Flow boiling in the microchannel with the ultrasound is regarded as a promising method for confronting the challenge posed by heat dissipation in microelectronic devices. During this process, the nucleation is vital for the thermal performance, but the nucleation mechanism with the interplay of ultrasonic, thermal, and flow fields remains inadequately explored. This study first endeavors to reveal the nucleation mechanism of flow boiling within the ultrasonic field through the experimental inquiry into the impact of ultrasound on the onset of nucleate boiling (ONB). It is ascertained that ultrasound plays a pivotal role in promotion of the nucleation. An evident decrease of the wall superheat at ONB, specifically 20.7 %, is achieved by activating abundant vapor embryos at a relatively low wall superheat. Meanwhile, associated bubble generation rate increases by approximately two orders of magnitude, owing to the noteworthy reduction in the temporal requisites within the ultrasonic field for the generation of an equivalent number of bubbles. Furthermore, the elevation in ultrasonic power and operating time lead to a substantial reduction of 18.6 % and 16.7 %, respectively, in the wall superheat required to ONB. Concomitant with the rise in mass flux, the heat flux at ONB exhibits a remarkable ascent of 52.1 %.
{"title":"Experimental study on ONB of flow boiling in microchannel within an ultrasonic field","authors":"Yong Guo , Zong-Bo Zhang , Chuan-Yong Zhu , Liang Gong","doi":"10.1016/j.ijheatmasstransfer.2024.126388","DOIUrl":"10.1016/j.ijheatmasstransfer.2024.126388","url":null,"abstract":"<div><div>Flow boiling in the microchannel with the ultrasound is regarded as a promising method for confronting the challenge posed by heat dissipation in microelectronic devices. During this process, the nucleation is vital for the thermal performance, but the nucleation mechanism with the interplay of ultrasonic, thermal, and flow fields remains inadequately explored. This study first endeavors to reveal the nucleation mechanism of flow boiling within the ultrasonic field through the experimental inquiry into the impact of ultrasound on the onset of nucleate boiling (ONB). It is ascertained that ultrasound plays a pivotal role in promotion of the nucleation. An evident decrease of the wall superheat at ONB, specifically 20.7 %, is achieved by activating abundant vapor embryos at a relatively low wall superheat. Meanwhile, associated bubble generation rate increases by approximately two orders of magnitude, owing to the noteworthy reduction in the temporal requisites within the ultrasonic field for the generation of an equivalent number of bubbles. Furthermore, the elevation in ultrasonic power and operating time lead to a substantial reduction of 18.6 % and 16.7 %, respectively, in the wall superheat required to ONB. Concomitant with the rise in mass flux, the heat flux at ONB exhibits a remarkable ascent of 52.1 %.</div></div>","PeriodicalId":336,"journal":{"name":"International Journal of Heat and Mass Transfer","volume":"236 ","pages":"Article 126388"},"PeriodicalIF":5.0,"publicationDate":"2024-11-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142663708","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-11-08DOI: 10.1016/j.ijheatmasstransfer.2024.126374
Chuang Zhang , Qin Lou , Hong Liang
A synthetic iterative scheme is developed for thermal applications in hotspot systems with large temperature variance. Different from previous work with linearized equilibrium state and small temperature difference assumption, the phonon equilibrium distribution shows a nonlinear relationship with temperature and mean free path changes with the spatial temperature when the temperature difference of system is large, so that the same phonon mode may suffer different transport processes in different geometric regions. In order to efficiently capture nonlinear and multiscale thermal behaviors, the Newton method is used and a macroscopic iteration is introduced for preprocessing based on the iterative solutions of the stationary phonon BTE. Macroscopic and mesoscopic physical evolution processes are connected by the heat flux, which is no longer calculated by classical Fourier’s law but obtained by taking the moment of phonon distribution function. These two processes exchange information from different scales, such that the present scheme could efficiently deal with heat conduction problems from ballistic to diffusive regime. Numerical tests show that the present scheme could efficiently capture the multiscale heat conduction in hotspot systems with large temperature variances. In addition, a comparison is made between the solutions of the present scheme and effective Fourier’s law by several heat dissipations problems under different sizes or selective phonon excitation. Numerical results show that compared to the classical Fourier’s law, the results of the effective Fourier’s law could be closer to the BTE solutions by adjusting effective coefficients. However, it is still difficult to capture some local nonlinear phenomena in complex geometries.
