4 can be an alternative heat transfer fluid to conventional fluids in conical helical tube heat exchangers, improving heat transfer while maintaining an adequate pressure drop. Furthermore, as the Dean Number augments, the heat transfer coefficient (HTC) demonstrates an upward trend for all considered volume fractions of the hybrid nanofluids. Additionally, this phenomenon is ascribed to the intensified fluid velocity and interaction with the twisted wire, creating rotational and turbulent motion within the fluid, which leads to more frequent interaction between the coil wall and the fluid, therefore ameliorating the HTC between the two fluids which this value will be higher for nanofluids with a more significant volume fraction. At a constant Dean Number of 4250, the HTC was improved by approximately 200 % using hybrid nanofluid Water/ M O S 2 − F e 3 O 4 with a φ = 0.7 in comparison with pure water. Besides, the optimum thermal performance across all Dean Numbers is observed in models with volume fractions φ 1 = φ 2 = 0.7, peaking at about 2.72 for the hybrid nanofluid of Water/ M O S 2 − F e 3 O 4 at De = 3560.
