Experimental Study On Heat Exchange Coefficient Of Porous Materials In Summer Environment Of South China Sea Islands

South China Sea has a vast ocean area and many islands.Its meteorological elements such as air temperature,relative humidity,and solar radiation are relatively high all year round.In addition,the marine environment tends to produce a large area of high-concentration salt fog and monsoon prevalence,forming a significant difference compared to the mainland of China.The unique climate of South China Sea is high temperature,high humidity,strong radiation,and high salt fog.Nowadays,more and more projects are being built on the islands of the South China Sea.It is imperative to design the building envelope to adapt to the local climate.The external surface heat transfer coefficient is an important parameter for analyzing building energy consumption,and it is also an important boundary condition for the study of enclosure structure and indoor and outdoor thermal environment.However,the study of surface heat transfer coefficient under this special climate is very scarce at this stage.In this paper,red ceramic permeable bricks are used as experimental objects,and the dynamic changes of the surface heat transfer coefficient are studied through the hot-humid climate wind tunnel experiment.Following specific studies were carried out:(1)Determine the experimental principle and experimental scheme.The heat balance method was used to establish the calculation method of each heat transfer coefficient item;the reflectivity and emissivity of the specimens under different water cuts were measured;and the typical summer days of five sites were selected from the“Standard for weather data of building energy efficiency”(JGJ/T346-2014),including four island reefs(Dongsha Island,Xisha Island,Nansha Island and Yongshu Reef)in the South China Sea and one land city(Sanya);through ultrasonic atomization and atmospheric sampling techniques,the hot and humid climate wind tunnel has been transformed to achieve the control of salt fog at a concentration of 6 mg/m~3,which more accurately reproduces the climatic environment of the South China Sea in summer.(2)Dry and wet comparison analysis of heat transfer coefficient in non-salt conditions.Through the experiments at five stations without salt fog,the hourly averaged values of the surface heat transfer coefficients of the dry specimen and the wet specimen were respectively obtained,and the similarities and differences of the heat transfer coefficients items of the material under the two conditions were compared and studied.The results showed that during the nighttime radiation heat transfer coefficient and convection heat transfer coefficient are relatively stable,and the dry and wet specimens are not much different;and the absolute value of the heat transfer coefficient of the wet test piece during the day is generally larger than the dry test piece,especially around noon;the material evaporation heat transfer coefficient is small.(3)The effect of salt fog on the sub-items of heat transfer coefficients was analyzed.Through experiments on five sites with salt fog,the influence of salt fog on the sub-items of various heat transfer coefficients was studied on the basis of the above.It was found that the effect of salt fog on the heat transfer coefficient was significant at several hours before and after noon day,regardless of whether the specimens were dry or wet.However,as a whole,there is no consistent pattern for the relationship between the coefficient of each factor in the presence or absence of salt fog,and the salt fog hardly affect the evaporation heat transfer coefficient of the material.