Heat Transfer最新文献

This research examines how mixed convection influences the heat and fluid flow behavior of non-Newtonian fluid flow, driven by an exponentially increasing pressure gradient over a slender cylinder. In accordance with the flow assumptions, the proposed problem is mathematically formulated using coupled nonlinear partial differential equations, and the obtained results are satisfied by appropriate boundary conditions. The dimensional model is converted into a non-dimensional form by introducing appropriate scaling variables. The problem is solved by applying the Finite Difference Method for discretization, wherein derivative terms are replaced with finite differences. Finally, the resulting data are imported into Tecplot-360 for graphical representation. An analysis of key fluid flow and thermal parameters involved in the flow model is carried out to investigate their influence on velocity and temperature profiles, as well as their respective gradients. The results demonstrate that exponentially increasing pressure gradients can enhance the flow velocity near the surface, which may lead to a reduction in skin friction, even in the case of shear-thickening ($��\; ��n�\; �>�\; �1��$) fluids. These findings are validated through both graphical and tabular representations, with accuracy ensured by the application of proper boundary conditions. The novelty of the proposed work is based on the combination of slender cylinder geometry and non-Newtonian fluid which is less frequently studied.

This paper outlines the thermal performance of parabolic trough collectors with internally finned absorbers using computational tools. The main purpose of this study revolves around the thermal improvement procedures for an absorber tube containing 12 long fins and Syltherm-800 as working fluid. In more detail, to optimize the performance of the finned absorber tube, various fins' thickness (1–6 mm) and length (2–20 mm) configurations are examined with different volume flow rate (VFR) values (50–250 L/min) using computational fluid dynamics simulation. The outcomes are elucidated in connection with the thermal heat flux, pressure drop, and thermal efficiency. A full factorial design of experiments framework has been applied to pinpoint the most influential factors affecting the thermal enhancement of the parabolic trough solar system. In light of the ultimate findings, the employment of an internally finned absorber leads to an optimum thermal efficiency enhancement for a 6-mm fin thickness, 20-mm fin length, and 50-L/min VFR.

The study examines the steady boundary layer flow and heat and mass transfer of a power-law fluid over an inclined cylinder that is expanding or contracting. The nonlinear ODEs are obtained from the governing PDEs of energy, momentum, and concentration by applying the appropriate similarity transformations to address temperature, velocity, and concentration distributions. These nonlinear equations are solved numerically in Matlab software using the bvp4c function. The velocity, temperature, and concentration profiles are analyzed for varying parameter values to understand their influence on the boundary layer development. Contour plots of the Nusselt and Sherwood numbers are produced with regard to the important parameters to visualize the local heat and mass transfer rates. The findings indicate that the power-law index significantly modifies the velocity, thermal, and solutal boundary layers, while the inclination angle regulates buoyancy-driven effects. The stretching parameter enhances flow stability and heat and mass transfer, whereas shrinking promotes boundary-layer separation. Thermal and solutal Grashof numbers further intensify convection, as evident from the Nusselt and Sherwood number contours. These findings provide practical guidance for engineering applications such as polymer extrusion, wire coating, and chemical processing, where control of boundary-layer behavior is crucial for design improvements and efficiency enhancement in real-world thermal and mass transport systems.

An incompressible, electrically incompressible hydromagnetic flow of viscous fluid induced by a rotating disk is examined. The fluid movement is also caused due to periodic oscillation of the stretchable disk. The flow thermal phenomenon is affected by thermal radiation. Moreover, the melting process is incorporated in terms of the boundary condition at the disk surface. The highly nonlinear system of time-based partial differential equations is first normalized through well-established similarity variables, and then the resulting system is solved by means of a built-in package in Maplesoft. The graphical representations of velocity and thermal fields in all relevant directions against the dimensionless parameters are shown. The numerical values of shear stresses, tangential stresses, and heat transfer rate for selected values of physical quantities are calculated and shown in tabular form. Such effects are quantified and interpreted using statistical modeling through multiple linear regression, heatmap-based correlation graphs, and sensitivity analysis. The graphical results are found in good alignment with existing literature. It is deduced that an increase in the melting parameter reduces the temperature curves and the axial velocity field. Furthermore, such a parameter also resulted in a reduction in heat transfer rate at the melting surface.

