A computational fluid dynamics (CFD) analysis is conducted to systematically investigate heat transfer enhancement in tubes fitted with grooved twisted tapes and to identify the groove geometry that provides the best thermo-hydraulic performance. Three grooved twisted tape configurations-circular-grooved twisted tapes (CGTT), rectangular-grooved twisted tapes (RGTT), and triangular-grooved twisted tapes (TGTT)-are evaluated and compared with a smooth tube and a conventional twisted tape over a Reynolds number range of 5000-20,000 under isothermal wall conditions. The grooved twisted tapes enhance heat transfer through the combined effects of swirl-induced secondary flows and groove-generated flow disturbances, which intensify turbulent mixing and reduce the thickness of the thermal boundary layer. Compared with the plain tube, the grooved configurations increase the Nusselt number by 1.472-1.98 times while increasing the friction factor by 3.21-3.58 times. Relative to the conventional twisted tape, the grooved designs provide an additional 8.0-12.1% enhancement in heat transfer with only a marginal increase of 0.2-1.5% in friction factor. The thermodynamic analysis indicates that the CGTT configuration exhibits the lowest entropy generation rate and exergy loss throughout the investigated Reynolds number range. In particular, the CGTT achieves a Bejan number of 0.999841 at Re = 5000, demonstrating an excellent balance between heat transfer enhancement and frictional losses. Furthermore, the CGTT attains the highest thermal performance factor (TPF) of 1.294 at Re = 5000 and maintains TPF > 1.0 over the entire Reynolds number range. The overall performance ranking is consistently established as CGTT > TGTT > RGTT based on comprehensive analyses of velocity fields, streamline patterns, turbulent kinetic energy distributions, temperature contours, and thermodynamic characteristics. Although the present study identifies the circular-groove configuration as the optimal design for a twist ratio (y/W) of 3.0, further parametric investigations involving variations in twist ratio, groove dimensions, and groove pitch are required to develop generalized design guidelines.

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.

This study investigates heat transfer enhancement in the cooling channels of gas turbine blade turbulators using modified transverse baffles with isosceles triangular sawtooth perforations. The proposed baffle design aims to improve convective heat transfer by promoting flow mixing and disrupting the thermal boundary layer. Experiments were conducted in a rectangular channel with an aspect ratio of 3.75 under constant heat flux conditions using air (Pr = 0.7) as the working fluid. The effects of Reynolds number (Re = 6000–24,000), sawtooth width ratio (a/W = 0.0, 0.0625, 0.125, 0.25, and 0.5), and sawtooth height ratio (b/e = 0.0, 0.25, 0.5, 0.75, and 1.0) were systematically investigated. The blockage ratio (e/H) and pitch ratio (P/H) were maintained at 0.3 and 1.5, respectively. Heat transfer characteristics were evaluated using the thermochromic liquid crystal (TLC) technique, while thermal–hydraulic performance was assessed in terms of the Nusselt number (Nu), friction factor (f), and thermal performance factor (TPF). The results demonstrate that introducing sawtooth perforations significantly enhances heat transfer compared with a smooth channel, yielding Nusselt number ratios (Nu/Nus) between 1.6 and 2.6. The highest heat transfer enhancement was achieved at a/W = 0.0625 and b/e = 0.25, where the relatively small sawtooth openings generated stronger jet impingement, enhanced flow mixing, and more effective disruption of the thermal boundary layer. However, these geometric modifications also increased the pressure loss due to intensified flow blockage and recirculation, resulting in friction factor ratios (f/fs) ranging from 8.9 to 14.9. The maximum pressure-drop penalty occurred at b/e = 0.25 because the smaller openings produced stronger turbulence and increased flow resistance. Despite the increased friction loss, the optimum configuration (a/W = 0.0625 and b/e = 0.25) achieved the highest thermal performance factor of 1.2 at Re = 6000.

