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Pattern Formations in heat convection Problems

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Chinese Annals of Mathematics,Series B 2009年第6期30卷 769-784页

作者： Takaaki NISHIDA Yoshiaki TERAMOTO Department of Mathematics Waseda UniversityTokyo 169-8555Japan Department of Mathematics and Physics Setsunan UniversityNeyagawa 572-8508Japan

After Bénard＇s experiment in 1900, Rayleigh formulated heat convection problems by the Oberbeck-Boussinesq approximation in the horizontal strip domain in 1916. The pattern formations have been investigated by the bifurcation theory, weakly nonlinear theories and computational approaches. The boundary conditions for the velocity on the upper and lower boundaries are usually assumed as stress-free or no-slip. In the first part of this paper, some bifurcation pictures for the case of the stress-free on the upper boundary and the no-slip on the lower boundary are obtained. In the second part of this paper, the bifurcation pictures for the case of the stress-free on both boundaries by a computer assisted proof are verified. At last., Bénard-Marangoni heat convections for the ease of the free surface of the upper boundary are considered.

关键词： Oberbeck-Boussinesq equation heat convection Pattern formation Computer assisted proof

Importance of Marangoni convection in Laser Full—Penetration Welding

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Chinese Physics Letters 2002年第6期19卷 788-790页

作者：叶晓虎陈熙 DepartmentofEngineeringMechanics TsinghuaUniversityBeijing100084

We study the effects of welding speed, Marangoni convection and natural convection on heat transfer and melt flow in a laser full-penetration welding using a three-dimensional modelling approach. The computed results demonstrate the importance of considering Marangoni convection. The predicted weld pool profile is favourably compared with experimental observation

关键词： heat convection

WAVELET ANALYSIS OF MULTIFRACTAL AND ITS APPLICATION TO PROCESSING TEMPERATURE DATA IN RAYLEIGH-BENARD convection

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Journal of Hydrodynamics 2001年第4期13卷 34-41页

作者： Fu, Qiang Xia, Ke-Qing Div. of Appl. Mech. Inst. of Sci. Univ. of Sci. and Technol. of PLA Nanjing 211101 China

Wavelet transform was firstly used to analyze te singularity of a given signal, and then with the method of wavelet transform modulus maximum(WTMM), the characters of fractal set of triadic Cantor was studied. The results show that one can, not only determine the position of singular of signal, but also estimate the Holder exponent h which describes the strength of singularity and other parameters, such as D(h) and τ(q) correctly. Finally, after applying this method to process temperature data in the Rayleigh-Benard convection further, we found that the multifractal hierarchical and multi-scale structure underlying this flow could be entirely revealed from the parameters h, D(h) and τ(q), and the obtained results agree well with the ones determined from the viewpoint of fractal measures.

关键词： heat convection Wavelet transforms

Simulation of gas-solids heat transfer in cyclone pyrolyzer using CFD-DEM model

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Particuology 2024年第2期85卷 155-166页

作者： Nan Zhang Xueer Pan Jingxuan Yang Qian Liu Wenhao Lian Xiao Du Zhonglin Zhang Xiaogang Hao Guoqing Guan College of Chemical Engineering and Technology Taiyuan University of TechnologyTaiyuan030024China School of Chemistry and Chemical Engineering North University of ChinaTaiyuan030051China Shanxi Jinke Technology Service Company Limited Taiyuan030000China Labraory of Eey onveron Engineerng Institute f Rgional Innvation(RI)Hosaki Univerty3-BunkychoHiroak036-8561Japan

Fast heat transfer in the pyrolyzer can increase the yield of pyrolysis gas and tar,and improve the quality of *** with the downer pyrolyzer,the cyclone pyrolyzer can simultaneously achieve high solids holdup and violent turbulence,and correspondingly faster heat *** this work,the heat transfer behavior in the cyclone pyrolyzer is specifically studied using the computational fluid dynamics-discrete element *** simulation results reveal that the gas-solids heat convection contributes mainly to the heat transfer process,and the heat radiation and conduction are relatively small and almost negligible,*** with the downer pyrolyzer under the same operating conditions,the heating rate is significantly increased in the cyclone *** analyzing the flow characteristics in the cyclone pyrolyzer,it is found that the region of high convective heat transfer rate coincides with that of natural cyclone ***,the final coal temperature increases with the increase of gas velocity and exists a maximum *** results can offer some qualitative understanding of the heat transfer behavior in the cyclone pyrolyzer.

