This study conducts a numerical investigation into the heat transfer enhancement of $\mathrm{Fe}_3 \mathrm{O}_4$-distilled water nanofluid within a magnetically influenced environment. The research is centered on the analysis of the impact of varying magnetic field strengths on the heat transfer characteristics in a controlled tube setting. The tube, possessing an inner diameter of 25.4 mm and a length of 210 mm, serves as the medium for the flow of nanofluid, initially at 300 K. The influence of magnetism on the nanofluid's thermal boundary layer and the formation of fluid vortices is meticulously examined, leveraging the application of magnetic fields ranging from one to three Teslas. In this context, the study observes the behavior of magnetic particles under these fields, revealing their attraction or repulsion, subsequently inducing turbulence and modifying flow patterns. It is noted that increased flow velocities tend to shield the magnetic field's thermal effects. A key focus is placed on the Nusselt number and $\mathrm{Y}^{+}$ as indicators of heat transfer efficiency, both of which demonstrate significant variations with changes in the magnetic field strength and fluid velocity. The Nusselt number, in particular, escalates to a peak value of 128.7 when exposed to a 0.1 m/s flow velocity and a magnetic field of 3 Teslas. The findings suggest an interrelation between increased magnetic field strengths and the entrance of the fluid into a turbulent state, thereby facilitating an efficient temperature transfer to the fluid. Notably, this research sheds light on the prospect of using ferrofluid-based cooling systems in electrical equipment, highlighting the potential of magnetically manipulated nanofluids to enhance heat transfer capabilities. The investigation delineates how the interplay between magnetic fields, fluid velocity, and nanofluid properties can be optimized for improved thermal management in various applications.

This investigation examines the effects of varied nanoparticle concentrations, such as zinc oxide (ZnO), copper oxide (CuO), and aluminum oxide (Al₂O₃), on the mass fraction and melting characteristics within nano-enhanced phase change materials (NEPCMs). Employing numerical simulations via ANSYS-FLUENT, the study explores these dynamics within a square enclosure subjected to distinct thermal gradients. The enclosure, measuring 10cm×10cm, incorporates a heat-supplying wall, partitioned into quarters, each exhibiting a unique temperature gradient. This setup provides a comprehensive understanding of boundary conditions relevant to NEPCM behavior. The focus lies on a comparative analysis of NEPCM’s thermal properties under varying nanoparticle concentrations: 0.1, 0.3, and 0.5 weight percent. A low-temperature wall, lined with paraffin wax and integrated with these nanomaterials, facilitates the assessment of their impact on the phase change materials (PCMs). Remarkably, an inverse relationship is observed between nanoparticle concentration and mass fraction, ranging from 0.86 to 0.08. This finding underscores the significant role of nanoparticle integration in modulating NEPCM properties. Among the nanoparticles studied, CuO emerges as the most efficacious in enhancing melting due to its low density and high thermal conductivity. The temperature distribution profile within the paraffin wax shifts from a dispersed state to a more uniform and curved pattern upon nanoparticle incorporation. Such a transformation indicates an improved thermal response of the NEPCM system. The implications of this study are manifold, extending to the design and optimization of thermal energy storage systems. These insights are particularly valuable for applications in energy conservation within buildings, solar energy equipment, transportation, and storage solutions. The research elucidates the criticality of selecting appropriate nanoparticle concentrations for achieving desired phase change properties in NEPCM-based systems. Furthermore, it contributes to a deeper understanding of how nanoparticle characteristics influence the thermal behavior of PCMs, thus offering a guide for future innovations in this field.

In the domain of compact flat plate heat exchangers, enhancing efficiency remains a pivotal challenge, primarily due to the low thermal conductivity characteristic of the gas phase. This investigation explores efficiency improvements in such exchangers by the integration of modified delta-wing longitudinal vortex generators (LVGs). The focus is centered on geometric modifications and alterations in the size ratios of the traditional delta-wing design as documented in pertinent literature. The geometric modifications include partial surface removal and elevation from the attachment surface, as well as a combination of these approaches. Concurrently, size ratio alterations involve a systematic reduction in the overall dimensions of the modified LVGs to 75%, 50%, and 25% of their initial size. Employing ANSYS Fluent, the study conducts numerical simulations to evaluate air flow at various Reynolds numbers ($Re$ = 2,000 – 10,000). Analyses include examining temperature progression along the axial distance, mapping temperature contours, and applying the Q-criterion for in-depth understanding. Performance evaluation of each modification was undertaken by calculating the thermal enhancement factor (TEF) in relation to a baseline scenario of two unmodified flat plates, utilizing the Nusselt number and the friction factor for comprehensive comparison. To ensure reliability, the study demonstrates mesh independence in results and validates the computational model through comparative analysis with established correlations and experimental data from existing literature on delta-wing LVG designs. Findings indicate that geometric modifications of vortex generators, as explored in this research, do not markedly decrease head loss nor significantly enhance system performance. In contrast, size ratio modifications, particularly the reduction of vortex generator dimensions to 75% and 50% of the original size, show an increase in TEF ranging from 3% to 9% compared to the conventional delta-wing design. This underscores the potential of incorporating an array of such modified LVGs on each plate of a flat plate heat exchanger to boost its efficiency significantly.

