Pub Date : 2024-11-02DOI: 10.1016/j.ijheatfluidflow.2024.109609
Daud Hasan, Arman Habib Polash, Hamim Faisal, Ahmed Imtiaz Rais, Md. Jisan Mahmud
This study numerically investigates conjugate mixed convection heat transfer, magnetohydrodynamic effects, and internal heat generation within a lid-driven triangular wavy enclosure with a rotating solid cylinder at its center. The significance of this work is to provide insights into the complex interplay of heat transfer, fluid flow, and magnetic field effects in a geometrically challenging enclosure for thermal management systems. The inclined chamber edges are stationary and maintained at a constant cold temperature, while a constant elevated temperature is applied to the uniformly sliding bottom edge. A steady magnetic field is applied to the enclosure while the solid cylinder rotates in a clockwise manner. By varying the Reynolds (31.623–316.23), Richardson (0.1–10), Grashof (103–105), and Hartman number (0, 50, 100) along a given speed ratio of the spinning cylinder, parametric simulation is performed. Qualitative findings are illustrated with streamline and isotherm plots. On the other hand, the quantitative thermal performance and flow characteristics of the configuration are determined by means of the average Nusselt number, average drag coefficient, normalized Nusselt number, as well as average fluid temperature. This investigation shows that the use of a magnetic field provides better control over the temperature distribution, along with a decreasing trend in heat transmission due to the rise in Hartmann number. The optimal design of the controlling parameters can be ascertained using the available detailed data.
{"title":"Impact of magnetic field on conjugate mixed convection heat transfer in a lid-driven triangular enclosure with an inclined wavy wall and internal heat generation","authors":"Daud Hasan, Arman Habib Polash, Hamim Faisal, Ahmed Imtiaz Rais, Md. Jisan Mahmud","doi":"10.1016/j.ijheatfluidflow.2024.109609","DOIUrl":"10.1016/j.ijheatfluidflow.2024.109609","url":null,"abstract":"<div><div>This study numerically investigates conjugate mixed convection heat transfer, magnetohydrodynamic effects, and internal heat generation within a lid-driven triangular wavy enclosure with a rotating solid cylinder at its center. The significance of this work is to provide insights into the complex interplay of heat transfer, fluid flow, and magnetic field effects in a geometrically challenging enclosure for thermal management systems. The inclined chamber edges are stationary and maintained at a constant cold temperature, while a constant elevated temperature is applied to the uniformly sliding bottom edge. A steady magnetic field is applied to the enclosure while the solid cylinder rotates in a clockwise manner. By varying the Reynolds (31.623–316.23), Richardson (0.1–10), Grashof (10<sup>3</sup>–10<sup>5</sup>), and Hartman number (0, 50, 100) along a given speed ratio of the spinning cylinder, parametric simulation is performed. Qualitative findings are illustrated with streamline and isotherm plots. On the other hand, the quantitative thermal performance and flow characteristics of the configuration are determined by means of the average Nusselt number, average drag coefficient, normalized Nusselt number, as well as average fluid temperature. This investigation shows that the use of a magnetic field provides better control over the temperature distribution, along with a decreasing trend in heat transmission due to the rise in Hartmann number. The optimal design of the controlling parameters can be ascertained using the available detailed data.</div></div>","PeriodicalId":335,"journal":{"name":"International Journal of Heat and Fluid Flow","volume":"110 ","pages":"Article 109609"},"PeriodicalIF":2.6,"publicationDate":"2024-11-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142573461","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}
Direct numerical simulation (DNS) is conducted to investigate the impact of solid particles on heat transfer in a plane channel flow. For comparison, two corresponding DNSs of unladen channel flow are also performed. The numerical simulation of the particle-laden case employs a two-way coupled Eulerian–Lagrangian computational model, which allows for the consideration of momentum transfer between the two phases: discrete particles and the continuous fluid phase. The presence of particles results in an increase in the mean temperature, the root mean square (rms) of temperature fluctuations, and the streamwise turbulent heat flux within the core region. Furthermore, particles exert a more significant influence on these characteristics at higher solid volume fractions. Additionally, the correlation between velocity and temperature is affected by the presence of particles. When comparing heat transfer in particle-laden channel flow to that in the corresponding unladen channel flow, it is observed that the difference in heat flux arises from changes in the rms of the wall-normal velocity and temperature fluctuations. The impact of particles on turbulent heat flux transport is significant in the vicinity of the wall, while their influence within the core region is relatively small.
