Pub Date : 2025-01-06DOI: 10.1016/j.ijheatfluidflow.2024.109741
Ziwei Xia , Minxiang Su , Shuai Li , Jiaxin Shi , Wei Yu
Employing a combined approach of offline experiments and numerical simulations, this study investigates the temperature distribution of steel rods under various air temperatures during forced air-cooling to elucidate the cooling mechanisms of steel rods. At a wind speed of 22 m/s, an increase in air temperature significantly reduces the convective heat transfer coefficient. Continuous airflow creates regions of low Reynolds numbers at the top of the rod and high Reynolds numbers along its sides, significantly enhancing the side convective heat transfer coefficient over the top. Empirical formulas for heat transfer coefficients at different rod positions were derived from experimental and simulation results and validated experimentally with a calculation error of less than 4 %.
{"title":"The influence of air temperature on heat transfer coefficient under forced air-cooling conditions","authors":"Ziwei Xia , Minxiang Su , Shuai Li , Jiaxin Shi , Wei Yu","doi":"10.1016/j.ijheatfluidflow.2024.109741","DOIUrl":"10.1016/j.ijheatfluidflow.2024.109741","url":null,"abstract":"<div><div>Employing a combined approach of offline experiments and numerical simulations, this study investigates the temperature distribution of steel rods under various air temperatures during forced air-cooling to elucidate the cooling mechanisms of steel rods. At a wind speed of 22 m/s, an increase in air temperature significantly reduces the convective heat transfer coefficient. Continuous airflow creates regions of low Reynolds numbers at the top of the rod and high Reynolds numbers along its sides, significantly enhancing the side convective heat transfer coefficient over the top. Empirical formulas for heat transfer coefficients at different rod positions were derived from experimental and simulation results and validated experimentally with a calculation error of less than 4 %.</div></div>","PeriodicalId":335,"journal":{"name":"International Journal of Heat and Fluid Flow","volume":"112 ","pages":"Article 109741"},"PeriodicalIF":2.6,"publicationDate":"2025-01-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143140881","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"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 : 2025-01-04DOI: 10.1016/j.ijheatfluidflow.2024.109742
Weiwei Cui , Yuqiang Liu , Long Zhang , Xinyuan Chen , Cuiping Wang
The clearance flow is closely linked to the tip flow characteristics and instability mechanisms of axial compressor rotor. Therefore, both experimental and numerical studies were conducted to investigate the influences of variations in clearance size on tip flow behaviors and instability mechanisms within a subsonic compressor rotor. The results show that the subsonic rotor has two distinct low-velocity zones due to tip leakage flow and suction surface separation at near-stall condition. As clearance size increases, suction surface separation decreases while tip leakage flow increases continuously. Within the small clearance size range (SCS range), the energy of leakage flow remains significantly lower than that of the surrounding mainstream at near-stall condition, leading it to be expelled from the tip channel by the mainstream. Thus, the substantial separation near suction surface induced by a pronounced positive angle of attack at leading edge, becomes the primary factor for tip flow instability in rotor at near-stall condition. Conversely, as clearance size further increased into large clearance size range (LCS range), suction surface separation nearly vanished near blade tip at near-stall condition, and the strong tip leakage vortex then dominates major disturbance in tip region. The low-velocity fluids generated by leakage vortex during unsteady fragmentation and dissipation obstructs the incoming mainstream in tip channel, contributing significantly to rotor stall. Consequently, it’s this progressively increasing leakage flow that leads to the stall margin of rotor showing an increasing and then decreasing trend in the clearance size monotonically increasing process, and fundamentally changes the stall inducing mechanism of the subsonic compressor rotor.
