Heat Transfer最新文献

This study coupling the lattice Boltzmann method (LBM) with Artificial Neural Networks (ANNs) to explore combined convection within a moving-wall square cavity containing variably shaped heated blocks, targeting applications in thermal management of electronic components such as lithium-ion batteries. This hybrid approach significantly reduces computational cost and time while enabling accurate prediction of thermal behavior for different geometries. The enclosure is stuffed with air (Pr = 0.71) and cooled from its vertical sides by a constant cold temperature, $��\; ��T_C^{\prime }��$, while the horizontal walls are thermally insulated, with the top wall is driven at a uniform velocity, $��\; ��u_0^{\prime }��$. For Richardson numbers between 0.01 and 100, the investigation has been conducted for various geometrical shapes of the heated block under consideration, including square, rhombus, circular, horizontal, and vertical ellipses. The ANN is employed to forecast new cases, thereby reducing computational effort while also serving to validate the numerical results obtained. The findings are graphically displayed as stream function contours, temperature contours, mean fluid temperature, and average heat transfer (HT) in relation to the aforementioned controlling parameters. The results indicate that, across all Ri values, the horizontal elliptical block (HEB) achieves the highest HT rate, while the circular block (CB) exhibits the lowest. More precisely, changing the block shape from CB to the horizontal elliptical one (HEB) increases the HT rate to about 20.43% at Ri = 0.01. Finally, the ANN predictions showed excellent accuracy, with results closely aligning with numerical simulations, thereby confirming the reliability and robustness of the hybrid ANN–LBM approach.

This study numerically investigates the effect of different microchannel geometries integrated into the absorber tube on the thermal performance of a parabolic trough solar collector. Four configurations were analyzed: empty (straight pipe), circular, square, and triangular microchannels. Computational Fluid Dynamics simulations were conducted using ANSYS Fluent 19.0, adopting a Finite Volume Method with a pressure-based solver, the SIMPLE algorithm for pressure–velocity coupling, and second-order upwind discretization for momentum and energy equations. Simulations were performed across mass flow rates ranging from 0.25 to 1.0 kg/h, with an inlet fluid temperature of 25°C and a constant solar irradiance of 884 W/m². The corresponding Reynolds numbers ranged approximately from 110 to 420, indicating laminar flow across all cases. Among the configurations, the triangular microchannel exhibited the best performance. At 0.25 kg/h, it achieved an outlet temperature of 101.73°C and a thermal efficiency of 85%, compared with 92°C and 37.15% in the nonchanneled base case. At 1.0 kg/h, the triangular design reached a Nusselt number of 30.48, more than double that of the baseline (14.45), indicating superior convective heat transfer. Validation against published results showed a maximum deviation of only 2.6%, confirming the accuracy of the simulation model. The findings highlight that triangular and square microchannels significantly enhance heat transfer and thermal efficiency, particularly at low flow rates, making them promising designs for advancing solar thermal energy systems.

Drying of medicinal herbs like Justicia adhatoda is essential to maintaining their bioactive constituents, but conventional methods tend to degrade quality by subjecting them to excessive heat for long periods. To overcome this, the current research compares and assesses the drying kinetics, phytochemical retention, and optical quality of J. adhatoda leaves under cabinet tray drying (CTD) and microwave drying (MD). Since the plant has pharmacological importance, the research seeks to select a drying process that guarantees efficiency and quality retention. Experimental drying was carried out at different temperatures (45°C–75°C) for CTD and microwave powers (200–700 W) for MD. Among the 11 thin-layer models, Page's model proved to be the most reliable in predicting drying behavior for both processes (R² = 0.999) for CTD and (R² = 0.996) for MD. MD under 360 W took the shortest time, whereas 200 W maintained the maximum total flavonoids and tannin contents. Antioxidant activity was maximum at 360 W, indicating maximum retention of functional constituents under optimal microwave power. Microwave-dried samples exhibited better color preservation, demonstrating its capability to retain sensory as well as commercial acceptability. The results of this study have important consequences for the herbal processing industries, allowing scalable, high-quality drying schemes to be developed that protect the therapeutic and cosmetic worth of medicinal crops.

The design freedom of three-dimensional (3D) concrete printing (3DCP) enables complex building envelopes with integrated air cavities; however, their thermal performance in extreme climates poses a critical challenge, particularly for cavities with nonuniform geometries. This study presents a combined experimental and numerical analysis of conjugate heat transfer in a real 3DCP building envelope featuring variable-thickness air cavities under hot-arid conditions. A comprehensive methodological framework was employed: (1) in situ U value measurements on north and slanted east cavity walls (3.75 m tall; max cavity width, 900 mm) with and without interior insulation, (2) development of a robust numerical model to simulate conjugate heat transfer across laminar to turbulent flow regimes, and (3) whole-building cooling load estimation for the 168 m² structure. Results demonstrate that wide cavities (> 25 mm) develop strong buoyancy-driven circulation (Ra ≈ 10¹¹ at ΔT = 20 K), severely degrading insulating performance and yielding high U values of 2.67–3.29 W/(m² K) for uninsulated walls—approximately 30% higher cooling loads than standard construction. Crucially, parametric analysis reveals that filling cavities with low-conductivity porous media (e.g., sand and k = 0.27 W/[m K]) effectively suppresses convection, restoring thermal performance to near pure conduction levels and reducing U values by up to 82% when complemented with insulation. These findings provide essential, practical strategies for optimizing energy efficiency in future 3DCP buildings constructed in hot-arid climates.

