VELOCITIES OF FALLING FILMS OF WATER ON TEFLON®, GLASS AND STAINLESS STEEL SURFACES

SUMMARY— The velocities of falling films of water on a stainless steel plate (8 by 1.5 ft) with No. 4 surface finish were measured by the salt conductivity method for flows varying from 50 to 250 Ib/min. The downflow times between 2 fixed electrodes, 6 feet apart on the plate, were measured by a Solu-Bridge flow timer. The film velocity measurements were made with the plate vertical and inclined 30 degrees from vertical, with water at 70 and 140°F. Another setup with a smaller plate (4 by 1.5 ft) and a constant flow of 45 lb/min was used to study the characteristics of falling films of water on Teflon, glass and stainless steel surfaces. The plates could be positioned at any positive or negative angle. The effects on wave structures were recorded photographically. The results showed highest velocities when the plates were vertical. Velocities increased with flow rate and temperature. At a given slope, film velocities were higher for the flow clinging to the underside of the surface than for the flow down the upper side of the surface.