Heat Transfer最新文献

The aim of the present study is to analyze the effects of thermo-solutal nonlinear convection in a nanofluid flow past a vertical permeable plate in the presence of heat generation/absorption and a first-order chemical reaction. The effects of Brownian motion and thermophoresis have been included in this study. By using similarity transformations, the ordinary differential equations (ODEs) are obtained from the governing partial differential equations (PDEs). Then by using a Runge-Kutta (R-K) method coupled with a shooting technique, numerical solutions are obtained. The effects of the relevant physical parameters on the velocity, the temperature, and the nanoparticle volume fraction are analyzed. When the magnitude of the thermal buoyancy parameter and solutal buoyancy parameter increase, the fluid velocity initially rises rapidly and then diminishes. But the temperature and concentration fields reduce. Near the plate, the fluid velocity is found to enhance with increasing values of the thermo-quadratic convection parameter as well as with the rising values of the solutal-quadratic convection parameter. However, both the temperature and the nanoparticle volume fraction reduce. The results of this study are interesting and motivating for further investigations on the problem for different situations and with different geometries.

Many engineering and industrial applications rely on heat transfer (HT) as a basic and central process. Therefore, engineers and researchers place significant emphasis on optimizing HT rates. Here, we numerically attempt to maximize the heat transmission rate of mixed convection of nanoencapsulated phase change material in a square compartment. The compartment is differentially heated and incorporates two cold rotating cylinders. The Galerkin finite element approach is utilized for addressing the system governing equations. A range of various factors affecting the thermal activity in the compartment were considered. These factors include the speed of spinning cylinders (Re = 0–1000), the porousness of the compartment (Da = 10⁻⁵–10⁻²), the magnetic field intensity (Ha = 0–100), and the concentration of nanoadditives (ϕ = 0%–8%). The obtained numerical findings demonstrated that the thermal activity inside the compartment is positively correlated to the speed of the spinning cylinders, the concentration of nanoadditives, and the porousness of the compartment. In contrast, increasing the intensity of the magnetic field obstructs the heat transmission. It was noted that at the highest Re number, the average Nusselt number augmented by 257% and 13.6% when increasing Da and ϕ, respectively.

The present work is interested in investigating the impacts of chemical reaction, magnetic field, thermal radiation, heat sink, and thermal diffusion on a steady two-dimensional MHD convection-free heat and mass transfer flow past a semi-infinite upright porous plate. The dimensionless domain equations are solved analytically using the perturbation technique for two distinct scenarios: (a) small suction and (b) large suction. The effects of various crucial parameters on velocity, temperature, concentration, as well as on the skin friction, Nusselt number, and Sherwood number are graphically illustrated, and the subsequent discussion is rooted on the derived outcomes. Graphical representations were created utilizing MATLAB software. The results suggest that an increase in the Soret effect elevates both the momentum and concentration boundary layers while reducing the mass transfer rate, regardless of the suction intensity. Our research also identified a captivating result where fluid velocity escalates with higher magnetic values in the scenario of large suction, while it demonstrates contrasting behavior under small suction condition. The present investigation holds significant relevance across various industrial sectors, including uranium enrichment, petrology, petroleum reservoirs, polymer fractionation, among others.

This study presented a numerical model to evaluate a novel design of a hybrid heat sink incorporating perforated foam fins (PFFs) instead of solid fins (SFs) within a phase change material (PCM). This innovation is designed to enhance thermal performance in electronic cooling applications. The base of the heat sink was subjected to constant heat fluxes of 2, 3, and 4 kW/m². The effect of the perforation location (top, center, and bottom) within the foam fin and foam porosities (0.85, 0.90, and 0.95) were investigated. The results showed that the hybrid PFF design demonstrably improved thermal efficiency compared to the SF configuration. This innovative approach offered three benefits: a significant reduction in overall heat sink weight, an augmentation of the thermal conductivity of PCM, and the intermixed molten PCM between the fins passages through perforations. The PFF heat sink extended the operational time by 6%–8% for the range of heat fluxes at SPT of 70°C and led to a 24.5% increase in PCM volume, compared to the SF configuration. Complete melting of the PCM in the PFF heat sink is observed at 29 min for the highest heat flux of 4 kW/m², while the melting rates are 25% and 62% for the applied heat flux of 2 and 3 kW/m². Perforation location within the foam fin (top, center, and bottom) achieved equivalent heat transfer capabilities, enabling design flexibility for perforation location. The PFF with a porosity of 0.85 demonstrated superior thermal performance.