{"title":"Variations of stall mechanism induced by the changes of tip clearance size in a subsonic compressor rotor","authors":"Weiwei Cui , Yuqiang Liu , Long Zhang , Xinyuan Chen , Cuiping Wang","doi":"10.1016/j.ijheatfluidflow.2024.109742","DOIUrl":"10.1016/j.ijheatfluidflow.2024.109742","url":null,"abstract":"<div><div>The clearance flow is closely linked to the tip flow characteristics and instability mechanisms of axial compressor rotor. Therefore, both experimental and numerical studies were conducted to investigate the influences of variations in clearance size on tip flow behaviors and instability mechanisms within a subsonic compressor rotor. The results show that the subsonic rotor has two distinct low-velocity zones due to tip leakage flow and suction surface separation at near-stall condition. As clearance size increases, suction surface separation decreases while tip leakage flow increases continuously. Within the small clearance size range (SCS range), the energy of leakage flow remains significantly lower than that of the surrounding mainstream at near-stall condition, leading it to be expelled from the tip channel by the mainstream. Thus, the substantial separation near suction surface induced by a pronounced positive angle of attack at leading edge, becomes the primary factor for tip flow instability in rotor at near-stall condition. Conversely, as clearance size further increased into large clearance size range (LCS range), suction surface separation nearly vanished near blade tip at near-stall condition, and the strong tip leakage vortex then dominates major disturbance in tip region. The low-velocity fluids generated by leakage vortex during unsteady fragmentation and dissipation obstructs the incoming mainstream in tip channel, contributing significantly to rotor stall. Consequently, it’s this progressively increasing leakage flow that leads to the stall margin of rotor showing an increasing and then decreasing trend in the clearance size monotonically increasing process, and fundamentally changes the stall inducing mechanism of the subsonic compressor rotor.</div></div>","PeriodicalId":335,"journal":{"name":"International Journal of Heat and Fluid Flow","volume":"112 ","pages":"Article 109742"},"PeriodicalIF":2.6,"publicationDate":"2025-01-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143140159","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"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 : 2025-01-04DOI: 10.1016/j.ijheatfluidflow.2024.109728
Van Thuan Hoang, Azadeh Jafari, Benjamin Cazzolato, Maziar Arjomandi
Burst events in the near-wall region of turbulent boundary layers are the main contributors to skin friction drag in wall flows. This paper shows how synthetic jets modify the near-wall burst events in turbulent boundary layers, leading to local drag reduction. Different characteristics of synthetic jets including various non-dimensional jet frequencies, ranging from 0.025 to 0.063, at two non-dimensional jet amplitudes of 0.1 and 0.2 were examined by conducting hot-wire measurements at a Reynolds number of 1050. Statistical analysis utilizing a variable-interval time-averaging (VITA) technique illustrated a reduction of up to 15% in burst intensity and a decrease of approximately 10% in burst durations within the near-wall region, , indicating that synthetic jets lifted turbulent kinetic energy and weakened burst events in this region. Consequently, there was a reduction of up to approximately 14% in turbulence intensity near the wall, contributing to diminished shear stresses and local skin-friction drag. Furthermore, the synthetic jets generated a displacement of the inner peak of turbulent energy away from the wall, indicating that the synthetic jets shifted turbulent kinetic energy away from the wall. As the jet frequency or amplitude increased, the modification of the boundary layer became more pronounced.
{"title":"Modification of burst events in the near-wall region of turbulent boundary layers by synthetic jets","authors":"Van Thuan Hoang, Azadeh Jafari, Benjamin Cazzolato, Maziar Arjomandi","doi":"10.1016/j.ijheatfluidflow.2024.109728","DOIUrl":"10.1016/j.ijheatfluidflow.2024.109728","url":null,"abstract":"<div><div>Burst events in the near-wall region of turbulent boundary layers are the main contributors to skin friction drag in wall flows. This paper shows how synthetic jets modify the near-wall burst events in turbulent boundary layers, leading to local drag reduction. Different characteristics of synthetic jets including various non-dimensional jet frequencies, ranging from 0.025 to 0.063, at two non-dimensional jet amplitudes of 0.1 and 0.2 were examined by conducting hot-wire measurements at a Reynolds number of <span><math><mrow><mi>R</mi><msub><mrow><mi>e</mi></mrow><mrow><mi>θ</mi></mrow></msub><mo>≈</mo></mrow></math></span> 1050. Statistical analysis utilizing a variable-interval time-averaging (VITA) technique illustrated a reduction of up to 15% in burst intensity and a decrease of approximately 10% in burst durations within the near-wall region, <span><math><mrow><msup><mrow><mi>y</mi></mrow><mrow><mo>+</mo></mrow></msup><mo>≤</mo><mn>12</mn></mrow></math></span>, indicating that synthetic jets lifted turbulent kinetic energy and weakened burst events in this region. Consequently, there was a reduction of up to approximately 14% in turbulence intensity near the wall, contributing to diminished shear stresses and local skin-friction drag. Furthermore, the synthetic jets generated a displacement of the inner peak of turbulent energy away from the wall, indicating that the synthetic jets shifted turbulent kinetic energy away from the wall. As the jet frequency or amplitude increased, the modification of the boundary layer became more pronounced.