{"title":"Synthetic iterative scheme for thermal applications in hotspot systems with large temperature variance","authors":"Chuang Zhang , Qin Lou , Hong Liang","doi":"10.1016/j.ijheatmasstransfer.2024.126374","DOIUrl":"10.1016/j.ijheatmasstransfer.2024.126374","url":null,"abstract":"<div><div>A synthetic iterative scheme is developed for thermal applications in hotspot systems with large temperature variance. Different from previous work with linearized equilibrium state and small temperature difference assumption, the phonon equilibrium distribution shows a nonlinear relationship with temperature and mean free path changes with the spatial temperature when the temperature difference of system is large, so that the same phonon mode may suffer different transport processes in different geometric regions. In order to efficiently capture nonlinear and multiscale thermal behaviors, the Newton method is used and a macroscopic iteration is introduced for preprocessing based on the iterative solutions of the stationary phonon BTE. Macroscopic and mesoscopic physical evolution processes are connected by the heat flux, which is no longer calculated by classical Fourier’s law but obtained by taking the moment of phonon distribution function. These two processes exchange information from different scales, such that the present scheme could efficiently deal with heat conduction problems from ballistic to diffusive regime. Numerical tests show that the present scheme could efficiently capture the multiscale heat conduction in hotspot systems with large temperature variances. In addition, a comparison is made between the solutions of the present scheme and effective Fourier’s law by several heat dissipations problems under different sizes or selective phonon excitation. Numerical results show that compared to the classical Fourier’s law, the results of the effective Fourier’s law could be closer to the BTE solutions by adjusting effective coefficients. However, it is still difficult to capture some local nonlinear phenomena in complex geometries.</div></div>","PeriodicalId":336,"journal":{"name":"International Journal of Heat and Mass Transfer","volume":"236 ","pages":"Article 126374"},"PeriodicalIF":5.0,"publicationDate":"2024-11-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142664082","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Dissolution and exsolution of gases are common in many engineering applications. Dissolution and exsolution occur across a gas-liquid interface when the equilibrium condition is disturbed. This study presents experimentally measured data on the exsolution and dissolution kinetics of ethane and bitumen (a viscous liquid) system across a temperature range of 80–140 °C and pressure differences of 0.69 and 0.35 MPa. Analytical models were adopted to estimate the exsolution and dissolution coefficients from the measured data for the ethane/bitumen system. The diffusivity values for the exsolution and dissolution processes were estimated to range from (2.65–10.48) × 10−8 m2/s and (0.73–6.18) × 10−9 m2/s, respectively, at a pressure difference of 0.69 MPa, and from (1.61–8.33) × 10−8 m2/s and (0.89–10.78) × 10−9 m2/s, respectively, at a pressure difference of 0.35 MPa. For both pressure differences, the exsolution kinetics were shown to be faster than dissolution in the ethane/bitumen system. This was also confirmed by higher activation energy for the exsolution process calculated using the Arrhenius equation. The results offer valuable insights into the kinetics of gas exsolution and dissolution, with applications in designing and optimizing processes where nonequilibrated gases and liquids are brought into contact.
{"title":"Kinetics of ethane exsolution and dissolution in bitumen","authors":"Shakerullah Turkman, Devjyoti Nath, Mahmood Abdi, Hassan Hassanzadeh","doi":"10.1016/j.ijheatmasstransfer.2024.126413","DOIUrl":"10.1016/j.ijheatmasstransfer.2024.126413","url":null,"abstract":"<div><div>Dissolution and exsolution of gases are common in many engineering applications. Dissolution and exsolution occur across a gas-liquid interface when the equilibrium condition is disturbed. This study presents experimentally measured data on the exsolution and dissolution kinetics of ethane and bitumen (a viscous liquid) system across a temperature range of 80–140 °C and pressure differences of 0.69 and 0.35 MPa. Analytical models were adopted to estimate the exsolution and dissolution coefficients from the measured data for the ethane/bitumen system. The diffusivity values for the exsolution and dissolution processes were estimated to range from (2.65–10.48) × 10<sup>−8</sup> m<sup>2</sup>/s and (0.73–6.18) × 10<sup>−9</sup> m<sup>2</sup>/s, respectively, at a pressure difference of 0.69 MPa, and from (1.61–8.33) × 10<sup>−8</sup> m<sup>2</sup>/s and (0.89–10.78) × 10<sup>−9</sup> m<sup>2</sup>/s, respectively, at a pressure difference of 0.35 MPa. For both pressure differences, the exsolution kinetics were shown to be faster than dissolution in the ethane/bitumen system. This was also confirmed by higher activation energy for the exsolution process calculated using the Arrhenius equation. The results offer valuable insights into the kinetics of gas exsolution and dissolution, with applications in designing and optimizing processes where nonequilibrated gases and liquids are brought into contact.</div></div>","PeriodicalId":336,"journal":{"name":"International Journal of Heat and Mass Transfer","volume":"236 ","pages":"Article 126413"},"PeriodicalIF":5.0,"publicationDate":"2024-11-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142664066","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-11-07DOI: 10.1016/j.ijheatmasstransfer.2024.126415
Hui Han , Liang Liu , Jiachen Cui , Yan Li , Zhengxiong Su , Yuxing Li , Yunfei Wang
