| 摘要 |
A web dryer has a plurality of nozzle assemblies. Each nozzle assembly is provided with a flat pressure plate adapted to form a gas flow zone with a moving web. A primary nozzle of the airfoil Coanda type is disposed at the upstream end of the pressure plate and continuously directs gas downstream along the face of the plate. A single secondary nozzle of the impingement type is disposed at the generally right angled downstream terminus of the pressure plate to continuously direct gas initially substantially perpendicularly to the web and to gas flowing downstream along the gas flow zone. The position of the secondary nozzle assures that the full width of the pressure plate is utilized. The gas flow volume through the secondary nozzle is less than half that of the primary nozzle. Furthermore, the gas flowing from the secondary or impingement nozzle turns to take the downstream direction of the main gas flow and also serves to cause compression of the main gas flow against the web downstream of the pressure plate and nozzle assembly terminus. An increase in the rate of heat transfer to the web is thus produced in the free area between adjacent nozzle assemblies. The compressive restriction of the main gas also tends to increase its unidirectional air flow velocity, which in turn isolates the web from the effects of miscellaneous gas flow currents within the enclosed dryer housing. The overall result is a slight back pressure or increase in static pressure in the gas flow zone which assists in keeping the moving web spaced from the pressure plate, but the back pressure is insufficient to reverse the direction of main gas flow.
|