Silicon nitride (Si3N4) ceramics are indispensable in aerospace bearings and semiconductor substrates due to their exceptional mechanical and thermal properties. However, achieving damage-free, atomic-level surface finishes remains problematic. Traditional mechanical polishing induces subsurface microcracks, while chemical mechanical polishing (CMP) is plagued by low material removal rates and environmental toxicity. This review critically evaluates femtosecond laser polishing as a transformative, “green” non-contact alternative. We first elucidate the laser-matter interaction mechanisms specific to wide-bandgap Si3N4 (Eg≈5.3 eV), clarifying how multiphoton absorption enables “cold ablation” by suppressing the heat-affected zone (HAZ) via the two-temperature model (TTM) dynamics. A distinct material removal mechanism driven by rapid thermal decomposition (Si3N4→Si+N2) and phase explosion is highlighted. Synthesizing recent experimental data, we establish a quantitative process window. Operating slightly above the ablation threshold (F≈1.4 J/cm2) with high spot overlap (70%–90%) is critical to balance surface leveling against the incubation effect, which otherwise triggers porosity. Furthermore, we address the unique challenges of inducing periodic structures (LIPSS) on dielectric surfaces and propose a hybrid manufacturing strategy—integrating high-speed laser roughing with CMP finishing—to resolve efficiency constraints. Finally, an industrial roadmap involving high-throughput polygon scanners and AI-driven closed-loop control is outlined, providing a comprehensive reference for advancing femtosecond laser polishing toward scalable, high-precision manufacturing.

This paper proposes an experimental, intelligent optimization approach to improve the thermal cooling performance of an overclocked graphics processing unit (GPU). A closed-loop liquid-cooling system was built and tested utilizing deionized water and a silver (Ag) nanofluid coolant (0.015% vol.) across a variety of microchannel heat sink topologies with varying fin spacing. Key thermal performance indicators, including GPU temperature, coolant outlet temperature, and thermal resistance, were measured at different coolant flow rates. Experiments revealed that raising the flow velocity and decreasing the fin gap considerably enhanced cooling performance, while the Ag nanofluid consistently lowered GPU temperature by 1-3 degrees C compared to water. An Artificial Neural Network (ANN) surrogate model was constructed and trained using experimental data to support predictive analysis and system optimization, achieving excellent predictive accuracy with low RMSE. The trained ANN model was combined with the Non-dominated Sorting Genetic Algorithm II (NSGA-II) to perform multi-objective optimization, aiming to minimize GPU temperature and thermal resistance while improving heat removal. The Pareto-optimal solutions revealed that nanofluid-based cooling offered the best trade-off circumstances, with optimal designs occurring at moderate flow rates and small fin spacing. The ANN-NSGA-II multi-objective optimization results indicated that the best thermal performance of the GPU cooling system was achieved when using Ag nanofluid (0.015 vol.%) as the coolant, with an optimal coolant flow rate in the range of 1.30-1.84 LPM and an optimal fin/channel spacing of 0.57-0.71 mm, producing GPU temperatures of 29.18-29.66 degrees C, coolant outlet temperatures of 29.06-29.41 degrees C, and a minimized thermal resistance of 0.0106-0.0152 degrees C/W; thus, overall, the suggested ANN-NSGA-II framework works well as a practical design tool for improving GPU cooling systems and may be used to other high-heat-flux electronic thermal management applications.

