AC-19 Mixed Convection Heat Transfer Outside High-finned Tube Bundles in Low Airflow

S. A. Bouhairie

Modeling natural-draft air coolers requires accurate prediction of airside heat transfer coefficients at low airflow rates. HTRI has collected additional data from the Air-cooled Unit (ACU) to develop a correlation for mixed convection that predicts low airflow heat transfer. The improved correlation, based on Rayleigh and Reynolds numbers, results in an average predicted-to-measured ratio of 98% for the heat transfer coefficient, with an average deviation of 33% in Xace® 9.0. Based on these results, using the mixed convection coefficient method in Xace 9.0 is more effective than using the correlational adjustment from AC-9 as implemented in Xace 8.2 and earlier versions.