Mixed alkanes are widely used as refrigerants in applications such as natural gas liquefaction, especially in the Floating Liquefied Natural Gas (FLNG) process. To elucidate the mechanisms underlying the weakening of phase transition in mixed refrigerants and to develop enhanced heat transfer methods, a pool boiling experimental setup is established in this study to investigate the boiling heat transfer characteristics of n-pentane/n-hexane mixtures on three different microstructure surfaces. By combining visual observation of bubble dynamics with analysis of the effects of composition conditions, micro-surface geometry, and wall heat flux conditions on the boiling heat transfer characteristics, it is revealed that the heat transfer coefficient (HTC) on the pyramid surface and the cylindrical surface, compared to the smooth surface, maximum increase by up to 345 % and 203 %, respectively. Compared with pure components, the mixture with a mass fraction of 0.5 n-pentane shows the greatest heat transfer deterioration. Microstructure surfaces significantly enhanced the HTC of the mixed refrigerants. Additionally, the microstructures activate more nucleation sites and higher bubble departure frequency. The guiding effect of the pyramid surface effectively decreases the possibility of bubble aggregation under high Eo and Ga numbers, thereby delaying the formation of mushroom bubbles. Therefore, the pyramid surface shows its advantages at different component ratios. The HTC correlations for pure and mixed refrigerants are developed. The predictions for pure and mixed refrigerants HTCs agree with most of the experimental data with a deviation of ±10 % and ±25 %, respectively.
{"title":"Experimental study of pool boiling characteristics for non-azeotropic mixtures n-pentane / n-hexane on microstructure surfaces","authors":"Hui Han , Liang Liu , Jiachen Cui , Yan Li , Zhengxiong Su , Yuxing Li , Yunfei Wang","doi":"10.1016/j.ijheatmasstransfer.2024.126415","DOIUrl":"10.1016/j.ijheatmasstransfer.2024.126415","url":null,"abstract":"<div><div>Mixed alkanes are widely used as refrigerants in applications such as natural gas liquefaction, especially in the Floating Liquefied Natural Gas (FLNG) process. To elucidate the mechanisms underlying the weakening of phase transition in mixed refrigerants and to develop enhanced heat transfer methods, a pool boiling experimental setup is established in this study to investigate the boiling heat transfer characteristics of n-pentane/n-hexane mixtures on three different microstructure surfaces. By combining visual observation of bubble dynamics with analysis of the effects of composition conditions, micro-surface geometry, and wall heat flux conditions on the boiling heat transfer characteristics, it is revealed that the heat transfer coefficient (HTC) on the pyramid surface and the cylindrical surface, compared to the smooth surface, maximum increase by up to 345 % and 203 %, respectively. Compared with pure components, the mixture with a mass fraction of 0.5 n-pentane shows the greatest heat transfer deterioration. Microstructure surfaces significantly enhanced the HTC of the mixed refrigerants. Additionally, the microstructures activate more nucleation sites and higher bubble departure frequency. The guiding effect of the pyramid surface effectively decreases the possibility of bubble aggregation under high <em>Eo</em> and <em>Ga</em> numbers, thereby delaying the formation of mushroom bubbles. Therefore, the pyramid surface shows its advantages at different component ratios. The HTC correlations for pure and mixed refrigerants are developed. The predictions for pure and mixed refrigerants HTCs agree with most of the experimental data with a deviation of ±10 % and ±25 %, respectively.</div></div>","PeriodicalId":336,"journal":{"name":"International Journal of Heat and Mass Transfer","volume":"236 ","pages":"Article 126415"},"PeriodicalIF":5.0,"publicationDate":"2024-11-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142664074","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-11-07DOI: 10.1016/j.ijheatmasstransfer.2024.126396
Kaiyan Jin , Jin Zhao , Guice Yao , Dichu Xu , Dongsheng Wen
Being a promising method for thermal protection system, transpiration cooling has received wide interest recently. Numerical simulation for transpiration cooling, however, has been limited due to the mis-matching between the pore-scale two-phase flow and external high-temperature aerothermodynamic environment, which induced by conventional decoupled or iterative one-way coupled simplification methods. In this work, a fully coupled continuum-scale and pore-scale model is established for transient transpiration cooling at the interface between boundary layer flow and porous medium through coupling Computational Fluid Dynamics (CFD) and Pore-Network Model (PNM), termed as the multiscale CFD-PNM coupled method. The coupled method allows to capture detailed displacement and phase change of two-phase flow at pore-scale, revealing the strong interaction of the water vapor with the external free flow within a high temperature boundary layer. After successfully validating the new coupled model by comparing with the Two-Phase Mixture Model (TPMM) solution, a number of cases mimicking the cooling at the interface of typical blunt bodies are simulated. The results show that the multiscale CFD-PNM coupled method can not only provide the thermal protection effect prediction, but also reveal many critical features that beyond the reach of continuum-scale studies. Some pore-scale phenomena that are important to the overall transpiration cooling effects are revealed, including transient phase change and composition variation of water vapor, imbibition and drainage of two-phase flow related to pore-scale capillary thresholds and applied boundary pressures, as well as the two-way mass transfer at the interface, such as the invasion of external hot air.
