Experimental Thermal and Fluid Science最新文献

{"title":"Coalescence position of two confined droplets with unequal lengths in microchannels","authors":"Wei Dong ,&nbsp;Yuqing Zhao ,&nbsp;Lei Tang ,&nbsp;Liangkang Xie ,&nbsp;Xiaoda Wang ,&nbsp;Wei Du","doi":"10.1016/j.expthermflusci.2025.111419","DOIUrl":"10.1016/j.expthermflusci.2025.111419","url":null,"abstract":"<div><div>The coalescence of two droplets with unequal lengths through a head-to-rear collision in the microchannel with a double T-junction is an important passive method to construct droplet reactors. However, the accurate prediction of the coalescence position is still not achievable. This work aimed to explore the coalescence position by analyzing the droplet dynamics. Firstly, the velocity variation of the paired droplets moving in a straight microchannel was analyzed to divide the whole process into several stages. Then, based on the experimental investigations, mathematical models were developed to describe the distances of the droplet-pairs moving in each stage to predict the coalescence position in the straight microchannel. In addition, the coalescence position, as well as the coalescence mechanism, was analyzed for the paired droplets in an expansion microchannel to explore the more possibilities of intensifying the construction of droplet reactors in microchannels.</div></div>","PeriodicalId":12294,"journal":{"name":"Experimental Thermal and Fluid Science","volume":"163 ","pages":"Article 111419"},"PeriodicalIF":2.8,"publicationDate":"2025-01-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143134853","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":"Micro-PIV experimental measurements of vortex evolution inside generated droplets in T-inlet microchannel","authors":"Wang Cao ,&nbsp;Qingjun Yang ,&nbsp;Ruikai Guo ,&nbsp;Qi Mao","doi":"10.1016/j.expthermflusci.2025.111418","DOIUrl":"10.1016/j.expthermflusci.2025.111418","url":null,"abstract":"<div><div>The evolution of swirling intensity within droplets during the formation of squeezing microdroplets in T-inlet microchannel devices was experimentally investigated utilizing the microparticle image velocimetry (micro-PIV) technique. Swirling intensity is quantitatively characterized by defining the average rotational angular velocity of fluid units under shear-free conditions. The effects of the continuous phase capillary number and the dispersed phase flow velocity on the evolution of swirling intensity within the droplets were investigated experimentally. Experimental results indicate that the internal vortex evolution process of droplets during the formation of squeezing microdroplets can be categorized into four distinct phases. An increase in the capillary number of the continuous phase effectively shortens the microdroplet formation period while enhancing the recirculation swirling intensity within the droplets. Conversely, by adjusting the flow velocity of the dispersed phase fluid, variations in the droplet formation period can be achieved without altering the swirling intensity. These findings provide a theoretical foundation for improving mixing, mass and heat transfer processes within microdroplets.</div></div>","PeriodicalId":12294,"journal":{"name":"Experimental Thermal and Fluid Science","volume":"163 ","pages":"Article 111418"},"PeriodicalIF":2.8,"publicationDate":"2025-01-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143134924","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":"Local heat transfer approach to the start-up analysis of an ultra-thin loop heat pipe","authors":"Luca Pagliarini ,&nbsp;Kelvin G. Domiciano ,&nbsp;Larissa Krambeck ,&nbsp;Fabio Bozzoli ,&nbsp;Marcia B.H. Mantelli","doi":"10.1016/j.expthermflusci.2025.111421","DOIUrl":"10.1016/j.expthermflusci.2025.111421","url":null,"abstract":"<div><div>Loop heat pipes are two-phase, passive heat transfer devices that exhibit attractive features for thermal management applications, including micro-electronics and battery packs cooling. To enhance the modelling and optimization of such heat transfer devices, a better understanding of their working behaviour is needed, especially in terms of device response to start-up transients. To this aim, a novel local heat transfer approach is proposed and applied to the experimental investigation of a copper loop heat pipe partially filled with ethanol, whose ultra-thin layout has been specifically designed for embedment in electronic devices. The evaporator section is heated by means of an electrical resistance, while the condenser is cooled by free convection. The outer wall temperature along the whole condenser is monitored during the start-up phase of the device at varying heat loads through a medium-wave infrared camera. The temperature signals, referred to six wall sections, are post-processed by means of the Inverse Heat Conduction Problem resolution approach, resulting in the assessment of the heat fluxes exchanged between the working fluid and the device wall over time in both the vapor and liquid lines. The inverse method is successfully validated by means of synthetic data, whereas the experimental procedure is calibrated and verified by preliminary experimental tests. Start-up results show comparable trends in the wall-to-fluid heat flux profiles with the heat input, exhibiting peak values of about 2300 W/m². Through the present non-intrusive technique, fluid velocity in the vapour line is also estimated in the range 0.008 - 0.012 m/s. To the authors’ knowledge, this represents one of the first attempts of characterizing both local heat transfer quantities and inner fluid dynamics in loop heat pipes via experimental approaches.