Experimental Thermal and Fluid Science最新文献

{"title":"Dancing vapor clouds above evaporating sessile droplets: Insights from parabolic flight microgravity experiments","authors":"Senthil Kumar Parimalanathan ,&nbsp;Hatim Machrafi ,&nbsp;Adam Chafai ,&nbsp;Alexey Rednikov ,&nbsp;Pierre Colinet","doi":"10.1016/j.expthermflusci.2025.111687","DOIUrl":"10.1016/j.expthermflusci.2025.111687","url":null,"abstract":"<div><div>Evaporation of a sessile droplet is studied in a parabolic flight campaign. The setup elements are similar to some past or planned microgravity experiments in space: pure refrigerant Hydrofluoroether (HFE)-7100 for the liquid, droplet pinning at a 2 mm radius microgroove, nearly normal conditions. The droplet is injected onto a flat substrate through a small central outlet up to a volume between <span><math><mrow><mo>∼</mo><mn>6</mn><mspace></mspace><mi>μ</mi></mrow></math></span>L and <span><math><mrow><mn>10</mn><mspace></mspace><mi>μ</mi></mrow></math></span>L (contact angles from <span><math><mrow><mo>∼</mo><mn>4</mn><msup><mrow><mn>5</mn></mrow><mrow><mo>∘</mo></mrow></msup></mrow></math></span> to 70°) at the beginning of each ‘parabola’ (microgravity period lasting up to <span><math><mo>∼</mo></math></span>20 s). Although an unfortunate ‘parasitic post-injection’ (persisting after the pump is off, a quite typical anomaly in microgravity) might have interfered with evaporation-rate measurements, such gaps are bridged using digital holographic vapor interferometry and axisymmetric simulations. Thus, we find that evaporation rates are significantly affected by residual gravity fluctuations in the plane (‘g-jitter’, <span><math><mrow><mo>∼</mo><mn>1</mn><msup><mrow><mn>0</mn></mrow><mrow><mo>−</mo><mn>2</mn></mrow></msup></mrow></math></span>g here). Quite accordingly, vapor clouds ‘dancing’ following the g-jitter are interferometrically disclosed, in good agreement with simulations. All this provides a noteworthy example of a possible difference between parabolic-flight experiments and those at other platforms (such as sounding rockets) approaching 0 g more precisely. The simulations reveal an independence with respect to high-frequency g-jitter sampling but highlight that each parabola is unique, with its own g-jitter signature. A detailed benchmark analysis is carried out motivated by the question of why the evaporation rates are appreciably higher for periods of negative (upward) g-jitter compared to positive (downward) ones. This is partly related to thermal Marangoni convection, concurrent or not to g-jitter buoyancy convection.</div></div>","PeriodicalId":12294,"journal":{"name":"Experimental Thermal and Fluid Science","volume":"173 ","pages":"Article 111687"},"PeriodicalIF":3.3,"publicationDate":"2026-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145880163","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Strategically located microchannel regions to enhance defrosting performance on vertical aluminum plates","authors":"Margaret M. Hennessy,&nbsp;Rhett J. Bendure,&nbsp;Giancarlo Corti,&nbsp;Andrew D. Sommers","doi":"10.1016/j.expthermflusci.2025.111670","DOIUrl":"10.1016/j.expthermflusci.2025.111670","url":null,"abstract":"<div><div>This work aims to improve defrosting performance in heating, ventilation, air conditioning, and refrigeration (HVAC&amp;R) systems while striking a balance in terms of the manufacturing cost. Minimizing the cost was achieved by mitigating the “edge effect” through microchannels (101.6 to 500 μm wide, 3.175 to 12.7 mm tall) that were strategically located along the bottom edge of vertical surfaces and then coupled in some cases with a fluorosilane coating. The “edge effect” refers to the phenomena where water droplets cling to the bottom edge of a vertical surface due to surface tension during drainage and are not removed. By treating only the bottom edge of the plate, manufacturing times were significantly reduced, and the defrosting performance remained comparable to fully-treated plates. Moreover, at <em>T</em>_w = -12 °C and RH = 60 % these plates improved defrosting percentages by as much as 20 % when compared to the baseline case, while also significantly reducing the manufacturing cost. Full-plate silica nanospring (SN) coatings were also studied and observed to have defrosting percentages as high as 90.3 %, but their current cost is not competitive for HVAC&amp;R applications. General observations about surface defrosting performance in terms of efficiency metrics were also outlined and discussed.