{"title":"A fully coupled multiscale phase-change model at the porous interface for transpiration cooling: coupling dynamics pore-scale networks to continuum-scale free flow","authors":"Kaiyan Jin , Jin Zhao , Guice Yao , Dichu Xu , Dongsheng Wen","doi":"10.1016/j.ijheatmasstransfer.2024.126396","DOIUrl":"10.1016/j.ijheatmasstransfer.2024.126396","url":null,"abstract":"<div><div>Being a promising method for thermal protection system, transpiration cooling has received wide interest recently. Numerical simulation for transpiration cooling, however, has been limited due to the mis-matching between the pore-scale two-phase flow and external high-temperature aerothermodynamic environment, which induced by conventional decoupled or iterative one-way coupled simplification methods. In this work, a fully coupled continuum-scale and pore-scale model is established for transient transpiration cooling at the interface between boundary layer flow and porous medium through coupling Computational Fluid Dynamics (CFD) and Pore-Network Model (PNM), termed as the multiscale CFD-PNM coupled method. The coupled method allows to capture detailed displacement and phase change of two-phase flow at pore-scale, revealing the strong interaction of the water vapor with the external free flow within a high temperature boundary layer. After successfully validating the new coupled model by comparing with the Two-Phase Mixture Model (TPMM) solution, a number of cases mimicking the cooling at the interface of typical blunt bodies are simulated. The results show that the multiscale CFD-PNM coupled method can not only provide the thermal protection effect prediction, but also reveal many critical features that beyond the reach of continuum-scale studies. Some pore-scale phenomena that are important to the overall transpiration cooling effects are revealed, including transient phase change and composition variation of water vapor, imbibition and drainage of two-phase flow related to pore-scale capillary thresholds and applied boundary pressures, as well as the two-way mass transfer at the interface, such as the invasion of external hot air.</div></div>","PeriodicalId":336,"journal":{"name":"International Journal of Heat and Mass Transfer","volume":"236 ","pages":"Article 126396"},"PeriodicalIF":5.0,"publicationDate":"2024-11-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142664076","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-11-06DOI: 10.1016/j.ijheatmasstransfer.2024.126380
Zheheng Liu, Pan Jia, Zheng Zhong
<div><div>In this paper, we study the Prandtl number effect on Rayleigh–Bénard convection systems modulated by an oscillatory bottom plate. Direct numerical simulations are carried out in a Prandtl number range of <span><math><mrow><mn>0</mn><mo>.</mo><mn>2</mn><mo>≤</mo><mi>P</mi><mi>r</mi><mo>≤</mo><mn>4</mn><mo>.</mo><mn>6</mn></mrow></math></span> and a fixed Rayleigh number of <span><math><mrow><mi>R</mi><mi>a</mi><mo>=</mo><mn>1</mn><msup><mrow><mn>0</mn></mrow><mrow><mn>8</mn></mrow></msup></mrow></math></span>. The initial drop and subsequent rise evolutionary behaviour of the heat transfer efficiency, characterised by the Nusselt number at the bottom plate <span><math><mrow><mi>N</mi><msub><mrow><mi>u</mi></mrow><mrow><mi>b</mi></mrow></msub></mrow></math></span>, with respect to the characteristic oscillatory velocity <span><math><msub><mrow><mi>V</mi></mrow><mrow><mi>o</mi><mi>s</mi><mi>c</mi></mrow></msub></math></span> is observed in the whole parameter space under consideration. If the oscillatory bottom plate does not induce boundary layer instabilities but thickens the boundary layer only, then one observes a heat transfer reduction, corresponding to a high <span><math><mrow><mi>P</mi><mi>r</mi></mrow></math></span> and a low <span><math><msub><mrow><mi>V</mi></mrow><mrow><mi>o</mi><mi>s</mi><mi>c</mi></mrow></msub></math></span>. If periodic boundary layer instabilities are triggered, then both heat transfer reduction and enhancement are possible. The reduction is generally seen when <span><math><mrow><mi>P</mi><mi>r</mi><mo>≤</mo><mn>1</mn><mo>.