Experimental Thermal and Fluid Science最新文献

{"title":"Error analysis and improvement of water displacement method in measuring gas desorption volume from coal particles","authors":"Xingyi Nie ,&nbsp;Qingquan Liu ,&nbsp;Liang Wang ,&nbsp;Biao Lv ,&nbsp;Yuanping Cheng","doi":"10.1016/j.expthermflusci.2024.111333","DOIUrl":"10.1016/j.expthermflusci.2024.111333","url":null,"abstract":"<div><div>The water displacement method is widely employed in experiments to investigate the adsorption and desorption characteristics of coal gas. However, conventional desorption apparatus faces challenges in accurately quantifying gases with low desorption rates, leading to significant inaccuracies in experimental assessments of residual gas content and adsorption–desorption hysteresis. In order to solve the issue, a new desorption device was invented to carry out isothermal ultimate desorption experiments together with the conventional device under two different equilibrium pressures with coal samples of four particle sizes. The results reveal that after 100 min, the gas desorption rate gradually decreases, with the desorption percentage of the conventional device remaining relatively constant, while that of the new device continues to rise. By the end of the experiment, the conventional device measured gas residual percentages ranging from 30 % to 50 %, whereas the new device recorded percentages between 10 % and 25 %. The lower residual percentages obtained by the new device prove the effectiveness to solve the issue that the conventional devices struggle to quantify low-rate desorption gas.</div><div>When applying the conventional device, as desorption progresses, the desorption rate decreases, and the pressure within the coal sample tank increases more slowly, which results in the difficulty for the gas to reach a pressure of 71.18 Pa to overcome fluidic constraints and enter into the graduated cylinder and ultimately accumulates in the soft, large-volume silicone pipeline. In contrast, the new device, designed with its gas outlet strategically positioned above the liquid level, bypasses the constraints of liquid forces. Additionally, the modest inner diameter of the rigid tube undergoes minimal deformation under experimental conditions. Differences in liquid forces and piping allow the new device to accumulate 71 mL less gas than the conventional device. The utilization of the new device in coal gas desorption experiments effectively mitigates experimental errors stemming from low desorption rates, thereby driving advancements in the investigation of coal seam gas parameters and residual gas content.</div></div>","PeriodicalId":12294,"journal":{"name":"Experimental Thermal and Fluid Science","volume":"160 ","pages":"Article 111333"},"PeriodicalIF":2.8,"publicationDate":"2024-10-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142433308","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":"Impact of piezoelectric driving waveform on performance characteristics of vibrating mesh atomizer (VMA)","authors":"Roopitha Kaimal ,&nbsp;Jiarui Feng ,&nbsp;Dunant Halim ,&nbsp;Yong Ren ,&nbsp;Voon-Loong Wong ,&nbsp;Kean How Cheah","doi":"10.1016/j.expthermflusci.2024.111331","DOIUrl":"10.1016/j.expthermflusci.2024.111331","url":null,"abstract":"<div><div>Vibrating mesh atomizer (VMA) is a specific type of ultrasonic atomizer known for its low power consumption and production of uniformly fine droplets. While previous research has provided a basic understanding of VMA operation, it has primarily focused on driving the piezoelectric actuator with continuous and symmetrical waveforms, such as sine and square waveforms. This study aims to experimentally investigate the impact of different driving waveforms on the ultrasonic atomization process and the associated performance characteristics. Specifically, the effects of pulse waveforms (Gauss and Lorentz pulse) were analyzed with high rates of energy deposition and asymmetrical hybrid waveforms (trapezia and absolute sine), featuring distinct negative cycles, by comparing them with conventional symmetrical waveforms (sine and square). Pulse waveforms suppress the growing stage but provide a high flux of input energy, facilitating the detachment of liquid into fine droplets, resulting in uniformly distributed droplets with VMDs of 5.84 μm and 4.71 μm for Gauss and Lorentz waveforms, respectively. Conversely, shorter negative cycles in asymmetrical hybrid waveforms reduce liquid suction into the micronozzle, leading to higher energy flux during subsequent positive cycles that promote the growing stage, producing larger droplets with VMDs of 10.82 μm and 11.86 μm for trapezia and absolute (abs) sine waveforms, respectively. Additionally, high-speed imaging reveals irregular pulsating behaviors in the atomization process when using pulse waveforms, suggesting a reciprocating-pump-like operation mechanism in VMA atomization. These new insights contribute to an improved understanding of the atomization mechanism in VMAs.