Drying and gas or vapor contact with solids – Apparatus – Rotary drums or receptacles
Patent
1989-05-03
1990-06-12
Bennet, Henry A.
Drying and gas or vapor contact with solids
Apparatus
Rotary drums or receptacles
34160, 226 97, F26B 1300
Patent
active
049321404
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention concerns an arrangement of pressure nozzles intended for the treatment of webs, comprising a nozzle box, which has a carrying face placed facing a web, two nozzle slots that blow towards each other being provided in connection with the carrying face, the nozzle slots being placed in the outer part of the space defined by the inner walls and the outer walls or equivalent of the nozzle box.
The nozzle arrangement subject of the invention is intended for contact-free supporting and treatment, such as drying, heating or cooling, of paper webs and other continuous webs.
Apparatuses based on the blowing of gas are used commonly in the manufacture and processing of paper. In the apparatuses meant above, the gas to be blown is guided by means of various nozzle arrangements to one side or to both sides of the web, whereupon the treatment gas is sucked off for reuse or for exhaust, and/or the treatment gas is allowed to be discharged to the sides of the web.
The prior-art apparatuses based on contact-free treatment of the web consist of a number of nozzle boxes, out of whose nozzles a gas flow that supports and dries the web is directed at the web. The prior-art nozzles in said apparatuses can be divided into two groups: nozzles with positive pressure and nozzles with negative pressure, where of the operation of the nozzles with positive pressure is based on the air-cushion principle, and the nozzles with negative pressure attract the web and stabilize the run of the web. The attractive force applied to the web is, as is well known, based on a gas flow field parallel to the web, the field forming a static negative pressure between the web and the carrying face of the nozzle.
Both in nozzles with positive pressure and in those with negative pressure, the so-called Coanda effect is commonly used to guide air in the desired direction.
The force applied to the web from prior-art nozzles with negative pressure is relatively low, for which reason these nozzles cannot be used for the treatment of heavy webs or when the tension of the web is low. Thus, nozzles with negative pressure are, as a rule, used in apparatuses whose length does not exceed 5 m and at both sides of which guide rolls are provided to support the web.
The force applied by positive-pressure nozzles to the web is relatively high. Thus, by means of pressure nozzles it is possible to treat heavy and fully untensioned webs. Most of the prior-art pressure nozzles, however, direct sharp jets substantially perpendicularly to the web, thereby producing an uneven distribution of the heat transfer factor in the longitudinal direction of the web, which frequently results in damage to the quality of the web to be treated.
The blowing out of the prior-art pressure nozzles is also unstable, so that the blow jet may turn, e.g. by the effect of the running of the web, directly from the blow opening into the suction space between the nozzles, thereby causing a lowering of the heat transfer factor and an unstable running of the web.
The prior art discussed above comprising, e.g., the U.S. Pat. No. 3,549,070 as well as from the SE Patents Nos. 341,870 and 352,121. These publications suggest nozzles in which, by means of the Coanda effect, attempts have been made to make the blow jets turn and become parallel to the web. Since the outlet directions of the jets form an angle of 90.degree. relative the web, the jets do not have time to turn and to become parallel to the web they are separated from the guide face of the nozzle. In the paper by D. W. McGlaughine and I. Greber, "Experiments on the Separation of a Fluid Jet from a Curved Surface", The American Society of Mechanical Engineers, Advances in Fluids, 1976, it has also been established that a jet discharged out of a nozzle can, without being separated, follow along with a curved face 45.degree.. . . 70.degree., and a following angle of 70.degree. cannot be exceeded. A separated jet collides against the web and causes a peak of the heat transfer factor at the collision point, wh
REFERENCES:
patent: 4058244 (1977-11-01), Vits
patent: 4384666 (1983-05-01), Koponen et al.
Bennet Henry A.
Sollecito John
Valmet Paper Machinery Inc.
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