Dynamics And Heat Transfer Of Convective System On A Triangular Roof

Building energy conservation plays an important role in carbon neutrality,and thus the study of dynamics and heat transfer of buildings is of significance in fundamental research and of value in engineering.The roof on building receives considerable sun radiation,and is a main part of heat transfer between the inner and outer of building.The roof can be,after heated,inducing complex convective flows,which are one of the main ways of heat and mass transportation around buildings.That is,the study of convection system on the roof is the basis for understanding building environment and building energy conservation,and the corresponding outcomes may be applied for environmental protection and energy saving design.In the thesis,dynamics and heat transfer of convection system on the roof are investigated using scaling analysis,numerical simulation and experimental measurement.The results are as follows:Dynamics analysis models of convection system on an isothermal roof and a time dependent heat flux roof are established,respectively,possible evolutions of dynamics and heat transfer of convection system on the roof are revealed,and scaling laws of typical variables such as thickness,velocity and heat and mass transportation under different regimes are presented and validated by numerical results.Three-dimensional numerical model for the transition of convection system on the roof is presented,a supercritical transition route with Hopf bifurcation,period doubling bifurcation and quasi-periodic bifurcation is uncovered,typical bifurcation phenomena are characterized,dynamical regimes are analyzed,and the scaling law of heat transfer in the transition is given.Experimental rigs for the study of the transition of convection system on the roof are designed and built,temperature data are obtained using phase shifting interferometer and temperature probes,the transition is characterized,and regimes of bifurcations induced by environmental disturbances are revealed.In the thesis,results reveal that the convective system on the roof is mainly controlled by Rayleigh number,Prandtl number and aspect ratio.Features of dynamics and heat transfer of convection system on the roof are summarized,regime evolutions are elucidated,scaling laws under different regimes are presented,and bifurcations in transition routes are revealed.These results may be applied for building design and environmental prediction under static wind condition.