This study conducts a detailed numerical investigation into the thermo-hydraulic behavior of a two-dimensional solar air heater duct equipped with a two-step transverse rib roughened absorber surface. The simulations, performed using ANSYS Fluent 2025 R2 and the RNG k-ε turbulence model, explore flow conditions corresponding to Reynolds numbers ranging from 5000 to 20,000. Twelve distinct rib configurations are examined by altering both the rib height ( e = 1.3, 1.95 and 2.6 mm ) and the rib pitch ( P = 10, 15, 20 and 25 mm ), resulting in relative roughness pitches ( P/e ) ranging from 3.84 to 19.23 and relative roughness heights ( e/D ) between 0.039 and 0.078. A mesh independence test confirms that reliable results are achieved with 142,356 elements. Model validation against the Dittus–Boelter correlation and previously published experimental data shows deviations of less than 5 % , confirming the accuracy of the numerical approach. The results provide an in-depth analysis of both average heat transfer coefficients and frictional losses for ribbed duct configurations. Under a uniform heat flux of 1000 W/m2 the findings highlight that the Reynolds number, rib pitch, and rib height play dominant roles in determining the overall thermo-hydraulic behavior. Moreover, the study identifies the optimal two-step transverse rib geometry that ensures the best compromise between enhanced heat transfer and pressure drop, thereby achieving maximum overall thermo-hydraulic performance.

The operating temperature of photovoltaic modules critically affects electrical efficiency and long-term reliability, particularly under high solar irradiance. While passive cooling using phase change materials has been widely investigated, most research focuses on single-phase change material systems or has not systematically optimized fin geometry under constant phase change material volume and realistic inclination angles. To address these limitations, this study proposes a fully passive finned photovoltaic-phase change material heat-sink design integrating two phase change materials with different melting temperatures (RT-35 and RT-25HC) arranged in multi-layer configurations. A stepwise numerical optimization is first performed to identify an optimal fin geometry, followed by a comparative analysis against a smooth configuration using the same total phase change material volume. Key geometric parameters, including fin length, fin thickness, and fin number, are systematically evaluated. Results indicate that increasing the fin thickness from 1 mm to 3 mm reduces the maximum photovoltaic operating temperature by about 5.5 degrees C. Based on this optimization, a configuration with seven fins combined with a multiple-phase change material arrangement corresponding to Case 3 (10 mm RT-35 and 30 mm RT-25HC) provides the best overall thermal and electrical performance, reducing photovoltaic temperature by up to 16.29 degrees C and increasing electrical efficiency by 8.21% compared to the smooth system. Overall, optimizing fin geometry, especially fin thickness, significantly enhances passive thermal management in photovoltaic systems with integrated phase change materials.

The performance of photovoltaic (PV) panels is significantly impacted by their operating temperature. As the temperature rises, the ability of solar cells to convert sunlight into electricity decreases, resulting in a drop in electrical efficiency. To mitigate this effect, a passive cooling strategy using RT25 as a phase change material (PCM) combined with aluminum fins was investigated. Numerical simulations were performed in COMSOL Multiphysics using the finite element method, coupling heat transfer in solids and fluids with laminar flow to capture conduction and natural convection within the PCM. The present work focused on three key parameters: the inclination angle of the PV-PCM system, the number of fins, and their location on the panel surface. A numerical analysis was conducted to evaluate the electrical and thermal performance of the PV-PCM system. The investigation considered various fin spacing configurations of different distances (d) to determine the optimal design. The configuration with d = 16 mm showed the lowest temperature compared with all other configurations. At an inclination angle of 60 degrees, the configuration with d = 16 achieved the best cooling performance by reducing the average temperature of the PV panel by 53.20 % and 6.43 % compared with the only PV and PV-PCM, respectively. It exhibited a significant electrical efficiency enhancement, with increases of 18.699 % and 1.84 % compared with the only PV and PV-PCM cases, respectively.

