Pub Date : 2024-11-06DOI: 10.1016/j.ijheatfluidflow.2024.109635
Kui Yin , Yongjia Wu , Donghao Zhao , Wenting Lin , Nan Zhou , Zhiyong Li , Tingzhen Ming
Ultra-thin heat pipes are extensively utilized in heat dissipation systems for portable electronic devices, and their thermal performance is mainly affected by the wick. A mathematical model of the ultra-thin heat pipe with composited wick of the copper mesh and copper fiber bundle was developed. Based on the mathematical model, the composited wick was optimized to enhance the maximum heat transfer capacity. The optimization results indicated that the heat pipe achieved optimal heat transfer performance with a single layer of copper mesh, a 0.75 mm width copper fiber bundle, and zero position. The optimized wick structure enhanced the maximum heat transfer capacity of the heat pipe by 40.03 % compared to its capacity before optimization.
{"title":"Methods for performance optimization of ultra-thin heat pipes with composited wick","authors":"Kui Yin , Yongjia Wu , Donghao Zhao , Wenting Lin , Nan Zhou , Zhiyong Li , Tingzhen Ming","doi":"10.1016/j.ijheatfluidflow.2024.109635","DOIUrl":"10.1016/j.ijheatfluidflow.2024.109635","url":null,"abstract":"<div><div>Ultra-thin heat pipes are extensively utilized in heat dissipation systems for portable electronic devices, and their thermal performance is mainly affected by the wick. A mathematical model of the ultra-thin heat pipe with composited wick of the copper mesh and copper fiber bundle was developed. Based on the mathematical model, the composited wick was optimized to enhance the maximum heat transfer capacity. The optimization results indicated that the heat pipe achieved optimal heat transfer performance with a single layer of copper mesh, a 0.75 mm width copper fiber bundle, and zero position. The optimized wick structure enhanced the maximum heat transfer capacity of the heat pipe by 40.03 % compared to its capacity before optimization.</div></div>","PeriodicalId":335,"journal":{"name":"International Journal of Heat and Fluid Flow","volume":"110 ","pages":"Article 109635"},"PeriodicalIF":2.6,"publicationDate":"2024-11-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142593037","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 : 2024-11-06DOI: 10.1016/j.ijheatfluidflow.2024.109620
Bahare Jahani, Michael MacDonald, Stuart E. Norris
This paper investigates the turbulent structure of stratified open-channel flow subjected to a radiative volumetric heat source modelled by the Beer–Lambert law, for Prandtl numbers () varying from 0.07 to . Direct Numerical Simulation (DNS) was employed to model the open-channel flow. To overcome the increased computational resources required to resolve the thermal fields when , a multi-resolution method using quadratic interpolation was employed to resolve the temperature and momentum fields on different spatial and temporal resolutions. This scheme was implemented in an in-house computational fluid dynamics (CFD) code. To further reduce the computation cost, the DNS of and 7 fluids were initialised using the outputs of minimal channel simulations. The simulations were conducted for , 0.22, 0.71, 2.2, and 7 under neutral (), near-neutral (), and stable () thermal stratification. The results demonstrate that significantly affects the flow structure and turbulence characteristics of stratified flows, particularly near the free surface. This includes higher velocity, temperature gradient, and buoyancy effects for compared to lower values. For stratified flow, examination of the Reynolds stresses and turbulent heat flux reveals significant damping of turbulence near the surface, with flow displaying near-laminar behaviour.