我们进行了直接数值模拟（DNS），以研究固体颗粒对平面通道流传热的影响。为了进行比较，还对无负载通道流进行了两次相应的 DNS 模拟。载颗粒情况的数值模拟采用了双向耦合欧拉-拉格朗日计算模型，可以考虑两相（离散颗粒和连续流体相）之间的动量传递。颗粒的存在导致核心区域内的平均温度、温度波动均方根（rms）和流向湍流热通量增加。此外，固体体积分数越高，颗粒对这些特性的影响越明显。此外，颗粒的存在也会影响速度和温度之间的相关性。在比较含有颗粒的通道流与相应的未含有颗粒的通道流的传热时，可以发现热通量的差异来自于壁面正常速度和温度波动的均方根值的变化。颗粒对湍流热通量传输的影响在壁面附近非常明显，而在核心区域内则相对较小。
{"title":"Direct numerical simulation of turbulent flow and heat transfer in a particle-laden turbulent channel flow","authors":"Yifan Pei , Wenlei Chen , Xue-Lu Xiong , Xinhai Xu , Yi Zhou","doi":"10.1016/j.ijheatfluidflow.2024.109617","DOIUrl":"10.1016/j.ijheatfluidflow.2024.109617","url":null,"abstract":"<div><div>Direct numerical simulation (DNS) is conducted to investigate the impact of solid particles on heat transfer in a plane channel flow. For comparison, two corresponding DNSs of unladen channel flow are also performed. The numerical simulation of the particle-laden case employs a two-way coupled Eulerian–Lagrangian computational model, which allows for the consideration of momentum transfer between the two phases: discrete particles and the continuous fluid phase. The presence of particles results in an increase in the mean temperature, the root mean square (rms) of temperature fluctuations, and the streamwise turbulent heat flux within the core region. Furthermore, particles exert a more significant influence on these characteristics at higher solid volume fractions. Additionally, the correlation between velocity and temperature is affected by the presence of particles. When comparing heat transfer in particle-laden channel flow to that in the corresponding unladen channel flow, it is observed that the difference in heat flux arises from changes in the rms of the wall-normal velocity and temperature fluctuations. The impact of particles on turbulent heat flux transport is significant in the vicinity of the wall, while their influence within the core region is relatively small.</div></div>","PeriodicalId":335,"journal":{"name":"International Journal of Heat and Fluid Flow","volume":"110 ","pages":"Article 109617"},"PeriodicalIF":2.6,"publicationDate":"2024-11-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142573460","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 : 2024-11-01DOI: 10.1016/j.ijheatfluidflow.2024.109605
Alessandro Canova , Taihang Zhu , Jonathan F. Morrison
This work investigates the wake behind an axisymmetric bluff body at and applies control via four types of travelling jets which consist of different jet profiles undergoing travelling motion near the base edge. A comparison between these and the unforced wake is presented. Mean velocity, pressure fields, turbulence kinetic energy, and spectral proper orthogonal decomposition (SPOD) are employed to characterise the coherent structures within the flow. Our investigation confirms the presence of dominant modes and extends the previous findings to the velocity and pressure field on several planes parallel and perpendicular to the streamwise direction. These modes, as shown by SPOD, represent the wake’s bulk energy and therefore are the main target for travelling jets to pursue drag reduction. In the interest of achieving pressure recovery, several types of actuators have been proposed and investigated: the baseline travelling jet obtains the highest drag reduction with a pressure recovery of , which is followed by the oscillatory travelling jet with and the pulsed travelling jet with ; conversely, the sweeping travelling jet dramatically increases the drag with a reduction in base pressure. Focusing on the baseline travelling jet, pressure recovery is achieved via a combination of dominant modes suppression, entrainment reduction, and wake’s elongation and narrowing.
本研究对 ReD∼2⋅105 时轴对称崖体后方的尾流进行了研究，并通过四种类型的行进射流进行了控制，这些射流由在基底边缘附近进行行进运动的不同射流剖面组成。对这些喷流和非强制尾流进行了比较。采用平均速度、压力场、湍流动能和光谱正交分解（SPOD）来描述流内的相干结构。我们的研究证实了主导模式的存在，并将先前的研究结果扩展到了与流向平行和垂直的几个平面上的速度场和压力场。如 SPOD 所示，这些模式代表了尾流的大量能量，因此是行进中的喷气机减少阻力的主要目标。为了实现压力恢复，已经提出并研究了几种类型的激励器：基线游动喷流的阻力降低率最高，压力恢复率为 +62%，其次是振荡游动喷流，压力恢复率为 +34%，脉冲游动喷流为 +32%；相反，横扫游动喷流会显著增加阻力，基础压力降低率为 -460%。以基线流动射流为重点，压力恢复是通过抑制主导模式、减少夹带以及拉长和缩小尾流等综合措施实现的。
{"title":"Control of a bluff body wake using travelling jets","authors":"Alessandro Canova , Taihang Zhu , Jonathan F. Morrison","doi":"10.1016/j.ijheatfluidflow.2024.109605","DOIUrl":"10.1016/j.ijheatfluidflow.2024.109605","url":null,"abstract":"<div><div>This work investigates the wake behind an axisymmetric bluff body at <span><math><mrow><mi>R</mi><msub><mrow><mi>e</mi></mrow><mrow><mi>D</mi></mrow></msub><mo>∼</mo><mn>2</mn><mi>⋅</mi><mn>1</mn><msup><mrow><mn>0</mn></mrow><mrow><mn>5</mn></mrow></msup></mrow></math></span> and applies control via four types of travelling jets which consist of different jet profiles undergoing travelling motion near the base edge. A comparison between these and the unforced wake is presented. Mean velocity, pressure fields, turbulence kinetic energy, and spectral proper orthogonal decomposition (SPOD) are employed to characterise the coherent structures within the