The efficiency of photovoltaic (PV) panels is strongly affected by high operating temperatures, which remains a major challenge for solar energy applications, particularly in hot climatic regions. To address this issue, the present study proposes an original passive cooling strategy based on a hybrid fin configuration combining circular and rectangular aluminum fins integrated with the phase change material (PCM) RT-28HC. The circular fins are designed to accelerate heat diffusion and PCM melting, while the rectangular fins enhance heat dissipation to the ambient environment through natural convection. The study investigates the influence of circular fin geometry (radius and thickness), the number of rectangular fins, and PCM type (RT-28HC and RT-35) on the thermal and electrical performance of the PV module. A twodimensional transient numerical model was developed using COMSOL Multiphysics to simulate the coupled heat transfer and phase-change processes under realistic meteorological conditions corresponding to a hot summer day (July 1st, 2025) in Oujda. The results demonstrate that the proposed hybrid fin-PCM configuration significantly improves the thermal regulation of the PV panel. Among all investigated cases, the optimal configuration (P-36RF) achieved the best performance at an inclination angle of 60 degrees. At peak operating conditions, the PV temperature reduction reached 24.48 degrees C (30.17%), while the maximum electrical efficiency enhancement reached 14.72% compared with the smooth case. Considering the average performance over the entire operating period, the proposed configuration reduced the average PV temperature by 10.12 degrees C (19.39%) and improved the average electrical efficiency by 5.34%. In addition, the comparison between RT-28HC and RT-35 revealed that RT-28HC provided better thermal regulation due to its higher latent heat storage capacity. The findings confirm the potential of the proposed hybrid passive cooling strategy for improving PV performance under severe summer operating conditions.

In this study, we investigated the micro-scale dynamics of droplet impact on solid surfaces with varying wettability, using a 3D modeling approach to capture the intricate behavior of microdroplets. We employed the multi-relaxation times pseudopotential lattice Boltzmann method to simulate the interaction between fluids of different densities, with interface tension playing a key role. The analysis focused on two distinct wetting scenarios: hydrophobic (non-wetting) and hydrophilic (wetting) surfaces, examining the droplet dynamics during both the spreading (propagation) and recoiling phases of impact. By manipulating the bulk modulus parameter kappa and the corresponding surface tension gamma, we were able to explore how wettability and surface tension influence droplet behavior, including deformation and stability. The study also validated key aspects of our computational framework through reference validations such as contact angle measurements and Laplace's law. Our results provide valuable comprehension of the mixed effects of wettability and surface tension, offering a comprehensive understanding of droplet interactions on different surfaces. This work contributes to the broader knowledge of fluid dynamics and surface engineering, with implications for applications in fields such as inkjet printing, coating technologies, and material science.

This study presented a novel approach to solving thermal problems (convection and conduction) using the multi-relaxation time lattice Boltzmann method (MRT-LBM) coupled with Runge-Kutta finite difference schemes to perform numerical simulations of natural convection in a conjugate heat condition for two types of geometries recognized by the scientific community within a square cavity. The study examined the effects of Rayleigh number (Ra) and the solid/fluid conductivity ratio (Kr=Ks/Kf) on flow and heat transfer. In contrast to previous studies, this research varied the Kr ratio from 1 to 1000 for the square body and from 1 to 100 for the circular body. The results displayed that heat transfer and flow characteristics become more complex and turbulent as the Ra increases. Moreover, as the Kr ratio increased, heat transfer from the solid bodies to the fluid was enhanced, with an improvement of 238% for the circular obstacle case, while the square obstacle case showed a 29.8% enhancement. Additionally, an increase in fluid motion within the cavity, controlled by the Rayleigh number, results in an improvement of approximately 288% for Ra=106 compared to Ra=103 for the circular obstacle and a 71.4% increase for the square obstacle. This study provided valuable insights into natural convection phenomena in a conjugate heat condition of the two bodies confined within a cavity and has potential applications in various industrial and engineering fields.

In this study, the behavior of bubbles and droplets during boiling and condensation processes on a wettable horizontal plate with variable density (?w) is investigated using pseudopotential lattice Boltzmann model for multiphase flow. The analysis focuses on the complete life cycle of bubbles and droplets, from their appearance to their disappearance under the effect of gravity. The main objectives of this study are to analyze the propagation of bubbles or droplets on the horizontal surface (l*) and to study their evolution as a function of time, characterized by h*, for different values of the wetting surface density. To ensure the reliability of our model in simulating these phenomena, the hydrodynamic effect and Laplace's law were. This combination of approaches demonstrated a good compromise between our results and the references, confirming the model's reliability. Furthermore, we present results that showcase the density behaviors for different wetting surfaces, allowing us to analyze droplet behavior on the horizontal plate. It was observed that for large values of ?w, significant droplet spreading occurred, and this process took time to subside. Conversely, for small values of ?w, spreading was minimal, enabling rapid droplet detachment. Interestingly, in the case of boiling, the observed behaviors were reversed compared to condensation. Moreover, the heat flux analysis for the single-density case provided insights into the temperature behavior around bubbles during the nucleation process and droplets during the droplet condensation process, while maintaining a fixed density value on average. These findings contribute to a better understanding of the thermal dynamics associated with boiling and condensation phenomena.