</div></div>","PeriodicalId":12294,"journal":{"name":"Experimental Thermal and Fluid Science","volume":"173 ","pages":"Article 111670"},"PeriodicalIF":3.3,"publicationDate":"2026-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145797528","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Open-path measurement of temperature and CO concentration in AP–HTPB composite propellant flames using calibration-free wavelength modulation spectroscopy","authors":"Zhenhai Wang ,&nbsp;Xiaoliang Chen ,&nbsp;Wensheng Qiao ,&nbsp;Xing Chao","doi":"10.1016/j.expthermflusci.2025.111660","DOIUrl":"10.1016/j.expthermflusci.2025.111660","url":null,"abstract":"<div><div>A compact, robust and portable prototype laser absorption sensor is presented for temperature and CO concentration measurements in AP–HTPB composite propellant flames using calibration-free wavelength modulation spectroscopy. Open-path monitoring of AP–HTPB composite propellant flames exhibits unprecedented challenges for <em>in situ</em>, quantitative, and real-time combustion sensing, including high luminosity and opacity, strong beam-steering and significant optical transmission losses. We present here detailed design, optimization and demonstration of a compact, robust prototype laser absorption sensor, including laser transmission system, detection system and retroreflection system, to cope with the challenges associated with the harsh AP–HTPB composite propellant combustion behaviors. A mid-infrared interband cascade laser with 1 kHz scan rate and 50 kHz modulation rate is used to access two CO absorption transitions located at 2059.91 cm⁻¹ and 2060.33 cm⁻¹. Time-resolved diagnostics of temperature and CO concentration are accomplished in the open-path measurement of the AP–HTPB composite propellant flames. The whole combustion process consists of three stages, namely, flame propagation stage (<span><math><mrow><mi>t</mi><mo>=</mo><mn>0</mn><mo>∼</mo><mn>1</mn><mo>.</mo><mn>14</mn></mrow></math></span> s), flame retreating stage (<span><math><mrow><mi>t</mi><mo>=</mo><mn>1</mn><mo>.</mo><mn>14</mn><mo>∼</mo><mn>1</mn><mo>.</mo><mn>30</mn></mrow></math></span> s), and flame extinction stage (<span><math><mrow><mi>t</mi><mo>=</mo><mn>1</mn><mo>.</mo><mn>30</mn><mo>∼</mo><mn>1</mn><mo>.</mo><mn>875</mn></mrow></math></span> s). The average temperature and CO concentration in flame propagation stage are determined to be 1681.3 K and 13.9%, with a standard deviation of LOS-averaged temperature to 561.9 K and absolute CO concentration of 12.6%, respectively. High-fidelity measurement is achieved with a single-scan CO concentration detection limit of 1200 ppm at the measured condition of 1540.6 K, 1 atm, and 6.07% CO at <span><math><mrow><mi>t</mi><mo>=</mo><mn>0</mn><mo>.</mo><mn>568</mn></mrow></math></span> s. The measured uncertainties for temperature and CO concentration are estimated to be 4.89% and 6.02% at <span><math><mrow><mi>t</mi><mo>=</mo><mn>0</mn><mo>.</mo><mn>568</mn></mrow></math></span> s, respectively. The developed compact and portable prototype CO absorption sensor is capable of providing robust and accurate measurements in the open-path test of AP–HTPB composite propellant flames and can be readily generalized to relevant combustion environments with similar challenges.