flow. Our investigation confirms the presence of dominant modes and extends the previous findings to the velocity and pressure field on several planes parallel and perpendicular to the streamwise direction. These modes, as shown by SPOD, represent the wake’s bulk energy and therefore are the main target for travelling jets to pursue drag reduction. In the interest of achieving pressure recovery, several types of actuators have been proposed and investigated: the baseline travelling jet obtains the highest drag reduction with a pressure recovery of <span><math><mrow><mo>+</mo><mn>62</mn><mtext>%</mtext></mrow></math></span>, which is followed by the oscillatory travelling jet with <span><math><mrow><mo>+</mo><mn>34</mn><mtext>%</mtext></mrow></math></span> and the pulsed travelling jet with <span><math><mrow><mo>+</mo><mn>32</mn><mtext>%</mtext></mrow></math></span>; conversely, the sweeping travelling jet dramatically increases the drag with a <span><math><mrow><mo>−</mo><mn>460</mn><mtext>%</mtext></mrow></math></span> reduction in base pressure. Focusing on the baseline travelling jet, pressure recovery is achieved via a combination of dominant modes suppression, entrainment reduction, and wake’s elongation and narrowing.</div></div>","PeriodicalId":335,"journal":{"name":"International Journal of Heat and Fluid Flow","volume":"110 ","pages":"Article 109605"},"PeriodicalIF":2.6,"publicationDate":"2024-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142573458","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 : 2024-10-31DOI: 10.1016/j.ijheatfluidflow.2024.109628
Panxi Yang , Guangju Ma , Xifeng Liu , Guoming Lv , Benren Wang , Suke Yang , Xiao Chen , Bolun Yang , Zhiqiang Wu
The steel industry faces the challenges of high energy consumption, high carbon emissions and high solid waste production. At present, the recycling and treatment of steel slag solid waste is the most serious problem, with the utilization rate of steel slag being only 30 %. Steel slag solid waste contains a high content of f-CaO (free calcium oxide), which reacts with water causing expansion and deformation. It is necessary to pre-digest the f-CaO in steel slag to improve the quality of steel slag. Using CO2 to react with steel slag can not only effectively strengthen the digestion reaction of f-CaO, but also realize the in-situ sequestration of CO2 emitted from steel mills and reduce carbon emissions from the iron and steel industry. However, there is currently limited development of equipment for the carbonation process of steel slag, and most existing equipment is either fluidized beds or moving beds designed for continuous operation, which have the high particle size requirements for steel slag raw materials and high operational energy consumption. Therefore, in this study, based on the dry carbonation process route of steel slag, the traditional hot smothering process was modified for carbonation. A new type of fixed-bed pressurized reactor for steel slag carbonation with both steel slag modification and in situ carbon sequestration was developed. The physical structure of the reactor was designed in detail, and a numerical model of gas–solid two-phase reaction flow based on the carbonation reaction of steel slag was established. The intermittent dry carbonation process of steel slag in the modified device was simulated, and the effects of slag temperature, gas amount, particle size and reaction time on the carbonation effect of steel slag were studied. The calculation results showed that the increase of initial slag temperature, flue gas inflow and reaction time as well as the decrease of particle size can promote the carbonation reaction of steel slag in different degrees. For the steel slag system with an initial f-CaO content of 4.48 wt%, when the initial temperature of the slag was 873.15 K, and the total amount of flue gas was equivalent to digesting the f-CaO to 1.00 wt%, the f-CaO content of steel slag of all particle sizes was less than 4 wt% after a reaction time of 2.5 h, meeting the requirement for the f-CaO content of steel slag in the Chinese national standard.
钢铁工业面临着高能耗、高碳排放和高固体废物产生量的挑战。目前，钢渣固体废弃物的回收和处理是最严重的问题，钢渣的利用率仅为 30%。钢渣固体废弃物中含有大量 f-CaO（游离氧化钙），会与水发生反应，导致膨胀和变形。有必要对钢渣中的 f-CaO 进行预消化，以提高钢渣的质量。利用 CO2 与钢渣反应，不仅能有效强化 f-CaO 的消化反应，还能实现钢厂排放的 CO2 就地封存，减少钢铁行业的碳排放。然而，目前用于钢渣碳化工艺的设备开发有限，现有设备大多为流化床或移动床，设计为连续运行，对钢渣原料粒度要求高，运行能耗大。因此，本研究在钢渣干法碳化工艺路线的基础上，对传统的热闷烧工艺进行了碳化改造。开发了一种新型固定床加压反应器，用于钢渣碳化，同时兼具钢渣改性和原位固碳的功能。详细设计了反应器的物理结构，建立了基于钢渣碳化反应的气固两相反应流数值模型。模拟了钢渣在改进装置中的间歇干法碳化过程，研究了钢渣温度、气体量、粒度和反应时间对钢渣碳化效果的影响。计算结果表明，初始炉渣温度、烟气流入量和反应时间的增加以及粒度的减小都能不同程度地促进钢渣的碳化反应。对于初始 f-CaO 含量为 4.48 wt%的钢渣体系，当钢渣初始温度为 873.15 K，烟气总量相当于将 f-CaO 消解到 1.00 wt%时，反应时间为 2.5 h 后，各种粒度钢渣的 f-CaO 含量均小于 4 wt%，满足中国国家标准对钢渣 f-CaO 含量的要求。
