A rotary dryer using counter-current flow is to be used to dry 12000 kg/hr of wet salt containing 5% water (wet basis) to 0.1% water (wet basis). Heated air at 147C with a WBT of 50C is available. The specific heat of the salt is 0.21 kcal/kg C. The outlet temperatures of air and salt are 72C and 93C respectively. Calculate the diameter of the dryer required.