{"title":"Turbulent stratified open channel flow with solar heating up to Pr=7 using Direct Numerical Simulation","authors":"Bahare Jahani, Michael MacDonald, Stuart E. Norris","doi":"10.1016/j.ijheatfluidflow.2024.109620","DOIUrl":"10.1016/j.ijheatfluidflow.2024.109620","url":null,"abstract":"<div><div>This paper investigates the turbulent structure of stratified open-channel flow subjected to a radiative volumetric heat source modelled by the Beer–Lambert law, for Prandtl numbers (<span><math><mrow><mi>P</mi><mi>r</mi></mrow></math></span>) varying from 0.07 to <span><math><mrow><mi>P</mi><mi>r</mi><mo>=</mo><mn>7</mn></mrow></math></span>. Direct Numerical Simulation (DNS) was employed to model the open-channel flow. To overcome the increased computational resources required to resolve the thermal fields when <span><math><mrow><mi>P</mi><mi>r</mi><mo>></mo><mn>1</mn></mrow></math></span>, a multi-resolution method using quadratic interpolation was employed to resolve the temperature and momentum fields on different spatial and temporal resolutions. This scheme was implemented in an in-house computational fluid dynamics (CFD) code. To further reduce the computation cost, the DNS of <span><math><mrow><mi>P</mi><mi>r</mi><mo>=</mo><mn>2</mn><mo>.</mo><mn>2</mn></mrow></math></span> and 7 fluids were initialised using the outputs of minimal channel simulations. The simulations were conducted for <span><math><mrow><mi>P</mi><mi>r</mi><mo>=</mo><mn>0</mn><mo>.</mo><mn>07</mn></mrow></math></span>, 0.22, 0.71, 2.2, and 7 under neutral (<span><math><mrow><mi>λ</mi><mo>=</mo><mn>0</mn></mrow></math></span>), near-neutral (<span><math><mrow><mi>λ</mi><mo>=</mo><mn>0</mn><mo>.</mo><mn>1</mn></mrow></math></span>), and stable (<span><math><mrow><mi>λ</mi><mo>=</mo><mn>0</mn><mo>.</mo><mn>5</mn></mrow></math></span>) thermal stratification. The results demonstrate that <span><math><mrow><mi>P</mi><mi>r</mi></mrow></math></span> significantly affects the flow structure and turbulence characteristics of stratified flows, particularly near the free surface. This includes higher velocity, temperature gradient, and buoyancy effects for <span><math><mrow><mi>P</mi><mi>r</mi><mo>=</mo><mn>7</mn></mrow></math></span> compared to lower <span><math><mrow><mi>P</mi><mi>r</mi></mrow></math></span> values. For stratified <span><math><mrow><mi>P</mi><mi>r</mi><mo>=</mo><mn>7</mn></mrow></math></span> flow, examination of the Reynolds stresses and turbulent heat flux reveals significant damping of turbulence near the surface, with flow displaying near-laminar behaviour.</div></div>","PeriodicalId":335,"journal":{"name":"International Journal of Heat and Fluid Flow","volume":"110 ","pages":"Article 109620"},"PeriodicalIF":2.6,"publicationDate":"2024-11-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142593036","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}
Pub Date : 2024-11-06DOI: 10.1016/j.ijheatfluidflow.2024.109625
Rui Wang , Xu Yang , Gao Li , Wenxiu Zheng , Zhenhai Zou , Chengzhen Sun
The development of deep shale gas is critical for the sustainable growth of unconventional energy resources. Deep shale formations are characterized by a high illite content, which necessitates a thorough understanding of the structural and flow dynamics of methane and water within illite nanoslits. In this study, molecular dynamics simulations were employed to examine the flow characteristics of methane and water in slit-shaped illite nanopores. The investigation sheds light on the effects of water saturation, acceleration, and pore size on two-phase flow behavior. The results reveal that water molecules preferentially adsorb onto the illite channel surface. As water saturation increases, the water phase evolves into various forms, including water films, water bridges, and water locks, ultimately trapping methane in nanobubbles encased by the water phase. The presence of water significantly reduces the flow space available for methane. With increasing water saturation, the methane density peaks near the channel walls decrease, and the density distribution curves transition into parabolic profiles. The methane flow flux decreases notably as water saturation increases, especially from 0% to 40%. When the Sw reaches 40%, the methane flow flux is reduced by 84% compared to methane single-phase flow. Additionally, the flow fluxes of both water and methane increase with larger pore sizes in illite slits. These findings are expected to provide valuable insights for developing deep shale gas reservoirs, optimizing hydraulic fracturing designs, and improving production performance predictions.