This study explores the impact of the magnetic field on heat transfer and entropy generation in a simulated electronic device using magnetohydrodynamic principles through a three-dimensional hybrid Runge-Kutta and lattice Boltzmann method. By varying Rayleigh number (Ra) from 103 to 106 and Hartmann number (Ha) between 0 and 100, the research evaluated the influence of these parameters on the average Nusselt number (< Nu >), heat exchange ratio (R), and entropy generation within a confined cavity. The results demonstrated that higher Ra values, particularly for Ra >= 10(5), significantly enhance convective heat transfer, as reflected by an increase in < Nu >. However, introducing a magnetic field (Ha = 50, 100) diminishes this effect by damping fluid motion, resulting in a reduction of < Nu >. The heat exchange ratio increases with Ra, reaching a peak value of 0.93 for Ha = 100 and Ra = 10(5), indicating improved heat dissipation under the magnetic influence. In terms of entropy generation, at low Ra (Ra = 10(3)), thermal conduction is the predominant heat transfer mechanism, with entropy primarily generated due to thermal effects. As Ra increases to 10(6), the system shifted toward a convection-dominated regime, where entropy generated by viscous effects becomes more significant. Under stronger magnetic fields, particularly at Ha = 100, magnetic entropy generation emerges as a dominant factor, further increasing energy dissipation. These results suggested that magnetic fields can be strategically applied to optimize thermal management in electronic devices by controlling both heat transfer and entropy generation. The effectiveness of this approach, however, is highly dependent on the specific flow conditions and the strength of the applied magnetic field.

This research employed the pseudopotential multi-relaxation times lattice Boltzmann method to investigate the impact process of a droplet on solid surfaces, focusing on the influence of surface wettability for three different Reynolds numbers (Re = 100, 200, and 500). Initially, the impact process is studied on both hydrophobic and hydrophilic surfaces, revealing distinct behaviors characterized by spreading and recoiling stages. Subsequently, the investigation extends to a mixed wettability wall, offering insights into the droplet's density behaviors. Through this study, we demonstrate that the wettability of the surface plays a crucial role in determining the contact dynamics with the impacting droplet. Notably, the average velocity of the droplet exhibits a monotonic increase with higher wettability. Furthermore, the droplet profile responds to variations in the Reynolds number, though droplet deformation remains relatively limited even when the interaction with the wetting surface intensifies. Our findings shed light on the complex interplay between wettability, droplet dynamics, and surface interactions during impact processes.

This paper presents a 2D numerical analysis of thermal conduction and convection phenomena using a hybrid Lattice Boltzmann-Finite Difference (LB-FD) model. The study focuses on the simulation of conjugate heat transfer in a cavity filled with air. This cavity is characterized by two cold vertical walls and a relatively thick bottom part, considered solid and heated from below. The study aims to examine the impact of the choice of solid material on the heat exchange process. Analysis of the findings indicates that increasing the value of the thermal conductivity of the material increases the rate of heat transfer inside the cavity. For example, for a Rayleigh number set at 10^6 , the results show that heat exchange increases by 156.97

This study used the multi-relaxation time pseudopotential lattice Boltzmann method to examine the impact dynamics of droplets on circular bodies, focusing on the influence of the surface wettability, the viscosity of droplets by choosing three distinct Reynolds numbers (Re = 100, 300, and 500), and the body diameters. Initially, the study examined impact behavior under non-wetting and wetting conditions, revealing distinct behaviors characterized by dimensional stretch lengths in horizontal and vertical directions. Furthermore, the study evaluated the impact of viscosity by varying the Reynolds number, providing a better understanding of droplet behavior on the solid body. In addition, the effect of changing the diameter of the circular body was examined. This research underlines the importance of surface wettability in the dynamics of contact with the droplets impinging on it. In particular, higher wettability correlates with a monotonic increase in viscosity by acting on the Reynolds number. In addition, the droplet profile responds to changes in Reynolds number, albeit with relatively limited deformation, even in the case of intense interaction with the wetting surface. These results highlight the complex interplay between wettability, droplet dynamics, viscosity, body dimensions, and surface interactions during impact processes.