This study explores the durability of plasticized polyvinyl chloride (PVC-P) geomembranes in hydraulic engineering anti-seepage structures, particularly under varying operational temperature conditions. Employing accelerated thermal air aging tests on three distinct PVC-P geomembrane variants, the study assesses their mechanical properties, specifically axial tensile strength, using an electronic universal testing machine. A comprehensive thermal air aging model, based on the Arrhenius equation, has been developed, offering insights into the lifespan prediction of these geomembranes. Results demonstrate that factors such as annual average temperature, plasticizer content, and membrane thickness significantly influence the geomembranes' service life. Post-aging observations include a notable yellowing and increased brittleness of the geomembranes, coupled with a decline in tensile strength and elongation. Elongations exhibit a decreasing trend, aligning with a first-order degradation kinetics equation. Under conditions of 50℃ over a period of 120 days, the elongation of polyvinyl chloride (PVC)-HX, PVC2.0-JT, and PVC2.5-JT geomembranes was reduced to 255.88%, 430.11%, and 434.58%, respectively. Predictions indicate that at an operational temperature of 20℃, the expected lifespans for these geomembranes are 19, 45, and 48 years, with material failure correlating to plasticizer loss rates of 58.2%, 32.5%, and 24.8%, respectively. These findings offer valuable guidance for the selection of geomembrane materials in hydraulic engineering projects, considering various designed service durations.

In the design of shell and tube heat exchangers encompassing a condensing zone, meticulous attention is required due to the complexities surrounding forced convection in multiphase systems. Despite extensive research, the intricacies within these multiphase systems have remained elusive, rendering the heat transfer coefficient unresolved. In this study, a novel methodology is introduced to elucidate the thermal characteristics of forced convection within the condensing region of shell and tube condensers. An amalgamation of theoretical methods, specifically the Logarithmic Mean Temperature Difference (LMTD), and empirical data sourced from industrial operations forms the foundation of this approach. Upon rigorous analysis employing both Power Law Analysis and Logarithmic Linear Regression, a correlation in terms of ${N_u}=C \cdot {Re}^m \cdot {Pr}^{\mathrm{n}}$ within the condensing region was discerned using Buckingham Pi Theorem. Findings revealed coefficients of C=1.15, m=0.893, and n=13.442. For optimization purposes, the Particle Swarm Optimization (PSO) Algorithm was employed. A focused examination of parameters such as tube length, tube outside diameter, baffle spacing, shell diameter, number of tube passings, and tube wall thickness revealed that by attenuating their values by 30%, 46%, 80.3%, 8%, 50%, and 61.9% respectively, a substantial increase in condenser effectiveness was observed, elevating the value from 0.9473 to 4.299.

In this study, a numerical investigation into heat transfer and entropy generation characteristics using confined-slot jet impingement was conducted. Comparisons were drawn between the heat transfer and entropy generation attributes of two wing ribs positioned on the heated impinging target surface and those of a rib-less surface. The influences of variations in the spacing between the stagnation point and the rib (B) of (10-30 mm), ranging from 10 to 30 mm, rib heights (A) between 0.5 to 2 mm, and a Reynolds number of the jet (Re) between 3000 to 8000 on fluid flow, heat transfer, and entropy generation were elucidated. Employing the Finite Volume Method (FVM) managed the continuity, momentum, and energy equations in adherence to the principles of the SIMPLE methodology. Results revealed that the Nusselt number $(\overline{N u})$, pressure drop, and total entropy $\left(\bar{S}_{\text {total }}\right)$ escalated in accordance with Re and A. Conversely, they diminished with reduced spacing from the stagnation point to B. Notably, a superior heat transfer rate was observed when employing a target plate integrated with wing ribs in contrast to a rib-less configuration. Performance Evaluation Criteria (PEC) values were noted to augment with rib height increment. It is demonstrated that the PEC increases as A increases. Also, the lower value of PEC equals 1.044 at A of 2 mm, B of 10 mm, and Re of 8000, while the higher value of the PEC equals 1.68 at A of 2 mm, B of 10 mm, and Re of 3000. The findings suggest that slot-Jet impingement complemented by wing ribs plays a pivotal role in enhancing the cooling efficiency of electronic devices.

This investigation elucidates the intertwined effects of magnetic fields and porous media on the flow of nanofluids towards a stretching sheet, contemplating variable viscosity and convective boundary conditions. A nanofluid model, incorporating the influences of thermophoresis and Brownian motion, is adopted. Via judicious transformations, the fundamental governing coupled non-linear partial differential equations are condensed, and the consequent transformed equations are numerically resolved employing the Finite Element Method (FEM). Paramount emphasis is accorded to parameters embodying notable physical significance, inclusive of the Prandtl number (Pr), Hartmann number, Lewis number (Le), Brownian motion number (Nb), thermophoresis number (Nt), and permeability parameter. The numerical results acquired, as particular instances of the aforementioned study, are found to be congruent with previously reported findings, substantiating the accuracy and reliability of the proposed methodology. A thorough examination of the collective impact of the selected parameters on flow and heat transfer characteristics has been systematically undertaken, revealing intricate dependencies and fostering a deeper understanding of the complex phenomenon under consideration. This study, hence, paves a pathway towards bolstering the comprehension of flow mechanics in porous media under the influence of magnetic fields, contributing valuable insights to the overarching field of fluid dynamics in nano-engineering applications.

