Experiments on heat transfer between spheres and air flow were carried out in the range of Reynolds numbers from 3.5 to 1.44 × 105 and Grashof numbers from 1 to 105 . Empirical formulas for forced, natural, and combined convection are presented and comparison made with other investigations. A graphical procedure, based on experimental results, is used to predict the heat-transfer performance for combined natural and forced convection.