The radial void fraction distribution of equal sized spheres in cylindrical packed bed tubes with low diameter aspect ratios (1 less than or equal to D/d less than or equal to 2) is determined from the spheres＇ center coordinates, the local radial void faction and the radial positions within the tubes. A correlation that closely predicts the local radial void fraction at a radial position is determined from the radial void fraction distributions. The correlation is a function of the diameter aspect ratio and the radial position in the cylindrical packed bed tubes.