Heat Transfer最新文献

This study comprehensively examines magnetohydrodynamic heat transport characteristics within a thin nanofluid film on a stretchable sheet embedded in a composite medium. By considering factors such as the unsteady nature of sheet velocity, Brownian motion, thermophoresis, thermally radiative heat, irregular heat generation/sink, chemical reactions, and dissipation due to viscous fluid, the research provides valuable insights into the variations in fluid velocity, temperature, and nanoparticles concentration. The computational solution utilizes the efficient numerical method that enables accurate predictions of system behavior under varying conditions. Notable findings include the influence of Schmidt numbers on nanoparticle concentration distribution, the opposing impact of thermophoresis parameter values, and the influence of Brownian motion and heat source/sink on temperature profiles in thin nanofluid film. Also, nanoliquid film thickness is reduced by enhancing the porous parameter values and Hartmann number values. The nanoliquid film becomes thinner when the space-dependent heat source/sink parameter is considered compared to the temperature-dependent heat source/sink coefficient. In space-dependent and temperature-dependent cases, the increase in these parameters leads to a decrease in the temperature gradient. Furthermore, it is observed that higher thermophoresis values correspond to reduced nanoparticle concentration gradient profiles. Also, enhancement in the chemical reaction values leads to an expansion in the solutal boundary region surrounding nanoparticles, and as a consequence, the concentration gradient of nanoparticles is enhanced. This research has significant potential for optimizing heat performance and advancing innovation in industrial and engineering processes.

This study presents a novel approach to investigating the combined influence of fin position and shape on the constrained melting behavior of phase change material (PCM) within a spherical capsule (S.C.) through numerical analysis. Unlike previous research, which predominantly focused on single fin shapes or positions, this work uniquely explores the impact of double, simple, and easily manufacturable fin shapes. A two-dimensional computational model employing the enthalpy–porosity method assesses melting behavior, temperature distribution, and PCM flow. Numerous fin shapes, namely rectangular, trapezoidal converging, trapezoidal diverging stepped, inverse stepped, and triangular, are considered in the analysis. The study reports the influence of the location of two identically shaped fins on the thermal performance. The fins' cross-sectional area and base thickness are kept equal in all cases. The thermal performance of an S.C.-integrated fin system is evaluated by analyzing various attributes such as total saving in the duration of melting, enhancement ratio, and Nusselt number. The results indicate that the position of the fins has a more significant impact on melting performance than the fin shape. The best performance is achieved when fins are placed in the lower half of the capsule, followed by the center and upper halves, regardless of fin shape. For rectangular fins, shifting the position of the fin from the bottom half to the center increases the melting time by 24.7% and the top half by 68.3%. The shortest melting time of 93 min is observed for lower-half rectangular fins, followed by center-placed triangular fins (94 min). This study offers a theoretical foundation for optimizing the performance of different technologies using latent heat thermal energy storage systems such as packed-bed, cascaded thermal energy storage systems.

The current work extensively investigates double-diffusive of nano-encapsulated phase change material in a thermal storage system partially filled with porous foam. The generation of irreversibilities and the influence of Soret/Dufour and magnetohydrodynamic effects are also considered. The circular cold cavity contains a corrugated hot cylinder covered by an annular foam. The considered parameters are Rayleigh number (10³–10⁵), fusion temperature (0.1–0.9), Stefan number (0.1–0.9), volume concentration of nanoparticles (0–0.05), Darcy number (10⁻⁴–10⁻¹). Hartmann number (0–80) and the undulations of the inner (3–9). The numerical analysis has exploited the finite element approximations. The results indicate that Rayleigh and Hartmann numbers greatly influence the fluid flow, isotherms, concentrations and the melting/solidification region. The fusion has also a great influence on the melting/solidification region while there is no evident influence on the flow, isotherms and the concentrations where both Nusselt and Sherwood numbers change with around 5% with the change of the fusion temperature and Stefan number. In contrast, both values are decreased by around 30% by decreasing the Da number from 0.1 to 10⁻⁴. Furthermore, the change of the undulations number has very low influence on heat transfer, mass transfer and the melting/solidification region.

