Summary
A proposed solar drying system which consists of a solar housing and perforated rotary drum dryer was studied to clarify the rapid drying of the sludge while being discharged from the drum. the sludge was pushed out gradually through small holes around the periphery while the drum was rotating. Sludge movement and discharge were observed with a video camera using a drum made from transparent flexiglass. The following findings discuss the relationship between the sludge discharge, hole size and the drum speed.HomePage
1. The sludge was carried up with the rotation of the drum up to certain angle. This motion was explained by the friction between the inner surface of the drum and the sludge. The angle of repose in the drum was calculated with the theoretical model when the rotating rate of the drum was low. At high rotating rate, the angle of the repose was larger because the sludge did not slip on the drum surface and the slipping occured only within the sludge layer.
2. The amount of the discharge sludge was proportional to the 1.9th power of the hole diameter and to the 0.53th power of rotation rate of the drum. The discharge was independent of the sludge height in the drum.
3. The drying rate during the discharge process was measured using the formed samples. The rate was proportional to the square root of the Reynolds number while evaporation was proportional to the 1.5th power of the bar diameter.
4. The hole diameter must be smaller because drying rate was higher at smaller bar diameter. Sludge particle diameter and admixtures must be considered in selecting the best hole diameter.Keywords: sludge, solar thermal energy, rotating drying drum, discharge drying