</div></div>","PeriodicalId":12294,"journal":{"name":"Experimental Thermal and Fluid Science","volume":"173 ","pages":"Article 111660"},"PeriodicalIF":3.3,"publicationDate":"2026-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145622798","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Experimental investigation of wettability dependence on the contact radius of hydrophobic surfaces using a photoelectric combination method","authors":"Shiyu Zhang ,&nbsp;Lingkun Han ,&nbsp;Chuntian Liu","doi":"10.1016/j.expthermflusci.2025.111667","DOIUrl":"10.1016/j.expthermflusci.2025.111667","url":null,"abstract":"<div><div>Hydrophobic surfaces are widely employed in both nature and industry. However, the dependence between the contact radius and the wettability of hydrophobic surfaces at different time scales has not been clearly established. Therefore, developing a method to measure the contact radius of these surfaces across multiple time scales is critical for understanding this relationship. This paper presented an innovative approach to contact radius measurement based on the photoelectric combination method, addressing the aforementioned challenges. By integrating electrical and optical techniques, this method leveraged the ultra-high spatiotemporal resolution of the electrical method to overcome the limitations of optical methods, particularly in capturing contact radius over short time intervals. An experimental setup was used to measure the contact radius of hydrophobic surfaces using this photoelectric combination method. The experimental results demonstrated that the contact radius remained unaffected by changes in wettability during the initial stage. However, as wettability decreased in the later stage, the contact radius significantly decreased.</div></div>","PeriodicalId":12294,"journal":{"name":"Experimental Thermal and Fluid Science","volume":"173 ","pages":"Article 111667"},"PeriodicalIF":3.3,"publicationDate":"2026-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145623448","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Vortex dynamics of novel whale-biomimetic and conventional wings: Influence of aspect ratio on tip and fragmented flow structures","authors":"Halil Hakan Açıkel ,&nbsp;Sinem Keskin ,&nbsp;Mustafa Serdar Genç ,&nbsp;Mustafa Özden ,&nbsp;Eren Anıl Sezer ,&nbsp;Mehmet Sincar ,&nbsp;Muhammer Ayvazoğlu ,&nbsp;Rumeysa Şahin","doi":"10.1016/j.expthermflusci.2025.111681","DOIUrl":"10.1016/j.expthermflusci.2025.111681","url":null,"abstract":"<div><div>The interaction of the tip vortex and the fragmented vortex on novel humpback whale-biomimetic wings with different low aspect ratios and their effects on aerodynamic performance are presented in this study. A baseline NACA 0015 airfoil and a modified configuration were tested at a chord-based Reynolds number of 0.975 × 10⁴ for different aspect ratios (AR = 1, 2, 3, and infinite). The oil flow visualisation and force measurements were used to explore the effects of the tubercle modification on flow topology, unsteady flow, stall mechanisms, and fluid–structure interactions. Moreover, time-dependent force results were served for spectrogram analysis, which was presented first in this study, to reveal flow modes occurring. The results demonstrate that the whale-inspired geometry alters the laminar separation bubble dynamics by fragmenting large coherent structures into smaller three-dimensional bubbles, which are less susceptible to tip vortex interactions. Time-resolved lift measurements and spectrogram analyses showed that the whale-inspired leading-edge fragmented laminar separation bubbles into smaller, higher-momentum structures, generating higher-frequency flow (fragmented laminar separation bubble-induced and whale flow interaction-induced) modes that mitigated coherent vortex shedding. In AR2, AR3, and 2D wings, two dominant modes emerged. This can be attributed to the intensification of leading-edge vortices interacting with the whale structure, with an increasing aspect ratio. The modified wings exhibited enhanced lift coefficient and delayed stall, particularly for higher aspect ratios, where a mild stall replaced abrupt stall in baseline wings. However, at post-stall conditions, the lift force exhibited higher fluctuation-based stability index values for the whale wings, indicating that while the modification improved overall aerodynamic performance, it slightly reduced flow stability. While studies in the literature have shown that high aspect ratio whale wings provide significant aerodynamic enhancement, particularly at high angles of attack, this study observed that this effect is accompanied by increased vibration due to small, fragmented vortices. Increased vibration is likely to lead to stability issues.