</div></div>","PeriodicalId":12294,"journal":{"name":"Experimental Thermal and Fluid Science","volume":"160 ","pages":"Article 111331"},"PeriodicalIF":2.8,"publicationDate":"2024-10-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142422191","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Impact of a compound droplet on a solid surface: The effect of the shell on the core","authors":"Yuying Du ,&nbsp;Li Dai ,&nbsp;Lijuan Qian ,&nbsp;Fang Zhou ,&nbsp;Yuechao Ma","doi":"10.1016/j.expthermflusci.2024.111330","DOIUrl":"10.1016/j.expthermflusci.2024.111330","url":null,"abstract":"<div><div>The dynamic behavior of compound droplets impacting a solid surface was studied via experiments over <span><math><mi>κ</mi></math></span> (defined as the ratio of the compound droplet shell thickness <em>h</em> to the diameter <em>D₀</em> of compound droplet) ranging from 0 to 0.34, <em>We</em> ranging from 25 to 325 and <em>Re</em> ranging from 165.3 to 3405.2. The spreading diameter ratio, the maximum spreading dynamic contact angle and spreading speed of the core were investigated. Four modalities of the core of compound droplets were observed on the solid surface, including a) core rebound, b) no rebound, c) core splitting rebound, d) core splitting. The results revealed that the thickness of the shell, <em>We,</em> and the viscosity of the shell have a significant effect on the rebound and spreading processes of the core of the compound droplet. The high viscosity oil shell is conducive to its spreading. As the thickness of the oil shell increases, its cushioning effect on the water core also increases. In addition,<span><math><mrow><mi>κ</mi><mo>=</mo><mn>0.02254</mn><msup><mrow><mi>We</mi></mrow><mrow><mn>0.503</mn></mrow></msup><mo>,</mo><mi>κ</mi><mo>=</mo><mo>-</mo><mn>0.336</mn><msup><mrow><mi>e</mi></mrow><mfenced><mrow><mo>-</mo><mfrac><mrow><mi>We</mi></mrow><mrow><mn>121.056</mn></mrow></mfrac><mo>+</mo><mn>0.319</mn></mrow></mfenced></msup></mrow></math></span> and <span><math><mrow><mi>κ</mi><mo>=</mo><mn>0.06086</mn><msup><mrow><mi>e</mi></mrow><mrow><mo>-</mo><mfrac><mrow><mi>We</mi></mrow><mrow><mn>121.056</mn></mrow></mfrac></mrow></msup><mo>+</mo><mn>0.07716</mn><msup><mrow><mi>e</mi></mrow><mrow><mo>-</mo><mfrac><mrow><mi>We</mi></mrow><mrow><mn>121.70598</mn></mrow></mfrac></mrow></msup><mo>+</mo><mn>0.01595</mn></mrow></math></span> were used to divide the modal boundary of the compound droplet core. Further analysis reveals the correlation between <em>We</em>, <em>Re</em>, <span><math><msub><mi>β</mi><mi>m</mi></msub></math></span> and.<span><math><mrow><mi>κ</mi><mo>,</mo><mspace></mspace><mfenced><mrow><mn>12</mn><mo>+</mo><mi>W</mi><mi>e</mi></mrow></mfenced><msub><mi>β</mi><mi>m</mi></msub><mspace></mspace><mo>=</mo><mn>8</mn><mo>+</mo><mn>3</mn><mfenced><mrow><mn>1</mn><mo>-</mo><mi>c</mi><mi>o</mi><mi>s</mi><mfenced><mrow><mn>22.78</mn><mo>+</mo><mn>84.57</mn><mi>κ</mi></mrow></mfenced></mrow></mfenced><msubsup><mi>β</mi><mrow><mi>m</mi></mrow><mn>3</mn></msubsup><mo>+</mo><mn>0.955</mn><mfrac><msup><mrow><mi>We</mi></mrow><mrow><mn>1.05</mn></mrow></msup><mrow><mi>Re</mi></mrow></mfrac><msubsup><mi>β</mi><mrow><mi>m</mi></mrow><mrow><mn>6.5</mn></mrow></msubsup><mspace></mspace><mo>.</mo></mrow></math></span></div></div>","PeriodicalId":12294,"journal":{"name":"Experimental Thermal and Fluid Science","volume":"160 ","pages":"Article 111330"},"PeriodicalIF":2.8,"publicationDate":"2024-10-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142422190","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":"Characteristics of Gas–Liquid Two-Phase flow in rectangular narrow slits with varying cross sections driven by large pressure drop","authors":"Zhendong Yang,&nbsp;Haiyang Li,&nbsp;Haibo Liu,&nbsp;Suqi Shi,&nbsp;Jiaxiang Sun,&nbsp;Qiaoling Zhang,&nbsp;Guodong Li","doi":"10.1016/j.expthermflusci.2024.111328","DOIUrl":"10.1016/j.expthermflusci.2024.111328","url":null,"abstract":"<div><div>Pressure pipelines and vessels inevitably contain some defects. Under the most unfavorable load combinations, these defects