A New Set Of Analytical Correlations For Predicting Convective Heat Transfer In Fenestration Glazing Cavities

CCAnalytically modeling the complex fluid flow phenomena that occurs during natural convective heat transfer in fenestration system cavities (windows, doors, skylights, curtain-walls, etc.) is a complex task. Laminar flow of a fluid in a tall vertical glazing cavity can occur in the form of single cell or as a stable multicellular flow. Until the early 1980s, experimental results were mostly available, along with limited analytical studies based on theoretical considerations. Empirical heat transfer correlations, based on experimental results for tall cavities, are still widely used to determine the heat transfer through the fenestration glazing cavities. The correlations currently in use are primarily functions of the Rayleigh number, RaBLB, and sometimes the aspect ratio, A (ratio of cavity height to width). However, the dependence of heat transfer coefficients on the aspect ratio A has not been completely resolved. In this work, based on the numerical results obtained using finite element calculation methods, a new set of analytical correlations are developed as functions of both RaBLB and A. The numerical analysis was performed over a range of aspect ratios from A=5 to 80 with Rayleigh numbers within the laminar flow regime, which covers a range of conditions typical of fenestration systems and solar energy collectors. The standard deviation between the numerical results and the analytical correlations developed from them is less 2 than percent. The new correlations are also in good agreement with available experimental data and other numerical calculations as shown in the results and discussion section. The new correlation is formulated as two equations applicable for two ranges of Rayleigh numbers, making them easy to use in engineering practice.