EP0044529A1 - Deflecting means for a fluid current and its use in an apparatus - Google Patents

Abstract

The inlet grid (11) is constituted by a thin corrugated sheet having, facing the flow of regularly rounded parallels (15), the flanks (16, 16 ') of two adjacent rounded constituting channels (19) converging on a perforated bottom (23). The invention is particularly applicable to dryers.

Description

The invention relates to a deflection grid and a circulation device using it. It is particularly applicable to "circulation chambers" used for bringing a gas into contact with a solid in an apparatus such as a dryer or an oven, or else for bringing into contact with a liquid or a solid in suspension. in an apparatus, such as a washing, absorption, or cooling tower.

Fluid circulation chambers usually include a fluid inlet distributor grid and a fluid outlet or take-up grid. The purpose of the inlet grids is to cause a deflection of the flow with deceleration of the fluid, and the outlet grate a deflection of the flow with acceleration of the fluid, so as to establish a uniform velocity field between these grids.

In the usual embodiments of rooms of this type, use is made of air inlet and / or return distribution grids made of thin and flat perforated sheets, generally associated with inlet and outlet corridors of constant height. As the thin-edge perforations of these grids have no straightening effect on the tangential components of the air at the inlet, there remain, despite a flow distribution effect at the inlet, significant oblique components of flow in the room which, combined with the wall effects of the room, allow poor air distribution to remain.

The correcting system for entering the fluid can be improved by creating a flow rectifying effect using a thick perforated sheet, such that the ratio of the thickness of this sheet to the diameter of the perforations is sufficiently high and greater than five. The fluid, which penetrates in an oblique jet into the perforations sticks to the walls of said perforations, then exits in jets of direction substantially normal to the plane of this sheet. This arrangement has the disadvantage of requiring either the use of thick, heavy and costly sheets, or of very thinly perforated sheets of medium thickness, which makes them sensitive to fouling by solid particles which may be in suspension. in the drying air.

A variant sometimes used with some success consists in using panels in the shape of a honeycomb in thickness sufficient health to obtain a good recovery of the flow. However, the honeycomb has the disadvantage of a low pressure drop and of very variable value depending on the angle of incidence of the fluid on its surface. Its application thus remains limited to situations in which the fluid to be diverted is itself brought to the panel with a very regular speed and direction, which can lead to adding a perforated sheet metal to create an additional distributing average pressure drop. In addition, the glued honeycombs have very limited temperature resistance.

Similarly, at the exit of the chamber, the perforated sheet having no deflector effect on the air which passes therethrough almost normally, it is created, to set in motion the air at high speed in a generally parallel direction at the grid in the outlet passage, a significant difference in pressure in this passage with respect to its end arranged at the intake of a fan. To remedy this pressure difference, which unbalances the distribution of the flow in the chamber, it is advisable to give the outlet grid an extremely high pressure drop to compensate for this difference in suction which is exerted through. We are thus led to use sheets with excessive pressure drops for a poor result, even when using divergent lanes.

The object of the invention is simply to obtain good uniformity of the fluid stream downstream of an inlet grid and / or upstream of an outlet grid, this without creating without excessive pressure drop.

The invention particularly relates to a deflection grid of a fluid stream to receive an incident fluid stream arriving in a direction of incidence and to form an emerging fluid stream flowing in a substantially uniform manner over its entire section at distance from the grid in a direction of emergence differing by more than 45 ° from the direction of incidence, this grid having orifices distributed over its entire surface, characterized in that it has the general shape of a panel made up by at least one thin corrugated and perforated sheet, the direction of the waves being perpendicular to both the directions of incidence and of emergence, each wave forming at least two bands, substantially planar, the lengths of which extend in this direction of waves, the perforations of this sheet constituting said orifices and at least some of them being produced in strips or the sheet is substantially perpendicular to the direction of flow nt downstream.

• chaque onde de la tôle comporte en partant du côté d'émergence, - une bande de fond sensiblement plane parallèle au plan moyen, avec une largeur au plus égale à 1,5 fois la projection du pas d'ondulation sur un plan perpendiculaire à la direction d'incidence,
• - deux bandes de flanc sensiblement planes situées de part et d'autres de cette bande de fond et divergeant à partir de celle-ci,
• - et une bande de sommet incurvée raccordant une des bandes de flanc de cette onde à une bande de flanc de l'onde adjacente, la concavité étant disposée du côté du fluide émergent, des perforations principales étant formées dans la bande de fond.