This study presents a comparative thermal assessment of Fe₃O₄ nanofluid-cooled copper-foam mini-channel heat sink configurations for prismatic lithium-ion battery packs. An experimental investigation combined with a three-dimensional Eulerian two-phase computational fluid dynamics (CFD) model was developed to evaluate the thermal performance of six cooling configurations, including a conventional liquid cooling jacket (Model I), copper-foam embedded design (Model II), optimized cooling pattern (Model III), and fin-enhanced copper foam structures with straight, wavy, and curved fins (Models IV–VI). The results demonstrate that integrating copper foam significantly enhances heat dissipation and temperature uniformity by increasing thermal conductivity and the solid–fluid interfacial area. At low discharge rates (1 C), the thermal improvement is moderate, wit peak temperature reductions of approximately 1–3% compared to the baseline. However, at 3 C, Model V exhibited the best thermal performance among the fin-enhanced configurations, achieving the lowest maximum temperature of 39.83 °C and the smallest temperature difference of 9.39 °C. At a low discharge rate of 1 C, the thermal improvement was moderate, with peak-temperature reductions of approximately 1–3% relative to Model I. The findings highlight that coupled structural modifications, including porous media integration and fin geometry optimization, play a critical role in improving thermal performance, particularly under high heat load conditions. These results provide design guidelines for advanced liquid-cooled battery thermal management systems for high-power, fast-charging applications.

This study aims to experimentally evaluate and compare the electrical–thermal performance of a 20-cell 18650 lithium-ion battery pack cooled by a pure phase change material (PCM) and a PCM/TiO2 nanoparticle composite to identify an effective passive thermal management approach for EV battery applications. Using a controlled charging–discharging system, thermocouple-based temperature mapping, and systematic tests across multiple C-rates (0.75 C–1.5 C), the study measures the variations in battery temperature, generated heat, and voltage behavior as functions of depth of discharge (DOD) and state of charge (SOC). The results show that the PCM/nanoparticle mixture markedly improves thermal conductivity, reduces peak temperature by approximately 8–10 °C compared with pure PCM, delays thermal saturation at higher C-rates, and enables a wider safe DOD range with reduced voltage sag and lower heat accumulation. Based on the experimental temperature/voltage trends in this study, limit DOD to ≤40–50% at high power (≈1.5 C), ≤50–60% at moderate power (≈1 C), and ≤60–70% at low power (≈0.75 C) (i.e., target SOC windows roughly 60–100% SOC at 1.5 C, 40–100% SOC at 1 C, and 30–100% SOC at 0.75 C), with an absolute practical upper DOD limit of ~70% to avoid frequent deep discharge damage; these limits keep peak temperatures below ~40–45 °C, reduce severe voltage sag near cutoff, and greatly extend cycle life because shallower cycling (e.g., 50% vs. 100% DOD) produces many times more cycles. These improvements enhance battery safety, performance stability, and cycle life, making the nanoparticle-enhanced PCM a practical, compact, and energy-efficient solution for passive battery thermal management in electric vehicles.

This study numerically investigates the flow characteristics around single and tandem cylinders positioned in close proximity to a moving wall at a Reynolds number of Re = 100. Using the finite volume method, simulations were performed for aspect ratios (AR) ranging from 1 to 5, while maintaining a fixed gap ratio (G/A = 0.5) and spacing ratio (S/A = 0.5). The results demonstrate that the moving wall significantly influences flow dynamics and stabilizes the wake. For an aspect ratio of 1, the merging of shear layers leads to the formation of elongated, steady vortices. As the aspect ratio increases from 2 to 5, the wake becomes increasingly smooth and the magnitude of positive vortices decreases, resulting in steady wake formation without significant oscillations. Force analysis reveals that the upstream cylinder exhibits chaotic drag (Cd) and lift (CL) coefficients, whereas the downstream cylinder shows a consistent trend. Notably, the upstream cylinder maintains a higher drag coefficient than the downstream cylinder, with both being lower than that of a single isolated cylinder. The observed suppression of vortex shedding is primarily attributed to the interaction and coupling of shear layers between the moving wall and the cylinders, identifying shear alignment rather than viscous damping as the core mechanism of wake control.

