Finite element model of turbulent flow and heat transfer in a fenestration system
There have been a number of analytical studies made for predicting heat transfer in high aspect ratio (cavity height to width) glazing cavities, but very few studies have been performed for situations where the flow in the cavity is turbulent. For high aspect ratio (A) glazing cavities, buoyancy driven turbulent flow will occur at moderate Rayleigh Numbers ([special characters omitted]). The presence of turbulence in the glazing cavity can have a significant effect on the cavity flow pattern and heat transfer rate.
In the present study, two-dimensional laminar and turbulent natural convection heat transfer of air in high aspect ratio rectangular cavities was analyzed using a finite element turbulent computational fluid dynamic solution method. The numerical analysis includes the effects of laminar and turbulent natural convection and radiation heat transfer within the cavity. The testing was performed in a calibrated Hot Box at winter night-time conditions following ASTM C1199 and C976, and ISO/DIS 12567 Fenestration Test Standards conditions. The fenestration systems studied were prototype casement windows designated as prototype fenestration models 1 (PFM01) and 2 (PFM02), and an argon filled double gazing unit studied in the International Energy Agency (IEA) Task 18, Project B14. Comparisons of the laminar- and turbulent heat transfer calculation results are made with the experimental results. The laminar and turbulent heat transfer model calculated results showed good agreement with the experimental results for cavity flows in the transitional region between the laminar and turbulent flow regimes.
Two-dimensional laminar natural convection heat transfer of air in a rectangular cavity is numerically calculated. The laminar flow numerical calculations were performed for aspect ratios of A = 20, 30, 40, 50, and 74 and a Rayleigh number range that extends into the turbulent flow regime. The laminar flow calculations will be compared to similar calculations on turbulent flow and provide some insight into the transition from laminar to turbulent flow.
Two-dimensional turbulent natural convection of air in a rectangular cavity is numerically calculated and compared to experimental data. The numerical calculations were performed for aspect ratios of 5, 10, 20, 30, 40, 50, 60, and 80 and a Rayleigh number range that extends into the fully turbulent regime. The turbulent flow calculations are used as a basis for a numerical heat transfer correlation for turbulent cavity flow.