In this study, we investigated the thermal performance of nanoencapsulated phase-change material (NEPCM) under magnetohydrodynamic (MHD) mixed convection in a three-dimensional lid-driven trapezoidal chamber featuring a zigzag-shaped lower wall. The approach of enthalpy–porosity was employed to model the phase changing progression, and the impacts of key parameters—including Reynolds number (Re = 0–500), Hartmann number (Ha = 0–100), zigzag number (N = 0–4), NEPCM volume fraction (ϕ = 0%–8%), and magnetic field inclination angle (α = 0°–90°)—were examined. We found that increasing Re significantly increased the average Nusselt number, driven by stronger lid-driven convection. In contrast, increasing Ha suppressed fluid motion via the Lorentz force, resulting in a reduction of up to 65% in heat transfer efficiency compared with the nonmagnetic case (Ha = 0). Increasing the zigzag number from N = 0 to 4 reduced the average Nusselt number by approximately 23%, primarily due to flow obstruction and geometric resistance. Higher NEPCM volume fractions improved heat storage capacity and promoted more extensive melting by sustaining temperature gradients. Additionally, the inclination angle of the magnetic field had a notable influence. As θ increased from 0° to 90°, the magnetic field became more perpendicular to the main flow direction, which intensified the damping effects and further decreased both the heat transfer and entropy generation efficiencies. These findings demonstrate that the combined effects of magnetic field orientation, field strength, cavity geometry, and NEPCM concentration play a crucial role in optimizing thermal performance and phase-change behavior in MHD-driven thermal energy storage systems.

This study investigates the influence of the Soret effect on unsteady, two-dimensional magnetohydrodynamic (MHD) heat and mass transfer in a rotating fluid confined between parallel porous plates under a transverse magnetic field and thermal radiation. The primary objective is to quantitatively predict flow behavior using a hybrid approach combining numerical simulation with artificial neural networks (ANNs). Governing partial differential equations are non-dimensionalized via similarity transformations and solved numerically using MATLAB's bvp4c solver. A deep-learning model is then trained on the synthetic data set to validate and forecast velocity, temperature, and concentration profiles. Key findings reveal that an increase in the Prandtl number suppresses thermal diffusion, while the Soret number enhances mass transfer. The ANN predictions exhibit high accuracy (R² > 0.94), confirming the robustness of the data-driven methodology. This study demonstrates the efficacy of machine learning in capturing nonlinear transport phenomena in rotating porous MHD systems, offering a computationally efficient alternative for industrial thermal-fluid design.

This investigation focused on the drying properties and mathematical modeling of moringa leaves under infrared drying. The moringa leaves were dried at thermal conditions (40°C, 50°C, and 60°C), with emitter distances of 7.5, 12.5, and 17.5 cm, respectively. The initial moisture content of the sample was 73.41% (wet basis). Under drying conditions of 60°C and a bed depth of 7.5 cm, the maximum drying rate of 0.054 g/min was recorded at 30 min. Among the ten models evaluated for drying kinetics, the Wang and Singh model exhibited the best fit, yielding an R² of 0.9997 and RMSE of 0.0054 at 60°C and 7.5 cm emitter distance. Drying kinetics were evaluated using a total of ten mathematical models, among which the Wang and Singh model exhibited the most accurate fit, with an R² (0.9997) and an RMSE (0.0054) at 60°C and an emitter distance of 7.5 cm. This study emphasized that during infrared drying, drying parameters, including temperature and emitter distance, significantly affect how rapidly moisture evaporates from moringa leaves. This study emphasized that during infrared drying, the drying parameters, particularly temperature and emitter distance, play a crucial role in governing the rate of moisture evaporation from moringa leaves. These insights into drying behavior and model suitability might assist in improving infrared drying methods for moringa leaves.