</div></div>","PeriodicalId":12294,"journal":{"name":"Experimental Thermal and Fluid Science","volume":"173 ","pages":"Article 111681"},"PeriodicalIF":3.3,"publicationDate":"2026-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145797533","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Experimental study on flow pattern transition on horizontal flat tubes with large height-width ratio","authors":"Wenjie Deng ,&nbsp;Zhenhua Quan ,&nbsp;Yaohua Zhao ,&nbsp;Chunduo Song ,&nbsp;Lincheng Wang","doi":"10.1016/j.expthermflusci.2025.111686","DOIUrl":"10.1016/j.expthermflusci.2025.111686","url":null,"abstract":"<div><div>The flow pattern between tubes significantly influences the liquid film distribution and flow state on the lower tube bundle in the falling film evaporator, and its transition behavior is critical to the heat transfer performance of the equipment. This study develops a visualization platform to examine flow pattern transitions between horizontal flat tubes with large height-width ratio, utilizing ethylene glycol, ethanol, and water as working fluids. The findings reveal that ethylene glycol exhibits the lowest critical Reynolds number (<em>Re</em>_c), while ethanol shows a more distinct and clearer gas–liquid interface morphology. The <em>Re</em>_c for flow pattern transition increases with higher spray height (<em>H</em>), inlet liquid temperature (<em>T</em>_in), and circulating water temperature (<em>T</em>_cir), with <em>T</em>_in showing the most substantial impact. Flow hysteresis manifests in flow pattern transitions and strengthens with increasing <em>H</em>, <em>T</em>_in and <em>T</em>_cir, with water displaying the most pronounced effect. Based on experimental data, an empirical correlation and flow pattern map better suited for flow pattern transition on horizontal flat tubes is developed, with a maximum relative root mean square error of 12.76%. Research demonstrates that horizontal flat tubes show a lower <em>Re</em>_c for transition to sheet flow compared with horizontal tubes, indicating superior liquid film flow performance. This investigation advances the understanding of flow pattern transition mechanisms on horizontal flat tubes, providing theoretical and experimental foundations for the structural optimization and efficient operation of falling film evaporators.</div></div>","PeriodicalId":12294,"journal":{"name":"Experimental Thermal and Fluid Science","volume":"173 ","pages":"Article 111686"},"PeriodicalIF":3.3,"publicationDate":"2026-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145797529","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Sensitivity analysis of kirigami geometry on a rectangular cylindrical flow","authors":"Hao Meng ,&nbsp;Haoqi Hu ,&nbsp;Shuaihang Lin ,&nbsp;Haiyang Yu","doi":"10.1016/j.expthermflusci.2025.111663","DOIUrl":"10.1016/j.expthermflusci.2025.111663","url":null,"abstract":"<div><div>This study investigated the impacts of kirigami scales on aerodynamic control in cylindrical structures, as well as their effectiveness in reducing aerodynamic forces and turbulence characteristics. Using particle image velocimetry (PIV) in wind tunnel experiments, we conducted detailed flow field measurements on rectangular prisms fitted with elliptical and triangular kirigami scales. The Reynolds number (<em>Re</em>) was set at (1.3–3.1) × 10⁴. The experimental findings revealed that the implemented scales effectively suppressed lift fluctuations and the distributions of Reynolds shear stress (RSS) and turbulent kinetic energy (TKE), achieving remarkable reduction efficiencies of 50 % and 70 %, respectively. By varying the shape and folding angles of the scales, we assessed their impact on flow field control, finding them particularly effective at large folding angles in suppressing pressure fluctuations and dynamic characteristics. The sensitivity to the folding angle varied among scales of different shapes. Notably, the kirigami scales demonstrated efficacy in mitigating <em>Re</em>-sensitivity for lift fluctuations within this range, though their drag reduction effect remained modest. Furthermore, through proper orthogonal decomposition (POD), we further analyzed the wake characteristics, demonstrating that kirigami scales can significantly alter the flow field structure, reduce energy concentrations, and thereby enhance the safety and lifespan of structures.