| Radiation air conditioning system has the advantages of energy saving,comfort,economy and environmental protection,and its wide application is of great significance to promote low-carbon development,but the problem of condensation on the cooling surface of radiation plate limits its cooling capacity.Therefore,aiming at the condensation mechanism of cooling surface,this paper constructed a new type of selective transmissivity radiation device using selective transmissivity membrane material with high infrared transmissivity in the long wave range of 8～13μm,that is,the selective transmissivity membrane wraps the radiation plate surface with a closed gas sandwich.The dew-preventing ability and heat transfer performance of selective radiation transmission device were studied by means of experiment and simulationFirstly,the mechanism of preventing dew formation of the selective radiation device is analyzed theoretically.The selective radiation membrane isolates the cooling surface of the radiation plate from indoor wet air by utilizing the characteristics of thermal radiation,so as to break through the limit of indoor dew point temperature.By analyzing the heat transfer process of the selective radiation transmission device,it is concluded that the factors affecting the anti-condensation and heat transfer performance mainly include the internal parameters of the device,such as the thickness of the gas interlayer,the moisture content in the gas interlayer,the type of gas,and the operating conditions of the system.Secondly,the effects of different gas interlayer thickness,moisture content and water supply temperature on the anti-condensation ability and heat transfer performance of the selective radiation transmission device were experimentally studied.The experimental results of changing the thickness of gas interlayer show that the temperature of selective permeation film increases with the increase of interlayer thickness.When the thickness is 2cm,the surface temperature of radiant plate increases to 14.2 and the film temperature increases to25.8,which can effectively avoid dew formation.The results show that under the same sandwich thickness,the temperature difference between the radiation plate surface and the selective transmittance film is 11.6 ～7.6 when the water supply temperature ranges from 9to 17.The larger the temperature difference is,the more cooling capacity of the radiant panel will be,and the smaller the impact of the reduction of convective cooling capacity will be,and the heat exchange performance of the radiant device will be better at 9.The experimental results of changing the air moisture content in the gas interlayer show that,when the water supply temperature is higher than 9 and the air moisture content in the gas interlayer is lower than 10g/kg,no condensation occurs on the surface of the cold plate and the membrane in the selective transmission radiation device.Therefore,there may be low moisture content in the gas interlayer,and it has almost no influence on the heat transfer performance of the radiation device.Finally,the cooling model of small room based on selective penetrating radiation device is established to conduct numerical simulation analysis on the thickness optimization of gas interlayer and the influence factors of gas type（or vacuum）in the interlayer.The results show that the gas interlayer thickness which is not less than 2cm can effectively prevent condensation,and with the increase of gas interlayer thickness,the radiation cooling capacity increases,the convection heat exchange capacity decreases significantly,and the total cooling capacity decreases slightly.Compared with the thickness of 1cm,the total cooling capacity of gas interlayer with 4cm thickness is reduced by 5.8%,so the optimum thickness of the gas interlayer should be designed to 2cm.Under the same gas interlayer thickness,the smaller the thermal conductivity of interlayer gas,the stronger the anti-condensation ability of radiation terminal device.The anti-condensation effect of interlayer in vacuum state is the best,and its heat exchange performance is opposite,so the gas interlayer is suitable for filling air or nitrogen.The new radiation terminal device can prevent condensation and has good heat exchange performance. |
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