Air-cooled heat exchangers employing twisted-tape passive inserts exist in many forms; however, designing tapes that are practical to manufacture while enhancing heat transfer without incurring excessive pressure drop remains challenging. This study therefore introduces gradient quadruple twisted tapes (GQTT), which gradually vary the pitch across four tapes to control swirl and mix along the tube. In addition, the turn count changes in steps along the four tapes, which triggers extra turbulence near each change and keeps the flow well mixed downstream. This simple and manufacturable pattern aims to boost heat transfer while keeping the added friction under control. Our objective is to evaluate whether GQTT can improve overall performance while keeping the pressure drop within a practical range, in comparison with a plain tube and a constant-turn tape. A realizable k-epsilon turbulence model, rigorously validated against benchmark data, was applied to eight GQTT variants and benchmarked against a plain tube and a constant-turn tape for Reynolds numbers (Re) between 5000 and 19,000. Spatial second-order schemes, grid-independence testing, and strict residual criteria ensured solution accuracy. Among the candidates, the descending-opposite-pitch configuration (Ds-OPSD) consistently delivered the highest performance. First-law analysis reveals a peak thermal performance factor (TPF) of 1.42 at Re = 5000, equating to a 42 % gain in overall thermo-hydraulic efficiency over the plain tube, with the Nusselt number (Nu) climbing from 57.5 to 100 across the examined Re window. Second-law metrics corroborate this superiority. At the same Re of peak TPF, the Ds-OPSD cuts exergy destruction from 291.4 to 62 W (approximate to 79 % reduction versus the plain tube and approximate to 22 % versus the constant-turn tape). Total entropy generation remains minimal and nearly constant (Stotal approximate to 0.206-0.212), while the Bejan number stays high (approximate to 0.999-0.971), indicating that the enhancement is achieved without excessive frictional penalties.

This study conducts an investigative exploration of thermal and hydraulic performance regarding hybrid inserts which combine perforated twisted tapes with vortex generator wings mounted inside circular tubes. The insert design makes use of both swirl flow and secondary vortex generation which breaks up the thermal boundary layer and boosts convective heat transfer rates. During this investigation, researchers utilized water as the working fluid at Reynolds number (Re) from 3000 to 21,000 to study the effect of three perforation diameter ratio (d/D) 0.143, 0.19, and 0.238 and respective Vortex generator (VG) edge cut ratio (a/D) 0.143, 0.19, and 0.238. Nusselt number (Nu) reach 182.3 % and thermal enhancement factor (TEF) achieve 1.68 at Re = 15,000 when using the enhanced tube compared to a smooth tube. The industrial application of larger VG openings at standard spacing produced a beneficial relationship between thermal performance and flow resistance when the pressure rise reached 345 %. The analysis of entropy generation showed heat transfer irreversibility gave way to frictional irreversibility when both perforation dimension and Re became larger. System design optimization prerequisites involved trade-offs which met Bejan number (Be) analysis trends. The Random Forest machine learning model combined with ANN and Linear Regression models contributed to thermal parameter prediction (Nu, f, TEF) by delivering a predictive accuracy level with less than 6.6 % deviation. The research leads to vital knowledge needed for developing compact heat exchangers integrating passive enhancement methods.

This study presents a comparative thermal assessment of ferrofluid-cooled copper-foam mini-channel heat sink configurations for prismatic lithium-ion battery packs. An experimental investigation combined with a three-dimensional Eulerian two-phase computational fluid dynamics (CFD) model was developed to evaluate the thermal performance of six cooling configurations, including a conventional liquid cooling jacket (Model I), copper-foam embedded design (Model II), optimized cooling pattern (Model III), and fin-enhanced copper foam structures with straight, wavy, and curved fins (Models IV–VI). The results demonstrate that integrating copper foam significantly enhances heat dissipation and temperature uniformity by increasing thermal conductivity and the solid–fluid interfacial area. At low discharge rates (1C), the thermal improvement is moderate, with peak temperature reductions of approximately 1–3% compared to the baseline. However, at higher discharge conditions (3C), the performance enhancement becomes more pronounced, with fin-enhanced configurations achieving up to a ~6% reduction in peak temperature. Among all designs, Model V exhibits the best temperature uniformity, while Model VI achieves the lowest peak temperature. The experimental and numerical results show good agreement, with deviations generally below 6%, confirming the reliability of the proposed model. The findings highlight that coupled structural modifications, including porous media integration and fin geometry optimization, play a critical role in improving thermal performance, particularly under high heat load conditions. These results provide design guidelines for advanced liquid-cooled battery thermal management systems for high-power, fast-charging applications.