{"title":"Pattern and dynamics of methane/water two-phase flow in deep-shale illite nanoslits","authors":"Rui Wang , Xu Yang , Gao Li , Wenxiu Zheng , Zhenhai Zou , Chengzhen Sun","doi":"10.1016/j.ijheatfluidflow.2024.109625","DOIUrl":"10.1016/j.ijheatfluidflow.2024.109625","url":null,"abstract":"<div><div>The development of deep shale gas is critical for the sustainable growth of unconventional energy resources. Deep shale formations are characterized by a high illite content, which necessitates a thorough understanding of the structural and flow dynamics of methane and water within illite nanoslits. In this study, molecular dynamics simulations were employed to examine the flow characteristics of methane and water in slit-shaped illite nanopores. The investigation sheds light on the effects of water saturation, acceleration, and pore size on two-phase flow behavior. The results reveal that water molecules preferentially adsorb onto the illite channel surface. As water saturation increases, the water phase evolves into various forms, including water films, water bridges, and water locks, ultimately trapping methane in nanobubbles encased by the water phase. The presence of water significantly reduces the flow space available for methane. With increasing water saturation, the methane density peaks near the channel walls decrease, and the density distribution curves transition into parabolic profiles. The methane flow flux decreases notably as water saturation increases, especially from 0% to 40%. When the <em>S</em><sub>w</sub> reaches 40%, the methane flow flux is reduced by 84% compared to methane single-phase flow. Additionally, the flow fluxes of both water and methane increase with larger pore sizes in illite slits. These findings are expected to provide valuable insights for developing deep shale gas reservoirs, optimizing hydraulic fracturing designs, and improving production performance predictions.</div></div>","PeriodicalId":335,"journal":{"name":"International Journal of Heat and Fluid Flow","volume":"110 ","pages":"Article 109625"},"PeriodicalIF":2.6,"publicationDate":"2024-11-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142593039","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 : 2024-11-06DOI: 10.1016/j.ijheatfluidflow.2024.109646
Long He , Feng-Yu Zhao , Wen-Jing He , Shao-Kun Ren , Rui Lou , Bing-Ye Song
As a CO2 capture, utilization, and storage (CCUS) technology, water-alternating-CO2 (WAG) injection has demonstrated excellent results in enhancing oil recovery. Current research on WAG injection primarily focused on factors such as increasing injection pressure and optimizing the water–gas slug ratio (W:G) to enhance the driving force, reduce instability due to the significant viscosity difference between oil and CO2, thereby inhibiting fingering phenomenon and improving oil recovery. However, in immiscible flooding, CO2 dissolution reduces the viscosity of the oil, changing the instability of the interfaces and affecting oil recovery. We employed computational fluid dynamics to study the effect of CO2 dissolution and viscosity reduction on fingering patterns and its effect on enhanced oil recovery (EOR) under capillary numbers Ca = 0.12 × 10−2–1.14 × 10−2 and W:G = 1:3–3:3. The results indicated that: (1) the dissolution of CO2 reduced oil viscosity, inhibiting the fingering phenomenon, promoting stable displacement and enhancing oil recovery. (2) The viscosity reduction effect of CO2 dissolution was more effective in viscous fingering. (3) Analysis of the EOR capacity after injecting a unit volume of displacement fluid confirmed that the optimal W:G remains 1:3. These findings highlight the importance of considering CO2 dissolution and its viscosity reduction effect to optimize WAG injection strategies for enhanced oil recovery.
{"title":"Fingering inhibition triggered by CO2 dissolution and viscosity reduction in water-alternating-CO2 injection","authors":"Long He , Feng-Yu Zhao , Wen-Jing He , Shao-Kun Ren , Rui Lou , Bing-Ye Song","doi":"10.1016/j.ijheatfluidflow.2024.109646","DOIUrl":"10.1016/j.ijheatfluidflow.2024.109646","url":null,"abstract":"<div><div>As a CO<sub>2</sub> capture, utilization, and storage (CCUS) technology, water-alternating-CO<sub>2</sub> (WAG) injection has demonstrated excellent results in enhancing oil recovery. Current research on WAG injection primarily focused on factors such as increasing injection pressure and optimizing the water–gas slug ratio (<em>W</em>:<em>G</em>) to enhance the driving force, reduce instability due to the significant viscosity difference between oil and CO<sub>2</sub>, thereby inhibiting fingering phenomenon and improving oil recovery. However, in immiscible flooding, CO<sub>2</sub> dissolution reduces the viscosity of the oil, changing the instability of the interfaces and affecting oil recovery. We employed computational fluid dynamics to study the effect of CO<sub>2</sub> dissolution and viscosity reduction on fingering patterns and its effect on enhanced oil recovery (EOR) under capillary numbers <em>Ca</em> = 0.12 × 10<sup>−2</sup>–1.14 × 10<sup>−2</sup> and <em>W</em>:<em>G =</em> 1:3–3:3. The results indicated that: (1) the dissolution of CO<sub>2</sub> reduced oil viscosity, inhibiting the fingering phenomenon, promoting stable displacement and enhancing oil recovery. (2) The viscosity reduction effect of CO<sub>2</sub> dissolution was more effective in viscous fingering. (3) Analysis of the EOR capacity after injecting a unit volume of displacement fluid confirmed that the optimal <em>W</em>:<em>G</em> remains 1:3. These findings highlight the importance of considering CO<sub>2</sub> dissolution and its viscosity reduction effect to optimize WAG injection strategies for enhanced oil recovery.</div></div>","PeriodicalId":335,"journal":{"name":"International Journal of Heat and Fluid Flow","volume":"110 ","pages":"Article 109646"},"PeriodicalIF":2.6,"publicationDate":"2024-11-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142593035","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}