In the quest to design a robust model for microwave heating systems with symmetrical octagonal tube cavities (MWHSO), a fuzzy-based approach, specifically the Takagi Sugeno Fuzzy Model, was explored to capture the dynamics of the heating process. To achieve this, the mathematical model was adaptively adjusted according to varying input conditions through the utilization of fuzzy logic. Input data were sourced from two magnetrons, with the system outputs derived from measurements acquired from five temperature sensors placed on the heated object. For performance evaluation, the Root Mean Square Error (RMSE) was employed. A comparison was drawn with the autoregressive model with exogenous variable (ARX), a traditional approach wherein the system's mathematical model remains static. Simulation studies were conducted, treating every probe measurement across all dataset validations as distinct cases. It was found that the T-S Fuzzy model surpassed the ARX40 in performance in 33 of the total cases, accounting for 92.49%. The most notable performance of the fuzzy-based approach was observed at a 180-Watt power input, recording an average RMSE of 0.00574 across the five sensors. In contrast, the ARX-based model registered an RMSE of 0.01256. These findings suggest that the fuzzy-based modeling approach presents a compelling alternative for representing the dynamic heating processes within MWHSO.

Helical or spiral coiled heat exchangers, prevalent in industries such as power generation, heat recovery systems, the food sector, and various plant processes, exhibit potential for performance enhancement through optimal fluid selection. Notably, nanofluids, distinguished by their superior thermophysical properties, including enhanced thermal conductivity, viscosity, and convective heat transfer coefficient (HTC), are considered viable candidates. In this study, the thermo-physical attributes of helical coil heat exchangers (HCHEs), when subjected to nanofluids, were meticulously examined. During the design phase, Creo parametric design software was employed to refine the geometric configuration, subsequently enhancing fluid flow dynamics, thereby yielding a design improvement for the HCHE. Subsequent computational fluid dynamics (CFD) simulations of the heat exchanger were conducted via the ANSYS CFX program. A CuO/water nanofluid, at a 1% volume fraction, served as the basis for the CFD analysis, incorporating the Re-Normalisation Group ($k-\varepsilon$) turbulence model. From these simulations, zones exhibiting elevated temperature and pressure were discerned. It was observed that the wall HTC value for the CuO/water mixture surpassed that of pure water by 10.01%. Concurrently, the Nusselt number, when the CuO/water nanofluid was employed, escalated by 6.8% in comparison to utilizing water alone. However, it should be noted that a 5.43% increment in the pressure drop was recorded for the CuO/water nanofluid in contrast to pure water.

A hybrid procedure FLT-HPM was proposed in this study, by combining the homotopy perturbation method (HPM) with Fourier transform and Laplace transform which aimed to find an approximate analytical solution to the problem of two-dimensional transient natural convection in a horizontal cylindrical concentric annulus bounded by two isothermal surfaces. The effect of the Grashof number, Prandtl number, and the radius ratio on fluid flow (air) and heat transfer with different values awreas discussed. Moreover, the velocity distributions and the mean Nusselt numbers were studied, and the Nusselt numbers were used to represent local and general heat transfer rates. Finally, the convergence of FLT-HPM was tested theoretically through the proof of some theorems. In addition, these theorems were applied to the results of the new solutions obtained using FLT-HPM.

The development of an effective cooling system is paramount for the optimal design of high altitude Unmanned Aerial Vehicles (UAVs). These vehicles often operate at or near supersonic speeds in thin atmospheric conditions to generate sufficient lift. It is emphasized that the necessity for air-cooling mandates the incorporation of cooling ducts into the initial design, striving for a balance between low-speed, high-density cooling air for efficient heat rejection, minimal drag, or even potential thrust augmentation. The proposition is that dedicated, meticulously optimized cooling air pathways may facilitate superior performance at high altitudes. The abstract further underscores that the longevity and efficiency of solar panels, commonplace in solar-powered UAVs, are substantially temperature-dependent. As such, high-altitude cooling poses a complex challenge. For conventionally fueled jet-powered UAVs, fuel may serve as a viable heat sink, necessitating a design approach that integrates Peltier cells within electronic components. An alternative approach involves the installation of a subsonic Meredith duct within the primary air intake of the main turbo engine. This duct operates by reducing air speed at the face of a high-efficiency air-to-liquid radiator and then expanding the heated air into a nozzle, making the application of radiators feasible, even for supersonic UAVs. The feasibility of deploying the Meredith duct with direct exposure to external air in subsonic UAVs is also explored. This investigation thus sheds light on innovative cooling mechanisms for UAVs operating at high altitudes, potentially leading to improved efficiency and lifespan of critical components. The findings are poised to enhance the understanding of UAV design and operation, contributing to their overall performance and effectiveness.