The present study investigated the enhancement of convective heat transfer in horizontal tubes using twisted tape inserts, particularly emphasizing the influence of modifications to their geometrical configurations. Three twisted tape models were designed using SolidWorks: a plain tape, a tape with curved edges, and a tape with curved edges and holes. Two twist ratios were considered, namely TR1 = 6.666 and TR2 = 5. Computational Fluid Dynamics (CFD) simulations were performed to evaluate the velocity and temperature fields, Nusselt number, and friction factor over a Reynolds number range of 15,000–25,000. The results indicate that employing twisted tape with curved edges and perforations leads to the greatest enhancement in heat transfer. Specifically, the Nusselt number increases from 410 for curved edges without perforations to 460, whereas the plain tape achieves 380 at Re = 25,000 and TR2. The tape with curved edges (without holes) demonstrated the most favorable improvement in friction factor, attaining a value of 0.024 versus 0.029 for the plain tape, corresponding to a 20.8% reduction. As a result, the performance evaluation factor achieved a peak value of 1.24, indicating a 30.5% improvement. These findings demonstrated that optimized twisted tape geometries significantly enhanced heat transfer performance while maintaining reasonable pressure drop penalties. This highlights their potential applicability in thermal system design, particularly in compact and energy-efficient heat exchangers.

Experimental observation of friction factor variation in regenerators at cryogenic temperatures

This study experimentally investigates the thermal–hydraulic performance of heat exchanger tubes fitted with wired twisted tapes, with particular emphasis on the effects of the hole spacing-to-width ratio (s/W) and edge margin-to-width ratio (e/W). Experiments were conducted over a Reynolds number range of 6000–20,000, and the results were compared with those of plain tubes and tubes equipped with conventional twisted tapes. The findings revealed that the incorporation of wires significantly enhanced heat transfer due to the combined action of longitudinal eddies generated by wire protrusions and swirling flow induced by the twisted tape. At identical Reynolds numbers, tubes with a smaller hole spacing (s/W = 0.16) exhibited superior heat transfer performance, achieving Nusselt number enhancements of up to 107.7% relative to plain tubes and 51.6% relative to conventional twisted tapes. Similarly, reducing the edge margin ratio intensified near-wall eddies and further disrupted the boundary layer. The friction factor was found to increase with decreasing hole spacing and edge margin, primarily due to additional flow obstructions and enhanced near-wall shear stresses. For wired twisted tapes with s/W = 0.16, the friction factor reached nearly six times that of a plain tube. Despite this penalty, the thermal performance factor (TPF) remained favorable, with values of up to 1.2, indicating that the heat transfer benefits outweighed the corresponding pressure losses.

The hollow fiber membrane humidification modules are used for indoor humidification in hot–dry regions and heating in winter. The module is composed of several flexible hollow fiber membranes, which are bent and displaced by gravity and fluid forces. This paper is a further study of previous work that reveals the internal relationship between the forces generated by vortex shedding and fiber vibration. The central trajectories of fibers in the flow field are described for various pulsating flow and fiber structure parameters. The effects of fiber displacement on fluid flow, heat transfer, and mass transfer performance at different parameters are discussed. The results show that the fiber displacement in the flow field consists of two components: (i) deformation caused by fluid drag force and gravity and (ii) periodic vibration caused by periodic lift and drag force as vortices shed at the fiber surface. The fiber vibration facilitates the vortex shedding on the fiber surface, which enhances the convective heat and mass transfer performance on the fiber surface. The average friction factor (fm,v), Nusselt number (Num,v), and Sherwood number (Shm,v) increased by 12.9%, 39.3%, and 20.0%, respectively, when the fiber vibrated compared to non-vibration. This implies that inducing fiber vibration can optimize the heat and moisture transfer performance.