This article presents the modal, non-modal, and resolvent analyses of the boundary layer developed over a heated flat-plate with temperature-dependent viscosity using linear stability theory. The governing equations are derived in the normal velocity–vorticity form by imposing small infinitesimal disturbances on the base flow with the Oberbeck-Boussinesq (OB) approximation. The spectral method is employed to discretize the governing stability equations in the wall-normal direction. The base flow comes from the similarity solution using R-K4th order method along with shooting techniques. The effects of viscosity stratification, inertia, shearing, and buoyancy on the stability of the boundary layer are investigated by varying the sensitivity parameter , Reynolds , Prandtl , and Richardson numbers . The modal analysis shows the time-asymptotic behavior of the disturbances and onset of instability is mainly caused by amplification of Tollmien–Schlichting (T-S) waves similar to as observe in the traditional Blasius case. The modal stability increases with increase in sensitivity parameter and stabilizing effects become more pronounced for liquid than gas. However, the thermal effects lead to destabilize the flow and strong destabilizing effects produced for higher Prandtl number. On the other hand, non-modal analysis displays an early transient growth of disturbances and an existence of these non-normality effects identified from the pseudospectra via. resolvent analysis. The non-modal growth increases with increase in even though T-S modes shift towards the damped region, which indicates the continuous modes in the eigenspectrum are more dominated than the discrete T-S modes due to the thermal effects. To clarify this qualitative change, a component-wise input–output analysis is performed to measure the receptivity to particular external disturbances. The results show the thermal energy of the disturbances is converted into kinetic energy due to thermal effects, resulting in strong receptivity amplification at the continuous mode due to the non-normality of the linear operator. Thus, the boundary layer under the influence of viscosity stratification, heating, and shearing effects is vulnerable to free-stream disturbances that could significantly affect bypass transition
{"title":"Stability and receptivity analyses of the heated flat-plate boundary layer with variable viscosity","authors":"Mayank Thummar , Ramesh Bhoraniya , Vinod Narayanan","doi":"10.1016/j.ijheatfluidflow.2024.109624","DOIUrl":"10.1016/j.ijheatfluidflow.2024.109624","url":null,"abstract":"<div><div>This article presents the modal, non-modal, and resolvent analyses of the boundary layer developed over a heated flat-plate with temperature-dependent viscosity using linear stability theory. The governing equations are derived in the normal velocity–vorticity form by imposing small infinitesimal disturbances on the base flow with the Oberbeck-Boussinesq (OB) approximation. The spectral method is employed to discretize the governing stability equations in the wall-normal direction. The base flow comes from the similarity solution using R-K4th order method along with shooting techniques. The effects of viscosity stratification, inertia, shearing, and buoyancy on the stability of the boundary layer are investigated by varying the sensitivity parameter <span><math><mrow><mo>(</mo><mi>ϵ</mi><mo>)</mo></mrow></math></span>, Reynolds <span><math><mrow><mo>(</mo><mi>R</mi><mi>e</mi><mo>)</mo></mrow></math></span>, Prandtl <span><math><mrow><mo>(</mo><mi>P</mi><mi>r</mi><mo>)</mo></mrow></math></span>, and Richardson numbers <span><math><mrow><mo>(</mo><mi>R</mi><mi>i</mi><mo>)</mo></mrow></math></span>. The modal analysis shows the time-asymptotic behavior of the disturbances and onset of instability is mainly caused by amplification of Tollmien–Schlichting (T-S) waves similar to as observe in the traditional Blasius case. The modal stability increases with increase in sensitivity parameter and stabilizing effects become more pronounced for liquid than gas. However, the thermal effects lead to destabilize the flow and strong destabilizing effects produced for higher Prandtl number. On the other hand, non-modal analysis displays an early transient growth of disturbances and an existence of these non-normality effects identified from the pseudospectra via. resolvent analysis. The non-modal growth increases with increase in <span><math><mi>ϵ</mi></math></span> even though T-S modes shift towards the damped region, which indicates the continuous modes in the eigenspectrum are more