</div></div>","PeriodicalId":12294,"journal":{"name":"Experimental Thermal and Fluid Science","volume":"173 ","pages":"Article 111663"},"PeriodicalIF":3.3,"publicationDate":"2026-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145600615","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Effect of confinement geometry on pool boiling performance of gold-coated copper surface","authors":"Gregor Bahč,&nbsp;Armin Hadžić,&nbsp;Matic Može,&nbsp;Matevž Zupančič,&nbsp;Iztok Golobič","doi":"10.1016/j.expthermflusci.2025.111685","DOIUrl":"10.1016/j.expthermflusci.2025.111685","url":null,"abstract":"<div><div>Pool boiling is widely employed in compact thermal management systems, but its performance can deteriorate significantly under geometric confinement. This study investigates the combined effects of vertical gap height and confinement plate diameter on pool boiling of distilled water at atmospheric pressure using gold-coated copper samples. The vertical gap between the boiling surface and an overhead plate varied from 0.1λ to 20λ, where λ = 2.5 mm is the capillary length of water, and three plate diameters were examined: 14 mm, 24 mm, and 39 mm. For large gaps (<em>k</em>_gap ≥ 2.5), the critical heat flux (CHF) remained at approximately 1100 kW<!--> <!-->m⁻² and the heat transfer coefficient (HTC) was comparable to unconfined boiling. As the gap decreases below 2.5λ, both CHF and HTC decrease sharply. At the smallest gap (0.1λ), CHF and HTC were reduced by up to 78 % and 85 %, respectively, relative to the unconfined reference. In the intermediate gap range (0.5λ–2.5λ), the plate diameter had a pronounced effect, with the largest plate producing substantially lower CHF and HTC than the smallest plate for the same gap height due to more restricted radial vapor escape. High-speed visualization confirmed that strong confinement promotes bubble coalescence, vapor accumulation beneath the plate, and intermittent dryout of the boiling surface. Based on the CHF data for all gap heights and plate diameters, empirical correlations were developed using a dimensionless gap ratio and a characteristic plate-size parameter, providing a predictive framework for assessing CHF under combined vertical gap height and confinement plate diameter.</div></div>","PeriodicalId":12294,"journal":{"name":"Experimental Thermal and Fluid Science","volume":"173 ","pages":"Article 111685"},"PeriodicalIF":3.3,"publicationDate":"2026-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145836375","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Advances in laser diagnostics for swirl combustion: current progress and future directions☆","authors":"Guoqing Wang,&nbsp;Mingming Gu,&nbsp;Liangliang Xu,&nbsp;Shuyue Lai,&nbsp;Xi Xia,&nbsp;Fei Qi","doi":"10.1016/j.expthermflusci.2025.111666","DOIUrl":"10.1016/j.expthermflusci.2025.111666","url":null,"abstract":"<div><div>Swirl combustion is a fundamental feature in modern energy conversion systems, particularly in gas turbines and aeroengines, where it enhances flame stabilization, mixing efficiency, and emissions control. The global shift toward low- and zero-carbon fuels, such as ammonia and hydrogen, introduces new challenges in swirl combustion environments, including altered flow dynamics, temperature distributions, and chemical reaction pathways. In this context, laser-based diagnostic techniques have undergone significant advances, enabling non-intrusive, high-resolution, time-resolved measurements of velocity fields, scalar distributions, and reaction zone structures in swirl-stabilized flames. This review summarizes recent progress in major laser diagnostic methods, including high-speed particle image velocimetry, planar laser-induced fluorescence, laser absorption spectroscopy, Rayleigh scattering, and Raman scattering based techniques. Developments in multiphysics and hybrid