may gradually develop into through-wall cracks. High-pressure subcooled fluid leaks through these cracks, and two-phase gas–liquid flow often occurs within the cracks. In this study, natural through-wall cracks were replaced with narrow rectangular slits with varying cross sections. Experiments were conducted to investigate the variation patterns of gas–liquid two-phase leakage flow rates and pressure drops. The study focused on four types of rectangular narrow slits with varying cross sections, a width of 28 mm, a length of 80 mm, and a gap gradually ranging from 0.134 to 0.334 mm. The liquid-phase mass flow rate ranged from 150 to 700 kg/h, whereas the gas-phase mass flow rate varied from 0 to 20 kg/h. A one-dimensional homogeneous flow model was established by coupling two-phase velocity of speed calculations. This calibrated model was then used to predict pressure drops and flow parameters for gas–liquid two-phase flow in narrow rectangular slits with varying cross sections. The experimental data were analyzed to determine the two-phase leakage characteristics of different test pieces. The results show that the inlet–outlet pressure drop and flow quality are key factors affecting the two-phase leakage flow rate. The frictional pressure drop constitutes a major part of the total pressure drop along the flow path in different test pieces. Compared with the acceleration pressure drop in the expanding slit, that in the constricting slit is higher, with an increase of approximately 32 %. Among several commonly used empirical formulas for calculating two-phase viscosity, the McAdams and Dukler empirical correlations were found to be less suitable for high-velocity two-phase flows. In contrast, the Cicchitti empirical correlation provides better predictions, with a mean absolute deviation (MAD) and mean relative deviation (MRD) of no more than 8 %. The viscosity of the gas-phase medium affects the two-phase flow characteristics in narrow slits, which should be considered in practical engineering applications.</div></div>","PeriodicalId":12294,"journal":{"name":"Experimental Thermal and Fluid Science","volume":"161 ","pages":"Article 111328"},"PeriodicalIF":2.8,"publicationDate":"2024-10-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142527905","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":"Investigation on intermittent flow characteristics in horizontal pipe by visualization measurement method","authors":"Bo Huang,&nbsp;Qiang Xu,&nbsp;Yeqi Cao,&nbsp;Haiyang Yu,&nbsp;Yuwen Li,&nbsp;Yingjie Chang,&nbsp;Liejin Guo","doi":"10.1016/j.expthermflusci.2024.111329","DOIUrl":"10.1016/j.expthermflusci.2024.111329","url":null,"abstract":"<div><div>Accurate measurement and prediction of the intermittent flow characteristics in horizontal pipes is important for constructing multiphase flow models and ensuring pipe flow safety. In this paper, a quantitative image post-processing technique for intermittent flow characteristics based on gray histogram image similarity is proposed, which can realize the measurement of slug frequency. In addition, the technique also has the ability to classify a large number of images, and can quickly find the elongated bubble head, liquid film area and liquid slug area of intermittent flow. On the basis of this technique, combined with image post-processing methods such as gas–liquid interface feature analysis, a set of intermittent flow image processing technique with perfect route is formed. Based on this post-processing technique, the similarity image oscillation trajectories of plug flow and slug flow are obtained. There are differences in the similarity image oscillation trajectories of the two intermittent sub-flow patterns, and the similarity image of the plug flow has an obvious platform period and trailing rising line, which can be used as a basis for the classification of the two intermittent sub-flow patterns. A correlation for predicting the slug frequency of intermittent sub-flow patterns is developed. The accuracy of this slug frequency prediction correlation can be improved by about 10 % compared to not dividing the sub-flow patterns. When the mixture Froude number <em>Fr_m</em> is less than 5.0, the radial position of the elongated bubble head decreases linearly as the <em>Fr_m</em> increases. When the <em>Fr_m</em> is greater than 5.0, the elongated bubble head oscillates near the middle of the pipe. Prediction correlations for the radial position of the elongated bubble head and the slug velocity are established separately, and the maximum error is ± 10 %. The modified mixed Froude number is proposed, and based on this, a new prediction model for the transition from plug flow to slug flow is established.