Abstract Enhancing heat transfer performance while maintaining acceptable pressure losses remains a critical challenge in the design of compact heat exchangers. In this context, surface modification techniques combined with advanced working fluids have attracted increasing attention as effective passive enhancement methods. This study numerically investigates the thermo-hydraulic performance of dimpled tube heat exchangers employing an Al 2 O 3 –CuO/water hybrid nanofluid, with the aim of identifying an optimal dimple configuration that maximizes heat transfer enhancement while minimizing flow resistance. The simulations are performed in ANSYS Fluent 2022 R2 using the RNG k – ε turbulence model under a constant heat flux of 25.5 kW m −2 . Two dimpled tube configurations Model 1 with three dimples and Model 2 with six dimples were analyzed over a Reynolds number range of 5000–15,000. Based on previous studies, the dimple diameter and pitch were fixed at 3 mm and 10 mm, respectively, corresponding to geometries reported to yield favorable thermo-hydraulic performance. The hybrid nanofluid was modeled at a volume fraction of 1%. The results demonstrate that the synergistic interaction between dimpled geometry and hybrid nanoparticles significantly enhance convective heat transfer by promoting flow mixing and thinning the thermal boundary layer. Compared with a smooth tube, Model 2a achieved a 35–56% increase in the Nusselt number and a 22–34% increase in the friction factor, resulting in the highest performance evaluation criterion (PEC = 1.68), corresponding to a 68% improvement in overall thermo-hydraulic efficiency. Numerical predictions showed excellent agreement with experimental data from the literature, with maximum deviations of 5.32% for the Nusselt number and 9.86% for the friction factor. Overall, this study provides new quantitative insights into the combined role of dimpled tube and Al 2 O 3 –CuO/water hybrid nanofluids as a promising passive technique for enhancing heat exchanger performance, offering valuable guidance for the design of high efficiency thermal systems.

This review develops a unified geometric framework for synthesizing global asymptotic laws, termed classical entanglement. The central tool is the entanglement operator, a Minkowski–La metric blend that couples asymptotic regimes through an index a>1, producing a nonlinear global state whose intermediate region is metrically non-separable and cannot be written as a linear combination of its limits. The framework reveals a universal transition knee whose curvature scales linearly with a, independent of amplitudes or local scales. We show that this geometric mechanism encompasses Orlicz norms, weighted Hölder metrics, and iterated Hölder constructions, the latter being structurally isomorphic to self-similar root approximants. A conceptual “Rosetta Stone” links practitioner terminology, geometric meta-language, and functional-analytic structures, clarifying how classical entanglement unifies empirical blending, metric curvature, and Calderón-type interpolation. Applications to turbulence (Darcy friction factor), fractional dynamics, and scale-dependent diffusion illustrate how classical entanglement provides stable, asymptotically consistent global states across multi-scale systems.

Characterizing friction factors in head loss causing non-Darcy flow on fractures with tortuosity and inertial effects

This study aims to provide a deeper and more realistic understanding by conducting a systematic comparison between the two approaches (Reynolds number and volumetric flowrate). The analysis emphasizes the impact of internal channel design, using inclined winglets and surface corrugation. An experimental investigation was carried out to prepare and characterize a TiO₂/H2O nanofluid at 1% volume concentration, including accurate measurements of its thermophysical properties and stability validation. A numerical model was also developed using ANSYS Fluent to simulate the hydrothermal behavior of two channel configurations (straight and corrugated), in which the effects of both Reynolds number and flowrate were evaluated across key parameters such as heat transfer coefficient, pressure drop, performance evaluation criterion, and wall temperature distribution. By observing the flow patterns inside the corrugated channel, three distinct flow behaviors were identified: axial flow along the channel, transverse flow induced by winglets, and swirling flow within the corrugated grooves. This combination of flow modes enhanced fluid mixing and significantly improved heat transfer performance. The results show that TiO₂ nanofluid significantly enhances the thermal–hydraulic performance, with the relative friction factor (Γ) increasing from 6.9 to 7.6 and the thermal enhancement ratio (En) reaching 2.8 (PEC ≈ 1.5) when evaluated using Reynolds number, while volumetric flow rate assessment (7–9 L/min) yielded higher Γ (3.9–4.2) and En/PEC (2.5/1.6). The effects of the internal enhancement techniques were found to be more pronounced when using flowrate as the reference indicator. This work represents a valuable scientific contribution by integrating three advanced enhancement strategies (surface corrugation, inclined winglets, and nanofluid), and it highlights the need to reconsider traditional thermal system design methods based solely on Reynolds number.

