First, they must provide good heat and mass transfer to heat and dry the ink. Second, they must transport the web without inducing web movement or contact, i.e. the web must be floated in a stable manner. Not much has really changed in these basic requirements since the inception of flotation dryers. However, the changes in press speeds and raw materials have significantly increased performance demands of such nozzle systems. Requirements Have Changed Press design speeds are now up to 3000 feet per minute.
Faster speeds require longer dryers.
Though modest gains in nozzle heat transfer can be obtained, the payback in reduced dryer length is not all that significant. This is because a substantial part of the drying process is rate-limited by solvent transport within the ink film thickness, and to a lesser extent by the convection transfer coefficients at the surface of the ink. Given a set of ink and paper characteristics, web temperature can be increased to speed drying. Therefore, high heat transfer rates are desired, especially early in the dryer to bring the web up to temperature, but heat transfer coefficients are only part of the picture. In addition to higher press speeds, paper characteristics have changed considerably in the last few years.