CONDENSATE FLOW INSIDE PAPER DRYER CYLINDERS

The rimming flow of condensate in horizontal rotating dryer cylinders has been studied computationally by solving the full Navier-Stokes equ ations coupled with a volume of fluid method for tracking the free sur face. It was shown that significant variations in both condensate velo city and thickness exist at moderate dryer speeds, whereas at higher s peeds the variations are of less significance. Regardless of dryer spe ed or condensate film thickness, the film can be divided into two dist inct regions: a viscous sub-layer adjacent to the cylinder wall and an inviscid, oscillating layer close to the free surface. The thickness of the viscous layer decreases as the dryer speed increases, whereas, for a certain speed, it is independent of the total film thickness. Th e computational results are compared with measurements of both the fil m thickness and the pressure normal to the cylinder wall. In both case s the agreement is excellent. Some implications for heat transfer thro ugh the condensate film are briefly discussed.