Fluid sprinkling – spraying – and diffusing – Rigid fluid confining distributor – Having interior filter or guide
Patent
1996-04-05
1998-10-06
Weldon, Kevin
Fluid sprinkling, spraying, and diffusing
Rigid fluid confining distributor
Having interior filter or guide
239597, 162341, D21F 102
Patent
active
058165070
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The invention relates to a device for the formation of a fan jet of a liquid; it relates more particularly to the formation of such a fan jet in the field of the mixing, couching, coating and manufacture of materials in the form of sheets or boards from particles in suspension in a fluid, especially from suspension of fibers in water.
The invention is particularly suitable for the papermaking industry in the formation of the sheet from fibrous suspensions; it also has various uses in the field of coating and in the couching of papers and cardboards.
Although, in the rest of the description, the invention is particularly described in its use for the manufacture of papers, it can also have other uses in mixtures, with or without heat exchange, in the chemical, agricultural food and pharmaceutical industries or in water treatment and in the manufacture of films from polymers or from molten metals or in the manufacture of asbestos cements.
PRIOR ART
In the manufacture of papers and cardboards, the fibrous suspension is converted into a jet of pulp emerging from the headbox.
As is known, a headbox must essentially ensure a uniform and homogeneous jet in the outlet nozzle, whilst reducing the irregularities in speed, pressure and concentration originating from the pulp feed distributor. Whatever the pulp feed device, a headbox must essentially ensure the following principal properties:
These properties must be stable in space, especially in the cross direction, and in time (that is to say, in the direction of travel of the jet), so that the gsm substance of the sheet remains constant and homogeneous.
If the lip opening is constant, any local variation in the gsm substance of the sheet originates either from a local speed variation or from a variation in concentration caused by the flocculation or even from both at the same time.
When the speed in the jet varies, this causes a variation in the material quantity, which may introduce variations of the order of 1 to 5% in time and over the width of the formed sheet.
The variations in speed in the cross direction are non-turbulent in origin. They may be random if the surface state of the outlet nozzle is perfect, otherwise they may be stationary. Attempts have therefore been made to render the pressure in the outlet nozzle uniform so as to obtain a uniform distribution of the speed range. However, this adjustment is difficult to obtain over nozzle widths of the order of or greater than three metres.
As is known, the fluctuations in fiber concentration are linked to flocculation, the intensity of which depends essentially on the hydrodynamic turbulence generated in the headbox. This turbulence causes the dislocation of the flocks. Thus, the vortices of small size, that is to say those of which the size is smaller than that of the flocks, dislocate the flocks to individual fibers, whilst the large vortices carry the flocks along in their movement. It is therefore an interaction of these two types of vortices relative to one another, and this may cause reflocculation.
The headboxes designed for high-concentration formation must be efficient concentrated system and maintain it in the free jet must make it possible to produce perfectly homogeneous flows with concentrations currently adopted.
To obtain this result, use is generally made of the principle of generation of conventional turbulence, with variances to a greater or less extent for dislocating the flocks. However, conventional turbulence is not sufficient for a complete dislocation of the flocks. Moreover, the hydrodynamic boundary layer in the outlet nozzle, which is involved especially in the distribution of the speeds in the jet, is not taken into account in the design of the headboxes.
The invention overcomes these disadvantages.
It is aimed at a device of the type in question, making it possible to generate a special turbulence, in which the size of the vortices is calibrated according to a discrete law over the entire length of flow in the device.
The invention is aimed more particularly
REFERENCES:
patent: 2329799 (1943-09-01), Thorsen
patent: 2451305 (1948-10-01), Shannon
patent: 2756651 (1956-07-01), Lee
patent: 3228067 (1966-01-01), Strong et al.
patent: 4031013 (1977-06-01), Skretting
patent: 4376014 (1983-03-01), Bergstron
patent: 5100513 (1992-03-01), Crawford
Cognet Gerard
Pierrard Jean-Marie
Skali Lami Salah
Centre Technique de l'Industrie des Papiers
Valmet Corporation
Weldon Kevin
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