</mo><mn>0</mn></mrow></math></span>. Under such circumstance, the velocity boundary layer is embedded in the thermal boundary layer, if the instability induced by a certain <span><math><msub><mrow><mi>V</mi></mrow><mrow><mi>o</mi><mi>s</mi><mi>c</mi></mrow></msub></math></span> is not strong enough to compensate the heat resistance of the thermal boundary layer, one still observes a reduction in spite of the boundary layer instabilities. The enhancement is generally seen for a low <span><math><mrow><mi>P</mi><mi>r</mi></mrow></math></span> and/or a high <span><math><msub><mrow><mi>V</mi></mrow><mrow><mi>o</mi><mi>s</mi><mi>c</mi></mrow></msub></math></span>, in which case violent boundary layer instabilities will be triggered, leading to a sufficient emission of hot plumes. Furthermore, the critical velocity <span><math><msub><mrow><mover><mrow><mi>V</mi></mrow><mrow><mo>̄</mo></mrow></mover></mrow><mrow><mi>c</mi></mrow></msub></math></span>, characterising the boundary layer instability, is found to be increasing with <span><math><mrow><mi>P</mi><mi>r</mi></mrow></math></span> as <span><math><mrow><mover><mrow><msub><mrow><mi>V</mi></mrow><mrow><mi>c</mi></mrow></msub></mrow><mrow><mo>̄</mo></mrow></mover><mo>∼</mo><mi>P</mi><msup><mrow><mi>r</mi></mrow><mrow><mn>0</mn><mo>.</mo><mn>5</mn></mrow></msup></mrow></math></span>; and the Reynolds number at the equilibrium state evolves in a
{"title":"Prandtl number effect on heat transfer and flow structures in Rayleigh–Bénard convection modulated by an oscillatory bottom plate","authors":"Zheheng Liu, Pan Jia, Zheng Zhong","doi":"10.1016/j.ijheatmasstransfer.2024.126380","DOIUrl":"10.1016/j.ijheatmasstransfer.2024.126380","url":null,"abstract":"<div><div>In this paper, we study the Prandtl number effect on Rayleigh–Bénard convection systems modulated by an oscillatory bottom plate. Direct numerical simulations are carried out in a Prandtl number range of <span><math><mrow><mn>0</mn><mo>.</mo><mn>2</mn><mo>≤</mo><mi>P</mi><mi>r</mi><mo>≤</mo><mn>4</mn><mo>.</mo><mn>6</mn></mrow></math></span> and a fixed Rayleigh number of <span><math><mrow><mi>R</mi><mi>a</mi><mo>=</mo><mn>1</mn><msup><mrow><mn>0</mn></mrow><mrow><mn>8</mn></mrow></msup></mrow></math></span>. The initial drop and subsequent rise evolutionary behaviour of the heat transfer efficiency, characterised by the Nusselt number at the bottom plate <span><math><mrow><mi>N</mi><msub><mrow><mi>u</mi></mrow><mrow><mi>b</mi></mrow></msub></mrow></math></span>, with respect to the characteristic oscillatory velocity <span><math><msub><mrow><mi>V</mi></mrow><mrow><mi>o</mi><mi>s</mi><mi>c</mi></mrow></msub></math></span> is observed in the whole parameter space under consideration. If the oscillatory bottom plate does not induce boundary layer instabilities but thickens the boundary layer only, then one observes a heat transfer reduction, corresponding to a high <span><math><mrow><mi>P</mi><mi>r</mi></mrow></math></span> and a low <span><math><msub><mrow><mi>V</mi></mrow><mrow><mi>o</mi><mi>s</mi><mi>c</mi></mrow></msub></math></span>. If periodic boundary layer instabilities are triggered, then both heat transfer reduction and enhancement are possible. The reduction is generally seen when <span><math><mrow><mi>P</mi><mi>r</mi><mo>≤</mo><mn>1</mn><mo>.</mo><mn>0</mn></mrow></math></span>. Under such circumstance, the velocity boundary layer is embedded in the thermal boundary layer, if the instability induced by a certain <span><math><msub><mrow><mi>V</mi></mrow><mrow><mi>o</mi><mi>s</mi><mi>c</mi></mrow></msub></math></span> is not strong enough to compensate the heat resistance of the thermal boundary layer, one still observes a reduction in spite of the boundary layer instabilities. The enhancement is generally seen for a low <span><math><mrow><mi>P</mi><mi>r</mi></mrow></math></span> and/or a high <span><math><msub><mrow><mi>V</mi></mrow><mrow><mi>o</mi><mi>s</mi><mi>c</mi></mrow></msub></math></span>, in which case violent boundary layer instabilities will be triggered, leading to a sufficient emission of hot plumes. Furthermore, the critical velocity <span><math><msub><mrow><mover><mrow><mi>V</mi></mrow><mrow><mo>̄</mo></mrow></mover></mrow><mrow><mi>c</mi></mrow></msub></math></span>, characterising the boundary layer instability, is found to be increasing with <span><math><mrow><mi>P</mi><mi>r</mi></mrow></math></span> as <span><math><mrow><mover><mrow><msub><mrow><mi>V</mi></mrow><mrow><mi>c</mi></mrow></msub></mrow><mrow><mo>̄</mo></mrow></mover><mo>∼</mo><mi>P</mi><msup><mrow><mi>r</mi></mrow><mrow><mn>0</mn><mo>.</mo><mn>5</mn></mrow></msup></mrow></math></span>; and the Reynolds number at the equilibrium state evolves in a","PeriodicalId":336,"journal":{"name":"International Journal of Heat and Mass Transfer","volume":"236 ","pages":"Article 126380"},"PeriodicalIF":5.0,"publicationDate":"2024-11-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142664072","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-11-06DOI: 10.1016/j.ijheatmasstransfer.2024.126379
Shuran Ye , Jianlin Huang , Zhen Zhang , Yiwei Wang , Chenguang Huang