</div></div>","PeriodicalId":335,"journal":{"name":"International Journal of Heat and Fluid Flow","volume":"112 ","pages":"Article 109728"},"PeriodicalIF":2.6,"publicationDate":"2025-01-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143140880","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The elliptical heat exchanger tube at the low-temperature heating surface of a 600 MW unit is taken as an example, and under the action of plane standing wave field, the whole domain solution is carried out inside and outside the boundary layer of the elliptical tube by numerical simulation method. Considering the influence of the parameters such as the aspect ratio (AR), the pulsating Strouhal number St0 and pulsating Reynolds number Re0 on the characteristics of the acoustic streaming outside the tube, the intrinsic mechanism of the enhanced heat transfer and the removal of fouling is elucidated by in-depth discussion of the acoustic streaming structure, the strength, the scale and so on. Research results indicate that as the AR increases from 0.2 to 1, the external acoustic streaming structure around the tube transitions from four internal vortices to eight vortices (four internal and four external) under different St0 and Re0, with the internal and external vortices rotating in opposite directions. Due to the influence of internal and external vortices, the velocity in the direction of the central angle α exhibits peak-to-trough fluctuations, showcasing rich velocity distribution characteristics at different distances s from the elliptical tube. The larger the AR, the better the heat transfer effect closer to the wall surface. The inner and outer vortex sizes show a similar variation pattern; the smaller the inner vortex size, the better the ash removal effect. The relative Nusselt number NU and relative shear rate SH quantify the effects of heat transfer and ash removal, respectively, and low-frequency high-intensity acoustic streaming is favourable for both. When given Re0 or St0, the SH reaches a maximum at AR = 0.4. This is due to drastic changes in the acoustic streaming characteristics for this tube shape, which is reflected in the first-order sound pressure, radial acoustic streaming velocity, and the size of internal and external vortices.
{"title":"Study on heat transfer characteristics of elliptical heat exchange tubes under acoustic streaming","authors":"Yu Zhou, Genshan Jiang, Yu Jiang, Jianhao Sun, Hao Li, Zishu Zhou","doi":"10.1016/j.ijheatfluidflow.2024.109738","DOIUrl":"10.1016/j.ijheatfluidflow.2024.109738","url":null,"abstract":"<div><div>The elliptical heat exchanger tube at the low-temperature heating surface of a 600 MW unit is taken as an example, and under the action of plane standing wave field, the whole domain solution is carried out inside and outside the boundary layer of the elliptical tube by numerical simulation method. Considering the influence of the parameters such as the aspect ratio (AR), the pulsating Strouhal number St<sub>0</sub> and pulsating Reynolds number Re<sub>0</sub> on the characteristics of the acoustic streaming outside the tube, the intrinsic mechanism of the enhanced heat transfer and the removal of fouling is elucidated by in-depth discussion of the acoustic streaming structure, the strength, the scale and so on. Research results indicate that as the AR increases from 0.2 to 1, the external acoustic streaming structure around the tube transitions from four internal vortices to eight vortices (four internal and four external) under different St<sub>0</sub> and Re<sub>0</sub>, with the internal and external vortices rotating in opposite directions. Due to the influence of internal and external vortices, the velocity in the direction of the central angle <em>α</em> exhibits peak-to-trough fluctuations, showcasing rich velocity distribution characteristics at different distances <em>s</em> from the elliptical tube. The larger the AR, the better the heat transfer effect closer to the wall surface. The inner and outer vortex sizes show a similar variation pattern; the smaller the inner vortex size, the better the ash removal effect. The relative Nusselt number NU and relative shear rate SH quantify the effects of heat transfer and ash removal, respectively, and low-frequency high-intensity acoustic streaming is favourable for both. When given Re<sub>0</sub> or St<sub>0</sub>, the SH reaches a maximum at AR = 0.4. This is due to drastic changes in the acoustic streaming characteristics for this tube shape, which is reflected in the first-order sound pressure, radial acoustic streaming velocity, and the size of internal and external vortices.</div></div>","PeriodicalId":335,"journal":{"name":"International Journal of Heat and Fluid Flow","volume":"112 ","pages":"Article 109738"},"PeriodicalIF":2.6,"publicationDate":"2025-01-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143140186","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"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 : 2024-12-31DOI: 10.1016/j.ijheatfluidflow.2024.109739
Xitong Liu , Kai Liu , Hanrui Qiu , Mingjun Wang , Chong Chen , Qi Lu , Jian Deng , Wenxi Tian , G.H. Su
