| Glass envelope is an important structural component for building lighting and resisting environmental load,but its thermal insulation ability is poor in building envelope,and it is also a weak part of building safety.How to effectively reduce building energy consumption and improve indoor environment while ensuring light transmittance and safety is the main research direction of glass envelope.Under the design background of"Near zero energy consumption building"which advocates the effective use of clean energy,filled paraffin into the glass interlayer to make the glass structure containing paraffin layer,which makes the phase change energy storage material and solar energy effectively utilized.However,due to the phase state,temperature and low thermal conductivity of paraffin,the optical properties such as light transmittance of glass structure will be affected,and the optical properties will affect its heat transfer and heat storage due to the change of paraffin phase state.The two affect each other,making the photothermal transmission properties of glass structure complex.At the same time,under the limit of the frame and the thermal expansion and cold contraction of the glass itself,the glass structure will produce temperature stress,and the temperature stress is an important index for the safe use design of the glass structure.Therefore,revealing photo-thermo-mechanical coupling properties of glass structure with paraffin layer not only has important theoretical value,but also has important guiding significance for the design of glass structure with paraffin layer.In this paper,the photo-thermo-mechanical coupling properties of glass structure with paraffin layer is studied by the combination of experimental research,theoretical analysis and numerical simulation.The main research contents and results are as follows:1.Thermogravimetric analysis(TGA)and differential scanning calorimetry(DSC)were used to characterize the structure of 17#,25#and 32#three common industrial paraffin,and the optical and thermal related physical parameters of paraffin were measured to obtain the thermal conductivity,specific heat,latent heat and transmittance of paraffin at different phase transition temperatures.The inversion model of material optical constants is established based on the"double thickness"method.The optical constants of paraffin are solved according to the measured transmittance,and the optical constants such as refractive index and absorption coefficient of solid-liquid two-phase paraffin in visible band(400-760nm band)are obtained.The results show that the thermal properties of the three kinds of paraffin wax are relatively stable under natural environmental conditions.The absorption coefficient of solid paraffin(288.11–545.27m-1)is much greater than that of liquid paraffin(0–5.34m-1).The absorption coefficient and transmittance of paraffin increase with the increase of paraffin phase transition temperature.2.Based on the basic theory of heat transfer and the theory of photothermal transfer performance of multilayer glass envelope,the calculation method of paraffin phase change latent heat is introduced,and the mathematical model of photothermal transfer performance of glass envelope containing paraffin layer under non-uniform temperature field is established.The dynamic environmental conditions with representative temperature range in severe cold areas of China are selected as boundary conditions,17#,25#and 32#three kinds of paraffin glass structures are analyzed comprehensively.The results show that the longer the phase transformation process is maintained,the better the energy-saving effect of the glass structure containing 17#the paraffin layer in this study is more suitable for the use in the severe cold areas of China.3.The thermal mechanical coupling 3D mathematical model of glass envelope containing paraffin is established and calculated by FEM.The influencing factors such as paraffin filling rate,paraffin thickness,glass thickness,frame material and frame coverage were analyzed.The results show that the thermal stress of glass structure increases with the increase of paraffin filling rate.The influence of glass thickness on thermal stress is obvious.When the glass thickness is?12mm,the increase of surface stress of glass envelope with paraffin layer is 2-3 times that of 12mm thick glass.The frame should be made of PVC,and the coverage rate should not be greater than 32%.4.The photothermal coupling analysis and thermal mechanical coupling analysis of glass envelope with paraffin layer are extended to the photo-thermo-mechanical three field coupling analysis.The photo-thermo-mechanical coupling characteristics of glass envelope with paraffin layer under four side shielding are studied,and the influence of paraffin layer on the surface stress distribution of glass structure under dynamic temperature and intermittent solar radiation is revealed.The change of thermal stress on the ipsilateral glass surface is most obvious at the cover of window frame and within 30mm from the frame.5.Combined with the glass fracture criterion,the thermal response of glass structure containing paraffin layer under extreme thermal conditions is discussed.The glass envelope with paraffin layer is compared with the hollow glass structure by numerical analysis.The results show that the thermal deformation temperature of glass envelope with paraffin layer reaching the fire surface is 55 s later than that of hollow glass structure under the condition of four fixed boundaries;The time of reaching the limit stress at the edge is delayed by 5s,and the fire resistance of paraffin glass envelope is good. |
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