Abed contains particles of unknown average size and average surface area. experimentally, the void fraction was determined to be 0.45. for a superficial velocity of 1.0 ft/min, the pressure drop over the packed bed was 12000lb/ft2. particles, having a density of 256.0 lb/ft3, were somewhat ‘cubic’, so the sphericity was estimated to be 0.8. what is the surface area per unit mass? what happens to this estimation if the void fraction was measured to be 0.47? what happens if the estimated sphericity is determined to be 0.77?