{"title":"Design and simulation of a new carbonation device with both steel slag modification and carbon sequestration functions","authors":"Panxi Yang , Guangju Ma , Xifeng Liu , Guoming Lv , Benren Wang , Suke Yang , Xiao Chen , Bolun Yang , Zhiqiang Wu","doi":"10.1016/j.ijheatfluidflow.2024.109628","DOIUrl":"10.1016/j.ijheatfluidflow.2024.109628","url":null,"abstract":"<div><div>The steel industry faces the challenges of high energy consumption, high carbon emissions and high solid waste production. At present, the recycling and treatment of steel slag solid waste is the most serious problem, with the utilization rate of steel slag being only 30 %. Steel slag solid waste contains a high content of f-CaO (free calcium oxide), which reacts with water causing expansion and deformation. It is necessary to pre-digest the f-CaO in steel slag to improve the quality of steel slag. Using CO<sub>2</sub> to react with steel slag can not only effectively strengthen the digestion reaction of f-CaO, but also realize the in-situ sequestration of CO<sub>2</sub> emitted from steel mills and reduce carbon emissions from the iron and steel industry. However, there is currently limited development of equipment for the carbonation process of steel slag, and most existing equipment is either fluidized beds or moving beds designed for continuous operation, which have the high particle size requirements for steel slag raw materials and high operational energy consumption. Therefore, in this study, based on the dry carbonation process route of steel slag, the traditional hot smothering process was modified for carbonation. A new type of fixed-bed pressurized reactor for steel slag carbonation with both steel slag modification and in situ carbon sequestration was developed. The physical structure of the reactor was designed in detail, and a numerical model of gas–solid two-phase reaction flow based on the carbonation reaction of steel slag was established. The intermittent dry carbonation process of steel slag in the modified device was simulated, and the effects of slag temperature, gas amount, particle size and reaction time on the carbonation effect of steel slag were studied. The calculation results showed that the increase of initial slag temperature, flue gas inflow and reaction time as well as the decrease of particle size can promote the carbonation reaction of steel slag in different degrees. For the steel slag system with an initial f-CaO content of 4.48 wt%, when the initial temperature of the slag was 873.15 K, and the total amount of flue gas was equivalent to digesting the f-CaO to 1.00 wt%, the f-CaO content of steel slag of all particle sizes was less than 4 wt% after a reaction time of 2.5 h, meeting the requirement for the f-CaO content of steel slag in the Chinese national standard.</div></div>","PeriodicalId":335,"journal":{"name":"International Journal of Heat and Fluid Flow","volume":"110 ","pages":"Article 109628"},"PeriodicalIF":2.6,"publicationDate":"2024-10-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142553935","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 : 2024-10-30DOI: 10.1016/j.ijheatfluidflow.2024.109614
Karol Wawrzak , Jakub Stempka , Artur Tyliszczak
This paper focuses on the flow dynamics of jets originating from circular and non-circular nozzles (square, triangular, hexagonal, hexagram) evolving in a co-flowing stream at the Reynolds numbers and . The jets are cold, 300 K, while the surrounding co-flow is heated up to 1000 K. This temperature difference results in a density ratio 0.3. We consider low Mach number non-reactive flows, though, the density/temperature levels are typical for configurations in which the auto-ignition and flame-lifting mechanisms are studied. The research aims to highlight the differences in the jet evolutions caused by its initial azimuthal non-uniformity. We apply the Large Eddy Simulation (LES) method and utilize ANSYS Fluent software and an in-house high-order code SAILOR. They are used separately, i.e., the ANSYS Fluent is employed to compute the flows inside the nozzles from which ends the inlet data are extracted for the jet simulations performed by the SAILOR code. The instantaneous solutions show that, depending on the nozzle shape and the Reynolds number, the jet shapes differ significantly. The corners of the nozzles induce azimuthal irregularity of the Kelvin–Helmholtz toroidal vortices (rings) and the appearance of elongated rib-like vortices connecting subsequent rings. The mutual interactions between generated small-scale vortices and naturally occurring toroidal vortices result in a fast breakup of the jets close to the nozzles. The axial velocity profiles show substantial variability of the potential core lengths and the downstream velocity decay rates. This manifests by significantly different growths of the mean temperature values ( K) and its fluctuations. The enhancement of the global mixing process is quantified by the entrainment rate and axial profiles of the temperature, averaged spatially in the radial direction. In the case of triangular and square jets, the near-field entrainment is more than twice that of the circular jet. This is accompanied by a proportional increase in the average temperature fluctuations and a slight rise in the mean temperature.