Two-phase flow and heat transfer characteristics under boiling condition possesses vital significance for pressurized water reactor (PWR) core design. Traditional system code or subchannel analysis code had been widely applied for safety analysis of reactor core, but the more elaborate distribution of three-dimensional parameters is unable to obtained. In this paper, a two-phase flow & boiling module is developed and implemented based on the previously proposed nuclear reactor core thermal–hydraulic characteristics analysis code CorTAF. The two-phase flow and boiling heat transfer analysis method under drift-flux model is established, combining constitutive model such as bubble formation, grid effect, turbulent mixing, coupled boiling heat transfer and the prediction of critical heat flux under diverse boiling states. The benchmarks including CE5 × 5 and PSBT are selected to perform the comprehensive code validation. Crucial physical parameters are compared with the experiment data. The maximum error of wall temperature is under 4 K in CE5 × 5, maximum error of void fraction and CHF in PSBT is under 0.07 and 15 % respectively, indicating that the two-phase flow & boiling module implemented in CorTAF is capable for accurate prediction of two-phase thermal–hydraulic characteristics in reactor core. Additionally, to visually demonstrate the calculation result by CorTAF, a brief simulation of multiple assemblies under partial blockage is also carried out. This work provides valuable references for safety analysis under reactivity insertion accident and further studies on multi-physics coupling of reactor core.
{"title":"Development and validation of two-phase flow & boiling module based on CorTAF framework","authors":"Xitong Liu , Kai Liu , Hanrui Qiu , Mingjun Wang , Chong Chen , Qi Lu , Jian Deng , Wenxi Tian , G.H. Su","doi":"10.1016/j.ijheatfluidflow.2024.109739","DOIUrl":"10.1016/j.ijheatfluidflow.2024.109739","url":null,"abstract":"<div><div>Two-phase flow and heat transfer characteristics under boiling condition possesses vital significance for pressurized water reactor (PWR) core design. Traditional system code or subchannel analysis code had been widely applied for safety analysis of reactor core, but the more elaborate distribution of three-dimensional parameters is unable to obtained. In this paper, a two-phase flow & boiling module is developed and implemented based on the previously proposed nuclear reactor core thermal–hydraulic characteristics analysis code CorTAF. The two-phase flow and boiling heat transfer analysis method under drift-flux model is established, combining constitutive model such as bubble formation, grid effect, turbulent mixing, coupled boiling heat transfer and the prediction of critical heat flux under diverse boiling states. The benchmarks including CE5 × 5 and PSBT are selected to perform the comprehensive code validation. Crucial physical parameters are compared with the experiment data. The maximum error of wall temperature is under 4 K in CE5 × 5, maximum error of void fraction and CHF in PSBT is under 0.07 and 15 % respectively, indicating that the two-phase flow & boiling module implemented in CorTAF is capable for accurate prediction of two-phase thermal–hydraulic characteristics in reactor core. Additionally, to visually demonstrate the calculation result by CorTAF, a brief simulation of multiple assemblies under partial blockage is also carried out. This work provides valuable references for safety analysis under reactivity insertion accident and further studies on multi-physics coupling of reactor core.</div></div>","PeriodicalId":335,"journal":{"name":"International Journal of Heat and Fluid Flow","volume":"112 ","pages":"Article 109739"},"PeriodicalIF":2.6,"publicationDate":"2024-12-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143140150","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"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 : 2024-12-30DOI: 10.1016/j.ijheatfluidflow.2024.109733
Huaqiang Chu , Chenhao Yang , Dong Wang , Weipeng Deng , Nian Xu
Boiling heat transfer is an efficient and green heat transfer method that is widely used in industrial production. Single bubble pool boiling is a specific case of pool boiling, which helps to observe the microscopic changes of bubbles and further study the heat transfer mechanism of bubbles in boiling heat transfer. This paper outlines a variety of approaches to single bubble generation. This review summarizes thermocouple, optical and acoustic techniques for quantitative or qualitative measurements of bubble parameters and their surrounding temperature fields during boiling. The geometrical structure and motion variations of microlayers, three phase lines and dry points in bubbles are described. This helps to further investigate the mechanism of heat and mass transfer in bubbles during boiling. To further improve the efficiency of boiling heat transfer, the effects of electric, magnetic and acoustic fields on bubble motion and heat transfer are presented. Because of the similar bubble phenomenon in boiling heat transfer and electrolytic hydrogen production, this paper outlines the application of single bubble enhancement technology in electrolytic hydrogen production. In addition, this paper reviews the advances in the study of single bubbles which are important for a deeper understanding and optimization of the boiling heat transfer process.