关键词： Cyclone pyrolyzer Rapidly heating heat convection Natural cyclone length CFD-DEM

A multi-objective study on the constructal design of non-uniform heat generating disc cooled by radial-and dendritic-pattern cooling channels

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Science China(Technological Sciences) 2021年第4期64卷 729-744页

作者： CHEN Chen YOU Jiang FENG HuiJun CHEN LinGen Institute of Thermal Science and Power Engineering Wuhan Institute of TechnologyWuhan 430205China School of Mechanical&Electrical Engineering Wuhan Institute of TechnologyWuhan 430205China §School of Optical Information and Energy Engineering Wuhan Institute of TechnologyWuhan 430205China College of Power Engineering Naval University of EngineeringWuhan 430033China

A three-dimensional disc model with non-uniform heat generating is built.A series of cooling channels are inserted to cool this disc which is strewn in a hierarchical *** reveal thermal and flow characteristics,a composite objective function comprised of the maximum temperature difference(MTD)and pumping power is *** deployment pattern of cooling channels contains two cases,i.e.,the radial-pattern and *** capitalizing on constructal design method together with finite element method,the diameter of radial-pattern cooling channels is optimized in the first ***,the diameter,angle coefficient and length coefficient of dendritic-pattern cooling channels are three degrees-of-freedom to be stepwise optimized at different heat generating ***,NSGA-II algorithm is introduced into the multiobjective *** obtaining its Pareto optimal solution set,Topsis method is invoked to yield the optimal solutions under given weighted *** heat generation over the entire body and the volume ratio of cooling channels operate as the primary *** on these premises,constructal design will be stepwise performed by varying three *** obtained results state that more heating components or devices should be installed as close to the cooling water inlet as *** can further reduce MTD at the same cost of pumping power,thereby improve thermal and flow performance and prolong the lifespan of *** optimized with two degrees-of-freedom,the MTD is reduced by 18.6%compared with the counterpart obtained from single degree-of-freedom optimization,while the pumping power is increased by 59.8%.As optimized with three degrees-of-freedom,the MTD is decreased by 6.2%compared with the counterpart from two degrees-of-freedom optimization,while the pumping power is increased by 3.0%.It is manifest that when two sub-objectives form a composite objective,the performance improvement of one sub-

关键词： constructal law non-uniform heat generating disc heat convection cooling channels multi-objective optimization generalized thermodynamic optimization

The silicothermic reduction of magnesium in flowing argon and numerical simulation of novel technology

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Journal of Magnesium and Alloys 2020年第3期8卷 752-760页

作者： Yusi Che Chao Zhang Jianxun Song Xiaojia Shang Xiping Chen Jilin He Henan Province Industrial Technology Research Institute of Resources and Materials Zhengzhou UniversityZhengzhou 450001China School of Material Science and Engineering Zhengzhou UniversityZhengzhou 450001China School of Energy and Environment Anhui University'of TechnologyMa'anshan 243002China

The silicothermic reduction of magnesium was investigated by the non-isothermal thermoanalysis in flowing argon,while the traditional investigations of silicothermic process for magnesium reduction were carried out under vacuum ***,the thermal gravimetric(TG)and derivative thermogravimetric(DTG)characteristic of briquettes prepared with calcined dolomite,ferrosilicon and fluorite were characterized by the thermogravimetric analyzer(TGA)at different heating *** intrinsic chemical kinetic mechanism was identified as a formal chemical reaction with the Nth order type which showed apparent activation energy E and reaction order n were 290.168 kJ mol^(-1) and 1.076,***,a novel technique of magnesium production without vacuum was put forward and a three-dimensional unsteady numerical model incorporating the chemical reaction,radiation,heat conduction and heat convection was established and simulated,which was verified by Pidgeon process and novel tech no *** nu merical results showed that the cycle time of the novel technique could be reduced when the argon temperature was higher than 1343 K and the argon entrance velocity was over 0.05 m s^(-1).And the effect of the argon temperature on reduction degree was much larger than that of entrance velocity.

关键词： Kinetics mechanism heat convection Silicothermic reduction Numerical simulation

Numerical simulation on thermal accumulation of cemented tailings backfill

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Journal of Central South University 2021年第7期28卷 2221-2237页

作者： ZHANG Xiao-yan ZHAO Min LIU Lang HUAN Chao SONG KI-IL XU Mu-yan WEN De Energy School Xi’an University of Science and TechnologyXi’an 710054China Key Laboratory of Western Mines and Hazards Prevention Ministry of Education of ChinaXi’an 710054China Department of Civil Engineering Inha UniversityIncheon 402-751Korea

Based on the collaborative exploitation of deep mineral resources and geothermal resources, the thermal accumulation process of cemented tailings backfill(CTB) was studied by numerical simulation. The effects of thermal accumulation time, slurry proportions and temperature conditions on the thermal accumulation of backfill are analyzed, the influence of the heat conduction between backfill and surrounding rock, the heat convection between backfill and airflow on thermal accumulation were compared simultaneously. The results show that the total thermal accumulation capacity increases by approximately 85% within 10-90 d. The influence of surrounding rock temperature and initial temperature on total thermal accumulation capacity is more significant and it is approximately 2 times of the influence of slurry proportions under the conditions of this study. It is clear that the rise of surrounding rock temperature and the decrease of initial temperature can improve the thermal accumulation capacity more effectively. Moreover, the heat conduction accounts for a considerable proportion in the process of thermal accumulation, the average heat conduction capacity is approximately 25 times of the heat convection capacity. This study can provide the theoretical basis and application reference for the optimization of thermal accumulation process of CTB in the exploitation of geothermal resources.

关键词： cemented tailings backfill thermal accumulation heat conduction heat convection total thermal accumulation capacity