</div></div>","PeriodicalId":12294,"journal":{"name":"Experimental Thermal and Fluid Science","volume":"160 ","pages":"Article 111329"},"PeriodicalIF":2.8,"publicationDate":"2024-10-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142422267","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 characterization of turbulent boundary layers around a NACA 4412 wing profile","authors":"Fermin Mallor ,&nbsp;Carlos Sanmiguel Vila ,&nbsp;Majid Hajipour ,&nbsp;Ricardo Vinuesa ,&nbsp;Philipp Schlatter ,&nbsp;Ramis Örlü","doi":"10.1016/j.expthermflusci.2024.111327","DOIUrl":"10.1016/j.expthermflusci.2024.111327","url":null,"abstract":"<div><div>An experimental characterization of the turbulent boundary layers developing around a NACA 4412 wing profile is carried out in the Minimum Turbulence Level (MTL) wind tunnel located at KTH Royal Institute of Technology. The campaign included collecting wall-pressure data via built-in pressure taps, capturing velocity signals in the turbulent boundary layers (TBLs) using hot-wire anemometry (HWA), and conducting direct skin-friction measurements with oil-film interferometry (OFI). The research spanned two chord-based Reynolds numbers (<span><math><mrow><mi>R</mi><msub><mrow><mi>e</mi></mrow><mrow><mi>c</mi></mrow></msub><mo>=</mo><mn>4</mn><mo>×</mo><mn>1</mn><msup><mrow><mn>0</mn></mrow><mrow><mn>5</mn></mrow></msup></mrow></math></span> and <span><math><mrow><mn>1</mn><msup><mrow><mn>0</mn></mrow><mrow><mn>6</mn></mrow></msup></mrow></math></span>) and four angles of attack (5°, 8°, 11° and 14°), encompassing a broad spectrum of flow conditions, from mild to strong adverse-pressure gradients (APGs), including scenarios where the TBL detaches from the wing surface. This dataset offers crucial insights into TBL behavior under varied flow conditions, particularly in the context of APGs. Key features include the quasi-independence of the pressure coefficient distributions from Reynolds number, which aids in distinguishing Reynolds-number effects from those due to APG strengths. The study also reveals changes in TBL dynamics as separation approaches, with energy shifting from the inner to the outer region and the eventual transition to a free-shear flow state post-separation. Additionally, the diagnostic scaling in the outer region under spatial-resolution effects is considered, showing further evidence for its applicability for small <span><math><msup><mrow><mi>L</mi></mrow><mrow><mo>+</mo></mrow></msup></math></span>, however with inconsistent results for larger <span><math><mrow><mi>L</mi><mo>+</mo></mrow></math></span>. The findings and database resulting from this campaign may be of special relevance for the development and validation of turbulence models, especially in the context of aeronautical applications.</div></div>","PeriodicalId":12294,"journal":{"name":"Experimental Thermal and Fluid Science","volume":"160 ","pages":"Article 111327"},"PeriodicalIF":2.8,"publicationDate":"2024-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142422266","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Experimental study of flame chemiluminescence for premixed methane based binary fuel flames","authors":"Zhengzhe Fang ,&nbsp;Yushuai Liu ,&nbsp;Yannis Hardalupas ,&nbsp;A.M.K.P. Taylor","doi":"10.1016/j.expthermflusci.2024.111326","DOIUrl":"10.1016/j.expthermflusci.2024.111326","url":null,"abstract":"<div><div>The growing requirements in using natural gas with varying compositions, biogas, syngas, and hydrogen enriched natural gas have increased the need for fuel composition and equivalence ratio sensing methods for modern gas turbine combustors. Chemiluminescence has been suggested as a promising heat release rate and equivalence ratio indicator in methane premixed flames. However, its ability in flames fuelled by the complex composition of fuels is less understood. Therefore, the main object of the present study is assessing the chemiluminescence based equivalence ratio and fuel composition sensors in binary mixtures fuelled premixed flames. The CH₄ + C₃H₈, CH₄ + CO₂, and CH₄ + H₂ fuel mixtures are selected since they are typical compositions for the interested fuel applications. A thorough analysis of chemiluminescence characteristics including spectrum, flame patterns, chemiluminescent intensities, and intensity ratios was conducted by the measurements in a counterflow burner. The results conclude that the OH*/CH(A) chemiluminescent intensity ratio with proper removal of background emission is competent for indicating fuel composition and equivalence ratio for the examined fuel mixtures. The intensity ratio between CO₂* and OH*, CH(A), and C₂* can be used to monitor the proportion of C₃H₈, H_2, and CO₂ respectively in the methane-based fuel mixtures.