表面粗糙度对混凝土对流换热影响的试验研究

Experimental Investigation into Effect of Surface Roughness on Convective Heat Transfer of Concrete

对流换热系数是混凝土重要的热工参数之一。目前关于混凝土结构的建筑节能、结构温度荷载及温度效应等温度相关的研究和工程应用中,在对流换热系数的选取上存在较大差异,且未考虑材料表面状况的影响,这直接影响了分析结果的准确性和可靠性。文中基于牛顿冷却定律和热平衡原理,设计和制备了一套混凝土表面对流换热系数的试验测定系统,以参数定量可控的方法开展不同粗糙度混凝土表面对流换热系数的试验研究,进一步改进和完善混凝土对流换热系数的定量计算方法。结果表明:所设计的测试系统和方法能很好地在构件尺度下测定混凝土表面的对流换热系数;表面粗糙度显著影响混凝土表面的对流换热,在10 m/s风速范围内,不同粗糙度的混凝土表面对流换热系数相差40.1%~77.4%;换热系数随表面粗糙度的增加而增大,且相比于自然对流,受迫对流受表面粗糙度的影响更大。基于试验数据的回归分析,得出了4种典型粗糙度混凝土表面对流换热系数的计算公式,同时给出了耦合风速和表面粗糙度影响的混凝土对流换热系数计算公式,并就工程中如何考虑混凝土表面粗糙度进行热交换系数取值给出了建议。

The convective heat transfer coefficient(CHTC)is one of the important thermal parameters of concrete.At present,there are great differences in the selection of CHTC in the temperature-related research and engineering applications of building energy efficiency,structural temperature loading and temperature effects of concrete structures,and the influence of material surface conditions is not considered,all these directly affect the accuracy and reliability of the analysis results.In this paper,based on Newton′s law of cooling and the principle of heat balance,a set of experimental determination system of CHTC of concrete surface was designed and constructed,and an experimental study on the CHTC of concrete surfaces with different roughness was carried out with a quantitative and controllable method of parameters to further improve and refine the quantitative calculation method of CHTC of concrete.The results show that the designed test system and method can well determine the CHTC of concrete surface in the component scale,and that the surface roughness significantly affects the convective heat exchange on concrete surface.At the wind speed of less than 10 m/s,the relative difference in CHTC of concrete surfaces with different roughness varies from 40.1%to 77.4%.The CHTC increases with the increase of surface roughness,and the forced convection is more greatly influenced by surface roughness than the natural convection.Moreover,based on the regression analysis of experimental data,the formulae for the CHTC of concrete surfaces with four typical roughness are derived,and the formulae for the CHTC of concrete considering the effects of coupled wind speed and surface roughness are also given.Some suggestions are finally given on how to determine the value of CHTC of concrete with the consideration of surface roughness in engineering.