Air drying technology was developed as an equipment for reduction of moisture content from wastewater treatment and waterworks sludge cake and to reproduce it by reusable matter. Advantage of cyclone type pneumatic dehydrator is simple and excellent drying performance. The air drying equipment was composed to the air ejector which make high-speed fluid field, and cyclone which make circling fluid field. Dewatered cake was crushed at the high-speed zone as first step, and formed with dried powder of sphere shape by the collision between particles at the circling fluid zone. In this study a CFD analysis has been performed to predict air-sludge particles flow in a cyclone and an ejector of pneumatic dehydrator. The computational results showed typical Rankine vortex structure which was frequently found in swirling flow phenomena. And the conical type wedge in lower part of a cyclone prevented to accumulate the sludge particles in a cyclone. Therefore, this technology was evaluated that drying the dewatered cake of waterworks sludge was more efficient than wastewater sludge, and also economical sludge handling technology due to drying the cake by only air.