Thermal convection is frequently observed in nature and widely used in industry, making it an important subject for many experimental and numerical studies. A well-researched paradigm for comprehending thermal convection is the system of thermally driven square cavities, one of the classical problems of natural convection. With the development of computational resources, methods for solving natural convection problems using deep learning techniques have flourished. In this study, a Physics-informed neural networks (PINNs) method is used to solve the thermal convection problem, with neural networks trained to simulate the velocity and temperature fields of natural convection at various Ra numbers ranging from to . Furthermore, a parameter-input PINNs model is constructed to further develop this approach. This framework has the advantage of concurrently and rapidly predicting the flow field outcomes for any Ra number scenario in the specified range. Additionally, the flow field outcomes of the parameter-input PINNs model are statistically analyzed to demonstrate the model’s generalization performance.
热对流在自然界中观察频繁，在工业中应用广泛，因此成为许多实验和数值研究的重要课题。热对流的一个研究范例是热驱动方形空腔系统，它是自然对流的经典问题之一。随着计算资源的发展，利用深度学习技术解决自然对流问题的方法蓬勃发展。本研究采用物理信息神经网络（PINNs）方法求解热对流问题，训练神经网络模拟从 Ra=103 到 Ra=108 的不同 Ra 数下自然对流的速度场和温度场。此外，还构建了一个参数输入 PINNs 模型，以进一步发展这种方法。该框架的优势在于可同时快速预测指定范围内任何 Ra 数情况下的流场结果。此外，还对参数输入 PINNs 模型的流场结果进行了统计分析，以证明该模型的泛化性能。
{"title":"Direct numerical simulation of natural convection based on parameter-input physics-informed neural networks","authors":"Shuran Ye , Jianlin Huang , Zhen Zhang , Yiwei Wang , Chenguang Huang","doi":"10.1016/j.ijheatmasstransfer.2024.126379","DOIUrl":"10.1016/j.ijheatmasstransfer.2024.126379","url":null,"abstract":"<div><div>Thermal convection is frequently observed in nature and widely used in industry, making it an important subject for many experimental and numerical studies. A well-researched paradigm for comprehending thermal convection is the system of thermally driven square cavities, one of the classical problems of natural convection. With the development of computational resources, methods for solving natural convection problems using deep learning techniques have flourished. In this study, a Physics-informed neural networks (PINNs) method is used to solve the thermal convection problem, with neural networks trained to simulate the velocity and temperature fields of natural convection at various Ra numbers ranging from <span><math><mrow><mi>R</mi><mi>a</mi><mo>=</mo><msup><mrow><mn>10</mn></mrow><mrow><mn>3</mn></mrow></msup></mrow></math></span> to <span><math><mrow><mi>R</mi><mi>a</mi><mo>=</mo><msup><mrow><mn>10</mn></mrow><mrow><mn>8</mn></mrow></msup></mrow></math></span>. Furthermore, a parameter-input PINNs model is constructed to further develop this approach. This framework has the advantage of concurrently and rapidly predicting the flow field outcomes for any Ra number scenario in the specified range. Additionally, the flow field outcomes of the parameter-input PINNs model are statistically analyzed to demonstrate the model’s generalization performance.</div></div>","PeriodicalId":336,"journal":{"name":"International Journal of Heat and Mass Transfer","volume":"236 ","pages":"Article 126379"},"PeriodicalIF":5.0,"publicationDate":"2024-11-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142664071","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-11-06DOI: 10.1016/j.ijheatmasstransfer.2024.126365
Guilong Peng , Senshan Sun , Zhenwei Xu , Juxin Du , Yangjun Qin , Swellam W. Sharshir , A.W. Kandeal , A.E. Kabeel , Nuo Yang
Machine learning's application in solar-thermal desalination is limited by data shortage and inconsistent analysis. This study develops an optimized dataset collection and analysis process for the representative solar still. By ultra-hydrophilic treatment on the condensation cover, the dataset collection process reduces the collection time by 83.3 %. Over 1,000 datasets are collected, which is nearly one order of magnitude larger than up-to-date works. Then, a new interdisciplinary process flow is proposed. Some meaningful results are obtained that were not addressed by previous studies. It is found that Radom Forest might be a better choice for datasets larger than 1,000 due to both high accuracy and fast speed. Besides, the dataset range affects the quantified importance (weighted value) of factors significantly, with up to a 115 % increment. Moreover, the results show that machine learning has a high accuracy on the extrapolation prediction of productivity, where the minimum mean relative prediction error is just around 4 %. The results of this work not only show the necessity of the dataset characteristics’ effect but also provide a standard process for studying solar-thermal desalination by machine learning, which would pave the way for interdisciplinary study.