Heat exchangers are crucial devices in industries, and enhancing their thermal performance while controlling pressure losses remains a significant challenge. This paper examines the idea that inclined perforated disk (IPD) inserts can be effectively used to improve heat transfer in circular tubes with constant heat flux conditions at acceptable levels of hydraulic penalties. Turbulent airflow with Reynolds numbers (Re) ranging from 5000 to 21,000 was examined in experiments, and three perforation indices (PI = 0.21, 0.24, and 0.27) were tested to determine the effects of hole density on thermal and hydraulic performance. Evidence showed that the Nusselt number (Nu) had been improved by over 86 % compared to plain tubes, with the thermal enhancement factor (TEF) reaching as high as 1.53 at PI = 0.27 and Re = 5000. Particle swarm optimization (PSO) and neural network modelling multi-objective optimization were used to test the results of the experiment and determine the best operating conditions at PI = 0.21. The paper has demonstrated that inclined perforated disk inserts can form a viable passive method for enhancing the efficiency of heat exchangers, as the swirl and jet flow patterns created by the perforations effectively break the thermal boundary layer, thereby increasing the rate of convective heat transfer.

This study numerically investigates heat transfer and thermodynamic behavior in twisted square and rectangular air ducts while keeping a constant hydraulic diameter (Dh = 30 mm). Three aspect ratios are considered (AR = 1.00, 0.75, and 0.50). The heated test section (900 mm) is divided into three equal segments, and three pitch patterns are examined: a uniform pitch (400–400–400 mm, P444) and two axial gradients (300–400–500 mm, P345; 500–400–300 mm, P543). All results are compared to a standard reference, the straight square duct (SD-AR1.00), to ensure fair comparisons across all cases with Reynolds numbers between 5000 and 20,000. Among the twisted ducts, the strongest rectangularity combined with the increasing pitch sequence, TSD-AR0.50-P345, provides the best overall balance. Its heat transfer rises from Nu = 39.39 to 88.62, giving Nu/Nu0 = 1.493 → 1.433, while the pressure penalty increases to f/f0 = 1.345 → 1.405. Under cube-root weighting of friction, this case maintains the highest thermal performance factor, TPF = 1.352 at Re = 5000 and TPF = 1.279 at Re = 20,000. Second-law trends support the same ranking: exergy destruction decreases from 12.81 W (baseline) to 8.44 W at Re = 5000 (≈34% reduction) and from 6.54 W to 4.84 W at Re = 20,000 (≈26% reduction). The Bejan number remains high at low Reynolds numbers (≈0.998), indicating heat-transfer irreversibility dominance, but drops at higher Reynolds numbers (≈0.87) as frictional effects become more important. In general, the results show that adding a small axial pitch increase to rectangularity can improve near-wall mixing while reducing losses downstream. This leads to a clear improvement in both first-law performance and exergy-based measures.

Path planning remains a critical research area in mobile robotics, yet current approaches often suffer from suboptimal path quality, limited sampling efficiency, and inadequate adaptability across diverse operational scenarios. To address these issues, this paper proposes an improved algorithm combining Artificial Potential Field (APF) and Restricted Path Time (RRT*) approaches. This algorithm employs an optimization model that combines dynamic sampling with potential field guidance, constructing a two-stage dynamic sampling mechanism. During sampling, candidate nodes with Gaussian noise are generated along the resultant force direction. Finally, path cost comparison and parent node reselection are performed within the dynamic optimization radius to ensure asymptotic optimality of the path. Experimental results show that in complex maps, path length is reduced by 33.41% and 26.64%, respectively, and planning time is reduced by 21.36% and 86.32%, respectively; in narrow passages, path length is reduced by 49.6% and 49.8%, respectively. The results confirm the effectiveness of the two-stage dynamic sampling mechanism, which not only preserves the probabilistic completeness of the RRT* algorithm but also adaptively adjusts the sampling strategy, improving both planning length and time.