{"title":"Advances in the study of bubbles in boiling and their application to electrolytic hydrogen production","authors":"Huaqiang Chu , Chenhao Yang , Dong Wang , Weipeng Deng , Nian Xu","doi":"10.1016/j.ijheatfluidflow.2024.109733","DOIUrl":"10.1016/j.ijheatfluidflow.2024.109733","url":null,"abstract":"<div><div>Boiling heat transfer is an efficient and green heat transfer method that is widely used in industrial production. Single bubble pool boiling is a specific case of pool boiling, which helps to observe the microscopic changes of bubbles and further study the heat transfer mechanism of bubbles in boiling heat transfer. This paper outlines a variety of approaches to single bubble generation. This review summarizes thermocouple, optical and acoustic techniques for quantitative or qualitative measurements of bubble parameters and their surrounding temperature fields during boiling. The geometrical structure and motion variations of microlayers, three phase lines and dry points in bubbles are described. This helps to further investigate the mechanism of heat and mass transfer in bubbles during boiling. To further improve the efficiency of boiling heat transfer, the effects of electric, magnetic and acoustic fields on bubble motion and heat transfer are presented. Because of the similar bubble phenomenon in boiling heat transfer and electrolytic hydrogen production, this paper outlines the application of single bubble enhancement technology in electrolytic hydrogen production. In addition, this paper reviews the advances in the study of single bubbles which are important for a deeper understanding and optimization of the boiling heat transfer process.</div></div>","PeriodicalId":335,"journal":{"name":"International Journal of Heat and Fluid Flow","volume":"112 ","pages":"Article 109733"},"PeriodicalIF":2.6,"publicationDate":"2024-12-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143140602","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"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 : 2024-12-30DOI: 10.1016/j.ijheatfluidflow.2024.109736
Jing Yang, Kui Deng, Shaoxian Bai
With the increasing requirement of multi-point working conditions, the problem of lubrication heat in liquid face seals attracts more attentions, which often results in a high risk of seal failure due to unstable opening force and leakage. The precise design considering heating effect of face grooves under complex working conditions is necessary. Here, based on the fluid lubrication theory, a thermo-dynamic model for liquid face seals with elliptical groove was established to analyze the lubrication heat behavior. The novelty of this model is to take the complex seal structure, cavitation effect and fluid thermo-viscous effect into consideration together, which was validated by experimental work. The temperature distribution and temperature rise were investigated for both smooth and elliptical groove face seals. The effects of rotational speed, film thickness and sealing pressure on temperature distribution and sealing performance of liquid film were further studied. When the film thickness increasing from 2 to 5 μm, the maximum temperature for face seals with elliptical groove and smooth surface decreases from 355.6 K to 350.45 K and from 354.9 K to 350.4 K, respectively. The values of maximum temperature present no obvious difference for both smooth and elliptical faces. However, it is found that elliptical groove presents an obvious influence on temperature distribution of liquid sealing film. The maximum temperature occurs near the inner diameter for the smooth face, but near the outer diameter for the elliptical groove face. The obtained results also suggest that the cavitation effect and hydrodynamic effect induced by shear effect make the sealing performance unstable, accompanying multi-peaks phenomena under multi-velocity and multi-pressure conditions. Face grooves could provide a potential way to control temperature distribution in precise sealing design.
