New natural convection heat transfer correlations in enclosures for building performance simulation

Abstract

This 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 < 10 7) and another one in turbulent regime (10 7 < Ra < 10 11). Moreover, two new correlations have been developed for floor and ceiling, one in laminar regime (Ra < 10 6) and another one in turbulent regime (Ra > 10 6). 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 (10 3-10 11) 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-ε 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.

Analysis of Aspect Ratio Effects of Left Heated 2D Cavity Using Energy Streamlines and Field Synergy Principle

“…This is due to the fact that the velocity at the boundaries is higher than velocity at the center of the cavity in Figure 3(l). [25,[35][36][37]. For low Ra (= 10 3 ) and as AR increases from 0.5 to 2, it is observed the presence of isotherms which are almost vertical as displayed in Figures 4(a, b, c).…”

“…The AR effects with 1 ≤ AR ≤ 2 for 10 6 ≤ Ra ≤ 10 8 in the 3D differentially heated cubical cavity was investigated by Ravnik et al [24] using the boundary element method. According to results reported by Rincon Casado et al [25] for AR= 1 threedimensional effects are less pronounced with a reduction of 2-4% compared to a 2D model for Ra ≤ 10 12 . This is due to the fact that the 3D effect of the boundary layer is not significant in the average Nusselt number with high Ra.…”

Calibration Methodology for CFD Models of Rooms and Buildings with Mechanical Ventilation from Experimental Results

“…In Table 4, all the necessary variables for the calculation of the GCI for the 12 temperature sensors are shown. The table shows the values of the GCI 12 , the GCI 23 indexes and the temperature sensor measurement bias error (0.5 error sensor, divided by measurement temperature sensor in percent). The small values for GCI confirm that the solution is grid independent.…”

“…Recently correlations have been developed to implement them in thermal simulation programmes of buildings [12]. These correlations are used for convective heat transfer calculations.…”

Proposal for a Simplified CFD Procedure for Obtaining Patterns of the Age of Air in Outdoor Spaces for the Natural Ventilation of Buildings

“…Wind promotes a controlled pressure distribution over the building envelope [1] (conditioning indoor air change through ventilation openings). Convective phenomena is generated by static pressure due to air density and temperature gradient [2]. In this process, indoor air is mixed with outdoor air supplied through the envelope due to various phenomena (openings, infiltrations, ducts, etc.)…”