Photovoltaic/thermal (PV/T) systems, which combine electricity and heat generation, are crucial for maximizing solar energy utilization; however, their performance is hindered by thermal-induced efficiency losses in high-irradiance environments. This study addresses the challenge of optimizing PV/T systems for arid, sunny climates, where elevated temperatures reduce electrical efficiency by up to 0.5% per °C. The aim is to develop a novel, energy-efficient PV/T system with low-flow-rate air cooling to enhance thermal and electrical performance while minimizing operational complexity. Using computational fluid dynamics (CFD) simulations in ANSYS Fluent, we model a PV/T system integrated with a solar air collector operating at a low airflow rate of 0.02 kg/s, compared to a conventional PV panel, across solar radiation levels ranging from 300 to 1000 W/m². Parametric analysis of airflow rates (0.01–0.05 kg/s) and tube diameters (20–50 mm) was conducted to optimize performance. The proposed system achieves a thermal efficiency of 52.88% (125.4% higher than the reference case's 23.46%), an electrical efficiency of 14.04% (1.66% improvement), and a 2.67 K reduction in panel temperature. It reduces fan power by 50%–70% (5–10 W/m²) compared to high-flow systems, increases exergy efficiency by 71%–186%, and enhances the sustainability index by 11.4%, leading to a 10%–15% reduction in CO₂ emissions. These findings demonstrate that the low-flow-rate PV/T design offers a scalable and sustainable solution for high-irradiance regions, such as the Middle East and North Africa, enabling efficient energy harvesting with reduced environmental impact.

This study presents a numerical and experimental investigation of the effect of flash evaporation on the thermal performance of a wickless heat pipe used in desalination applications. Moreover, this study examines the factors that affect flashing efficiency, such as the feed water mass flow rate, inlet temperature, and cooling water flow rate. The thermal performance of a wickless heat pipe with flash evaporation caused by a micro-scale jet nozzle with a 0.4 mm diameter is evaluated using 3D numerical simulations with ANSYS Fluent 22.2. The two configurations of the heat pipe are studied based on the nozzle position. In the first configuration, the nozzle is located far from the condenser. In the second configuration, the nozzle is positioned close to the condenser. These two cases are examined under three water mass flow rates (0.00138, 0.0022, and 0.0025 kg/s) to evaluate the influence of nozzle position on flash evaporation intensity and overall thermal performance. Results showed that the first configuration exhibits superior thermal performance, a higher condensation mass flow rate, and greater flash efficiency compared with the second configuration. The optimum performance is achieved at an inlet mass flow rate of 0.0022 kg/s, where the flash efficiency reaches up to 78%, confirming that increasing the distance between the nozzle and the condenser enhances the flashing and condensation processes.

This study investigates the effect of fin geometry, specifically fin number and fin height, on the thermal and hydraulic performance of heat sinks used in an air-cooling thermoelectric (TEC) system. In a combined numerical simulation experimental validation approach, a computational fluid dynamics (CFD) model was developed to analyze heat sink cooling with varying configurations of 15, 21, and 27 fins with varying fin heights of 28, 32, and 36 mm for air velocities ranging from 1 to 3 m/s. It was found that with a larger number of fins, from 15 to 27, a maximum enhancement of 15% for the convection heat transfer coefficient was obtained, with a maximum increment of roughly about 20% for pressure drop being obtained due to higher airflow resistance decreasing system efficiency. Increasing fin height from 28 to 32 mm increased dissipation rates, with a maximum value for thermal performance factor (TPF) of 1.09 being obtained. Optimal configuration was seen to be 21 fins with 32 mm fin height with a minimum cold side temperature of 7.5°C under 1 m/s airspeed while effectively trading off thermal transfer enhancement with airflow resistance. It was seen that experimental measurements precisely agreed with numerical calculations with approximate differences less than 5%, confirming the credibility of the CFD model. This study provides practical guidelines for optimizing heat sink geometries for thermoelectric air-cooled applications toward acceleration of effective compact environmentally nonhazardous solid-state cooling technologies.