{"title":"Numerical analysis of the mixing process in variable density jets emanating from polygonal nozzles","authors":"Karol Wawrzak , Jakub Stempka , Artur Tyliszczak","doi":"10.1016/j.ijheatfluidflow.2024.109614","DOIUrl":"10.1016/j.ijheatfluidflow.2024.109614","url":null,"abstract":"<div><div>This paper focuses on the flow dynamics of jets originating from circular and non-circular nozzles (square, triangular, hexagonal, hexagram) evolving in a co-flowing stream at the Reynolds numbers <span><math><mrow><mtext>Re</mtext><mo>=</mo><mn>5</mn><mspace></mspace><mn>000</mn></mrow></math></span> and <span><math><mrow><mtext>Re</mtext><mo>=</mo><mn>20</mn><mspace></mspace><mn>000</mn></mrow></math></span>. The jets are cold, 300 K, while the surrounding co-flow is heated up to 1000 K. This temperature difference results in a density ratio 0.3. We consider low Mach number non-reactive flows, though, the density/temperature levels are typical for configurations in which the auto-ignition and flame-lifting mechanisms are studied. The research aims to highlight the differences in the jet evolutions caused by its initial azimuthal non-uniformity. We apply the Large Eddy Simulation (LES) method and utilize ANSYS Fluent software and an in-house high-order code SAILOR. They are used separately, i.e., the ANSYS Fluent is employed to compute the flows inside the nozzles from which ends the inlet data are extracted for the jet simulations performed by the SAILOR code. The instantaneous solutions show that, depending on the nozzle shape and the Reynolds number, the jet shapes differ significantly. The corners of the nozzles induce azimuthal irregularity of the Kelvin–Helmholtz toroidal vortices (rings) and the appearance of elongated rib-like vortices connecting subsequent rings. The mutual interactions between generated small-scale vortices and naturally occurring toroidal vortices result in a fast breakup of the jets close to the nozzles. The axial velocity profiles show substantial variability of the potential core lengths and the downstream velocity decay rates. This manifests by significantly different growths of the mean temperature values (<span><math><mrow><mi>Δ</mi><mi>T</mi><mo>≈</mo><mn>200</mn></mrow></math></span> K) and its fluctuations. The enhancement of the global mixing process is quantified by the entrainment rate and axial profiles of the temperature, averaged spatially in the radial direction. In the case of triangular and square jets, the near-field entrainment is more than twice that of the circular jet. This is accompanied by a proportional increase in the average temperature fluctuations and a slight rise in the mean temperature.</div></div>","PeriodicalId":335,"journal":{"name":"International Journal of Heat and Fluid Flow","volume":"110 ","pages":"Article 109614"},"PeriodicalIF":2.6,"publicationDate":"2024-10-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142553934","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 : 2024-10-29DOI: 10.1016/j.ijheatfluidflow.2024.109622
Jinxing Wu, Shengguang Lu, Chenxu Wang, Jiawen Li
Changing the shape of the heat exchanger tube is an effective method to improve the heat transfer performance of the heat exchanger. However, most of the new heat exchange tubes have complex structures and are difficult to manufacture and apply in engineering. In this paper, a novel type of helically coiled grooved elliptical tube heat exchanger (HCGETHE) which is easy to manufacture is proposed. Using methane as the working fluid, the effects of the dimensionless groove diameter (Dg = 0.222, 0.333, 0.444, 0.556, 0.667), the dimensionless groove height (Hg = 0.6, 0.8, 1.0, 1.2) and the ratio of major axis to minor axis (a/b = 1.440, 1.596, 1.778) on the flow and heat transfer characteristics of the shell side are investigated by numerical simulation in the Reynolds number (Re) range of 10000 ∼ 50000 under the condition of constant wall temperature (tw = 300 K). The results show that when the working fluid flows through the groove of the grooved elliptical tube, backflow occurs and longitudinal vortices are formed in the groove, which improve heat transfer. As the dimensionless groove diameter increases, Nu decreases and f increases. The dimensionless groove height has little effect on Nu, but a significant effect on f. Both Nu and f decrease with the increase of the ratio of major axis to minor axis. Compared with the helically coiled circular tube heat exchanger (HCCTHE), the PEC of the HCGETHE can be increased by up to 59.53 %. The excellent thermal hydraulic performance proves that it has a good application prospect.
{"title":"Numerical study on heat transfer characteristics of helically coiled grooved elliptical tube heat exchanger","authors":"Jinxing Wu, Shengguang Lu, Chenxu Wang, Jiawen Li","doi":"10.1016/j.ijheatfluidflow.2024.109622","DOIUrl":"10.1016/j.ijheatfluidflow.2024.109622","url":null,"abstract":"<div><div>Changing the shape of the heat exchanger tube is an effective method to improve the heat transfer performance of the heat exchanger. However, most of the new heat exchange tubes have complex structures and are difficult to manufacture and apply in engineering. In this paper, a novel type of helically coiled grooved elliptical tube heat exchanger (HCGETHE) which is easy to manufacture is proposed. Using methane as the working fluid, the effects of the dimensionless groove diameter (<em>D</em><sub>g</sub> = 0.222, 0.333, 0.444, 0.556, 0.667), the dimensionless groove height (<em>H</em><sub>g</sub> = 0.6, 0.8, 1.0, 1.2) and the ratio of major axis to minor axis (<em>a/b</em> = 1.440, 1.596, 1.778) on the flow and heat transfer characteristics of the shell side are investigated by numerical simulation in the Reynolds number (<em>Re</em>) range of 10000 ∼ 50000 under the condition of constant wall temperature (<em>t</em><sub>w</sub> = 300 K). The results show that when the working fluid flows through the groove of the grooved elliptical tube, backflow occurs and longitudinal vortices are formed in the groove, which improve heat transfer. As the dimensionless groove diameter increases, <em>Nu</em> decreases and <em>f</em> increases. The dimensionless groove height has little effect on <em>Nu</em>, but a significant effect on <em>f</em>. Both <em>Nu</em> and <em>f</em> decrease with the increase of the ratio of major axis to minor axis. Compared with the helically coiled circular tube heat exchanger (HCCTHE), the <em>PEC</em> of the HCGETHE can be increased by up to 59.53 %. The excellent thermal hydraulic performance proves that it has a good application prospect.</div></div>","PeriodicalId":335,"journal":{"name":"International Journal of Heat and Fluid Flow","volume":"110 ","pages":"Article 109622"},"PeriodicalIF":2.6,"publicationDate":"2024-10-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142537121","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 : 2024-10-29DOI: 10.1016/j.ijheatfluidflow.2024.109597
