Heat Transfer最新文献

The Falkner–Skan model is widely used to describe boundary layer flows in various engineering systems. Incorporating magnetic fields, slip conditions, and chemical reactions is critical for understanding real-world applications involving non-Newtonian fluids in porous media. This study aims to examine the combined effects of magnetohydrodynamics, radiative heat transfer, internal heat generation/absorption, dual slip (momentum and thermal), and homogeneous–heterogeneous chemical reactions on non-Newtonian fluid flow over a permeable wedge. The governing partial differential equations are transformed into a system of coupled nonlinear ordinary differential equations using similarity transformations. These equations are then solved numerically using the Runge–Kutta–Fehlberg method along with the shooting technique, implemented in Maple software. The results show that increasing the Hartmann number, slip parameters, and reaction rates suppress fluid velocity and enhance thermal gradients, while reducing the thickness of the concentration boundary layer. The Prandtl number and the radiation parameter significantly affect the thermal distribution and heat transfer rate. Surface quantities such as skin friction and Nusselt number vary meaningfully with changes in magnetic intensity and chemical activity, and the results exhibit good agreement with existing literature.

Heat and mass transport in electrically conducting fluids under magnetic fields can be better understood by examining Magneto-Oberbeck convection in a rectangular enclosure with homogeneous mass and heat fluxes along the vertical sides. It may be used in technical domains, like, geophysics, metallurgy, and electronic device cooling. Transport phenomena, flow patterns, and stability are all impacted by the interaction between buoyancy-driven stream and magnetic forces. The study's conclusions aid in the optimization of thermal management and magnetohydrodynamics-related industrial operations. The natural convection that results from the combined effects of concentration and temperature buoyancy within a rectangular cavity with uniform mass and heat flow along the vertical sides with a magnetic field is investigated analytically in this paper. Magnetic fields are used in many sectors, such as everyday technology, engineering, and medicine. Convection affects the mass and heat transport rates in the boundary layer domain, where the analytical approach is accurate. An Oseen-linearized solution is reported foe tall spaces filled with mixtures characterized by $��\; ��\mathrm{Le}�\; �=�\; �1��$, and arbitrary buoyancy ratios. The impact of changing the Lewis number is shown by a similarity solution that works for $��\; ��L�\; �e�\; �>�\; �l��$ in flows driven by heat transfer and for $��\; ��\mathrm{Le}�\; �<�\; �1��$ in flows driven by mass transport. Graphical analyses of the solutions are performed for varying Rayleigh numbers, buoyancy ratios, and Chandrasekhar numbers.

The present study intends to examine how the viscoplasticity of the liquid affects heat transfer characteristics in a wavy channel that contains metallic porous blocks, taking into account the effect of conductive heat flow within the finite wall thickness. Additionally, the second aim of this initiative is to establish an Artificial Neural Network (ANN) framework capable of forecasting the thermohydraulic performance factor and average Nusselt number based on different combinations of thermal and rheological parameters. To examine the flow field, conductive heat flux field, conductive heat lines, average Nusselt number, and performance factor, parameters such as the Darcy number, Bingham number, and thermal conductivity of the solid wall are varied within a justified range. It turns out that the flow field is significantly influenced by its fluid's viscoplastic characteristics, which allow the vortex to disappear at larger Bingham numbers. The average Nusselt number and performance factor show a monotonic increase with increasing Bingham numbers at higher Darcy numbers. The same exhibits a nonmonotonic tendency for lower Darcy numbers. Interestingly, the performance has been shown to have a value larger than unity, indicating that the current design has promising potential for use in applications involving thermal management of heat. The current ANN model predicts the average Nusselt number and performance factor with great precision. This endeavor represents the first exploration of how the viscoplastic properties of the liquid affect heat transfer characteristics within a wavy channel with metallic porous blocks, as well as the impact of conductive heat flow in solid walls.

This study examines the effects of variable thermal conductivity and binary chemical reactions on hyperbolic tangent fluid flow within a porous microchannel in the presence of bioconvection. The combined influences of magnetism, Joule heating, and viscous dissipation are considered. To facilitate analysis, the governing system of partial differential equations is transformed into a system of ordinary differential equations using appropriate dimensionless transformations. The numerical solutions are obtained using the Runge–Kutta–Fehlberg fourth–fifth-order method in conjunction with the shooting technique. The impact of key governing parameters on velocity, temperature distribution, concentration, and motile microorganism density is analyzed in detail through graphical representations. The results indicate that the thermal field exhibits a dual behavior in response to variations in thermal conductivity and magnetic effects. A similar trend is observed in velocity profiles concerning the Weissenberg number. Furthermore, an increase in the Peclet number reduces the thickness of the actively moving microorganism layer, while a higher bioconvection Lewis number promotes the accumulation of motile microorganisms. The study also reveals that the chemical reaction rate diminishes with concentration levels, whereas an increase in activation energy enhances concentration. Additionally, the heat transfer rate improves with variable thermal conductivity at the microchannel walls, whereas the skin friction coefficient decreases with higher Weissenberg numbers. These findings have practical implications in various engineering and biomedical applications, such as microfluidic device design, biofuel production, drug delivery systems, and the control of microbial transport in porous media.