{"title":"Lubrication heating behavior of elliptical groove face seals under multi-point conditions","authors":"Jing Yang, Kui Deng, Shaoxian Bai","doi":"10.1016/j.ijheatfluidflow.2024.109736","DOIUrl":"10.1016/j.ijheatfluidflow.2024.109736","url":null,"abstract":"<div><div>With the increasing requirement of multi-point working conditions, the problem of lubrication heat in liquid face seals attracts more attentions, which often results in a high risk of seal failure due to unstable opening force and leakage. The precise design considering heating effect of face grooves under complex working conditions is necessary. Here, based on the fluid lubrication theory, a thermo-dynamic model for liquid face seals with elliptical groove was established to analyze the lubrication heat behavior. The novelty of this model is to take the complex seal structure, cavitation effect and fluid thermo-viscous effect into consideration together, which was validated by experimental work. The temperature distribution and temperature rise were investigated for both smooth and elliptical groove face seals. The effects of rotational speed, film thickness and sealing pressure on temperature distribution and sealing performance of liquid film were further studied. When the film thickness increasing from 2 to 5 μm, the maximum temperature for face seals with elliptical groove and smooth surface decreases from 355.6 K to 350.45 K and from 354.9 K to 350.4 K, respectively. The values of maximum temperature present no obvious difference for both smooth and elliptical faces. However, it is found that elliptical groove presents an obvious influence on temperature distribution of liquid sealing film. The maximum temperature occurs near the inner diameter for the smooth face, but near the outer diameter for the elliptical groove face. The obtained results also suggest that the cavitation effect and hydrodynamic effect induced by shear effect make the sealing performance unstable, accompanying multi-peaks phenomena under multi-velocity and multi-pressure conditions. Face grooves could provide a potential way to control temperature distribution in precise sealing design.</div></div>","PeriodicalId":335,"journal":{"name":"International Journal of Heat and Fluid Flow","volume":"112 ","pages":"Article 109736"},"PeriodicalIF":2.6,"publicationDate":"2024-12-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143140152","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"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 : 2024-12-30DOI: 10.1016/j.ijheatfluidflow.2024.109727
Takuki Kaminaga, Ye Wang, Mamoru Tanahashi
A machine-learning-based model is proposed for the wall heat flux in the flame–wall interaction (FWI). The model is trained by the neural network (NN), and the direct numerical simulation (DNS) database of FWI of head-on quenching and side-wall quenching are employed as the training data, considering the premixed methane–air combustion in a one-dimensional and two-dimensional constant volume vessel. In this NN model, the time-averaged wall heat flux, as the output quantity, is considered as a function of FWI characteristics, including combustion equivalence ratio, pressure, preheat temperature of unburned mixture, and wall temperature. The performance of the model is evaluated with analysis. Results indicate that the NN model trained solely with one-dimensional DNS results demonstrates satisfactory performance in predicting wall heat flux in head-on quenching scenarios under various thermochemical conditions, achieving a Pearson’s correlation coefficient of 0.95 or higher. For the prediction of wall heat flux in a two-dimensional turbulent combustion scenario, the NN model trained with both one-dimensional and two-dimensional DNS results also produces a correlation coefficient over 0.9. The prediction accuracy slightly decreases in turbulent combustion conditions, which is probably due to the limited incorporation of near-wall flame-turbulence interaction effect in the model training. The current study serves as an initial exploration of wall heat flux modeling by incorporating FWI characteristics as significant factors. Also, it underlines the FWI dynamics and wall heat transfer within wall-bounded combustion.
{"title":"Modeling of wall heat flux in flame–wall interaction using machine learning","authors":"Takuki Kaminaga, Ye Wang, Mamoru Tanahashi","doi":"10.1016/j.ijheatfluidflow.2024.109727","DOIUrl":"10.1016/j.ijheatfluidflow.2024.109727","url":null,"abstract":"<div><div>A machine-learning-based model is proposed for the wall heat flux in the flame–wall interaction (FWI). The model is trained by the neural network (NN), and the direct numerical simulation (DNS) database of FWI of head-on quenching and side-wall quenching are employed as the training data, considering the premixed methane–air combustion in a one-dimensional and two-dimensional constant volume vessel. In this NN model, the time-averaged wall heat flux, as the output quantity, is considered as a function of FWI characteristics, including combustion equivalence ratio, pressure, preheat temperature of unburned mixture, and wall temperature. The performance of the model is evaluated with <span><math><mrow><mi>a</mi><mspace></mspace><mi>p</mi><mi>r</mi><mi>i</mi><mi>o</mi><mi>r</mi><mi>i</mi></mrow></math></span> analysis. Results indicate that the NN model trained solely with one-dimensional DNS results demonstrates satisfactory performance in predicting wall heat flux in head-on quenching scenarios under various thermochemical conditions, achieving a Pearson’s correlation coefficient of 0.95 or higher. For the prediction of wall heat flux in a two-dimensional turbulent combustion scenario, the NN model trained with both one-dimensional and two-dimensional DNS results also produces a correlation coefficient over 0.9. The prediction accuracy slightly decreases in turbulent combustion conditions, which is probably due to the limited incorporation of near-wall flame-turbulence interaction effect in the model training. The current study serves as an initial exploration of wall heat flux modeling by incorporating FWI characteristics as significant factors. Also, it underlines the FWI dynamics and wall heat transfer within wall-bounded combustion.</div></div>","PeriodicalId":335,"journal":{"name":"International Journal of Heat and Fluid Flow","volume":"112 ","pages":"Article 109727"},"PeriodicalIF":2.6,"publicationDate":"2024-12-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143140904","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"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 : 2024-12-28DOI: 10.1016/j.ijheatfluidflow.2024.109737