Abstract Enhancing the thermal efficiency of heat exchangers is a critical objective in modern thermal management systems, aimed at achieving energy savings, material optimization, and improved performance. The turbulent heat transfer and flow properties of graphene oxide-water nanofluid in a horizontal tube under constant heat flux circumstances are investigated in this work using both theoretical and experimental methods. To address the limited understanding of graphene oxide nanofluids under turbulent regimes, both numerical simulations using the Finite Volume Method (FVM) and experimental validation were conducted for nanoparticle concentrations of 0.025-0.1 wt% and Reynolds numbers from 5000 to 18000. Results revealed that the Nusselt number increased with both nanoparticle concentration and Reynolds number, achieving a maximum enhancement of 36.36%, while the friction factor increased by 128.57% at a nanoparticle concentration of 0.1 wt%. Despite the moderate increase in pressure drop, the overall thermal performance improvement demonstrates the potential of graphene oxide-water nanofluids as efficient coolants for advanced heat exchangers and energy systems.

Corrugated pipes are widely used due to their mechanical flexibility; however, their corrugated internal geometry is associated with increased hydraulic losses. Previous studies have reported a non-classical increase in friction factors with pipe diameter at identical Reynolds numbers, although the underlying mechanisms and related energy implications have not been fully clarified. In this study, turbulent flow behavior and pumping power requirements in stainless-steel corrugated pipes are investigated using a validated three-dimensional Computational Fluid Dynamics (CFD) framework based on the SST k–ω turbulence model. The numerical predictions show good agreement with available experimental data, with maximum deviations remaining below approximately 12% across the validated range. The results indicate that both friction factor and pumping power increase systematically with pipe diameter under dynamically similar flow conditions, demonstrating that Reynolds-number similarity alone does not ensure flow similarity in corrugated geometries. From an energy perspective, an Energy Penalty Factor (EPF) is introduced to quantify corrugation-induced pumping requirements, and a surrogate correlation is developed to relate EPF to Reynolds number and selected dimensionless geometric parameters. The proposed formulation exhibits strong predictive performance within the investigated parameter space (R2 = 0.972) and enables rapid, CFD-free estimation of energy penalties for preliminary design and comparative evaluation of corrugated piping systems.

Abstract Brazed plate heat exchanger (BPHE) was analyzed using computational fluid dynamics (CFD) simulations by ANSYS Fluent to investigate the chevron‐patterned plates. The influence of geometric parameters, including corrugation pitch, depth, and angle was analyzed. The corrugation pitch was set to 2.5, 5, and 7.5 mm, the corrugation depth was varied at 2, 3, and 4 mm, and the corrugation angle was adjusted to 60°, 65°, and 70°. Under three Reynolds numbers, the results indicate that the lowest pressure drop was achieved when the plate parameters were set to a corrugation angle of 60°, a corrugation depth of 4 mm, and a corrugation pitch of 7.5 mm. In addition, the configuration with a corrugation angle of 60°, a corrugation depth of 2 mm, and a corrugation pitch of 7.5 mm achieves the lowest friction factors. Furthermore, at a fixed flow rate of 0.56 LPM, increasing the corrugation angle from 60° to 70° resulted in a pressure drop 2.36 times higher than that at 60°, increasing the corrugation depth from 2 to 4 mm reduced the pressure drop by up to 74%, while increasing the corrugation pitch from 2.5 to 7.5 mm led to a reduction of approximately 55%. Overall, the influence of geometric parameters on pressure drop was found to decrease in the order of corrugation angle, corrugation depth, and corrugation pitch. This work presents a systematic, pressure‐drop‐oriented comparison of the relative effects under various geometric parameters, offering quantitative guidance for chevron type BPHEs.