techniques are also discussed. Additionally, we emphasizes representative laser diagnostic advancements driven by high-temperature and low-carbon combustion technologies. The co-evolution of laser technology, diagnostic methods, and swirl combustion is discussed to show how advances in each area have accelerated progress in the others. Finally, the review outlines remaining scientific challenges, practical barriers to industrial application, and future research priorities, with emphasis on diagnostics for extreme conditions, AI-driven data analysis, and compact in-situ measurement solutions for next-generation swirl combustion systems.</div></div>","PeriodicalId":12294,"journal":{"name":"Experimental Thermal and Fluid Science","volume":"173 ","pages":"Article 111666"},"PeriodicalIF":3.3,"publicationDate":"2026-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145692350","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Splashing of impacting droplets on an artificial superhydrophobic surface: Effect of viscosity in hole-nucleation process","authors":"Kumar Gaurav ,&nbsp;Visakh Vaikuntanathan ,&nbsp;Sivakumar Deivandren","doi":"10.1016/j.expthermflusci.2025.111682","DOIUrl":"10.1016/j.expthermflusci.2025.111682","url":null,"abstract":"<div><div>The present study reports an experimental investigation on splashing of liquid droplets impacting on an artificial superhydrophobic (SHP) surface prepared by coating NeverWet hydrophobic solution. The prepared SHP surface exhibits micro-bumps decorated with nano-structures, as seen in Scanning Electron Microscopy (SEM) images and surface profilometry. The presence of micro-bumps causes the fragmentation of spreading lamella via hole-nucleation process, leading to a significant reduction in droplet contact time as shown in a recent study reported in the literature. The focus of the current study is on the effect of droplet viscosity on the hole-nucleation and contact time of impacting droplets. The experiments with droplet impact velocity, <span><math><msub><mrow><mi>U</mi></mrow><mrow><mi>o</mi></mrow></msub></math></span> ranging from 0.3 m/s to 3.6 m/s are conducted using three different droplet liquids – water (W), 20% glycerine and 80% water (G20), and 50% glycerine and 50% water (G50) – varying mainly in their dynamic viscosity. From high-speed videos of droplet impact dynamics, the various impact regimes are first identified and mapped in <span><math><mrow><mi>W</mi><mi>e</mi></mrow></math></span> (droplet Weber number) – <span><math><mrow><mi>R</mi><mi>e</mi></mrow></math></span> (droplet Reynolds number) plane for all three droplet liquids. Quantitative measurements of the temporal variation of lamella diameter, number of holes formed, time at which the first hole nucleates, critical impact velocity at which the hole-nucleation begins, and contact time are extracted. These measurements clearly show that the contact time reduction of splashing droplets decreases with increase in droplet viscosity. Moreover, the number of holes formed in the lamella film scales with the number of micro-bumps underneath the droplet at its maximum spreading which, in turn, decreases with increase in droplet viscosity. The time instant at which the first hole nucleates on the lamella film is seen to be independent of the droplet viscosity. A modified model is proposed to describe the effects of droplet viscosity and surface micro-characteristics (height and pitch of surface micro-bumps) on the critical velocity for hole nucleation, <span><math><msub><mrow><mi>U</mi></mrow><mrow><mi>c</mi><mo>,</mo><mi>h</mi></mrow></msub></math></span>. The predictions from this modified model seem to explain the experimental observations on <span><math><msub><mrow><mi>U</mi></mrow><mrow><mi>c</mi><mo>,</mo><mi>h</mi></mrow></msub></math></span> in the current study as well as in the literature.</div></div>","PeriodicalId":12294,"journal":{"name":"Experimental Thermal and Fluid Science","volume":"173 ","pages":"Article 111682"},"PeriodicalIF":3.3,"publicationDate":"2026-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145797531","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}