Abstract
ABSTRACTThis paper presents new correlations to calculate natural convection heat transfer coefficients (CHTC) in enclosures for building performance simulation. Current work related to the development of correlations is not oriented to building enclosures, and the influence of high numbers of Rayleigh (Ra) and aspect ratio on the CHTC has not been studied in detail. In this work, two new correlations have been developed for a vertical wall, one in laminar regime (Ra < 107) and another one in turbulent regime (107<Ra<1011). Moreover, two new correlations have been developed for floor and ceiling, one in laminar regime (Ra < 106) and another one in turbulent regime (Ra > 106). All correlations have been developed as function of the aspect ratio (H/L) and Ra numbers calculated from the enclosure average air temperature and wall surface temperature. By contrast, in previous works the Ra numbers have been calculated from the temperature difference of opposite walls. Computer Fluid Dynamics (CFD) simulations for different aspect ratios (H/L = 0.5–1–2) and Ra numbers (103–1011) have been carried out in order to obtain these correlations. The SIMPLE algorithm has been used for the solution of the Navier–Stokes equations and the realizable turbulence k- model with an enhanced wall-function treatment has been used. The correlations developed follow the expected trend for the low number of Ra in comparison with the expressions developed by other authors. For a high number of Ra, our correlations improve the previous correlations, because it is a function of the aspect ratio of the enclosure and the average air temperature of the enclosure. This approach is simple to implement in the construction of thermal simulation programs with low computational cost.
Highlights
Natural convection in closed enclosures has been widely studied both experimentally and numerically due to the special interest in many engineering applications: solar collectors, nuclear reactors, refrigeration in electronic components
The present paper shows new correlations for laminar and turbulent regimes in enclosures with natural convection of 103 ≤ Ra ≤ 5 · 1011 and an aspect ratio of 0.5 ≤ H/L ≤ 2
These correlations are oriented to building enclosures and implemented in thermal building simulation programs
Summary
Natural convection in closed enclosures has been widely studied both experimentally and numerically due to the special interest in many engineering applications: solar collectors, nuclear reactors, refrigeration in electronic components. In the last four decades, numerous theoretical and experimental studies on natural convection in enclosures have been carried out. Recent work shows that research is continuing on these issues, as presented by Altaç and Uğurlubilek (2016) with regard to three-dimensional effect and various turbulence models. Another recent study carried out by Obyn and Van Moeseke (2015) focuses on the impact of convection heat transfer coefficient (CHTC) expressions used for the calculation of heating and cooling loads of buildings
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