dominated than the discrete T-S modes due to the thermal effects. To clarify this qualitative change, a component-wise input–output analysis is performed to measure the receptivity to particular external disturbances. The results show the thermal energy of the disturbances is converted into kinetic energy due to thermal effects, resulting in strong receptivity amplification at the continuous mode due to the non-normality of the linear operator. Thus, the boundary layer under the influence of viscosity stratification, heating, and shearing effects is vulnerable to free-stream disturbances that could significantly affect bypass transition</div></div>","PeriodicalId":335,"journal":{"name":"International Journal of Heat and Fluid Flow","volume":"110 ","pages":"Article 109624"},"PeriodicalIF":2.6,"publicationDate":"2024-11-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142593038","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 : 2024-11-05DOI: 10.1016/j.ijheatfluidflow.2024.109633
Minfeng Yu, Xudong Peng, Xiangkai Meng, Jinbo Jiang, Yi Ma, Fan Wu
For mechanical seals used in high-speed turbo pumps, it is often observed that the seal face will fail due to high temperatures before excessive wear occurs. The textured side-wall with low dissipation and high heat transfer can effectively extend the life of high-speed mechanical seal. Numerical research is carried out with SST k- model and turbulence dissipation. The numerical results have been validated with published experiments and achieved good validity. The textured side-wall shows an excellent cooling effect over a wide range of flush flow. Even when the flush channel is narrow and flush flow almost non-existent, the reduction in the temperature of seal face is still significant. The flow field and turbulence dissipation of three different channels are analyzed under different flush flow. By means of commonly used design, the maximum temperature of seal face can be reduced by over 40 °C (22.2 %) when flush flow is nearly non-existent. The recommended flush flow is approximately 15 L/min, ignoring the shape of the flow channel. It can simultaneously achieve a more effective cooling effect and a reduction in turbulence dissipation.
{"title":"The research for the recommended flush flow of high-speed mechanical seal with textured side-wall","authors":"Minfeng Yu, Xudong Peng, Xiangkai Meng, Jinbo Jiang, Yi Ma, Fan Wu","doi":"10.1016/j.ijheatfluidflow.2024.109633","DOIUrl":"10.1016/j.ijheatfluidflow.2024.109633","url":null,"abstract":"<div><div>For mechanical seals used in high-speed turbo pumps, it is often observed that the seal face will fail due to high temperatures before excessive wear occurs. The textured side-wall with low dissipation and high heat transfer can effectively extend the life of high-speed mechanical seal. Numerical research is carried out with SST <em>k</em>-<span><math><mi>ω</mi></math></span> model and turbulence dissipation. The numerical results have been validated with published experiments and achieved good validity. The textured side-wall shows an excellent cooling effect over a wide range of flush flow. Even when the flush channel is narrow and flush flow almost non-existent, the reduction in the temperature of seal face is still significant. The flow field and turbulence dissipation of three different channels are analyzed under different flush flow. By means of commonly used design, the maximum temperature of seal face can be reduced by over 40 °C (22.2 %) when flush flow is nearly non-existent. The recommended flush flow is approximately 15 L/min, ignoring the shape of the flow channel. It can simultaneously achieve a more effective cooling effect and a reduction in turbulence dissipation.</div></div>","PeriodicalId":335,"journal":{"name":"International Journal of Heat and Fluid Flow","volume":"110 ","pages":"Article 109633"},"PeriodicalIF":2.6,"publicationDate":"2024-11-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142587206","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 : 2024-11-05DOI: 10.1016/j.ijheatfluidflow.2024.109631
Qiang Zhang , YiFan Shan , Ning Wang , Zhen Tian , ChaoTing Liu , Xiang Wu , KeWei Song
A novel arrangement of ellipsoidal dimples for a circle tube was established to improve the tube’s thermal performance. The impacts of axis ratio and depth of an ellipsoidal dimple with an attack angle of 45° on the thermohydraulic characteristics were numerically studied using the realizable k-ε model in the Re range of 10,000 to 40,000. The research shows that increasing the axis ratio of the ellipsoidal dimple from 4:3 to 6:3 leads to the increase in Nu by 15.83 %-18.4 %, with the corresponding increase in f by 19.03 %-30.76 %. The depth of the ellipsoidal dimple also significantly affects the heat transfer performance and pressure drop of the dimpled tube. When the dimple depth increases from 1 mm to 2 mm, Nu and f increase by up to 30.47 % and 64.12 %, respectively. The maximum performance evaluation criteria of 1.68 is achieved when the dimple depth is 2 mm. The proposed ellipsoidal dimple arrangement significantly improves the heat transfer compared with other arrangements in the open literature. The performance evaluation criteria of the studied model with d = 1.5 mm and a:b = 5:3 is up to 19 % larger than the models reported in the references.
