Pub Date : 2024-10-14DOI: 10.1016/j.expthermflusci.2024.111335
The anti-ice system is a crucial subsystem for ensuring aircraft safety. Water droplet evaporation on its surface is a frequent occurrence during flight. Investigating the characteristics of water droplet evaporation is essential for designing effective active or passive aircraft anti-ice systems. Previous research has primarily focused on the evaporation of small droplets under constant wall temperature conditions. The emergence of more electric aircraft has led to the adoption of electrical heating anti-ice systems, which typically operate under conditions of constant wall heat flux. Despite this shift, the quantitative characteristics of evaporation under different surface properties and constant wall heat flux conditions have not been thoroughly investigated. In this paper, an experimental test site was built to study the evaporation characteristics of water droplets on heating surfaces with various coatings and under different wall thermal conditions. The experimental results showed that the evaporation time for droplets on hydrophobic surfaces was longer than that on hydrophilic surfaces. The increase in evaporation time ranged from 5 to 13 times as the surface temperature was raised from 40 °C to 80 °C. Furthermore, the difference in evaporation time between small and large droplets was more pronounced under constant temperature conditions than that of constant heat flux conditions. For droplets on polished aluminum and hydrophilic surfaces, the evaporation rate was linearly related to the evaporation surface area. The findings of this study can inform future optimizations of anti-ice systems.
防冰系统是确保飞机安全的关键子系统。在飞行过程中，飞机表面经常会有水滴蒸发。研究水滴蒸发的特性对于设计有效的主动或被动飞机防冰系统至关重要。以往的研究主要集中在恒定壁温条件下的小水滴蒸发。随着更多电动飞机的出现，电加热防冰系统开始被采用，这些系统通常在恒定的壁面热通量条件下运行。尽管出现了这种转变，但对不同表面特性和恒定壁面热通量条件下蒸发的定量特征还没有进行深入研究。本文建立了一个实验测试场，研究不同涂层的加热表面在不同壁面热条件下的水滴蒸发特性。实验结果表明，水滴在疏水表面上的蒸发时间比在亲水表面上的蒸发时间长。当表面温度从 40 °C 升至 80 °C 时，蒸发时间增加了 5 至 13 倍。此外，在恒温条件下，小液滴和大液滴蒸发时间的差异比恒定热通量条件下的差异更为明显。对于抛光铝和亲水表面上的液滴，蒸发速率与蒸发表面积呈线性关系。这项研究的结果可为今后防冰系统的优化提供参考。
{"title":"Evaporation characteristics of water droplets on heated surfaces with various coatings and under different wall thermal conditions","authors":"","doi":"10.1016/j.expthermflusci.2024.111335","DOIUrl":"10.1016/j.expthermflusci.2024.111335","url":null,"abstract":"<div><div>The anti-ice system is a crucial subsystem for ensuring aircraft safety. Water droplet evaporation on its surface is a frequent occurrence during flight. Investigating the characteristics of water droplet evaporation is essential for designing effective active or passive aircraft anti-ice systems. Previous research has primarily focused on the evaporation of small droplets under constant wall temperature conditions. The emergence of more electric aircraft has led to the adoption of electrical heating anti-ice systems, which typically operate under conditions of constant wall heat flux. Despite this shift, the quantitative characteristics of evaporation under different surface properties and constant wall heat flux conditions have not been thoroughly investigated. In this paper, an experimental test site was built to study the evaporation characteristics of water droplets on heating surfaces with various coatings and under different wall thermal conditions. The experimental results showed that the evaporation time for droplets on hydrophobic surfaces was longer than that on hydrophilic surfaces. The increase in evaporation time ranged from 5 to 13 times as the surface temperature was raised from 40 °C to 80 °C. Furthermore, the difference in evaporation time between small and large droplets was more pronounced under constant temperature conditions than that of constant heat flux conditions. For droplets on polished aluminum and hydrophilic surfaces, the evaporation rate was linearly related to the evaporation surface area. The findings of this study can inform future optimizations of anti-ice systems.</div></div>","PeriodicalId":12294,"journal":{"name":"Experimental Thermal and Fluid Science","volume":null,"pages":null},"PeriodicalIF":2.8,"publicationDate":"2024-10-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142528946","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}
Pub Date : 2024-10-11DOI: 10.1016/j.expthermflusci.2024.111334
<div><div>Although developing gravity-driven slug flow frequently occurs in oil and gas, and energy systems, its development dynamics remain underexplored; this gap, in turn, has left the underlying relationships between flow evolution and transport phenomena in these applications inadequately characterized as well. The present study experimentally investigates the spatiotemporal-spectral development of gravity-driven air–water and CO<sub>2</sub>-water slug flows in a vertical 25.4 <span><math><mrow><mi>mm</mi></mrow></math></span> ID pipe. Enhanced flow visualization techniques, utilizing high-speed imaging and particle image velocimetry-planar laser induced fluorescence (PIV-PLIF), were employed to determine the behaviors of gas and liquid phases and interactions at four positions along the pipe axis. A machine vision-based algorithm was employed to extract slug unit cell characteristics and instantaneous void fraction signals, allowing for a comprehensive statistical analysis of gas phase behavior across the flow domain. A novel algorithm was also developed to preprocess raw PIV-PLIF images, facilitating phase discrimination