Improved calculation approach of the heat transfer in inclined insulating gas

Known calculation approaches for the determination of internal natural convection in inclined plane-parallel insulating gas layers have been developed above the critical Rayleigh number in the post-conductive regime. The most well-known correlation function which is used in solar thermal collector design assumes pure conduction below the critical Rayleigh number. However, recent measurements on insulating gas layers in standard flat-plate and insulating glass solar collectors show that this assumption leads to an underestimation of the heat transfer between the absorber and the front cover of the solar collector. In the presented study measurements on insulating glazing were carried out. A correction function is proposed which characterizes the heat transport processes below the critical Rayleigh number taking into account for convective heat transfer. The dependent variable of the correction function is the aspect ratio of the insulating gas layer, which has a significant influence on the flow regimes and thus the heat transport phenomena that occur.