{"title":"Numerical investigation on thermohydraulic characteristics in a circle tube with a novel arrangement of ellipsoidal dimples","authors":"Qiang Zhang , YiFan Shan , Ning Wang , Zhen Tian , ChaoTing Liu , Xiang Wu , KeWei Song","doi":"10.1016/j.ijheatfluidflow.2024.109631","DOIUrl":"10.1016/j.ijheatfluidflow.2024.109631","url":null,"abstract":"<div><div>A novel arrangement of ellipsoidal dimples for a circle tube was established to improve the tube’s thermal performance. The impacts of axis ratio and depth of an ellipsoidal dimple with an attack angle of 45° on the thermohydraulic characteristics were numerically studied using the realizable <em>k</em>-<em>ε</em> model in the <em>Re</em> range of 10,000 to 40,000. The research shows that increasing the axis ratio of the ellipsoidal dimple from 4:3 to 6:3 leads to the increase in <em>Nu</em> by 15.83 %-18.4 %, with the corresponding increase in <em>f</em> by 19.03 %-30.76 %. The depth of the ellipsoidal dimple also significantly affects the heat transfer performance and pressure drop of the dimpled tube. When the dimple depth increases from 1 mm to 2 mm, <em>Nu</em> and <em>f</em> increase by up to 30.47 % and 64.12 %, respectively. The maximum performance evaluation criteria of 1.68 is achieved when the dimple depth is 2 mm. The proposed ellipsoidal dimple arrangement significantly improves the heat transfer compared with other arrangements in the open literature. The performance evaluation criteria of the studied model with <em>d</em> = 1.5 mm and <em>a</em>:<em>b</em> = 5:3 is up to 19 % larger than the models reported in the references.</div></div>","PeriodicalId":335,"journal":{"name":"International Journal of Heat and Fluid Flow","volume":"110 ","pages":"Article 109631"},"PeriodicalIF":2.6,"publicationDate":"2024-11-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142587205","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 : 2024-11-05DOI: 10.1016/j.ijheatfluidflow.2024.109641
Yan Xing , Zihao Dong , Qingfei Fu , Lijun Yang , Ruo-Yu Dong
Surface waves have been used as a paradigm for pattern formation and hold significant potential for applications such as materials micro-molding and stability control of tankers. While the theory of unbounded surface waves has been extensively studied, challenges to control surface waves in containers persist due to the unknown isolated influences of interface parameters. In this work, we prepared a series of containers with various interface parameters through surface modifications. The relationship between surface waves and interface parameters was analyzed spatially and temporally using surface wave profile analyses and proper orthogonal decomposition methods. The effect from a single interface parameter in surface wave transition from harmonic to sub-harmonic waves was decoupled through energy analyses and mechanical force apparatus. It is revealed that an increase in bottom wall adhesion force, side wall curvature, or movement of the contact line could all lead to a corresponding increase in the transition threshold. This work might provide basis for understanding and controlling surface wave transition using a delicate combination of interface parameters.