and noise reduction before PIV cross-correlation analyses are conducted. The results showed a logarithmic growth in the lengths of Taylor bubbles, liquid slugs, and slug unit cells along the pipe, with liquid slugs constituting nearly 60 % of slug units downstream. Taylor bubble length distributions correlated well with log-normal fits, while liquid slug and unit cell lengths transitioned from log-normal patterns upstream to near-normal distributions downstream with broader and less peaked shapes. Taylor bubble velocities and appearance frequencies of the flow structures declined exponentially along the pipe, with Taylor bubble velocities showing narrower and more peaked near-normal distributions downstream. Instantaneous void fraction signals exhibited fewer, wider peaks and troughs with reduced small-amplitude oscillations downstream. The analysis of the signals indicated a complete bubbly-to-slug transition at <span><math><mrow><mi>Z</mi><mo>/</mo><mi>D</mi><mo>=</mo><mn>30</mn></mrow></math></span>. Gas-liquid phase interactions, classified as almost-zero, weak, and strong, impacted liquid phase velocity profiles and the behavior of Taylor bubbles, with minimum stable liquid slug lengths of 8–9 <span><math><mrow><mi>D</mi></mrow></math></span> and a wake length of 1.8 <span><math><mrow><mi>D</mi></mrow></math></span> observed. Empirical correlations were developed to represent the spatiotemporal-spectral aspects of flow development, with spectral parameters, particularly liquid slug frequency, identified as the most reliable indicators of the fully developed region, predicting entrance lengths of 114.0 <span><math><mrow><mi>D</mi></mrow></math></span> and 113.4 <span><math><mrow><mi>D</mi></mrow></math></span> for air–water and CO<sub>2</sub>-water, respectively. Gas density was found to strongly influence flow charact
{"title":"Characterizing the development of gravity-driven slug flows using high-speed imaging and PIV-PLIF techniques","authors":"","doi":"10.1016/j.expthermflusci.2024.111334","DOIUrl":"10.1016/j.expthermflusci.2024.111334","url":null,"abstract":"<div><div>Although developing gravity-driven slug flow frequently occurs in oil and gas, and energy systems, its development dynamics remain underexplored; this gap, in turn, has left the underlying relationships between flow evolution and transport phenomena in these applications inadequately characterized as well. The present study experimentally investigates the spatiotemporal-spectral development of gravity-driven air–water and CO<sub>2</sub>-water slug flows in a vertical 25.4 <span><math><mrow><mi>mm</mi></mrow></math></span> ID pipe. Enhanced flow visualization techniques, utilizing high-speed imaging and particle image velocimetry-planar laser induced fluorescence (PIV-PLIF), were employed to determine the behaviors of gas and liquid phases and interactions at four positions along the pipe axis. A machine vision-based algorithm was employed to extract slug unit cell characteristics and instantaneous void fraction signals, allowing for a comprehensive statistical analysis of gas phase behavior across the flow domain. A novel algorithm was also developed to preprocess raw PIV-PLIF images, facilitating phase discrimination and noise reduction before PIV cross-correlation analyses are conducted. The results showed a logarithmic growth in the lengths of Taylor bubbles, liquid slugs, and slug unit cells along the pipe, with liquid slugs constituting nearly 60 % of slug units downstream. Taylor bubble length distributions correlated well with log-normal fits, while liquid slug and unit cell lengths transitioned from log-normal patterns upstream to near-normal distributions downstream with broader and less peaked shapes. Taylor bubble velocities and appearance frequencies of the flow structures declined exponentially along the pipe, with Taylor bubble velocities showing narrower and more peaked near-normal distributions downstream. Instantaneous void fraction signals exhibited fewer, wider peaks and troughs with reduced small-amplitude oscillations downstream. The analysis of the signals indicated a complete bubbly-to-slug transition at <span><math><mrow><mi>Z</mi><mo>/</mo><mi>D</mi><mo>=</mo><mn>30</mn></mrow></math></span>. Gas-liquid phase interactions, classified as almost-zero, weak, and strong, impacted liquid phase velocity profiles and the behavior of Taylor bubbles, with minimum stable liquid slug lengths of 8–9 <span><math><mrow><mi>D</mi></mrow></math></span> and a wake length of 1.8 <span><math><mrow><mi>D</mi></mrow></math></span> observed. Empirical correlations were developed to represent the spatiotemporal-spectral aspects of flow development, with spectral parameters, particularly liquid slug frequency, identified as the most reliable indicators of the fully developed region, predicting entrance lengths of 114.0 <span><math><mrow><mi>D</mi></mrow></math></span> and 113.4 <span><math><mrow><mi>D</mi></mrow></math></span> for air–water and CO<sub>2</sub>-water, respectively. Gas density was found to strongly influence flow charact","PeriodicalId":12294,"journal":{"name":"Experimental Thermal and Fluid Science","volume":null,"pages":null},"PeriodicalIF":2.8,"publicationDate":"2024-10-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142444884","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}
Pub Date : 2024-10-10DOI: 10.1016/j.expthermflusci.2024.111333
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.