</div></div>","PeriodicalId":12294,"journal":{"name":"Experimental Thermal and Fluid Science","volume":"160 ","pages":"Article 111326"},"PeriodicalIF":2.8,"publicationDate":"2024-09-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142422264","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":"Advancements on the use of Filtered Rayleigh Scattering (FRS) with Machine learning methods for flow distortion in Aero-Engine intakes","authors":"Matteo Migliorini ,&nbsp;Ulrich Doll ,&nbsp;Nicholas J. Lawson ,&nbsp;Sergey M. Melnikov ,&nbsp;Jonas Steinbock ,&nbsp;Michael Dues ,&nbsp;Pavlos K. Zachos ,&nbsp;Ingo Röhle ,&nbsp;David G. MacManus","doi":"10.1016/j.expthermflusci.2024.111325","DOIUrl":"10.1016/j.expthermflusci.2024.111325","url":null,"abstract":"<div><div>In-flight measurements of aerodynamic quantities are a requirement to ensure the correct scaling of Reynolds and Mach number and for the airworthiness certification of an aircraft. The ability to obtain such measurement is subject to several challenges such as instrument installation, environment, type of measurand, and spatial and temporal resolution. Given expected, more frequent use of embedded propulsion systems in the near future, the measurement technology needs to adapt for the characterization of multi-type flow distortion in complex flow, to assess the operability of air-breathing propulsion systems. To meet this increasing demand for high-fidelity experimental data, the Filtered Rayleigh Scattering (FRS) method is identified as a promising technology, as it can provide measurements of pressure, temperature and 3D velocities simultaneously, across a full Aerodynamic Interface Plane (AIP). Τhis work demonstrates the application of a novel FRS instrument, to assess the flow distortion in an S-duct diffuser, in a ground testing facility. A comparison of FRS results with Stereo-Particle Image Velocimetry (S-PIV) measurements reveals good agreement of the out of plane velocities, within 3.3<!--> <!-->% at the AIP. Furthermore, the introduction of machine learning methods significantly accelerates the processing of the FRS data by up to 200 times, offering a substantial prospect towards real time data analysis. This study demonstrates the further development of the FRS technique, with the ultimate goal of inlet flow distortion measurements for in-flight environments.</div></div>","PeriodicalId":12294,"journal":{"name":"Experimental Thermal and Fluid Science","volume":"160 ","pages":"Article 111325"},"PeriodicalIF":2.8,"publicationDate":"2024-09-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142422265","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Droplet breakup and evaporation in liquid-fueled detonations","authors":"Calvin J. Young,&nbsp;Vasco O. Duke-Walker,&nbsp;Jacob A. McFarland","doi":"10.1016/j.expthermflusci.2024.111324","DOIUrl":"10.1016/j.expthermflusci.2024.111324","url":null,"abstract":"<div><div>In liquid-fueled detonations droplets are subjected to a myriad of complex codependent physical phenomena occurring on overlapping temporal and spatial scales, resulting in rapid vaporization. The rate at which droplets vaporize is enhanced by the concurrent hydrodynamic breakup processes. This article describes experiments where small (<span><math><mrow><mi>d</mi><mo>&lt;</mo><mn>125</mn><mspace></mspace><mi>μ</mi><mi>m</mi></mrow></math></span>) droplet breakup at high Weber number <span><math><mrow><mi>O</mi><mrow><mo>(</mo><mn>1</mn><msup><mrow><mn>0</mn></mrow><mrow><mn>4</mn></mrow></msup><mtext>–</mtext><mn>1</mn><msup><mrow><mn>0</mn></mrow><mrow><mn>5</mn></mrow></msup><mo>)</mo></mrow></mrow></math></span> is imaged in a self-sustained liquid-fueled detonation with laser optical Mie scattering imagery. Experimental initial conditions, including the droplet size and mass distribution, are characterized and reported. Child droplet clouds generated from droplet interactions with detonation waves are observed to persist for approximately 10 mm past the detonation front and grow to the order of millimeters in width. A velocity deficit of <span><math><mrow><mo>∼</mo><mn>10</mn><mtext>%</mtext></mrow></math></span> was observed for the