This paper presents a numerical investigation of the propagation of acoustic waves generated by a linear acoustic source using the lattice Boltzmann method (LBM). The main objective of this study is to compute the sound pressure and acoustic force produced by a rectangular sound source located at the center of the west wall of a rectangular cavity, filled with water. The sound source is discretized into a set of point sources emitting waves according to the acoustic point source method. The interference between the generated cylindrical waves creates an acoustic beam in the cavity. An analytical study is carried out to validate these numerical results. The error between the numerical and analytical calculations of the wave propagation is also discussed to confirm the validity of the numerical approach. In a second step, the acoustic streaming is calculated by introducing the acoustic force into the LBM code. A characteristic flow structure with two recirculating cells is thus obtained.

The exploration of interactions between magnetic fields and thermal convection represents an extremely interesting field of research, which has captured the considerable attention of the scientific community, as evidenced by several recent publications. This investigation opens up promising horizons in diverse fields of application, such as heat exchange systems, electronic devices, plasma analysis, magnetic cell separation, power generation, and many others. In this perspective, the present paper proposes a three-dimensional numerical study of the influence of the magnetic field on free convection and entropy generation in the presence of thermal conduction. The numerical methodology adopted incorporates the finite difference technique for temperature determination and the lattice Boltzmann method for characterizing fluid flows and the magnetic field. The aim is to perform a three-dimensional numerical study of the effect of changing magnetic field intensity, Rayleigh number, and thermal conductivity on heat exchange in a differentially heated cavity divided by a conducting solid, acting as a heat exchange device. The obtained results show that the heat exchange rate is inversely proportional to the increase of the magnetic field intensity and directly proportional to the thermal conductivity and Rayleigh number. In addition, the impact of the magnetic field on entropy production in the thermal system is examined in a second step. The results reveal that increasing the Hartmann number intensifies entropy production due to magnetic influence. However, this increase simultaneously leads to a reduction in the rate of entropy production, attributable to temperature gradients, fluid friction as well as total entropy production.

This article presents a three-dimensional numerical analysis of the phenomena of ultrasound propagation in air, thermal convection, and their interaction. The simulations are carried out using a hybrid numerical approach based on the lattice Boltzmann and the finite difference techniques. For validation purposes, our numerical model is verified in the case of the study of ultrasound propagation in the air without the presence of thermal convection. This is performed by comparing the numerically calculated acoustic pressure with the analytical results. After this verification, the focus is on the examination of the heat transfer improvement by the ultrasound emitted by the vibration of a circular piston. This acoustic source is mounted in the center of the left cold surface of a microcavity, which is differentially heated and filled with air. The obtained numerical results indicate that the heat transfer is significantly improved by using 10 MHz ultrasound.

The present article provides a three-dimensional numerical investigation of thermal convection and entropy generation. The lattice Boltzmann method, coupled with the finite difference approach, is applied to perform numerical simulations. The validation of these numerical approaches for thermal convection simulation and entropy calculation is performed by comparing our numerical results with those in the published literature for the case of benchmark problems. The physical geometry studied in this paper concerns a hot obstacle having the shape of a plus sign (+) placed in the center of a cubic enclosure. This cube is filled with air of a Prandtl number of 0.71 and characterized by two cold vertical walls. The heat exchange between the fluid and the hot body is studied as a function of the Rayleigh number (103 & LE;Ra & LE;107 ${10}<^>{3}\le {Ra}\le {10}<^>{7}$). The performed simulations show that the heat transfer rate can be increased by about 429% by switching from Ra=103 ${Ra}={10}<^>{3}$ to 107 ${10}<^>{7}$. The entropy generation due to fluid friction, heat transfer, and total entropy are also calculated and discussed. For an irreversibility coefficient & phi;=10-4 ${\varphi }={10}<^>{-4}$, the analysis of the results showed that for low values of the Rayleigh number (Ra=103 ${Ra}={10}<^>{3}$), the entropy production due to temperature gradients predominates over that produced by viscous effects. In the cases of Ra=104 ${Ra}={10}<^>{4}$ and 105 ${10}<^>{5}$, entropy generation is due to both fluid friction and heat transfer. However, when the Rayleigh number becomes large (Ra & GE;106 ${Ra}{\ge 10}<^>{6}$), entropy generation due to viscosity predominates over entropy production related to heat exchange. These results have important implications for the optimization and design of heat transfer systems in various industrial applications.