L. Villanueva , K. Truffin , M. Meldi
An online Data Assimilation strategy based on the Ensemble Kalman Filter (EnKF) is used to study the features of parametric optimization and synchronization of the physical state when applied to scale-resolved numerical simulations. To this purpose, the method is combined with Large Eddy Simulation (LES) for the analysis of the turbulent flow in a plane channel, . The algorithm sequentially combines the LES prediction with high-fidelity, sparse instantaneous data obtained from a Direct Numerical Simulation (DNS). It is shown that the procedure provides an augmented state that exhibits higher accuracy than the LES model and it synchronizes with the time evolution of the high-fidelity DNS data if the hyperparameters governing the EnKF are properly chosen. In addition, the data-driven algorithm is able to improve the accuracy of the subgrid-scale model included in the LES, the Smagorinsky model, via the optimization of a free coefficient. However, while the online EnKF strategy is able to reduce the global error of the LES prediction, a discrepancy with the reference DNS data is still observed because of structural flaws of the subgrid-scale model used.
基于集合卡尔曼滤波器（EnKF）的在线数据同化策略被用于研究应用于尺度分辨数值模拟时参数优化和物理状态同步的特点。为此，该方法与大涡模拟（LES）相结合，用于分析 Reτ≈550 平面通道中的湍流。该算法依次将 LES 预测与直接数值模拟（DNS）获得的高保真稀疏瞬时数据相结合。结果表明，如果适当选择 EnKF 的超参数，该程序提供的增强状态比 LES 模型的精度更高，并且与高保真 DNS 数据的时间演化同步。此外，数据驱动算法还能通过优化自由系数，提高 LES 所包含的子网格尺度模型（即 Smagorinsky 模型）的精度。不过，虽然在线 EnKF 策略能够减少 LES 预测的全局误差，但由于所使用的子网格尺度模型存在结构性缺陷，与 DNS 参考数据之间仍然存在差异。
{"title":"Synchronization and optimization of Large Eddy Simulation using an online Ensemble Kalman Filter","authors":"L. Villanueva , K. Truffin , M. Meldi","doi":"10.1016/j.ijheatfluidflow.2024.109597","DOIUrl":"10.1016/j.ijheatfluidflow.2024.109597","url":null,"abstract":"<div><div>An online Data Assimilation strategy based on the Ensemble Kalman Filter (EnKF) is used to study the features of parametric optimization and synchronization of the physical state when applied to scale-resolved numerical simulations. To this purpose, the method is combined with Large Eddy Simulation (LES) for the analysis of the turbulent flow in a plane channel, <span><math><mrow><mi>R</mi><msub><mrow><mi>e</mi></mrow><mrow><mi>τ</mi></mrow></msub><mo>≈</mo><mn>550</mn></mrow></math></span>. The algorithm sequentially combines the LES prediction with high-fidelity, sparse instantaneous data obtained from a Direct Numerical Simulation (DNS). It is shown that the procedure provides an augmented state that exhibits higher accuracy than the LES model and it synchronizes with the time evolution of the high-fidelity DNS data if the hyperparameters governing the EnKF are properly chosen. In addition, the data-driven algorithm is able to improve the accuracy of the subgrid-scale model included in the LES, the Smagorinsky model, via the optimization of a free coefficient. However, while the online EnKF strategy is able to reduce the global error of the LES prediction, a discrepancy with the reference DNS data is still observed because of structural flaws of the subgrid-scale model used.</div></div>","PeriodicalId":335,"journal":{"name":"International Journal of Heat and Fluid Flow","volume":"110 ","pages":"Article 109597"},"PeriodicalIF":2.6,"publicationDate":"2024-10-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142537120","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 research investigates the heat transfer mechanisms of nucleated bubbles on a vertical heating surface using 2.4 MHz ultrasonic waves. The experiments, conducted in a closed rectangular chamber filled with HFE-7100, a hydrofluoroether fluid, varied the surface heat flux from 4.91 kW/m2 to 12.06 kW/m2. The results revealed a notable reduction in temperature on the vertical heating surface due to the influence of 2.4 MHz ultrasound, leading to an average surface temperature decrease of up to 5.3 °C across the entire heat flux range. Analysis of acoustic streaming, flow patterns, and thermally nucleated bubbles using particle image velocimetry (PIV) and a high-speed camera demonstrated the pronounced impact of ultrasonic waves on heat transfer. Our findings highlight the crucial role of 2.4 MHz ultrasonic waves in influencing bubble behavior and enhancing heat transfer on the vertical heating surface. This enhancement is achieved by disturbing the near-wall flow, particularly at lower heat fluxes, with a peak velocity ratio of 5.27 times. This disturbance increases average velocities, indicating potential improvements in heat transfer. Consequently, our study showed a maximum heat transfer enhancement of 83 %. At higher heat fluxes, the interaction with the waves becomes more complex, increasing velocities but limiting streaming coverage in the lower region of the heating surface. The combined effect of 2.4 MHz ultrasound and nucleate boiling convection not only enhances near-wall heat transfer but also amplifies fluid mixing within the chamber. The examination of bubble evolution with and without 2.4 MHz ultrasonic waves underscored the role of acoustic streaming in sweeping bubbles, reducing the size of nucleation sites, and reducing their crowd density, particularly at lower heat fluxes.
