Improved calculation approach of the heat transfer in inclined insulating gas layers

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 d...

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Bibliographic Details
Published in:Solar energy 2022-01, Vol.231, p.252-261
Main Authors: Leibbrandt, Pascal, Giovannetti, Federico, Schabbach, Thomas, Jordan, Ulrike
Format: Article
Language:English
Subjects:
Aspect ratio
Calculation approach
Conductive/post-conductive regime
Convection
Convective heat transfer
Correction function
Dependent variables
Free convection
Glass cavity
Glazing
Heat transfer
Heat transport
Insulating glass
Insulation
Mathematical analysis
Rayleigh number
Solar collector
Solar collectors
Solar energy
Solar heating
Transport phenomena
Transport processes
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Summary: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. •Measurements on insulating glazing.•Convective heat transfer in the formerly known conductive regime.•Aspect ratio dependent correction for heat transfer below critical Rayleigh number.•New correction function for free convection calculation approach.
ISSN:0038-092X
1471-1257
DOI:10.1016/j.solener.2021.10.052