Rather than cooling an entire facility, local area cooling—achieved by placing simple-shaped heat exchangers near plants—could be an effective, low-energy climate regulation strategy for agricultural fields in greenhouses. In this study, a comparative analysis was performed for three serpentine-shaped heat exchangers varying in pipe diameter (12.7 and 15.88 mm) and pipe spacing (50 and 100 mm). Their heat transfer performance and air temperature distribution were measured in terms of local area cooling. Local air temperatures below the heat exchanger were also measured, whereas temperatures above the unit served as a reference. Both heat transfer performance and the pressure drop in the heat exchangers were investigated as well. Cooling experiments were conducted with inlet fluid temperatures from −5 to 10 °C and flow rates from 0.3 to 3.0 L/min (Re = 50–1394). The results showed that local air temperature reductions reached approximately 9 °C for the 12.7 mm pipe with 50 mm spacing, 10 °C for the 15.88 mm pipe with 50 mm spacing, and 5 °C for the 15.88 mm pipe with 100 mm spacing. Heat flux for the 15.88 mm pipe was two-thirds lower at a spacing of 50 mm and 1.5 times higher at a spacing of 100 mm compared to the pipes smaller in diameter. Moreover, pressure drops for the large-diameter pipes were about half those of the smaller pipes. The results from this experimental study are expected to contribute to practical greenhouse cooling applications and provide useful guidance for configuration selection for heat exchangers.

Enhanced circular tubes are widely employed in shell-and-tube heat exchangers, power-generation condensers, chemical reactors, refrigeration systems, and air-cooled heat exchangers, where improved convective performance can reduce the heat-transfer area required for a specified thermal duty. Helical screw tapes (HSTs) are passive inserts that promote sustained swirling motion and enhance convective heat transfer within such tubes. Although helical screw tapes and multiple-insert arrangements have been investigated previously, the combined thermohydraulic and second-law effects of increasing the number of co-rotating HSTs under fixed geometric ratios remain insufficiently quantified. In this investigation, turbulent airflow in a heated round tube was numerically investigated to examine the effect of tape number on heat transfer, pressure drop, thermal performance, total entropy generation (Stotal), and exergy destruction (ExD). Six HST configurations containing one to six tapes were examined over a Reynolds-number range of Re = 5000–20,000 in a circular tube with an inner diameter of DT = 31 mm, which was also adopted as the characteristic length for the Reynolds number, Nusselt number, and friction factor. The helical pitch P, screw diameter Ds, tape width W, and tape thickness t were 60 mm, 30 mm, 4.5 mm, and 0.2 mm, respectively, giving a pitch ratio of P/Ds = 2.0 and a width ratio of W/Ds = 0.15. A plain tube (PT) served as the baseline case. The results show that increasing the number of tapes intensifies swirl flow and enhances heat transfer but also leads to a continuous increase in pressure loss. For the optimum three-tape arrangement, the Nusselt number is increased by 126.0–158.8% and the thermal performance factor by 4.5–19.5% relative to the plain tube, while the total entropy generation and exergy destruction are simultaneously reduced by 7.9–61.0%. Among the configurations examined, HST-P2.0-W0.150-3, comprising three tapes at a pitch ratio of P/Ds = 2.0 and a width ratio of W/Ds = 0.15, achieved the best overall performance by delivering the highest thermal performance factor and the lowest total entropy generation and exergy destruction among the HST cases.