{"title":"Heat transfer mechanism of nucleated bubbles on vertical heating surface induced by 2.4 MHz waves in HFE-7100 liquid","authors":"Teerapat Thungthong , Shumpei Funatani , Weerachai Chaiworapuek","doi":"10.1016/j.ijheatfluidflow.2024.109619","DOIUrl":"10.1016/j.ijheatfluidflow.2024.109619","url":null,"abstract":"<div><div>This research investigates the heat transfer mechanisms of nucleated bubbles on a vertical heating surface using 2.4 MHz ultrasonic waves. The experiments, conducted in a closed rectangular chamber filled with HFE-7100, a hydrofluoroether fluid, varied the surface heat flux from 4.91 kW/m<sup>2</sup> to 12.06 kW/m<sup>2</sup>. The results revealed a notable reduction in temperature on the vertical heating surface due to the influence of 2.4 MHz ultrasound, leading to an average surface temperature decrease of up to 5.3 °C across the entire heat flux range. Analysis of acoustic streaming, flow patterns, and thermally nucleated bubbles using particle image velocimetry (PIV) and a high-speed camera demonstrated the pronounced impact of ultrasonic waves on heat transfer. Our findings highlight the crucial role of 2.4 MHz ultrasonic waves in influencing bubble behavior and enhancing heat transfer on the vertical heating surface. This enhancement is achieved by disturbing the near-wall flow, particularly at lower heat fluxes, with a peak velocity ratio of 5.27 times. This disturbance increases average velocities, indicating potential improvements in heat transfer. Consequently, our study showed a maximum heat transfer enhancement of 83 %. At higher heat fluxes, the interaction with the waves becomes more complex, increasing velocities but limiting streaming coverage in the lower region of the heating surface. The combined effect of 2.4 MHz ultrasound and nucleate boiling convection not only enhances near-wall heat transfer but also amplifies fluid mixing within the chamber. The examination of bubble evolution with and without 2.4 MHz ultrasonic waves underscored the role of acoustic streaming in sweeping bubbles, reducing the size of nucleation sites, and reducing their crowd density, particularly at lower heat fluxes.</div></div>","PeriodicalId":335,"journal":{"name":"International Journal of Heat and Fluid Flow","volume":"110 ","pages":"Article 109619"},"PeriodicalIF":2.6,"publicationDate":"2024-10-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142536198","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 : 2024-10-24DOI: 10.1016/j.ijheatfluidflow.2024.109621
Yi Tong Li, Hang Guo, Hao Chen, Fang Ye
The catalyst loading random distribution has a divergent effect on heat transfer and electrical property inside fuel cells than the catalyst loading homogeneous distribution, but the effects of different stoichiometric ratios and average platinum loadings on electrical property, heat as well as species transfer in the fuel cell considering catalyst content random setting are still unclear. Hence, the impacts of stoichiometric ratios and average platinum loadings on the electrical property of fuel cell considering catalyst content random distribution are explored in this paper by using a steady state, two-dimensional, two-phase, non-isothermal fuel cell model coupled the catalyst layer agglomerate model considering the multi-scale problem of catalyst layer. Results indicate that stoichiometric ratio and average platinum loading do not influence the effect direction of catalyst content distributed randomly on the output power. However, with the stoichiometric ratio rising, the impact degree of catalyst content distributed randomly on the output power first enhances and then diminishes. When the stoichiometric ratio is 1.3, the power density of uniform random distribution changes the most, decreasing by 3.91 %. As the average platinum loading rises, the impact degree of catalyst content distributed randomly on the output power gradually decreases. The power density of uniform random distribution decreases by 4.93 % when the catalyst content is 0.2 mg/cm2. Furthermore, the variation trends of temperature distribution, product and reactant content with stoichiometric ratio and average platinum loading under the platinum loading random distribution condition are consistent with that under the platinum loading homogeneous distribution condition. However, as the stoichiometric ratio rises, the reaction rate distribution becomes more uniform for normal random and homogeneous distributions, but the reaction rate distribution becomes uneven under uniform random distribution.