{"title":"Decoupling interface effects on surface wave transition","authors":"Yan Xing , Zihao Dong , Qingfei Fu , Lijun Yang , Ruo-Yu Dong","doi":"10.1016/j.ijheatfluidflow.2024.109641","DOIUrl":"10.1016/j.ijheatfluidflow.2024.109641","url":null,"abstract":"<div><div>Surface waves have been used as a paradigm for pattern formation and hold significant potential for applications such as materials micro-molding and stability control of tankers. While the theory of unbounded surface waves has been extensively studied, challenges to control surface waves in containers persist due to the unknown isolated influences of interface parameters. In this work, we prepared a series of containers with various interface parameters through surface modifications. The relationship between surface waves and interface parameters was analyzed spatially and temporally using surface wave profile analyses and proper orthogonal decomposition methods. The effect from a single interface parameter in surface wave transition from harmonic to sub-harmonic waves was decoupled through energy analyses and mechanical force apparatus. It is revealed that an increase in bottom wall adhesion force, side wall curvature, or movement of the contact line could all lead to a corresponding increase in the transition threshold. This work might provide basis for understanding and controlling surface wave transition using a delicate combination of interface parameters.</div></div>","PeriodicalId":335,"journal":{"name":"International Journal of Heat and Fluid Flow","volume":"110 ","pages":"Article 109641"},"PeriodicalIF":2.6,"publicationDate":"2024-11-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142587207","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 : 2024-11-04DOI: 10.1016/j.ijheatfluidflow.2024.109632
Di Wu , Gaige Zhao , Songyun Yang , Liu Liu , Ping Zhou , Rongjia Zhu , Dongling Wu
The heat accumulation effect of the iron ore packed bed leads to uneven temperature distribution within the iron ore sintering process. This causes the under-sintering and over-melting of the sinter, reducing its performance. To address this issue, a three-layered coke breeze distribution scheme was proposed. Nine cases were designed, and their transient sintering processes were simulated to explore their influence on the sintering performances of the iron ore. The results show that directly increasing the coke breeze ratio of the upper layer can raise the peak temperature and melt quantity index (MQI) of the entire layer while reducing the cooling rate of the upper layer, but it will increase the risk of over-melting. Keeping the total coke breeze ratio constant, reducing the coke breeze amount in the top layer, and increasing the coke breeze ratio in the upper layer has a minor impact on the peak temperature, but it will lead to a faster sintering rate, which in turn causes a decrease in the MQI and an increase in cooling rate. Keeping the total coke breeze ratio constant and shortening the thickness of the upper layer while increasing its coke breeze ratio has a minimal impact on the sintering performance. Keeping the total coke breeze ratio constant and lowering the coke breeze ratio in the lower layer while increasing it in the upper layer is the most effective method to optimize the sintering performances. It can effectively raise the peak temperature and MQI in the upper layer while reducing its cooling rate. Besides, the heat generated by the upper layer can be effectively transmitted to the lower layer, so the peak temperature, MQI, and cooling rate of the lower material layer are less affected by its reduced coke breeze ratio.
{"title":"Influence of a three-layered coke breeze distribution scheme on the iron ore sintering performances","authors":"Di Wu , Gaige Zhao , Songyun Yang , Liu Liu , Ping Zhou , Rongjia Zhu , Dongling Wu","doi":"10.1016/j.ijheatfluidflow.2024.109632","DOIUrl":"10.1016/j.ijheatfluidflow.2024.109632","url":null,"abstract":"<div><div>The heat accumulation effect of the iron ore packed bed leads to uneven temperature distribution within the iron ore sintering process. This causes the under-sintering and over-melting of the sinter, reducing its performance. To address this issue, a three-layered coke breeze distribution scheme was proposed. Nine cases were designed, and their transient sintering processes were simulated to explore their influence on the sintering performances of the iron ore. The results show that directly increasing the coke breeze ratio of the upper layer can raise the peak temperature and melt quantity index (<em>MQI</em>) of the entire layer while reducing the cooling rate of the upper layer, but it will increase the risk of over-melting. Keeping the total coke breeze ratio constant, reducing the coke breeze amount in the top layer, and increasing the coke breeze ratio in the upper layer has a minor impact on the peak temperature, but it will lead to a faster sintering rate, which in turn causes a decrease in the <em>MQI</em> and an increase in cooling rate. Keeping the total coke breeze ratio constant and shortening the thickness of the upper layer while increasing its coke breeze ratio has a minimal impact on the sintering performance. Keeping the total coke breeze ratio constant and lowering the coke breeze ratio in the lower layer while increasing it in the upper layer is the most effective method to optimize the sintering performances. It can effectively raise the peak temperature and <em>MQI</em> in the upper layer while reducing its cooling rate. Besides, the heat generated by the upper layer can be effectively transmitted to the lower layer, so the peak temperature, <em>MQI</em>, and cooling rate of the lower material layer are less affected by its reduced coke breeze ratio.