The Tanjungsari–Jatinangor Road in Sumedang Regency is a major corridor with high mobility that frequently experiences traffic congestion. The increasing number of vehicles and high side friction factors such as on-street parking, vehicle movements in and out of adjacent areas, and commercial activities have contributed to a decline in road performance. This condition is reflected in the increasing volume-to-capacity ratio and degree of saturation. This study aims to analyze the volume- to-capacity ratio (V/C) and determine the road level of service (LoS) on the Tanjungsari–Jatinangor segment. The research employed a field survey during peak hours and analysis based on the Indonesian Highway Capacity Manual (PKJI) 2023. The collected data include traffic volume, side friction, free-flow speed, and road capacity. The results indicate that the peak traffic volume reached 2,129 pcu/hour with a road capacity of 2,585 pcu/hour. The calculated V/C ratio of 0.82 and degree of saturation (DS) of 0.82 show that traffic conditions are nearing capacity. According to PKJI 2023, the Level of Service (LoS) is classified as D, indicating unstable flow, frequent delays, and reduced comfort for road users. After applying a side friction reduction scenario, the capacity increased to 2,818 pcu/hour, the DS decreased to 0.75, and the LoS improved to C. Therefore, side friction control, on-street parking management, and improved traffic management are necessary to enhance road performance.

In this investigation, the stream of bio-magnetic liquid specifically, blood flow containing copper nanoparticles, past a stretchy surface that is impacted by thermal radiation and a magnetic field, is studied. In this analysis, copper nanoparticles (Cu-NPs) are utilized due to their wide range of applications in biological research. Copper nanoparticles possess antibacterial, antimicrobial, and antifungal capabilities as a result of their characteristics. The non-linear partial differential equations (PDEs) are reduced to ordinary differential equations (ODEs) by the use of a similarity transformation. The physical solution was determined by applying neural network technology (NNT). The relevant dimensions of this model, including the radiation parameters, suction, slip, ferromagnetic, magnetic field, and radiation, are graphically illustrated for various profiles. One of the most important findings was that temperature and velocity decrease in proportion to increases in the ferromagnetic factor. The wall friction factor and Nusselt number exhibit a consistent declining pattern for the parameters of radiation conduction, and copper volume fraction. However, it establishes opposite trends for the ratio of free stream to stretching velocities. Also, a regression model curves, histograms, and MSE results are used to evaluate and verify the efficacy of the NNT. The outcomes achieved indicated that NNTs provide reliable predictions and performance enhancements.

This study explores the development of innovative microsink designs to enhance cooling efficiency at low pumping power for compact electronic devices. Three-dimensional simulations of conjugate heat transfer and fluid flow in rectangular microchannels were conducted, focusing on novel geometries fan-shaped cavities, fan-shaped cavities with ribs, fan-shaped cavities with secondary branches, and fan-shaped cavities with both secondary branches and ribs. Performance was evaluated using average friction factor, Nusselt number, and thermal performance across Reynolds numbers from 135 to 603. The highest thermal performance achieved by fan-shaped cavities with both secondary branches and ribs among the all channels. The systematic variation of the relative geometric variable of fan-shaped cavities with both secondary branches and ribs attain the highest thermal performance equal to 1.75 at Reynolds number of 603 with the combination of the secondary branch width equal 0.75, secondary branch angle equal to 0.166, fan-shaped cavity width equal to 1, fan shaped cavity length equal to 0.055, and pitch distance equal to 0.2. The disruption of thermal boundary layer by longitudinal and transverse vortices contributes to augment the heat transfer with cost of pressure drop. The role of vortex-induced mixing in heat transfer enhancement is comprehensively demonstrated.

Minimizing Entropy Generation in Heat Exchanger Tubes With Ball Inserts: Numerical Simulation

To augment the performance characteristics of a solar thermal collection device (STCD) for heating air, the present work utilizes the integration of cylindrical pin fins over a wavy absorbing surface. This unique combination has led to a superior heat transfer rate augmentation, while maintaining low levels of associated drop in pressure. With the imposition of a uniform 1 kW/m2 heat flux at the upper portion of the absorbing surface, the important parameters like thermo-hydraulic performance index (THPI), along with Nusselt number and friction factor, are studied thoroughly. The height of the cylindrical fin is taken to be 21 mm. Wavelength and amplitude of the wavy receiver surface are taken to be 137.5 and 17.18 mm, respectively. Reynolds number is altered in the range of 3,500–16,000. A three-dimensional simulation is performed in ANSYS FLUENT 23 using RNG k-ε turbulence model. An experimental set-up is developed to perform the experimentations to validate the solver. The performance of the proposed STCD is compared with other attractive designs recently reported in the literature and found to yield better results. The highest THPI of 2.14 is achieved, which establishes the superiority of the design based on hydraulic and heat-transmission performance.

