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Characterization of size effect of natural convection in melting process of phase change material in square cavity

Chinese Physics B 2021年第10期30卷 400-409页

作者： Shi-Hao Cao Hui Wang College of Civil Engineering Henan University of TechnologyZhengzhou 450001China School of Civil Engineering and Architecture Hainan UniversityHaikou 570228China

The accelerating effect of natural convection on the melting of phase change material(PCM)has been extensively ***,such an influence is directly dependent on the size and shape of domain in which phase change happens,and how to quantitatively describe such an influence is still *** the other hand,the simulation of natural convection process is considerably difficult,involving complex fluid flow in a region changing with time,and is typically not operable in *** overcome these obstacles,the present study aims to quantitatively investigate the size effect of natural convection in the melting process of PCM paraffin filled in a square latent heat storage system through experiment and simulation,and ultimately a correlation equation to represent its contribution is ***,the paraffin melting experiment is conducted to validate the two-dimensional finite element model based on the enthalpy ***,a comprehensive investigation is performed numerically for various domain *** results show that the melting behavior of paraffin is dominated by the thermal *** the melting time exceeds 50 s,a whirlpoor flow caused by natural convection appears in the upper liquid phase region close to the heating wall,and then its influencing range gradually increases to accelerate the melting of ***,its intensity gradually decreases as the distance between the melting front and the heating wall ***,it is found that the correlation between the total melting time and the domain size approximately exhibits a power *** the domain size is less than 2 mm,the accelerating effect of natural convection becomes very weak and can be ignored in ***,in order to simplify the complex calculation of natural convection,the equivalent thermal conductivity concept is proposed to include the contribution of natural convection to the total melting time,and an empirical correlation is given fo

关键词： phase change material natural convection size effect equivalent thermal conductivity

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Numerical study on the effective thermal conductivity and thermal tortuosity of porous media with different morphologies

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Science China(Technological Sciences) 2024年第6期67卷 1685-1694页

作者： DU Shen LI Dong LI Meng-Jie HE Ya-Ling Key Laboratory of Thermo-Fluid Science and Engineering of Ministry of Education School of Energy and Power EngineeringXi’an Jiaotong UniversityXi’an710049China

Effective thermal conductivity and thermal tortuosity are crucial parameters for evaluating the effectiveness of heat conduction within porous *** direct pore-scale numerical simulation method is applied to investigate the heat conduction processes inside porous structures with different *** thermal conduction performances of idealized porous structures are directly compared with real foams across a wide range of *** foam structures are reconstructed using X-ray computed tomography and image processing techniques,while Kelvin and Weaire-Phelan structures are generated through periodic unit cell *** detailed temperature fields inside the porous structures are determined by solving the heat conduction equation at the pore *** results present that the equivalent thermal conductivity of Kelvin and Weaire-Phelan structures is similar to and greater than that of the real foam structure with the same strut *** thermal tortuosity of real foam structure is relatively larger and the heat conduction path becomes straighter by adopting the anisotropic *** thermal tortuosity of the fluid channels for Kelvin,Weaire-Phelan,and real foam structures is close to *** thermal conductivity of porous structures with heat transfer fluid increases as the thermal conductivity ratio of fluid to solid becomes larger.A small porosity of porous media leads to a larger equivalent thermal conductivity due to the dominant contribution of porous skeleton in the heat conduction *** derived from parallel and series models,as well as the Maxwell-Eucken models,provide decent predictions of effective thermal conductivity,with an average error of less than 8%in the entire range of thermal conductivity ratio.

关键词： volumetric solar receiver porous morphology direct pore-scale simulation equivalent thermal conductivity thermal tortuosity empirical correlation

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thermal Resistance Simulation for CoF Packages

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Tsinghua Science and Technology 2015年第3期20卷 277-284页

作者： Chuan Chen Qian Wang Xiaotian Meng Lin Tan Jian Wang Chengqiang Cui Jian Cai the Institute of Microelectronics Tsinghua University Beijing 100084 China AKM Electronics Technology (Suzhou) Company Ltd. Suzhou 215000 China the Institute of Microelectronics and Tsinghua National Laboratory for Information Science and Technology Tsinghua University. Beijing 100084 China

Chip-on-Film （CoF） is a packaging technology that mounts Integrated Circuits （IC） chips directly on a flexible substrate surface. As both power and the number of pins in such packages increase, thermal conditions become more important. In this paper, the thermal resistance of CoF packages is studied using Ansys software to perform finite-element analysis. Because of circuit complexity, two equivalent methods-a length-weighted method and an image-recognition method--are proposed in place of an accurate model to get equivalent thermal conductivity of CoF package devices. In our experiments, the simulated value of thermal resistance based on the length-weighted method was 1.653 K/W, and the value based on the image-recognition method was 1.911 K/W. The real thermal resistance value of the CoF package device is 1.812 K/W. So the error between the real value measured by a tester and the simulated value based on the length-weighted method is 8.8%, and the error between the real value and the simulated value based on the image-recognition method is 5.5%. Hence, both methods can provide effective simulation results, and the image-recognition method is more accurate. In addition, we optimized the CoF package structure. From the simulation results, the drop in thermal resistance after the optimization is obvious.

关键词： Chip-on-Film (CoF) finite element analysis equivalent thermal conductivity

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Numerical simulation of a buried hot crude oil pipeline during shutdown

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Petroleum Science 2010年第1期7卷 73-82页

作者： Xu Cheng Yu Bo Zhang Zhengwei Zhang Jinjun Wei Jinjia Sun Shuyu Beijing Key Laboratory of Urban Oil and Gas Distribution Technology China University of Petroleum Beijing 102249China Zhejiang Department Preparatory Team PetroChina West East Gas Pipeline Company Hangzhou Zhejiang 310000 China State Key Laboratory of Multiphase Flow in Power Engineering Xi＇an Jiaotong University Xi＇an Shaanxi 710049 China Department of Mathematical Sciences Clemson University Clemson SC 29634-0975 USA

In this paper a mathematical model is built for a buried hot crude oil pipeline during shutdown, and an unstructured grid and polar coordinate grid are respectively applied to generating grids for the soil region and the three layers in the pipe （wax layer, pipe wall, and corrosion-inhibiting coating）. The governing equations are discretized using the finite volume method. The variations in temperatures of static oil and soil were investigated during pipeline shutdown in both summer and winter, in which some important parameters of the soil and crude oils of a Northeast pipeline are employed.

关键词： Moving boundary stagnation point equivalent thermal conductivity thermal influence region unstructured grid

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