Study On Wind Tunnel Test Method For Complex Heat Transfer Conditions On Building Surface

The problem of building energy consumption increases with the urbanization process and global climate change.The heat transfer coefficient of building surface is closely related to multi parameter complex climate conditions and building material characteristics,which is an important parameter for building energy consumption prediction.The research on complex heat transfer on building surface will provide an important basis for accurate prediction of building load,effective operation of building equipment and application of passive energy-saving technology.Wind tunnel experiment is an important method to study complex heat transfer on building surface.Due to the limitation of experimental conditions,the existing wind tunnel experiment focuses on the study of convective heat transfer,solar radiation heat transfer and evaporation latent heat on the building surface,that lacks the long wave radiation heat transfer from the sky.Therefore,this paper takes the complex heat transfer condition of building surface as the research object,uses the wind tunnel technology and environmental simulation technology to build the all-weather dynamic heat and humidity climate wind tunnel,and reappears the meteorological boundary condition of complex heat transfer on building surface.In view of the problems existing in the realization of various climate parameters in the wind tunnel,combined with theoretical analysis,numerical simulation and experimental test,the corresponding methods are proposed and verified.This paper has carried out the following work:1)Based on the flow field quality and the particularity of hot-humid climate wind tunnel,this paper optimized and simulated the key parts,such as transition section and guide vane,which affect the wind tunnel flow field.After optimization,the uniformity coefficient of velocity and temperature at the entrance of the test section are less than 2%and 1.9%respectively.The RSME of steady-state and dynamic control of wind speed are reduced to 0.04and 0.01 m/s respectively.2)Based on the stability requirements of the coupling control of various climate parameters in the wind tunnel,this paper focuses on the coupling control of temperature and humidity,and establishes a three-stage heating,three-stage dehumidification integrated regulation method with a segmented micro regulation method under extreme high humidity conditions.Through the experimental test,the RSME of temperature and relative humidity is reduced to 0.1°C and 0.4%respectively in the steady-state control,and to 0.2°C and 0.53%respectively in the dynamic control.Under the most unfavorable conditions of extreme high temperature and humidity with temperature of 40°C,relative humidity of 98%and wind speed of 1 m/s,after micro adjustment the RSME of temperature and humidity is reduced from 3.0°C to 0.1°C and 0.9%to 0.5%respectively.The frequency of humidity fluctuation decreased from12 times/h to 4 times/h.3)A high-level large-scale solar radiation simulation system is established,which is coupled with the sky long wave radiation system and applicable for multi parameter all-weather dynamic thermal and humid climate wind tunnel.The effective irradiance surface is 2.5×2.5m,and the characteristic size percentage of the effective irradiance surface is 83.3%,which is double of the same type and improves the utilization ratio of wide source.The radiation uniformity and stability meet the requirements of class B or above.The RSME of solar irradiance under steady and dynamic control is reduced to 1.14 and 0.96 W/m~2 respectively.4)Based on the calculation principle of long wave radiation heat transfer in the sky and combined the outdoor measured data and empirical calculation model,two methods of setting the effective temperature in the sky of the long wave radiation heat transfer system in the wind tunnel are defined.Then this paper built the corresponding modified model.The relative error value of the surface temperature of the test piece is reduced from 22.4%to 8%in the sunny condition and reduced from 12.3%to 2.4%in the cloud condition through the wind tunnel comparative experiment,which improves the wind tunnel test method of complex heat transfer on building surface.For the first time,this study designed and built a all-weather dynamic hot-humid climate wind tunnel,and developed a multi parameter realization method of the wind tunnel,then realized seven meteorological parameters conditions in the wind tunnel,including wind speed,temperature,humidity,solar radiation,long wave radiation in the sky,rainfall and salt fog,Moreover,a modified model of long wave radiation in the sky of the wind tunnel is established.This wind tunnel provided a new way for the scientific quantification of complex heat exchange on the building surface.