Heat transfer to a horizontal cylinder in a shallow bubble column

Heat transfer coefficient correlations for tall bubble columns are unable to predict heat transfer in shallow bubble columns, which have unique geometry and fluid dynamics. In this work, the heat transfer coefficient is measured on the surface of a horizontal cylinder immersed in a shallow air–water bubble column. Superficial velocity, liquid depth, and cylinder height and horizontal position with respect to the sparger orifices are varied. The heat transfer coefficient is found to increase with height until reaching a critical height, and a dimensionless, semi-theoretical correlation is developed that incorporates superficial velocity, liquid properties, and height. Additionally, the more minor effects of flow regime, column region, and bubble impact are discussed. Notably, the heat transfer coefficient can be as high in the region of bubble coalescence as in the bulk of the column, but only if bubbles impact the cylinder. The correlation and discussion provide a framework for modeling and designing shallow, coil-cooled bubble columns.