{"title":"The effect of dataset size and the process of big data mining for investigating solar-thermal desalination by using machine learning","authors":"Guilong Peng , Senshan Sun , Zhenwei Xu , Juxin Du , Yangjun Qin , Swellam W. Sharshir , A.W. Kandeal , A.E. Kabeel , Nuo Yang","doi":"10.1016/j.ijheatmasstransfer.2024.126365","DOIUrl":"10.1016/j.ijheatmasstransfer.2024.126365","url":null,"abstract":"<div><div>Machine learning's application in solar-thermal desalination is limited by data shortage and inconsistent analysis. This study develops an optimized dataset collection and analysis process for the representative solar still. By ultra-hydrophilic treatment on the condensation cover, the dataset collection process reduces the collection time by 83.3 %. Over 1,000 datasets are collected, which is nearly one order of magnitude larger than up-to-date works. Then, a new interdisciplinary process flow is proposed. Some meaningful results are obtained that were not addressed by previous studies. It is found that Radom Forest might be a better choice for datasets larger than 1,000 due to both high accuracy and fast speed. Besides, the dataset range affects the quantified importance (weighted value) of factors significantly, with up to a 115 % increment. Moreover, the results show that machine learning has a high accuracy on the extrapolation prediction of productivity, where the minimum mean relative prediction error is just around 4 %. The results of this work not only show the necessity of the dataset characteristics’ effect but also provide a standard process for studying solar-thermal desalination by machine learning, which would pave the way for interdisciplinary study.</div></div>","PeriodicalId":336,"journal":{"name":"International Journal of Heat and Mass Transfer","volume":"236 ","pages":"Article 126365"},"PeriodicalIF":5.0,"publicationDate":"2024-11-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142664070","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-11-06DOI: 10.1016/j.ijheatmasstransfer.2024.126401
Yiyang Luo, Nan Gui, Xingtuan Yang, Shengyao Jiang, Zhiyong Liu
A novel model for inter-particle contact thermal resistance based on analytical solutions is proposed. By applying the concept of heat flux weighted temperature difference in thermal resistance modeling for the first time, this model offers greater physical significance than traditional thermal resistance models. It effectively describes the dissipation in the heat transfer process and the influence of particle radius on thermal resistance, making it a generalized thermal resistance model suitable for multi-dimensional systems. The impact of applying different levels of uniform heat flux boundary conditions on thermal resistance is analyzed from the perspective of energy dissipation, revealing that a more uniform heat flux input results in lower thermal resistance. The effects of contact radius and particle size on the dimensionless generalized thermal resistance of inter-particle contact were studied, showing that the dimensionless resistance increases with larger particle contact radius and smaller particle size. Using the thermal discrete element method, the thermal resistance model with uniform heat flux density boundary conditions was applied to calculate the effective thermal conductivity of the pebble bed. Considering the distribution of contact radius, differences in effective thermal conductivity at various heights of the pebble bed due to different contact radii were examined and compared with the traditional fixed-coefficient contact resistance model. It was found that the difference between the two models decreases as the contact radius decreases. Finally, multiple sets of fixed contact radii were established under three different particle sizes, revealing that as the contact radius increases, the deviation between the new generalized resistance model and the traditional fixed-coefficient model rises from 8.18 % to 14.64 % for different particle radii.
