THE MODELING OF DROP BEHAVIOR IN SIPHON RISER TUBES IN PAPER DRYING CYLINDERS

A theoretical model has been developed for the drop behaviour in sipho n riser tubes in paper drying cylinders. Analytical solutions to the e quations are presented for the systems air-water at atmospheric pressu re and saturated steam-water. Numerical simulations are performed for a large number of input data. Calculated drop trajectories indicate th at the drops travel only a small part of the riser tube length before they are deflected to the frontside of the riser tube. For the system air-water the drop radial velocity when hitting the tube does not exce ed 50% of the gas velocity, while with the system steam-water the radi al velocity can be up to 90% of the gas velocity. The azimuthal drop v elocities are in the range 2-10 m/s. The condensate slip relative to t he cylinder results in an initial backward motion of the drops before they are accelerated to the frontside. Thus, part of the drops will hi t the backside wall resulting, in the formation of a liquid film. This film will also be subjected to the coriolis force resulting in a liqu id redistribution to the frontside wall. A criterion for cylinder floo ding to occur, based on the fundamental differential equations, is pre sented. Good agreement with experimental data is presented for the sys tem air-water in a 1.5 m model cylinder.