The paper presents a three-dimensional numerical study of the acoustic streaming induced by the dissipation of ultrasounds during their propagation in the air. The waves are generated by a circular acoustic source positioned at the center of the left wall of a parallelepipedic cavity. The simulations are performed with the lattice Boltzmann method associated with the D3Q19 multiple relaxation time model. A validation of this model is first performed by comparing the numerical and analytical acoustic intensities along the central axis of the acoustic source. The main objective of this study is to use two different methods to calculate the acoustic streaming flow. The first method is the direct calculation of the mean velocity fields as the mean values of the instantaneous velocities. The second method is an indirect technique, which first calculates the acoustic streaming force and then injects this force into the numerical code to produce the streaming. A comparison between the results obtained by the two methods was carried out and a good agreement was found between them. These different investigations, rather new in three-dimensional configurations, have allowed us to discuss the advantages and limitations of the lattice Boltzmann approach to simulate real situations of wave propagation and acoustic streaming.

In this paper, a three-dimensional (3D) numerical study of thermal convection and acoustic waves is presented using a hybrid method. This method consists of two computational approaches: the lattice Boltzmann method (LBM) with multiple relaxation times for the study of the fluid behavior and the finite difference method (FDM) for the description of the thermal exchange. The two approaches have been validated by studying two benchmark problems reported in the literature. The LBM was validated by simulating the flow induced by a lid-driven cavity. The FDM was checked by simulating natural convection in a differentially heated cubic cavity filled with air. After this validation, the main focus was on the study of enhancement of the heat transfer in a 3D cavity using a vibrating acoustic source. The numerical study is performed for different values of the wave amplitude, the Rayleigh number (Ra), and the sound source size. It shows that the heat transfer is significantly improved for a low Ra. However, for high Ra values, natural convection cannot be neglected in front of forced convection. The transfer is also influenced by the variation of the source size. This allows obtaining the optimal size corresponding to the maximum heat exchange.

In this paper, boiling and condensation phenomena are described on walls with mixed wettability using a hybrid thermal model with multiple relaxation times of the Boltzmann lattice type. We start this study by validating our code. To do so, different simulations are performed namely the spreading of a liquid droplet on an adjustable wettability surface by varying its density, the surface tension for different temperatures around the critical point using Laplace’s law which is used to compute the characteristic parameters (Taylor wavelength λ d , characteristic length l 0 and characteristic time t 0 ), the evaporation of a liquid droplet is evaluated in compraison with the literature work for constant thermal conductivity values. Subsequently, the power law is verified by processing the growth of a liquid droplet for three different cases of wettability. On the other hand, we study the behavior of condensation and boiling processes and their interactions between the boundaries of the solid surface in which they occur. For this purpose, the cavity walls are considered wetting in some areas and non-wetting in others. The results show different behaviors depending on the zones of the walls.

Numerical study of various physical phenomena in three dimensions has become a necessity to better understand the physical process than in two dimensions. Thus, in this paper, the code is elaborated to be adapted to the simulation of heat transfer in three dimensions. The numerical simulations are performed using a hybrid method. This method is based on the lattice Boltzmann approach for the computation of velocities, and on the finite difference technique for the calculation of temperature. The used numerical code is validated by examining the free convection in a cubic enclosure filled with air. Then, the analysis of the heat exchange between two cold vertical walls and a heated block located at the center of a cubic cavity is considered. The performed simulations showed that for a small value of the Rayleigh number (Ra=103 for example), the fluid exchanges its heat almost equally with all hot surfaces of the obstacle. However, for large values of Ra (Ra≥104), the numerical results found showed that the heat exchange rate is greater on the bottom face compared to the other faces of the obstacle.