Heat Transfer最新文献

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.

This paper examines the five fundamental models to study ferrohydrodynamics (FHDs). These models are important to study theoretically any physical phenomena of FHD flow. To yet, no researcher has examined the importance and limitations of these models. This study work is an attempt to present a complete set of equations for these models. This study also addresses the limitations and practical applicability of these models in FHDs. Neuringer–Rosensweig models are found to be suitable for cases where the applied magnetic field and the magnetization are parallel. The Jenkins model is important to deal with the problems related to lubrication since this model includes the role of material constants in the governing equations. The Shliomis model takes into account how fluid and magnetic particles interact when a magnetic field is present. This model is important for the problems related to rotational viscosity and considers the role of time-varying magnetic fields. Berkovsky's nonequilibrium magnetization model is useful when the magnetic field is not in an equilibrium position. In the couple stress models of Berkovsky, the imposed magnetic field interacts not only with magnetic particles by means of force as well as torque interactions. Researchers do not use it much, nevertheless, because of its high nonlinearity and difficulties. To increase the effectiveness of theoretical models in FHDs, these models should take into account variations in the volume concentration, size distribution of magnetic particles, chain formation effect, and stability of magnetic fluid.

Sweet orange peel, a major by-product of juice processing, is recognized as a bioactive-rich material abundant in phenolic compounds, offering substantial potential for valorization and sustainable by-product utilization. This study investigates the effect of plasma-activated water (PAW) pretreatment combined with hot-air tray drying on the drying behavior and quality attributes of debittered sweet orange peel. Drying was conducted under varying temperatures (50°C, 60°C, and 70°C) and air velocities (0.3, 0.6, and 0.9 m/s). The results demonstrated a significant reduction in drying time, from 465 to 225 min in treated samples (PAW-pretreated tray-dried) and from 420 to 165 min in control samples (non-pretreated tray-dried), as the temperature increased from 50°C to 70°C. Among the tested mathematical models, the logarithmic model provided the best fit for describing drying kinetics. The optimal drying condition, identified as 60°C and 0.9 m/s air velocity, resulted in sweet orange peel powder with enhanced phenolic content and improved functional, structural, and physical attributes. Treated samples exhibited significantly reduced oil absorption capacity, water absorption capacity, and swelling capacity compared with control samples. Scanning electron microscopy analysis revealed compact, dense structures in control samples, while treated samples displayed porous structures with visible spacing between particles. Relative crystallinity increased from 18.09% in control samples to 21.45% in treated samples, indicating structural transformation. Fourier-transform infrared spectroscopy confirmed the presence of key functional groups, such as hydroxyl and carbonyl, associated with the peel's bioactive compounds. These findings highlight the synergistic effect of PAW pretreatment and hot-air drying in enhancing the quality and properties of sweet orange peel powder, offering an effective strategy for the valorization of citrus fruit waste.

This study presents a comprehensive linear stability analysis of dual-diffusivity convection in a bidispersive porous medium, embedding a uniform vertical throughflow and variable gravity within the framework of the Darcy–Brinkman model. Three distinct gravity variation profiles—linear, parabolic, and exponential—are systematically examined to understand their impact on convective stability. A high-order Galerkin approximation is utilized to obtain solutions to the governing eigenvalue problem. The critical Darcy–Rayleigh number is evaluated as a function of key nondimensional parameters, including the Péclet number, gravity modulation parameter, solute Rayleigh number, permeability ratio, Lewis number, Darcy number, and the interphase momentum transfer parameter. Special attention is given to the role of throughflow direction and magnitude, with both upward and downward flows analyzed across varying gravity fields. The results indicate that exponential gravity variation markedly enhances system stability through intensified gravitational stratification, while higher permeability ratios and stronger interphase momentum transfer further stabilize the system by increasing viscous dissipation and drag coupling. A U-shaped, nonmonotonic variation of the critical Rayleigh number with the throughflow parameter is observed, demonstrating the destabilizing role of moderate throughflows and the stabilizing influence of strong throughflows. Overall, the findings provide key insights into the complex interplay of hydrodynamic and buoyancy-driven mechanisms in bidispersive porous systems, with implications for thermal management, geophysical flows, and engineered porous structures. The findings provide practical insights for optimizing geothermal reservoirs, chemical reactors, and environmental systems by controlling throughflow, interporosity exchange, and gravity variations to enhance stability and transport efficiency.