{"title":"Analytical generalized thermal resistance model for conductive heat transfer in pebble beds based on heat flux weighted temperature difference","authors":"Yiyang Luo, Nan Gui, Xingtuan Yang, Shengyao Jiang, Zhiyong Liu","doi":"10.1016/j.ijheatmasstransfer.2024.126401","DOIUrl":"10.1016/j.ijheatmasstransfer.2024.126401","url":null,"abstract":"<div><div>A novel model for inter-particle contact thermal resistance based on analytical solutions is proposed. By applying the concept of heat flux weighted temperature difference in thermal resistance modeling for the first time, this model offers greater physical significance than traditional thermal resistance models. It effectively describes the dissipation in the heat transfer process and the influence of particle radius on thermal resistance, making it a generalized thermal resistance model suitable for multi-dimensional systems. The impact of applying different levels of uniform heat flux boundary conditions on thermal resistance is analyzed from the perspective of energy dissipation, revealing that a more uniform heat flux input results in lower thermal resistance. The effects of contact radius and particle size on the dimensionless generalized thermal resistance of inter-particle contact were studied, showing that the dimensionless resistance increases with larger particle contact radius and smaller particle size. Using the thermal discrete element method, the thermal resistance model with uniform heat flux density boundary conditions was applied to calculate the effective thermal conductivity of the pebble bed. Considering the distribution of contact radius, differences in effective thermal conductivity at various heights of the pebble bed due to different contact radii were examined and compared with the traditional fixed-coefficient contact resistance model. It was found that the difference between the two models decreases as the contact radius decreases. Finally, multiple sets of fixed contact radii were established under three different particle sizes, revealing that as the contact radius increases, the deviation between the new generalized resistance model and the traditional fixed-coefficient model rises from 8.18 % to 14.64 % for different particle radii.</div></div>","PeriodicalId":336,"journal":{"name":"International Journal of Heat and Mass Transfer","volume":"236 ","pages":"Article 126401"},"PeriodicalIF":5.0,"publicationDate":"2024-11-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142664069","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-11-05DOI: 10.1016/j.ijheatmasstransfer.2024.126373
Gaoyuan Wang , Zhan-Chao Hu
Heat transfer at supercritical pressure (SCP) transiting from liquid-like (LL) to gas-like (GL) state is a compressible flow featured by a nonuniform density field. Pulsating flow has been confirmed as an effective approach to enhance heat transfer. However, pulsating flow introduces pressure waves, the interaction of which with the nonuniform density field remains an open question. This paper numerically studies a fundamental interaction problem to bridge the research gap. The physical model is a round GL fluid surrounded by LL fluid, forming a circular pseudo-interface for at an SCP of 7.6 MPa. A compression wave is introduced into the domain by the sudden moving of an imaginary piston at 1 m/s. The compression wave induces a complex wave system after interacting with the pseudo-interface. The nonuniform acceleration by the compression wave results in a higher velocity in the GL region than in the LL one. Due to the Kelvin–Helmholtz instability, decomposition and mixing of the GL region then take place. Overall, the uniformity of density and temperature is improved on the microsecond timescale, manifesting that heat transfer is enhanced. This paper reveals nonuniform acceleration and Kelvin–Helmholtz instability as fundamental mechanisms for enhancing heat transfer at supercritical pressures via pulsating flow.
{"title":"Fundamental insights into enhancing supercritical heat transfer via pulsating flow: Interaction between wave and pseudo-interface","authors":"Gaoyuan Wang , Zhan-Chao Hu","doi":"10.1016/j.ijheatmasstransfer.2024.126373","DOIUrl":"10.1016/j.ijheatmasstransfer.2024.126373","url":null,"abstract":"<div><div>Heat transfer at supercritical pressure (SCP) transiting from liquid-like (LL) to gas-like (GL) state is a compressible flow featured by a nonuniform density field. Pulsating flow has been confirmed as an effective approach to enhance heat transfer. However, pulsating flow introduces pressure waves, the interaction of which with the nonuniform density field remains an open question. This paper numerically studies a fundamental interaction problem to bridge the research gap. The physical model is a round GL fluid surrounded by LL fluid, forming a circular pseudo-interface for <span><math><msub><mrow><mi>CO</mi></mrow><mrow><mn>2</mn></mrow></msub></math></span> at an SCP of 7.6 MPa. A compression wave is introduced into the domain by the sudden moving of an imaginary piston at 1 m/s. The compression wave induces a complex wave system after interacting with the pseudo-interface. The nonuniform acceleration by the compression wave results in a higher velocity in the GL region than in the LL one. Due to the Kelvin–Helmholtz instability, decomposition and mixing of the GL region then take place. Overall, the uniformity of density and temperature is improved on the microsecond timescale, manifesting that heat transfer is enhanced. This paper reveals nonuniform acceleration and Kelvin–Helmholtz instability as fundamental mechanisms for enhancing heat transfer at supercritical pressures via pulsating flow.</div></div>","PeriodicalId":336,"journal":{"name":"International Journal of Heat and Mass Transfer","volume":"236 ","pages":"Article 126373"},"PeriodicalIF":5.0,"publicationDate":"2024-11-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142587452","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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