The low thermal conductivity of phase change materials (PCMs) remains a primary constraint on the performance of latent heat thermal energy storage (LHTES) systems. This review critically analyzes the extensive body of research dedicated to overcoming this limitation through the application of various fin geometries and designs. It delves into the geometrical parameters, dimensionless numbers, and placement strategies of fins, including rectangular, annular, spiral, plate, and novel biomimetic designs, evaluating their impact on thermal behavior through both numerical and experimental investigations. The analysis demonstrates that fin configuration fundamentally dictates the balance between conductive and convective heat transfer mechanisms. While longitudinally finned structures often provide the most practical enhancement due to their manufacturing simplicity, innovative designs like tree-shaped and spiral fins offer superior thermal performance at the cost of increased complexity. Key trade-offs are identified, notably between thermal performance gains and the concomitant reduction in PCM storage volume. The review concludes by highlighting critical research gaps, particularly the need for multi-objective optimization frameworks that concurrently consider thermal performance, energy density, and economic viability, and calls for long-term stability studies to assess the practicality of advanced fin designs.

Freshwater scarcity poses a global challenge, particularly in regions where conventional water resources are limited. Solar stills offer an economical, sustainable solution; however, their yield is limited. This study aims to evaluate a new tracking concentrated tilted tubular solar still equipped with a heat-pipe TTSS-HP. The novelty of the present work lies in four aspects: a novel trough U-channel design that improves the interception of reflected solar radiation, a novel hexagonal glass cover design. A receiver formed of four-sections, combined with a heat-pipe and dual trough concentrators. Outdoor experiments are carried out in Baghdad, Iraq (33.27° N, 44.37° E), to test the water depth (55 mm, 65 mm) and still tilt angles (10°, 15°) impact on stills' yield and efficiency. The reported yield for TTSS-HP was enhanced by 62.1% and 46.3% for water heights of 55 and 65 mm, respectively, when the still is tilted at 10° compared to the still with no heat pipe. While that for the still tilted at 15° was 41.6% and 29.3%. It has been found that increasing the water content of the still from 55 to 65 mm increases the freshwater yield by 14.9% for the still tilted at 10° and 21.3% for the still tilted at 15°. The optimum thermal efficiency was 21.6% for a maximum water depth of 65 mm and a still tilt angle of 15°. TTSS-HP achieves the highest daily yield of 5.34 L at a 15° tilt angle and 65 mm water depth, while the still without a heat-pipe HSS yields 3.31 L at a 10° tilt angle and a 65 mm water depth. It is concluded that TTSS-HP with trough reflectors improved freshwater yield by 62.1% and thermal efficiency by 49.12% compared to the baseline HSS.

Heat exchangers are essential for power plant energy transfer process optimization because they ensure that heat energy is transferred between materials efficiently. The challenge is to use various fluid blends to increase power plant heat exchanger performance and thermal efficiency. It seeks to solve issues including fluid compatibility and system complexity while improving heat transport, lowering energy consumption, and optimizing plant efficiency. The objectives include determining and selecting the optimal fluid mixes for heat exchangers, improving thermal efficiency, reducing energy consumption, ensuring compatibility with system components, maximizing power plant performance, and promoting sustainability. Power plant heat exchanger performance can be maximized by choosing fluid blends with optimal thermal characteristics, such as high thermal conductivity and low viscosity. The first step in the procedure is to analyze important properties of different fluid mixtures, such as heat capacity, flow behavior, and stability. After selection, the heat exchanger is designed and optimized to maximize energy efficiency by adjusting materials, size, and fluid dynamics. The chosen blends are then integrated into the plant's infrastructure, ensuring compatibility with existing systems. Performance testing and calibration ensure optimal heat transfer, minimizing energy loss and enhancing thermal efficiency, ultimately reducing operational costs and improving sustainability in power plant operations. Findings show that ammonia (1800 W/m²·K) provides the highest heat transfer, while Oil (1000 W/m²·K, 20.0 mPa·s viscosity) has the lowest. Ethylene Glycol (1300 W/m²·K) and Water-Glycol mix (1100 W/m²·K) offer moderate performance and are implemented in Python Software. Advanced fluid blends, nanofluids, and AI-based optimization strategies can all be investigated in future studies to improve heat exchanger performance even further while lowering emissions, energy use, and power plant operations’ sustainability.