</div></div>","PeriodicalId":335,"journal":{"name":"International Journal of Heat and Fluid Flow","volume":"110 ","pages":"Article 109632"},"PeriodicalIF":2.6,"publicationDate":"2024-11-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142578234","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}
Droplet formation is the basis for the design of droplet microfluidic chip. The droplet formation mechanism and discrete phase flow patterns in T-junction microchannels are numerically simulated. This research adopts an incompressible two-phase flow solver in the OpenFOAM® framework. Firstly, the effects of two-phase flow rate, surface tension and microchannel structure on droplet formation are investigated. It is found that the mechanism of droplet formation is classified into extrusion and shear mechanisms. And the discrete phase flow patterns can be divided into four modes, including slug flow, drip flow, jet flow, and parallel flow. Then, the distribution of discrete phase flow patterns in microchannels with different depth-to-width ratios are plotted. These distribution maps provide further insights into the mechanisms underlying the formation and transformation of different discrete phase flow patterns within microchannels. Finally, the droplet formation in the modified Venturi microchannels was compared with that in the ordinary T-junction microchannel. The efficiency of droplet formation in microchannels with Venturi components is superior. Specifically, with a component angle of 30°, the length of the droplets can be reduced by as much as 120 μm. The droplet generation frequency can be increased by approximately 122.4 %, rising from 25 Hz to 55.6 Hz. When the Venturi component is positioned at the entrance of the discrete phase, the minimal droplets can be generated uniformly at a higher frequency in the microchannel.
液滴形成是液滴微流控芯片设计的基础。本研究对 T 型微通道中的液滴形成机理和离散相流模式进行了数值模拟。本研究采用 OpenFOAM® 框架下的不可压缩两相流求解器。首先，研究了两相流速、表面张力和微通道结构对液滴形成的影响。研究发现，液滴形成机理可分为挤压机理和剪切机理。离散相流动模式可分为四种模式，包括弹流、滴流、射流和平行流。然后，绘制了不同深宽比的微通道中离散相流动模式的分布图。这些分布图进一步揭示了微通道内不同离散相流动模式的形成和转化机制。最后，比较了改良文丘里微通道与普通 T 型微通道中液滴的形成情况。在带有文丘里组件的微通道中，液滴形成的效率更高。具体来说，当元件角度为 30°时，液滴长度可减少 120 μm。液滴产生频率可提高约 122.4%，从 25 赫兹提高到 55.6 赫兹。当文丘里部件位于离散相的入口处时，最小液滴可在微通道中以更高的频率均匀生成。
{"title":"Numerical simulation on the characteristics of droplet generation and the distribution of discrete-phase flow patterns in T-junction microchannels","authors":"Weiwei Xu, Shijia Cui, Xing Xu, Shaobo Lu, Zhaozeng Liu, Qiang Li","doi":"10.1016/j.ijheatfluidflow.2024.109626","DOIUrl":"10.1016/j.ijheatfluidflow.2024.109626","url":null,"abstract":"<div><div>Droplet formation is the basis for the design of droplet microfluidic chip. The droplet formation mechanism and discrete phase flow patterns in T-junction microchannels are numerically simulated. This research adopts an incompressible two-phase flow solver in the OpenFOAM® framework. Firstly, the effects of two-phase flow rate, surface tension and microchannel structure on droplet formation are investigated. It is found that the mechanism of droplet formation is classified into extrusion and shear mechanisms. And the discrete phase flow patterns can be divided into four modes, including slug flow, drip flow, jet flow, and parallel flow. Then, the distribution of discrete phase flow patterns in microchannels with different depth-to-width ratios are plotted. These distribution maps provide further insights into the mechanisms underlying the formation and transformation of different discrete phase flow patterns within microchannels. Finally, the droplet formation in the modified Venturi microchannels was compared with that in the ordinary T-junction microchannel. The efficiency of droplet formation in microchannels with Venturi components is superior. Specifically, with a component angle of 30°, the length of the droplets can be reduced by as much as 120 μm. The droplet generation frequency can be increased by approximately 122.4 %, rising from 25 Hz to 55.6 Hz. When the Venturi component is positioned at the entrance of the discrete phase, the minimal droplets can be generated uniformly at a higher frequency in the microchannel.</div></div>","PeriodicalId":335,"journal":{"name":"International Journal of Heat and Fluid Flow","volume":"110 ","pages":"Article 109626"},"PeriodicalIF":2.6,"publicationDate":"2024-11-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142573459","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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