</div></div>","PeriodicalId":12294,"journal":{"name":"Experimental Thermal and Fluid Science","volume":"163 ","pages":"Article 111421"},"PeriodicalIF":2.8,"publicationDate":"2025-01-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143134852","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":"An experimental study on the influence of variable film-hole diameter and arrangement on unsteady cooling performance","authors":"Liwei Ma,&nbsp;Xinyu Liu,&nbsp;Wenhao Guo,&nbsp;Jianhua Wang,&nbsp;Jian Pu,&nbsp;Ran Yao","doi":"10.1016/j.expthermflusci.2025.111415","DOIUrl":"10.1016/j.expthermflusci.2025.111415","url":null,"abstract":"<div><div>To reduce the unsteadiness and enhance the time-averaged film coverage performance, a novel conception of variable hole-diameter and arrangement is suggested. Five rows of film-holes with diameters ranging from 0.0020 m to 0.0038 m are embedded on a flat plate, including five kinds of arrangements. The effects of arrangement scheme, blowing ratio and plate thickness on the unsteadiness and time-averaged behaviors are experimentally investigated by time-resolved quantitative light sheet technique. The spatial modes of large-scale structures are analyzed by proper orthogonal decomposition analysis, and the flow field are characterized by momentum thickness and velocity distribution. The present work reveals two important and valuable phenomena: 1) For the thin plate (small length-to-diameter ratio, <em>L</em>/<em>D</em>), the arrangement of “hole-diameter from large to small” can achieve the highest time-averaged film coverage performance and the lowest unsteadiness than the other arrangements. 2) Compared with the thick plate (large <em>L</em>/<em>D</em>) with unchanged hole-diameter, the thin plates with the arrangements of “hole-diameter from large to small” and “small hole-diameter in the middle” can provide higher time-averaged performance and lower unsteadiness. This exploration may provide the investigators and designers of film cooling with a new thread.</div></div>","PeriodicalId":12294,"journal":{"name":"Experimental Thermal and Fluid Science","volume":"163 ","pages":"Article 111415"},"PeriodicalIF":2.8,"publicationDate":"2025-01-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143134923","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":"Unsteady boundary-layer transition measurements with Temperature-Sensitive Paint under cryogenic conditions","authors":"Armin Weiss ,&nbsp;Christian Klein ,&nbsp;Ulrich Henne ,&nbsp;Anne Hebler","doi":"10.1016/j.expthermflusci.2025.111414","DOIUrl":"10.1016/j.expthermflusci.2025.111414","url":null,"abstract":"<div><div>The study presents the first measurement of boundary-layer transition on a harmonically-pitching airfoil under cryogenic conditions. The experiments were conducted in the cryogenic wind tunnel of the German–Dutch Wind Tunnels in Cologne using a test rig especially designed for harmonic pitch oscillations of a two-dimensional model equipped with the laminar NLF(2)-0415 airfoil. The tests were performed at free stream Reynolds and Mach numbers of <span><math><mrow><mi>R</mi><mi>e</mi><mo>=</mo><mn>6</mn><mo>×</mo><mn>1</mn><msup><mrow><mn>0</mn></mrow><mrow><mn>6</mn></mrow></msup></mrow></math></span> and <span><math><mrow><mi>M</mi><mo>=</mo><mn>0</mn><mo>.</mo><mn>34</mn></mrow></math></span>. Unsteady pitch oscillations were investigated at different pitch frequencies (up to 40<!--> <!-->Hz, i.e. a reduced frequency of 0.540) and pitch amplitudes, as well as for a steady angle-of-attack polar for comparison. The boundary-layer transition movement was captured by means of spatially high-resolving temperature-sensitive paint using a surface-integrated heating layer of carbon nanotubes (cntTSP) and fast-response pressure transducers. The cntTSP data was processed according to the already established “Differential Thermography” (DT) method as well as using a recently presented method based on the evaluation of the qualitative distribution of the heat-transfer coefficient (HTC). The techniques are described in detail and results are evaluated with respect to measurement-based thermal hysteresis as well as the influence of varying pitch frequency and amplitude. The latter could successfully be measured by all applied methods. The findings further reveal significant improvements in the detection of unsteady boundary-layer transition when applying the HTC method compared to DT. These are: a reduction of the measurement error in terms of the thermal hysteresis component in the results and an increased result density at pitch phases, where the DT method inherently fails to yield results.