Bikash Pattanayak , Hardik B. Kothadia
Nucleating bubbles contributes to improved heat transfer during the liquid–vapor phase transition and becomes beneficial in confined spaces where substantial energy transfer is necessary. The study is conducted to analyse the heat transfer mechanism and associated bubble behaviour during nucleate boiling at subcooled condition. The analysis is performed on horizontally oriented plates under ambient conditions. The temperature distribution over the plates at given heat flux is visualized using non-invasive IR thermal camera. The captured thermal images were initially analyzed to comprehend the impact of subcooling on different stages of the boiling process. It encompasses free convection from the surface, isolated heterogeneous nucleation, and the vertical agglomeration of detaching bubbles. The study gives an ideation to introspect the wall heat flux regime during subcooled pool boiling. Various phenomena associated with subcooled pool boiling, for instance, bubble ebullition, subcooling effect on heat transfer is discussed. The gradual shrinkage of bubble in the liquid pool is observed. The analysis of subcooled nucleate pool boiling on plates revealed intriguing insights into the spatio-temporal temperature variations, showcasing distinct patterns at different heat flux levels. Additionally, the study delved into the intricate wall heat flux partitioning among various boiling regimes, shedding light on the dynamics of bubble ebullition under subcooled conditions. An empirical correlation is suggested for predicting convective heat transfer coefficient for the subcooled pool boiling.
{"title":"Spatio-temporal temperature distribution and heat transfer analysis during subcooled nucleate pool boiling on plates","authors":"Bikash Pattanayak , Hardik B. Kothadia","doi":"10.1016/j.ijheatfluidflow.2024.109737","DOIUrl":"10.1016/j.ijheatfluidflow.2024.109737","url":null,"abstract":"<div><div>Nucleating bubbles contributes to improved heat transfer during the liquid–vapor phase transition and becomes beneficial in confined spaces where substantial energy transfer is necessary. The study is conducted to analyse the heat transfer mechanism and associated bubble behaviour during nucleate boiling at subcooled condition. The analysis is performed on horizontally oriented plates under ambient conditions. The temperature distribution over the plates at given heat flux is visualized using non-invasive IR thermal camera. The captured thermal images were initially analyzed to comprehend the impact of subcooling on different stages of the boiling process. It encompasses free convection from the surface, isolated heterogeneous nucleation, and the vertical agglomeration of detaching bubbles. The study gives an ideation to introspect the wall heat flux regime during subcooled pool boiling. Various phenomena associated with subcooled pool boiling, for instance, bubble ebullition, subcooling effect on heat transfer is discussed. The gradual shrinkage of bubble in the liquid pool is observed. The analysis of subcooled nucleate pool boiling on plates revealed intriguing insights into the spatio-temporal temperature variations, showcasing distinct patterns at different heat flux levels. Additionally, the study delved into the intricate wall heat flux partitioning among various boiling regimes, shedding light on the dynamics of bubble ebullition under subcooled conditions. An empirical correlation is suggested for predicting convective heat transfer coefficient for the subcooled pool boiling.</div></div>","PeriodicalId":335,"journal":{"name":"International Journal of Heat and Fluid Flow","volume":"112 ","pages":"Article 109737"},"PeriodicalIF":2.6,"publicationDate":"2024-12-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143140151","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The study investigates the flow of a hybrid nanofluid over a non-linear, permeable stretched sheet under Thomson and Troian boundary conditions, while also considering the Darcy-Forchheimer relationship. We employ the Cattaneo-Christov heat flux model and novel artificial neural networks for the first time. This paper describes a new way to use artificial neural networks to add carbon nanotubes to hybrid nanofluids with Thomson and Troian boundary conditions. This creates induced MHD. The MSE ranges from to . The AE range for all the cases lies around to . The value of mu is around , while gradient ranges from to . This shows the high accuracy and precision of the proposed scheme. This research highlights the variation of different parameters with velocity, temperature and concentration. As the solid volume fraction rises, fluid velocity diminishes and temperature rises. Nanofluids exhibit enhancement with elevated inertial coefficient and Eckert number values. Increased inertial coefficient and Eckert number values correspond to rising temperatures. Concentration diminishes with rising solid volume percentage; yet, elevated activation energy results in enhanced concentration dispersion. It proves superior thermal conductivity and heat transmission capabilities, with future studies investigating the additional factors. Potential areas for further investigation include the study of other nanoparticles and different hybrid nanofluids and the investigation of real engineering challenges associated to heat and mass transfer in porous media. A graphic comparison between simple and hybrid nanofluids is presented. It is shown that the solid volume fraction improves the temperature distribution while decreasing the velocity profile. Furthermore, hybrid nanofluids perform better in heat transfer and have higher thermal conductivity than simple nanofluids.