multiphase detonations wave speed when compared to calculations for the equivalent gaseous detonations. The bulk droplet survival distances and breakup cloud morphology are compared to the predictions of relevant evaporation and breakup models. Calculations indicate that evaporation alone would result in droplet survival distances orders of magnitude longer than those observed. A droplet process whereby breakup occurs over an extended time, concurrent with evaporation, provides a phenomenological explanation. Empirical models constructed for shock-driven breakup predicted larger child droplet sizes than theoretical models based on linear stability theory, yielding survival distances and cloud shapes within the range of values seen in experiments. Droplets were however observed to persist longer than either model would predict. The discrepancy between calculations and experiment indicate that development of models tailored to droplets subject to variable acceleration are necessary to fully explain the multiphase detonation.</div></div>","PeriodicalId":12294,"journal":{"name":"Experimental Thermal and Fluid Science","volume":"160 ","pages":"Article 111324"},"PeriodicalIF":2.8,"publicationDate":"2024-09-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142357735","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":"Hypergolic fuel impacting a gelled oxidizer wall: Droplet dynamics, heat release, ignition, and flame analysis","authors":"Gabriel Silva Dias ,&nbsp;Fábio Antônio da Silva Mota ,&nbsp;Lihan Fei ,&nbsp;Yingtao Wu ,&nbsp;Mingyang Liu ,&nbsp;Chenglong Tang ,&nbsp;Fernando de Souza Costa","doi":"10.1016/j.expthermflusci.2024.111322","DOIUrl":"10.1016/j.expthermflusci.2024.111322","url":null,"abstract":"<div><div>The combination of high-concentration solutions of hydrogen peroxide, known as High Test Peroxide (HTP), with the green fuel composed of tetramethylethylenediamine, dimethylaminoethanol, and methanol (TMEDA/DMEA/MeOH, 1:1:1 vol%), catalyzed by 1 wt% of copper chloride dihydrate, has significant potential for space hypergolic propulsion applications in terms of performance and safe operation. Besides the well-known and mature propulsion systems adopting liquid and solid propellants, gel propellants also present interesting characteristics that can be better explored to enable the creation of alternative propulsive systems. The present work employed HTP at 98 wt% with 6 wt% of fumed silica as a gelling agent to create gelled HTP (GHTP). Droplets of the green fuel impinged on a layer of GHTP placed over a glass slide, acting as a solid oxidizer, mimicked an element of a new hybrid gel/liquid hypergolic propulsion system. Data from infrared and visible light cameras enabled a detailed analysis of the dynamics of a reactive droplet impinging on a gelled oxidizer wall, as well as the heat release, ignition, and flame spread of the hypergolic GHTP/green fuel pair under open-air conditions. The heat release was observed to be distributed across concentric annular areas for both the fuel surrogate and the fuel with catalyst, before and after ignition, demonstrating a strong correlation with non-reactive droplet fluid dynamics, which was corroborated by spread diameter analysis processed from visible image data. Vapor and Ignition Delay Times (VDT and IDT) were found to be as low as 4 and 17 ms, respectively, for the highest droplet impact velocity and catalyst concentration. The reaction rate in the gas phase, considering the flame spread area, showed a dependency of both impact velocity and catalyst concentration, with the latter exhibiting a more pronounced and clear effect. The surface temperature ranges where first vaporization and ignition occurred were 60 °C <span><math><mo>∼</mo></math></span> 70 °C and 120 <span><math><mo>∼</mo></math></span> 170 °C, respectively, which is close to the boiling point of methanol and the auto-ignition temperature of TMEDA. This finding, along with the chemical mechanisms in the gas phase related to the presence of a catalyst in the fuel, may be important for hypergolic ignition. The relatively low ignition temperatures and the short ignition times represent additional advantages of the present hypergolic combination for propulsion applications.</div></div>","PeriodicalId":12294,"journal":{"name":"Experimental Thermal and Fluid Science","volume":"160 ","pages":"Article 111322"},"PeriodicalIF":2.8,"publicationDate":"2024-09-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142319395","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}