Radial porosity variations in packed beds

Abstract

The radial variation of void fraction in randomly packed beds of spheres, cylinders, Raschig rings, and Berl saddles was investigated. After packing, the beds were filled with paraffin, which was then allowed to solidify. Slabs were cut from the bed, and annular rings were removed by two different experimental techniques. An analysis of experimental error revealed that reproducibility, for the sample size used, between different parts of the same bed and different beds was quite good. For highly irregular shapes such as Berl saddles results indicate that the void fraction decreases regularly from one at the wall to the average porosity at about 1 particle radius from the wall. This is in agreement with work of other investigators using irregularly shaped packings; most commercial packings would probably fit in this category. For regularly shaped particles results are quite different. For spheres and cylinders cycling was observed for more than 2 particle diam. into the bed, the amplitude decreasing as distance from the wall was increased. The maxima and minima were observed at integral multiples of the particle radius. For Raschig rings a hump was observed at about 1/2 particle radius from the wall. The void fraction then decreased to its average value at 1 particle radius and then remained constant.