A new, easy-to-manufacture, and low-cost integrated cubical solar collector tank for domestic usage is concerned in this work. Three models are prepared, side by side, and tested to point out their seasonal performance. Tank Model I has three vertical sides, black painted and glazed to act as an absorber; the other sides are insulated. Tank Model II has two black painted and glazed sides, with four insulated surfaces. The models are south-oriented at different positions and tested versus the conventional tank (Model III) to validate and assess their performance in summer and winter. In summer, the temperatures in Models I and II are lower than those for Model III since they have insulated sides. Their glazed sides absorb a small amount of solar radiation since they are almost parallel to the incident solar radiation in summer. In winter, the water temperature in these models rises higher than that for Model III since their glazed sides work as solar collectors and have much lower heat loss to ambient. Therefore, the new design can provide a moderate temperature for summer and winter for residential use. Their water temperature does not exceed the ambient temperature at night in summer. It was higher than the ambient temperature in winter. The thermal efficiency for Models I and II in summer was 10.93% and 15.62%, respectively. While in winter, they were 15.09% and 19.46%, respectively.

The earlier studies investigated many parameters affecting the flat plate solar collectors (FPSCs) while employing an active approach to transmit the heat transfer fluid and running under a constant heat flux. In contrast, the presented study investigates enhancing the thermal performance through added fins with different heights and numbers to FPSC in a changing heat-flux condition and relies on a passive technique. Thus, Models A, B, and C included adding five fins along the riser-pipe with heights of 5, 7.5, and 10 mm, respectively, while Models D and E used four and three fins of 10 mm height, and the numerical calculations were conducted using ANSYS Fluent 2022R1. Then, the experimental work was done for the traditional model in Baghdad City, Iraq, to validate the results of numerical work, and the numerical and experimental work difference was found to be 10.17% for the tank's average temperature and the heat transfer liquid's temperature at the riser outlet is 10.14%. The numerical results indicate that the thermal efficiency of the system in all test models (A, B, C, D, and E) is enhanced than the classical model regarding the water's temperature in the tank and the working liquid's temperature at the pipe's outlet. In addition, the study concluded that Model C achieved a greater overall thermal efficiency than the traditional model by 38.59% and higher than Models A, B, D, and E by 11.77%, 6.65%, 8.19%, and 18.09%, respectively.

This research examines the appearance of a two-dimensional steady flow movement of a viscous, incompressible fluid undergoing chemical reactions along an infinitely long vertical porous plate. The flow is influenced by a transverse magnetic field, with the plate experiencing a uniform suction velocity. The research novelty lies in inspecting the impacts of ohmic dissipation and diffusion-thermo effects while maintaining constant heat and mass flux and considering heat and mass transfer in the presence of thermal radiation. Using perturbation techniques, the foremost calculations are solved, and the results are presented both graphically and in tables. The analysis shows that higher values of the diffusion-thermo parameter upsurge fluid velocity and temperature, whereas the presence of the transverse magnetic field decreases fluid velocity and temperature.

Passive heat transfer techniques in minichannel heat sinks (MCHS) provide effective thermal management solutions for high heat flux applications. The current study introduces a three-dimensional numerical analysis conducted to explore the flow and heat transfer characteristics of MCHS utilizing two passive techniques: incorporating pin fins with oblong-shaped cavities. Four types of pin fin shapes were developed, including tear-drop (MCOC-TDPF), pyramidal (MCOC-PPF), conical (MCOC-CPF), and oval (MCOC-OPF), respectively. The study is carried out under a laminar flow regime with Reynolds number ranging from 100 to 1000. The overall performance of these designs is assessed through a comparative analysis of traditional MCHS based on average Nusselt number, friction factor, and overall performance factor. Among these designs, MCOC-CPF exhibited superior thermal performance compared to the other three configurations, with a maximum performance factor of 2.25 at a Reynolds number of 1000. Furthermore, the influence of conical pin fin taper ratio (β) on the thermal enhancement of MCOC-CPF is also analyzed. Four values of conical pin fin taper ratio (β) have been considered, namely 1/6, 1/3, 1/2, and 2/3. The results revealed that β = 1/3 achieved an optimal overall performance of 2.39 at Reynolds number Re = 1000.

