多孔介质内传热及应用基础研究

发布时间：2018-02-24 22:30

本文关键词： 多孔介质自然对流传热实验应用基础　出处：《辽宁工程技术大学》2014年硕士论文　论文类型：学位论文

【摘要】：开展多孔介质内对流与传热的基础与应用研究,有利于建筑节能新技术的发展,是解决基础科学问题的需要。本文采用理论分析和实验研究的方法研究多孔介质内的传热问题,利用数值计算的方法研究流体瑞利数、达西数、模型高宽比对多孔介质流动与传热的影响,主要结论如下：首先,以理论为指导的实验研究结果表明：多孔介质内部的非稳态传热过程大致分为三个阶段,即受初始温度分布影响阶段、温度升高阶段、新的热平衡阶段；前两个阶段中,上部温度场最先受到边界影响,下部受到边界影响时间比较迟；温差越大,温度场越容易受到边界条件影响,初始温度影响的时间就越短；在第三个阶段,温度场中呈现明显的分层现象,上部温度高,下部温度低,这是由于多孔介质内部出现自然对流造成的结果。其次,将数值计算的结果与实验测定结果相比较发现：在新的热平衡状态下,数值计算结果与实验测定结果最大相对误差达到10.98%,验证了数值计算方法和参数设置的正确性。数值计算结果表明：流体瑞利数较小(Ra105)时,传热以导热为主,增大瑞利数,对流作用就占主导作用；达西数Da10-6时,增大达西数,流体流动变得越容易,对流作用就越强；模型高宽比为1时,努塞尔数Nu最大,传热效率最高；在线性高温条件下,中间位置以下部分,Nu为正值且随高度增加而减小,热量由高温壁面向腔内传热；中间位置以上部分,Nu为负值且随高度增加而减小,热量由腔内向高温壁面传热；底部加热时,增大瑞利数,系统稳定性被破坏,出现分叉现象。
[Abstract]:The basic and applied research on convection and heat transfer in porous media is beneficial to the development of new building energy saving technology and is the need to solve the basic scientific problems. In this paper, theoretical analysis and experimental study are used to study the heat transfer problem in porous media. The effects of Rayleigh number, Darcy number and aspect ratio of the model on the flow and heat transfer in porous media are studied by numerical method. The main conclusions are as follows: first, The experimental results under the guidance of theory show that the unsteady heat transfer process in porous media can be divided into three stages, namely, the stage affected by initial temperature distribution, the stage of temperature rise, the stage of new heat balance, the first two stages, The upper temperature field is first affected by the boundary, and the lower part is affected by the boundary. The larger the temperature difference is, the more vulnerable the temperature field is to the boundary condition, and the shorter the initial temperature effect is; in the third stage, There are obvious stratification phenomena in the temperature field, the upper temperature is high and the lower part is low, which is caused by the natural convection in the porous media. Secondly, By comparing the numerical results with the experimental results, it is found that in the new thermal equilibrium state, The maximum relative error between the numerical results and the experimental results is 10.98, which verifies the correctness of the numerical calculation method and the parameter setting. The numerical results show that the heat transfer is mainly heat conduction and increases the Rayleigh number when the Rayleigh number of fluid is smaller than that of Ra105). When the Darcy number is increased, the flow of the fluid becomes easier and the convection effect becomes stronger, the ratio of height to width is 1:00, the Nu number is the largest and the heat transfer efficiency is the highest. The lower part of the middle position is positive and decreases with the increase of height, and the heat is heat transfer from the high temperature wall to the cavity; the upper part of the middle position is negative and decreases with the increase of height, and the heat is heat transfer from the cavity to the high temperature wall; when the bottom is heated, When the Rayleigh number is increased, the stability of the system is destroyed and the bifurcation occurs.
【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】：2014
【分类号】：TU111

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