</div></div>","PeriodicalId":12294,"journal":{"name":"Experimental Thermal and Fluid Science","volume":"163 ","pages":"Article 111414"},"PeriodicalIF":2.8,"publicationDate":"2025-01-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143134850","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 on the effectiveness of plasma energy deposition in controlling transverse jet","authors":"Ao Wang ,&nbsp;Zhi Chen ,&nbsp;Liming Feng ,&nbsp;Shunxin Qu ,&nbsp;Hao Ding ,&nbsp;Lifeng Tian","doi":"10.1016/j.expthermflusci.2025.111420","DOIUrl":"10.1016/j.expthermflusci.2025.111420","url":null,"abstract":"<div><div>In this paper, we carried out an experimental study on the control of transverse jet via plasma energy deposition in a Mach 2.5 wind tunnel. The actuator operates at a discharge frequency of 10 kHz, generating thermal block effects upstream of the jet. Time-resolved schlieren system with 50 kHz shooting frequency, as well as wall static pressure taps, was utilized to measure the dynamic flow with and without excitation. This research delves into the feasibility of plasma energy deposition on controlling the transverse jets with varying injection total pressure (0, 200, 300, 400 kPa). The pressure increment within cavity resulting from discharge exists in all cases, attributed to the combined effects of plasma-induced shock and jet entrainment. Instantaneous schlieren images and the statistical analysis of their datasets were employed to investigate the unsteady characteristics of the flow field. The results indicate that discharge significantly elevates the energy contribution of unsteady modes, inhibits the low-frequency oscillations of the bow shock, and modulates the dominant frequency of the jet vortex shedding mode. Moreover, the increase in jet vorticity can be ascribed to the deformation of the precursor shock and the Richtmyer–Meshkov instability around thermal bubble/bow shock interaction region. As injection total pressure increases, the triangular-like region formed by the large eddy-induced shock, reflected shock, and the jet moves upstream and shrinks, consequently curtailing the region where jet pulsations amplify. After passing through bow shock, the effect of precursor shock on regulating the flow dampens with increasing injection total pressure. However, even at an injection total pressure of 400 kPa, coherent structures downstream of the bow shock can still be detected, demonstrating the broad control range of plasma energy deposition.</div></div>","PeriodicalId":12294,"journal":{"name":"Experimental Thermal and Fluid Science","volume":"163 ","pages":"Article 111420"},"PeriodicalIF":2.8,"publicationDate":"2025-01-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143134851","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":"Increased surface temperature at critical heat flux for single water droplet impact with alcohol additives","authors":"Chang Cai ,&nbsp;Chao Si ,&nbsp;Hong Liu","doi":"10.1016/j.expthermflusci.2025.111413","DOIUrl":"10.1016/j.expthermflusci.2025.111413","url":null,"abstract":"<div><div>Elevating the critical heat flux limit during droplet impact cooling is advantageous for the thermal management of various high-power equipment. This study presents the experimental observation that the surface temperature at the critical heat flux point decreases with droplet impact velocity. The findings also demonstrate that low-carbon alcohol additives at small concentrations markedly increase the critical heat flux temperature of an impacting water droplet. In particular, the critical heat flux temperatures of dilute alcoholic solution droplets at higher impact velocities exceed those of pure water droplets at lower impact velocities within the present test range. Accordingly, low-carbon alcohol additives at low volume fractions can assure high heat transfer rates at large Weber numbers while also reducing the detrimental effect of impact velocity on the critical heat flux temperature. The significantly increased critical heat flux temperature associated with low-carbon alcohol additives is supposed to be considerably favorable for efficient heat dissipation of high-heat-flux electronic components.</div></div>","PeriodicalId":12294,"journal":{"name":"Experimental Thermal and Fluid Science","volume":"163 ","pages":"Article 111413"},"PeriodicalIF":2.8,"publicationDate":"2025-01-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143134920","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":"Evaluation of surge propagation and discharge calculation in a sloping circular pipe","authors":"Jinlong Zuo ,&nbsp;Tibing Xu ,&nbsp;Yu Qian ,&nbsp;David Z. Zhu","doi":"10.1016/j.expthermflusci.2025.111409","DOIUrl":"10.1016/j.expthermflusci.2025.111409","url":null,"abstract":"<div><div>The generation and propagation of a positive surge in a sloping circular pipe were studied. Using a lab-scale model, positive surges were generated by rapidly closing a downstream gate, and the resulting flow patterns and surge propagation speeds were observed. The continuity and momentum equations were applied to derive an analytical solution for back-calculating discharge from measured surge speeds and hydraulic conditions. Experimental results showed the surge speed decreased with propagation distance, stabilizing beyond certain distances. The sequent depth ratio for positive surges was investigated, and the results showed that the sequent depth ratio for circular pipes was lower compared to that in a rectangular channel with the