Single slope solar still was built to study the impact of phase change material (PCM) on water output. Bottom along with four sides of the still are built from an aluminium sheet of 0.79 mm thickness. The base is coupled with a sinusoidal shaped basin liners (SSBL), a layer of aluminium fitted with copper tubes. The unit was fixed in a box of 19 mm thick ply to minimise heat loss from the bottom and side faces to the surroundings and completely sealed to reduce the leakage. Myristic and palmitic acid granules as PCM were filled in the copper tubes of 15 mm outer diameter. PCM changes its phase by absorbing excess energy during sunshine as a result of sensible heating till it hits the melting temperature. During the night, PCM solidifies by losing its heat of fusion to the water. The heat interaction between the glass cover and basin water was examined by the analysis of energy balance and internal heat transfer equations. The experiment was performed in three sets: without PCM, with PCM I, and with PCM II; however, the fixed quantity of 6 litres of tap water was taken to maintain 2 cm of water depth. Results showed that SSBL solar still with PCM I (myristic acid) and PCM II (palmitic acid) enhanced the overall yield by 16% and 9% in comparison to SSBL solar still without PCM, while condensate production in night with PCM I and PCM II increased by 75% and 38%, respectively, compared to the solar still output in night without PCM. Meanwhile, PCM I (myristic acid) showed the best performance, achieving the highest thermal (44.0%) and exergy (6.9%) efficiencies. It also offered the lowest cost per liter ($0.0116) and the highest sustainability index (1.076).

This study investigates the enhancement of natural convection heat transfer in a differentially heated square cavity by coupling fluid–structure interaction (FSI) with a nanofluid containing nanoencapsulated phase change material (NEPCM). This configuration is important for improving passive cooling in energy-efficient technologies, such as electronics, buildings, and electric vehicles. The novelty of this study lies in the integration of a sinusoidal oscillating flexible fin with latent-heat-enhanced nanofluids in a fully coupled FSI framework. A finite element method is used to solve the governing equations for fluid flow, heat transfer, and structural motion, with validation through grid independence tests and comparison against benchmark numerical and experimental data. Parametric studies were performed for fin oscillation amplitude (0.05–0.15), oscillation period (0.1–0.7), Rayleigh number (10⁴–10⁶), and Stefan number (0.2–0.7). Results show that increasing the amplitude to 0.15 enhances the mean Nusselt number by up to 10%; lower periods (τ_fin = 0.1) and Stefan numbers (Ste = 0.2) reduce heat transfer; higher Rayleigh numbers promote stronger convective currents and better thermal uniformity. These findings offer quantitative insights for optimizing thermally responsive structures using NEPCM fluids and flexible fins, enabling efficient heat transfer.

In this study, we employ a standard perturbation technique to analyze the onset of Rayleigh-Bénard convection in a horizontally oriented, electrically conductive fluid layer overlying a porous substrate. The system is bounded laterally by rigid, adiabatic walls and subjected to internal heat generation, a uniform vertical magnetic field, and local thermal nonequilibrium (LTNE) conditions. The analysis is conducted within the Darcy regime and incorporates various temperature gradient (TG) profiles. We investigate how different TG configurations influence the onset of convection, particularly under thermally adiabatic boundary conditions at the upper and lower surfaces. Critical Rayleigh numbers are determined by solving the corresponding eigenvalue problem for configurations with both rigid-bottom/free-top boundaries, incorporating surface tension-driven velocity boundary conditions. The study further examines the effects of parameters such as the modified porosity ratio, thermal diffusivity ratio, and heat source intensity, emphasizing their role in promoting LTNE under six distinct TG models. Perturbation analysis reveals that maximum convective activity occurs at the mid-plane for the inverted parabolic (Model-3) and Dirac delta (Model-6) temperature gradients. Magneto-convective behavior under LTNE is visualized in the presence of a vertical magnetic field and volumetric heat generation, providing insights into the thermal system's behavior under complex boundary and gradient conditions. The results align well with existing literature, supporting their relevance to thermal management in energy systems, biomedical devices, aerospace structures, electronic cooling, and geophysical processes.