Advanced passive heat transfer enhancement: numerical analysis of TiO₂-water nanofluid flow in tubes fitted with twisted tape and conical ring inserts

This research article investigated the effect of the triangular fins and triangular fins with ribs by the ANSYS Fluent-2018. Ribs are added at the side walls of the solar air heater to divert the flow on the teethed portion of the absorber plate, which was hidden in previous research designed of the roughened solar air heater. The comparison between the two designs of the solar air heaters was done based on the thermal performance factor. The best design is selected and validated experimentally. The outcomes of the study showed that the triangular fins have a higher thermal performance factor than the triangular fins with the ribs due to lower pressure drop in the triangular fins. However, triangular fins have a lower Nusselt number as compared to triangular fins with ribs. The Reynolds Number and pitch to height ratio were chosen as important parameters which investigated the performance of the triangular fins solar air heater through numerically. The friction factor, Nusselt Number, and the Thermal Performance Factor (TPF) are reduced as the pitch to height ratio increases. The rise in Reynolds Number reduces the friction factor, but the Nusselt Number and TPF increase for a triangular fin solar air heater. The maximum value of the Nusselt Number and TPF obtained are 114.95 and 1.89 for the Reynolds Number 10,000 and P/h ratio of 1. The minimum friction factor reached 0.023 at a Reynolds Number of 10,000 and a P/h ratio of 3. The numerical results are validated with the experimental results on the date 11/03/2025. The maximum outlet temperature of air, thermal efficiency, and exergy obtained through the experimental observation are 72.25°C, 77.18%, and 3.4% at noon at a mass flow rate of 0.08 kg/s. The numerical results are validated with the experimental results within an accuracy of 5%.

Effort estimation remains a critical challenge in Agile Software Development due to the high dynamics of requirement changes and the reliance on friction factors (FF) and dynamic factors (DF) that are inherently subjective, often leading to significant deviations between estimated and actual project effort. This study aims to improve the accuracy of Agile software effort estimation by optimizing FF and DF parameters using a hybrid metaheuristic approach based on Genetic Algorithm and Ant Colony Optimization (GACO). The proposed method integrates a pheromone-based guided search mechanism from Ant Colony Optimization to generate high-quality initial populations, which are subsequently refined through the evolutionary process of Genetic Algorithm to achieve more stable and systematic parameter optimization. Experimental evaluation was conducted using two datasets, namely the Ziauddin dataset representing Agile projects and the Maxwell dataset encompassing cross-domain software projects. The results demonstrate that the GACO approach consistently outperforms the conventional Genetic Algorithm, as indicated by a substantial reduction in Mean Absolute Error from 616.38 to 354.81. Furthermore, statistical validation using the Wilcoxon Signed-Rank Test confirms that the performance difference between the two approaches is statistically significant. These findings indicate that integrating Ant Colony Optimization into Genetic Algorithm effectively enhances the accuracy, stability, and robustness of software effort estimation, thereby supporting more reliable resource planning in Agile software development.

The solar air heater (SAH) is a simple device manufactured from locally available materials and used to heat air for various purposes, including heating, drying, and industrial applications. Despite its simplicity and low manufacturing cost, it has low thermal performance. Therefore, it has undergone several modifications in an attempt to improve its thermal performance. Among these attempts is the use of roughened air-duct to create turbulent flow of air and then improves heat transfer rates. The challenge was to improve heat transfer rates while simultaneously reducing frictional properties. This review focuses on recent advances in roughened surface used for improving the performance of SAHs. Comparison between different roughened surfaces in in terms of thermohydraulic performance, friction factor (f) is also of great interest in this work. The review results recommended using perforated rectangular fins as the roughened elements as it achieves the highest thermohydraulic performance parameter (THPP = 5.1) among the several roughened surfaces considered in this review. While the highest improvement in Nusselt number was achieved (47.7 times compared to smooth-duct) when punched baffles of delta-shaped winglets were used. The frustum jet impingement roughness showed the highest improvement in f. Based on the previous conclusions, combining perforated fins, punched baffles and frustum jet impingement roughness can result in the best performance of the solar air heaters.