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.
{"title":"Error analysis and improvement of water displacement method in measuring gas desorption volume from coal particles","authors":"","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":null,"pages":null},"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}
Pub Date : 2024-10-09DOI: 10.1016/j.expthermflusci.2024.111331
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.
{"title":"Impact of piezoelectric driving waveform on performance characteristics of vibrating mesh atomizer (VMA)","authors":"","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":null,"pages":null},"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}
Pub Date : 2024-10-05DOI: 10.1016/j.expthermflusci.2024.111330
The dynamic behavior of compound droplets impacting a solid surface was studied via experiments over (defined as the ratio of the compound droplet shell thickness h to the diameter D0 of compound droplet) ranging from 0 to 0.34, We ranging from 25 to 325 and Re 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, We, 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, and were used to divide the modal boundary of the compound droplet core. Further analysis reveals the correlation between We, Re, and.
{"title":"Impact of a compound droplet on a solid surface: The effect of the shell on the core","authors":"","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>D<sub>0</sub></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":null,"pages":null},"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}
Pub Date : 2024-10-05DOI: 10.1016/j.expthermflusci.2024.111328
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.
{"title":"Characteristics of Gas–Liquid Two-Phase flow in rectangular narrow slits with varying cross sections driven by large pressure drop","authors":"","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":null,"pages":null},"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}
Pub Date : 2024-10-02DOI: 10.1016/j.expthermflusci.2024.111329
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 Frm is less than 5.0, the radial position of the elongated bubble head decreases linearly as the Frm increases. When the Frm 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.
{"title":"Investigation on intermittent flow characteristics in horizontal pipe by visualization measurement method","authors":"","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<sub>m</sub></em> is less than 5.0, the radial position of the elongated bubble head decreases linearly as the <em>Fr<sub>m</sub></em> increases. When the <em>Fr<sub>m</sub></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":null,"pages":null},"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}
Pub Date : 2024-10-01DOI: 10.1016/j.expthermflusci.2024.111327
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 ( and ) 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 , however with inconsistent results for larger . 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.
{"title":"Experimental characterization of turbulent boundary layers around a NACA 4412 wing profile","authors":"","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":null,"pages":null},"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}
Pub Date : 2024-09-28DOI: 10.1016/j.expthermflusci.2024.111326
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, H2, and CO2 respectively in the methane-based fuel mixtures.
{"title":"Experimental study of flame chemiluminescence for premixed methane based binary fuel flames","authors":"","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 CH<sub>4</sub> + C<sub>3</sub>H<sub>8</sub>, CH<sub>4</sub> + CO<sub>2</sub>, and CH<sub>4</sub> + H<sub>2</sub> 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 CO<sub>2</sub>* and OH*, CH(A), and C<sub>2</sub>* can be used to monitor the proportion of C<sub>3</sub>H<sub>8</sub>, H<sub>2,</sub> and CO<sub>2</sub> respectively in the methane-based fuel mixtures.</div></div>","PeriodicalId":12294,"journal":{"name":"Experimental Thermal and Fluid Science","volume":null,"pages":null},"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}
Pub Date : 2024-09-28DOI: 10.1016/j.expthermflusci.2024.111325
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.
{"title":"Advancements on the use of Filtered Rayleigh Scattering (FRS) with Machine learning methods for flow distortion in Aero-Engine intakes","authors":"","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":null,"pages":null},"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}
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