The efficiency of photovoltaic (PV) solar panels is highly sensitive to operating temperatures, with increased temperatures leading to a significant decline in electrical output and overall performance. Despite extensive research into thermal management solutions for PV panels, there remains a gap in optimizing passive cooling systems, particularly air-cooled heat sinks, to achieve effective heat dissipation. This study addresses the challenge by conducting a detailed computational analysis of air-cooled heat sinks with varying fin configurations to enhance the thermal regulation of PV panels. Using computational fluid dynamics simulations, this work evaluates the influence of fin number and spacing on airflow dynamics and heat dissipation efficiency. Key findings from ANSYS Postprocessor simulations indicate that heat sinks with a higher number of fins improve heat dissipation, with the 11-fin configuration demonstrating the highest temperature drop of 38.44 K. Comparatively, the base model (nine fins, 0.05 m fin spacing) exhibited a maximum temperature of 331.46 K and a mean velocity of 1.58 m/s. A parametric study of finless designs showed a lower mean temperature of 321.28 K, but with significantly reduced airflow velocity. Intermediate designs, such as the six-fin and seven-fin heat sinks, also demonstrated improved thermal performance over the finless model but were outperformed by the 11-fin configuration. This study contributes to the ongoing efforts to optimize passive cooling for PV solar panels by demonstrating the critical impact of fin number on heat sink effectiveness. The findings offer valuable insights into the design of more efficient cooling mechanisms, potentially enhancing both the performance and longevity of PV systems.

The growing need for energy-efficient cooling solutions has driven the exploration of cutting-edge technologies in air-conditioning (AC) systems. Therefore, this research aims to improve the energy efficiency of a split AC system by incorporating a phase change material (PCM) heat transfer element into the AC system. PCM can release and store thermal energy, assisting in decreasing the load on the AC system during peak cooling periods. The PCM utilized in the study is Rubitherm RT18HC. The study includes numerical and experimental evaluations to assess the impact of the air–PCM unit on the split unit's performance. The numerical simulations were conducted using computational fluid dynamics models based on ANSYS-Fluent to choose the best design and conditions for the air–PCM unit. The experimental study was conducted in the hot environment of Iraq, where outdoor temperatures exceed 43°C. The numerical results showed that the best design and conditions concluded to be a 1-cm PCM height in the panels, 3 cm air channel height, 0.9 m/s air velocity for charging, 0.45 m/s air velocity for discharging, 7°C inlet air temperature for charging, and 25°C inlet air temperature for discharging. In the experimental part, after validating the theoretical results, two practical cases were conducted to evaluate the split unit performance with and without PCM. The results showed an average of 5% lower room temperature, 9.5% lower air entering the evaporator temperature, 10% lower energy consumption, and a 12.5% increase in the AC unit's coefficient of performance when using the air–PCM heat transfer unit.

This work presents exact solutions to analyze the effect of the Biot number on mixed convection flow in a vertical channel with asymmetric heating and flow reversal. The equations governing flow formation and temperature distributions are offered with convective boundary conditions. Closed-form solutions for temperature, velocity, and skin friction are found and simulated graphically.

The present study assesses the constant surface heat flux on a 2D steady convective flow of a micropolar fluid. The flow occurs along a vertical impermeable flat plate immersed in a fluid-saturated porous medium. Numerical methods are used to convert the governing partial differential equations to gather the locally equivalent ordinary differential equations. Local similarity solutions also visually depict the velocity distribution and microrotation (ω) in the boundary layer. Furthermore, the influence of the physical variables on the flow field is investigated. The numerical results show that the effect of porosity (ε) on the velocity profile demonstrates a negative correlation between ε and velocity. The correlation between microrotation (ω) involving the ε influence also depends on the similarity parameter (η). Although microrotation (ω) increases with porosity (ε) in the region where the fluid is near the surface, this trend changes as the flow moves further away from the surface. The dimensionless microrotation (ω) value remains constant, while rotation is not observed for the similarity parameter (η) values exceeding 4.5. The value of microrotation (ω) value is small for the similarity parameter (η) values in the interval (0 < η < 1.4). Nonetheless, the microrotation (ω) value is high for the similarity parameter (η) values up to η = 4.5. Therefore, the point at η = 1.4 represents a crucial point in the present study. The results of the present study have been validated, and the comparison with related articles showed an excellent matching between results. Outcomes from the current study are very beneficial to enhance the performance of solar panels by improving the cooling of such panels.