same Froude number. An equation was developed to evaluate the sequent depth ratio for positive surges in partially filled flow within a circular pipe. In practical applications, it is necessary to measure the initial water depth, the surge propagation distance, the average speed of the surge corresponding to this distance, and the water depth behind the surge wave front to estimate the discharge in the pipe. The results indicated that a longer observation distance from the disturbance location leads to a smaller error between the calculated and measured discharges, which is generally less than 10 % at measurement locations farther than 3 times the diameter length from the tailgate. Therefore, the proposed discharge calculation equation can be applied in sewer systems as an initial discharge estimation method for quick reference.</div></div>","PeriodicalId":12294,"journal":{"name":"Experimental Thermal and Fluid Science","volume":"163 ","pages":"Article 111409"},"PeriodicalIF":2.8,"publicationDate":"2025-01-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143134922","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":"Temporal instability and sheet breakup of a curved liquid sheet formed by jet impinging on a circular plane","authors":"Tianyu Kang (康天宇) ,&nbsp;Qingbo Yu (于庆波) ,&nbsp;Zhongyuan Liu (刘中元) ,&nbsp;Shengkai Tao (陶盛恺)","doi":"10.1016/j.expthermflusci.2025.111411","DOIUrl":"10.1016/j.expthermflusci.2025.111411","url":null,"abstract":"<div><div>For melt granulation, sheet breakup formed by melt jet impingement is an efficient treatment method. This paper theoretically and experimentally investigates the flow and breakup characteristics of a curved liquid sheet formed by jet impinging on a circular plane. The results show that the overall degree of sheet bending decreases with the increase in sheet velocity, which can be used to determine the streamline of liquid sheets by the configuration method. Based on the obtained knowledge of the sheet dynamic, the disturbance dispersion equation of a liquid sheet with variable velocity is derived first. In the instability analysis of the liquid sheet element, the acceleration force working due to the sheet bending stabilizes the sheet disturbance. However, combining the overall motion and instability of the liquid sheet shows that, with the sheet’s bending and spreading, the increasing sheet velocity and the decreasing sheet thickness still promote the development of sheet disturbance. For the dominant breakup mode, the bending of the liquid sheet contributes to the delay of sheet breakup for bell-like sheets at low velocity. In contrast, the bending of the liquid sheet contributes to the advance of sheet breakup for umbrella-like sheets at large velocity. For the critical jet Weber number, the experimental value of the curved sheet is less than that of the planar liquid sheet, due to the increase in sheet velocity. The prediction methods of breakup length and droplet radius are proposed.</div></div>","PeriodicalId":12294,"journal":{"name":"Experimental Thermal and Fluid Science","volume":"163 ","pages":"Article 111411"},"PeriodicalIF":2.8,"publicationDate":"2025-01-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143134921","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":"Advection-based multiframe iterative correction for pressure estimation from velocity fields","authors":"Junwei Chen,&nbsp;Marco Raiola,&nbsp;Stefano Discetti","doi":"10.1016/j.expthermflusci.2025.111407","DOIUrl":"10.1016/j.expthermflusci.2025.111407","url":null,"abstract":"<div><div>A novel method to improve the accuracy of pressure field estimation from time-resolved Particle Image Velocimetry data is proposed. This method generates several new time-series of velocity field by propagating in time the original one using an advection-based model, which assumes that small-scale turbulence is advected by large-scale motions. Then smoothing is performed at the corresponding positions across all the generated time-series. The process is repeated through an iterative scheme. The proposed technique smears out spatial noise by exploiting time information. Simultaneously, temporal jitter is repaired using spatial information, enhancing the accuracy of pressure computation via the Navier–Stokes equations. We provide a proof of concept of the method with synthetic datasets based on a channel flow and the wake of a 2D wing. Different noise models are tested, including Gaussian white noise and errors with some degree of spatial coherence. Additionally, the filter is evaluated on an experimental test case of the wake of an airfoil, where pressure field ground truth is not available. The result shows the proposed method performs better than conventional filters in velocity and pressure field estimation, especially when spatially coherent errors are present. The method is of direct application in advection-dominated flows, although its extension with more advanced models is straightforward.</div></div>","PeriodicalId":12294,"journal":{"name":"Experimental Thermal and Fluid Science","volume":"164 ","pages":"Article 111407"},"PeriodicalIF":2.8,"publicationDate":"2025-01-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143227272","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}