{"title":"Influence of operating conditions on heat and mass transfer in PEMFCs with platinum loading random distributions","authors":"Yi Tong Li, Hang Guo, Hao Chen, Fang Ye","doi":"10.1016/j.ijheatfluidflow.2024.109621","DOIUrl":"10.1016/j.ijheatfluidflow.2024.109621","url":null,"abstract":"<div><div>The catalyst loading random distribution has a divergent effect on heat transfer and electrical property inside fuel cells than the catalyst loading homogeneous distribution, but the effects of different stoichiometric ratios and average platinum loadings on electrical property, heat as well as species transfer in the fuel cell considering catalyst content random setting are still unclear. Hence, the impacts of stoichiometric ratios and average platinum loadings on the electrical property of fuel cell considering catalyst content random distribution are explored in this paper by using a steady state, two-dimensional, two-phase, non-isothermal fuel cell model coupled the catalyst layer agglomerate model considering the multi-scale problem of catalyst layer. Results indicate that stoichiometric ratio and average platinum loading do not influence the effect direction of catalyst content distributed randomly on the output power. However, with the stoichiometric ratio rising, the impact degree of catalyst content distributed randomly on the output power first enhances and then diminishes. When the stoichiometric ratio is 1.3, the power density of uniform random distribution changes the most, decreasing by 3.91 %. As the average platinum loading rises, the impact degree of catalyst content distributed randomly on the output power gradually decreases. The power density of uniform random distribution decreases by 4.93 % when the catalyst content is 0.2 mg/cm<sup>2</sup>. Furthermore, the variation trends of temperature distribution, product and reactant content with stoichiometric ratio and average platinum loading under the platinum loading random distribution condition are consistent with that under the platinum loading homogeneous distribution condition. However, as the stoichiometric ratio rises, the reaction rate distribution becomes more uniform for normal random and homogeneous distributions, but the reaction rate distribution becomes uneven under uniform random distribution.</div></div>","PeriodicalId":335,"journal":{"name":"International Journal of Heat and Fluid Flow","volume":"110 ","pages":"Article 109621"},"PeriodicalIF":2.6,"publicationDate":"2024-10-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142536252","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 : 2024-10-23DOI: 10.1016/j.ijheatfluidflow.2024.109615
Zhenwei Liu, Shoutong Ji, Yueting Zhou, Shiyang Chen, Ping Li
A novel low-drag twisted blade-like fin is proposed in this work to enhance the comprehensive thermal performance of gas turbine trailing edge cooling channel. The influence of the twist rate and relative height of the novel fin on flow and heat transfer performance is investigated within the Reynolds number range of 14,000 to 36,000. Results show that the relative Nusselt number decreases as Reynolds number increases, ranging from 1.49 to 2.56, while the relative friction factor increases with Reynolds number, ranging from 1.16 to 12.6. The comprehensive thermal performance is improved in all cases, and is optimal at a twist rate of 6.0°/mm and a relative height of 0.6 times channel height. The flow drag increases exponentially with the increase in relative height and twist rate, while the enhancement of heat transfer performance slows down. Fins with a relative height of 0.8 times channel height can achieve over 90 % of the heat transfer performance of fins with a relative height of 1.0 times channel height, with only half the flow drag. Compared to the conventional fins, the comprehensive thermal performance of the novel twisted blade-like fin is excellent. The friction factor can be less than 30 % of that of circular pin-fin with a comparable Nusselt number, and the comprehensive thermal performance is improved by more than 55 %. The twisted blade-like fins stimulate spanwise and normalwise secondary flows, promoting fluid exchange between the walls and the channel core, thereby enhancing the heat transfer performance of the channel, in which the normalwise secondary flow plays a dominant role.
{"title":"Heat transfer enhancement of gas turbine trailing-edge cooling channel with twisted blade-like fins arranged on endwalls","authors":"Zhenwei Liu, Shoutong Ji, Yueting Zhou, Shiyang Chen, Ping Li","doi":"10.1016/j.ijheatfluidflow.2024.109615","DOIUrl":"10.1016/j.ijheatfluidflow.2024.109615","url":null,"abstract":"<div><div>A novel low-drag twisted blade-like fin is proposed in this work to enhance the comprehensive thermal performance of gas turbine trailing edge cooling channel. The influence of the twist rate and relative height of the novel fin on flow and heat transfer performance is investigated within the Reynolds number range of 14,000 to 36,000. Results show that the relative Nusselt number decreases as Reynolds number increases, ranging from 1.49 to 2.56, while the relative friction factor increases with Reynolds number, ranging from 1.16 to 12.6. The comprehensive thermal performance is improved in all cases, and is optimal at a twist rate of 6.0°/mm and a relative height of 0.6 times channel height. The flow drag increases exponentially with the increase in relative height and twist rate, while the enhancement of heat transfer performance slows down. Fins with a relative height of 0.8 times channel height can achieve over 90 % of the heat transfer performance of fins with a relative height of 1.0 times channel height, with only half the flow drag. Compared to the conventional fins, the comprehensive thermal performance of the novel twisted blade-like fin is excellent. The friction factor can be less than 30 % of that of circular pin-fin with a comparable Nusselt number, and the comprehensive thermal performance is improved by more than 55 %. The twisted blade-like fins stimulate spanwise and normalwise secondary flows, promoting fluid exchange between the walls and the channel core, thereby enhancing the heat transfer performance of the channel, in which the normalwise secondary flow plays a dominant role.</div></div>","PeriodicalId":335,"journal":{"name":"International Journal of Heat and Fluid Flow","volume":"110 ","pages":"Article 109615"},"PeriodicalIF":2.6,"publicationDate":"2024-10-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142536199","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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