Effect of supply Reynolds number and room aspect ratio on flow and ceiling heat-transfer coefficient for mixing ventilation

• Published in: International journal of thermal sciences 2012-04, Vol.54, p.176-187
• Main Authors: Al-Sanea, Sami A., Zedan, M.F., Al-Harbi, M.B.
• Format: Article
• Language: English
• Subjects: Applied sciences; Building technical equipments; Buildings; Buildings. Public works; Ceilings; CFD simulation; Computational fluid dynamics; Environmental engineering; Exact sciences and technology; Fluid flow; Forced convection; Heat transfer; Heat-transfer coefficient; Mathematical models; Mixing air-distribution system; Ports; Reynolds number; Room ventilation; Turbulence; Turbulent flow; Ventilation. Air conditioning
• ISSN: 1290-0729; 1778-4166
• DOI: 10.1016/j.ijthermalsci.2011.12.007

A CFD study is conducted to simulate turbulent flow and heat-transfer inside mechanically ventilated rooms, using mixing air-distribution system, under forced convection conditions. Air enters room from side wall opening flush with isothermal ceiling and leaves through port in opposite wall flush with floor. Velocity and temperature distributions are determined by using a finite volume method employing the k−ɛ turbulence model. The numerical model is validated by comparing results with available experimental data. Sensitivity of results to turbulent Prandtl number, values of k and ɛ at supply port, and y+ is examined. The model is then used to investigate effects of supply Reynolds number (Red = 4000 to 10,000, where d is supply port height) and room aspect ratio (L/H = 0.5–6) on flow and heat-transfer characteristics within room. Variation of convection coefficient hx along ceiling is compared with isolated flat plate correlation. Results show that ceiling averaged convection coefficient (hav) increases with Red and decreases with L/H. Correlations for hav are constructed in terms of Red and L/H. Streamline plots show that flow pattern is independent of Red but strongly dependent on L/H. A single contour map of speed with values normalized by supply velocity is therefore sufficient to describe all speeds inside the room for different supply Reynolds numbers. Temperature contours illustrate that variation of temperature in the bulk of occupied zone is well within 0.5 °C compared to variation of 10 °C in region close to ceiling, reflecting good mixing characteristics in occupied zone. ► Forced convection CFD study of room ventilation using mixing air-distribution system. ► Sensitivity of results to model parameters is examined. ► Results are compared with experimental data and turbulent flat plate correlation. ► Ceiling hav increases with Red and decreases with increasing room L/H aspect ratio. ► Flow pattern is independent of Red but is dependent on L/H.