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多孔围护结构封闭腔体内部传热传质数值研究

发布时间:2018-04-09 04:24

  本文选题:多孔围护结构 切入点:自然对流 出处:《辽宁工程技术大学》2015年硕士论文


【摘要】:开展多孔围护结构封闭腔体内部传热传质研究,认识其自然对流传热传质的行为、基本特性规律,对包含外部围护结构下的建筑室内温度控制、微环境的创造以及建筑节能新技术的发展有巨大的指导意义。本文将理论分析与数值模拟的方法应用于多孔围护结构封闭腔体内部自然对流与传热传质的研究中;对多孔结构的厚度及位置、孔隙率、瑞利数、路易斯数、浮升比数以及研究对象的高宽比等影响因素等进行数值求解得到腔内流场分布、温度及浓度分布;进一步进行理论分析得出:自然对流传热传质行为、基本特性规律。首先,采用理论和数值方法研究二维多孔围护结构封闭腔体内部的传热传质问题,将数值计算的平均努赛尔数Nu与其基准解进行对比,得到其最大误差为0.81%,验证了数值方法的正确性。其次,利用一区域模型研究上述影响因素不同时模型内部的流动结构、传热和传质效果。得出:多孔结构厚度增加会削弱腔体内流体传热传质效果,并且多孔结构所在位置不同削弱程度不同,当多孔结构在腔体中间区域时蓄热效果最好;孔隙率ε增大,Nu与Sh减小,对流换热的强度与传质强度减弱;当Le1时,温度对传热传质的影响较剧烈,当Le1时,浓度对传热传质影响较剧烈,当Le=1,两种影响相当,Nu=Sh;在浮升比N=-1时,流体流动强度及传热传质强度最微弱,N-1,腔体内流动为逆时针方向,质浮升力占主导地位,N>-1,腔体内流动为顺时针方向,热浮升力占主导地位;Nu和Sh随着高宽比增大而增大,传热和传质的效果越来越明显;左侧垂直壁面为线性温度边界条件时,随着多孔结构的厚度的增大,腔内由对流为主的换热方式向以导热为主的换热方式过渡。局部高温壁面下,对于腔体内局部高温壁面不同位置处的传热传质情况,Nu和Sh先增大后减小,且B=0.6时Nu和Sh最大,而B的增加流动强度是增加的。再次,研究多孔围护结构封闭腔体模型应用在多孔介质接触型集热墙体传热分析中,得出:多孔结构起到有效的蓄热效果;对比材料中,石英岩蓄热效果最好;材料的热工性能对蓄热效果有直接影响。
[Abstract]:The study of heat and mass transfer inside the enclosed cavity of porous enclosure is carried out to understand the behavior of natural convection heat and mass transfer, the basic characteristic law, and to control the indoor temperature of the building including the external enclosure structure.The creation of micro-environment and the development of new building energy-saving technology have great guiding significance.In this paper, the theoretical analysis and numerical simulation are applied to the study of natural convection and heat and mass transfer in a closed cavity of a porous enclosure, and the thickness and location of porous structure, porosity, Rayleigh number, Lewis number,The flow field distribution, temperature and concentration distribution in the cavity are obtained by numerical solution of the factors such as the floating ratio and the aspect ratio of the studied object, and the theoretical analysis shows that the natural convection heat and mass transfer behavior and the basic characteristics of the flow field are obtained.Firstly, the heat and mass transfer problem in a closed cavity of a two-dimensional porous enclosure structure is studied by using theory and numerical method, and the numerical average Nussel number Nu is compared with its datum solution.The maximum error is 0. 81, which verifies the correctness of the numerical method.Secondly, the flow structure, heat transfer and mass transfer effect of the above factors are studied by using a regional model.It is concluded that the effect of heat and mass transfer of fluid in the cavity will be weakened by increasing the thickness of porous structure, and the effect of heat storage is best when the porous structure is located in the middle region of the cavity, and the porosity 蔚 increases and decreases with the decrease of Nu and Sh.The intensity and mass transfer intensity of convection heat transfer is weakened, the effect of temperature on heat and mass transfer is more intense when Le1, concentration on heat and mass transfer is more intense when Le1, and the two kinds of effects are quite different when Le1 is 1, and when the ratio of floating rise is N- 1, the effect of temperature on heat and mass transfer is more severe.The fluid flow intensity and heat and mass transfer intensity are the weakest, the flow in the cavity is counterclockwise, the mass floating lift is dominant, the flow in the cavity is clockwise, and the thermal floating lift is dominant, Nu and Sh increase with the increase of the ratio of height to width.The effect of heat and mass transfer is more and more obvious, and when the left vertical wall is linear temperature boundary condition, with the increase of the thickness of porous structure, the heat transfer mode in the cavity is from convection to heat conduction.In the case of local high temperature wall, Nu and Sh increase first and then decrease under different positions of local high temperature wall, and Nu and Sh are the largest at B0. 6, but the increase of flow intensity of B is increased.Thirdly, the closed cavity model of porous enclosure structure is applied to the heat transfer analysis of contact heat collecting wall in porous media. It is concluded that the porous structure plays an effective heat storage effect, and the quartzite has the best heat storage effect in contrast materials.The thermal properties of the materials have a direct effect on the thermal storage effect.
【学位授予单位】:辽宁工程技术大学
【学位级别】:硕士
【学位授予年份】:2015
【分类号】:TU111.4

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