{"title":"Novel artificial neural network approach for hybrid nanofluid flow over nonlinear permeable stretching sheets with Thomson and Troian boundary conditions","authors":"Shazia Habib , Zeeshan Khan , Esraa N. Thabet , A.M. Abd-Alla , S.H. Elhag","doi":"10.1016/j.ijheatfluidflow.2024.109721","DOIUrl":"10.1016/j.ijheatfluidflow.2024.109721","url":null,"abstract":"<div><div>The study investigates the flow of a hybrid nanofluid over a non-linear, permeable stretched sheet under Thomson and Troian boundary conditions, while also considering the Darcy-Forchheimer relationship. We employ the Cattaneo-Christov heat flux model and novel artificial neural networks for the first time. This paper describes a new way to use artificial neural networks to add carbon nanotubes to hybrid nanofluids with Thomson and Troian boundary conditions. This creates induced MHD. The MSE ranges from <span><math><mrow><msup><mn>10</mn><mrow><mo>-</mo><mn>08</mn></mrow></msup></mrow></math></span> to <span><math><mrow><msup><mn>10</mn><mrow><mo>-</mo><mn>09</mn></mrow></msup></mrow></math></span>. The AE range for all the cases lies around <span><math><mrow><msup><mn>10</mn><mrow><mo>-</mo><mn>03</mn></mrow></msup></mrow></math></span> to <span><math><mrow><msup><mn>10</mn><mrow><mo>-</mo><mn>07</mn></mrow></msup></mrow></math></span>. The value of mu is around <span><math><mrow><msup><mn>10</mn><mrow><mo>-</mo><mn>08</mn></mrow></msup></mrow></math></span>, while gradient ranges from <span><math><mrow><msup><mn>10</mn><mrow><mo>-</mo><mn>07</mn></mrow></msup></mrow></math></span> to <span><math><mrow><msup><mn>10</mn><mrow><mo>-</mo><mn>08</mn></mrow></msup></mrow></math></span>. This shows the high accuracy and precision of the proposed scheme. This research highlights the variation of different parameters with velocity, temperature and concentration. As the solid volume fraction rises, fluid velocity diminishes and temperature rises. Nanofluids exhibit enhancement with elevated inertial coefficient and Eckert number values. Increased inertial coefficient and Eckert number values correspond to rising temperatures. Concentration diminishes with rising solid volume percentage; yet, elevated activation energy results in enhanced concentration dispersion. It proves superior thermal conductivity and heat transmission capabilities, with future studies investigating the additional factors. Potential areas for further investigation include the study of other nanoparticles and different hybrid nanofluids and the investigation of real engineering challenges associated to heat and mass transfer in porous media. A graphic comparison between simple and hybrid nanofluids is presented. It is shown that the solid volume fraction improves the temperature distribution while decreasing the velocity profile. Furthermore, hybrid nanofluids perform better in heat transfer and have higher thermal conductivity than simple nanofluids.</div></div>","PeriodicalId":335,"journal":{"name":"International Journal of Heat and Fluid Flow","volume":"112 ","pages":"Article 109721"},"PeriodicalIF":2.6,"publicationDate":"2024-12-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143140153","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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