As an efficient cooling technique, two-phase loop thermosyphon (TPLT) has great application prospects in power electronics, and it is necessary to improve and strengthen its cooling performance. In this study, an experimental visualization setup was set up to study the mechanism of enhancement of heat transfer by a square-rib surface. The behaviors of bubble growth, slide, and suction were captured. Results indicate that the bubble growth promotes the disturbance of the coolant at the top of the rib and strengthens the heat transfer in the boundary layer. The large bubble sliding between the ribs significantly enhanced heat transfer on the heating surface, and the bubble suction strengthened the heat transfer away from the heating surface. The cooling performance of TPLT with various rib heights and widths was investigated. The heat transfer characteristics of the TPLT can be significantly improved by increasing the rib height or reducing the rib width. The rib height and width have little effect on the two-phase flow characteristics of the TPLT. The experimental frictional pressure drop and heat transfer coefficient are compared with the prediction. The results indicate that the Friedel and Gungor and Winterton correlations are applicable for cooling performance prediction of TPLT.

The increasing rise in fossil fuel prices, the growing concern about its depletion, the repercussions of the global gas crisis, in addition to climate change as a result of global warming, all of these factors have led to the urgent need to access renewable energy bases to meet the growing demand for clean energy. To promote the process of sustainable development completely, solar energy is adopted as a pure, cheap, in addition to permanent energy that can be used with different systems. All these qualities of solar energy are of interest to many researchers. The analysis of energy is most important in examining the effectiveness of the process on the other side, exergetic examination is also a significant tool to study the accurate activities of a process relating to some energy damages and internal irreversibility. This article aims to highlight the importance of using different forms and designs of solar air heaters, as well as their applicability and effectiveness of each type, from a thermodynamic perspective. Various studies have also been listed that discussed the most prominent improvements that enhance the effectiveness of the system and their impact on energy and exergy efficiency.

Carbon nanotubes (CNTs) have garnered a lot of interest lately since they are thought to be among the most promising novel materials for a variety of technological uses. The study of CNTs in a micropolar fluid model provides a path to significantly improve the mechanical properties of biodegradable nanocomposites in tissue engineering. In view of this, the present article focuses on the mass and heat transport analysis of the stagnation-point flow of micropolar nanofluid across a stretching/shrinking sheet. Also, the single-walled carbon nanotubes (SWCNTs) and multiwalled carbon nanotubes (MWCNTs) in the fluid flow are analyzed. Additionally, the influence of suction/injection, gyration velocity, and velocity slip conditions on the fluid flow is considered. The governing partial differential equations are converted into ordinary differential equations (ODEs) using similarity variables. Furthermore, the ODEs are solved using the exact method. The behavior of velocity, temperature, and concentration profiles for various parameters is depicted with the graphical representation. The comparison of MWCNT and SWCNT for various parameters, including velocity, thermal, and concentration profiles, is provided. The derived exact solutions offer a single solution for the sheet elongation case, whereas the sheet dwindling case offers two solutions in a particular region. It is mainly observed that the linear velocity profile is lowered by velocity slip. The concentration profile decelerates for escalating values of chemical reaction and Schmidt number. These findings seek applications in biochemistry, such as biosensors, increased drug lifespan, and tissue engineering.

This study investigates the potential of enhancing heat transfer in smooth tubes by incorporating various roughness geometries. Computational fluid dynamics (CFD) simulations were conducted to evaluate the performance of heat exchanger tubes with different roughness shapes (dimple, protrusion), pitch spaces (80–140 mm), and diameters (4–8 mm). The Reynolds number was varied from 5000 to 30,000. Results demonstrate a significant increase in heat transfer compared to smooth tubes, with a maximum Nusselt number enhancement factor of 2.8. A positive correlation was observed between heat transfer and Reynolds number, while friction factor decreased. Furthermore, Nusselt number increased with larger pitch spaces between roughness elements. The optimal thermal-hydraulic performance, with a maximum performance evaluation criterion (η) of 2.128378783, was achieved using a combination of dimple and protrusion shapes at a Reynolds number of 30,000 and a pitch space of 120 mm. This study highlights the significant potential of roughness-based techniques for improving the thermal efficiency of heat exchange systems. This study addresses a critical challenge in thermal engineering: how to enhance the efficiency of heat exchangers while minimizing energy losses. Heat exchangers are integral to a wide range of industrial applications such as power generation, HVAC systems, chemical processing, and automotive cooling where improved thermal performance can lead to substantial energy savings and reduced operational costs. Traditional smooth tubes in heat exchangers often suffer from low heat transfer rates, which leads to increased energy use or oversized. The economic viability of this study is improved heat transfer efficiency, reduction in energy losses, optimization of flow conditions, potential for extended heat exchanger lifespan.