Tapered fins are widely used in heat sinks cooled by forced convection. In this study, maximal forced convective heat transfer from a set of tapered fins in cross-flow is investigated based on the constructal design method. The tapering of the fins is done for a three-fin base-to-tip ratio (taper ratio). The first taper ratio is TR = 0.5 (fin base < fin tip), the second taper ratio is TR = 1 (fin base = fin tip, straight fin), and the third taper ratio is TR = 2 (fin base > fin tip). In all these cases, the fin length is constant. The fins are heated at constant surface temperature and they are cooled by cross-flow. A constant pressure difference pushes the cross-flow toward the fins. The Bejan number ranges from 10⁵ to 10⁷. The forced convective heat transfer density is maximized from the fins for the three taper ratios, and a comparison between them is carried out. The maximization is conducted by numerical and scale analysis. In the numerical analysis, the pressure-driven flow equations (continuity, momentum, and energy) are solved by means of the finite volume method. In the scale analysis, two extremes are considered. The first extreme is for TR < 1, and the second extreme is for TR > 1. These two extremes are intersected to find the maximal forced convective heat transfer density. The results obtained from numerical and scale analysis confirmed that the maximal forced convective heat transfer density occurs for straight fins (TR = 1) in the whole range of the Bejan number. The heat transfer density from straight fins (TR = 1) is higher than that of tapered fins (TR = 2) by 45.2%, and it is higher than that of tapered fins (TR = 0.5) by 52.7% at Be = 10⁷.

In the present work, heat transfer dynamics between the substrate and the deposited metal is investigated to assess its effect on the evolution of defects and the quality of the product. A series of experiments involving the deposition of Al4043 wire were conducted on Al4043 aluminum alloy substrate at a voltage range of 13–19 V. A one-dimensional inverse computational model was adopted to estimate the heat flux transients. The metal/substrate interfacial heat flux was correlated with the microstructure evolution during the solidification of the metal. The experimental results clearly indicated that heat transfer plays a dominant role in the final finish and quality of the product and is controlled by variables, such as voltage, gas flow rate (GFR), wire feed rate (WFR), and forward traversal speed. At an integral heat flow (HF) in the range of 3000–5000 kJ/m² corresponding to voltages between 13.8 and 14.5 V, argon GFR of 12–15 L/min, and a WFR of 4.1 mm/min, the porosity in the additively manufactured component was found to be minimum. The ultimate tensile strength was found to be 65 and 76 MPa, corresponding to the voltage of 13.5 and 14.5 V, respectively, and decreased to 25 MPa for a higher voltage of 19 V. At the GFR range of 8–10 L/min, the HF was in the range of 450–510 kJ/m² with increased porosity (33%–42%). Porosity was found to decrease (15%–22%) with 12–15 L/min range of GFR and the corresponding HF was in the range of 700–950 kJ/m². The specimens fabricated under these optimal parameters exhibited superior mechanical properties.

In this work, we investigate the heat and mass transfer of elastico-viscous magnetohydrodynamic fluid (Walter's $��\; ��B�\; �\text{'}��$ model) flow through a porous medium bounded by an oscillating porous plate in a slip-flow regime subjected to a uniform transverse magnetic field. The primary objective of this study is to examine the flow under forced convection, incorporating diffusion-thermo and thermo-diffusion effects, which represents the novelty of this research. The governing equations of the flow are solved numerically using a regular perturbation method for small $��\; ��ϵ�\; �>�\; �0��$. With practically feasible parameter values, numerical simulations are conducted to demonstrate the effects of associated parameters on the flow dynamics. Velocity, temperature, and concentration profiles are presented graphically for varying parameters, and skin friction ($��\; ��C_f��$), Nusselt number ($��\; ��N�\; �u��$), and Sherwood number ($��\; ��S�\; �h��$) are computed. It is observed that increasing the diffusion-thermo effect reduces the thickness of the thermal boundary layer. Furthermore, a nonlinear relationship is observed between the thermal- diffusion effect and the concentration distribution of the flow field.