In the case where it is a question of realizing an entry grid perpendicular to the direction of emergence and ensuring a distribution function it seems advantageous to adopt the following arrangement:

• each wave of the sheet comprises, starting from the emergence side, - a substantially flat bottom strip parallel to the mean plane, with a width at most equal to 1.5 times the projection of the undulation pitch on a plane perpendicular to the bearing direction,
• - two substantially flat flank strips located on either side of this bottom strip and diverging from it,
• - and a curved top band connecting one of the bands flank of this wave to a flank band of the adjacent wave, the concavity being disposed on the side of the emerging fluid, main perforations being formed in the bottom band.

Preferably the height of the waves is between 1.5 and 5 times the width of the bottom strip.

• - une bande de guidage sensiblement plane qui dévie l'écoulement incident vers des perforations,
• - une bande perforée sensiblement perpendiculaire au plan du panneau,
• - les perforations s'étendant sur toute la largeur de cette bande perforée de manière que le fluide débouche desdites perforations en jets obliques décollés du panneau, ces jets reconstituant après diffusion un écoulement aval uniforme fortement incliné sur le plan du panneau.

In the case of an outlet grid making it possible to obtain a direction of emergence which is strongly inclined on the plane of the grid, it seems advantageous to adopt the following arrangement each wave of the sheet consists of:

• - a substantially flat guide strip which deflects the incident flow towards the perforations,
• - a perforated strip substantially perpendicular to the plane of the panel,
• - The perforations extending over the entire width of this perforated strip so that the fluid emerges from said perforations in oblique jets detached from the panel, these jets reconstituting after diffusion a uniform downstream flow strongly inclined on the plane of the panel.

The invention also relates to a fluid for interacting an object with a fluid in uniform flow in an internal chamber, this circulation chamber being characterized in that it comprises an inlet grid according to claim 2 and means to place said object downstream of this grid a distance at least equal to 10 times the undulation pitch of the latter.

• La figure 1 représente une vue schématique en coupe transversale d'un séchoir selon l'art antérieur.
• La figure 2 représente une vue schématique en coupe transversale d'un dispositif selon l'invention, ce dispositif constituant ici un séchoir.
• La figure 3 représente une vue en perspective schématique partielle de la grille d'entrée du séchoir selon la figure 1, cette grille étant une grille de déflexion selon l'invention.
• La figure 4 est une vue en perspective schématique d'une autre grille de déflexion selon l'invention, également utilisable pour un séchoir.
• La figure 5 est une vue en perspective schématique partielle de la grille de sortie du séchoir selon la figure 1, cette grille étant encore une grille de déflexion selon l'invention.

The characteristics and advantages of the invention will emerge from the description of an embodiment given by way of example and illustrated in the drawing, in the context of an elongated pasta dryer.

• Figure 1 shows a schematic cross-sectional view of a dryer according to the prior art.
• 2 shows a schematic cross-sectional view of a device according to the invention, this device here constituting a dryer.
• FIG. 3 represents a partial schematic perspective view of the inlet grid of the dryer according to FIG. 1, this grid being a deflection grid according to the invention.
• Figure 4 is a schematic perspective view of another deflection grid according to the invention, also usable for a dryer.
• Figure 5 is a partial schematic perspective view of the dryer outlet grid according to Figure 1, this grid also being a deflection grid according to the invention.

In drying, and in particular in the drying of a multitude of elaborate or pasty objects which cannot be placed in bulk in contact with one another, it is necessary to use drying chambers of large dimensions where the product to be dried offers little resistance to the flow of hot coolant gas. It is necessary to create throughout the extent of the drying chamber at the same time a circulation at uniform speed of the fluid itself brought to uniform temperature to obtain a dried product of regular quality, and to ensure a speed of said fluid sufficiently high to increase the dryer production and reduce the cost of investments and heat losses through the dryer walls. Correspondingly, for reasons of economy, the heat transfer fluid, suitably heated and dried, generally by extraction of hot humid air and admission of fresh dry air, is recycled on the product to be dried. For the same economic reasons, the space reserved for housing the fluid recycling circuits is so small that the recycled fluid flows through it at a speed much higher than that which it had when passing through the drying chamber; it is therefore necessary to control its admission under high speed into the drying chamber and its resumption at the outlet thereof, functions which are carried out by the use of deflection grids according to the invention ensuring at the same time the distribution functions or of recovery.

In Figure 1 the drying chamber 1 of the dryer contains the sheets of pasta ₁ 8 suspended on horizontal rods 2 which run perpendicular to the plane of the drawing in the dryer. The dryer shown has for simplicity only one layer of pasta. The air contained in the heat-insulated enclosure 6 of the dryer is recycled by a fan 3 and a heating battery 4 installed in a lateral corridor 5, then is admitted into an upper entry corridor 7 through a flat entry grille 11 on the pasta curtain. The speed in lane 7 can reach a value greater by at least three to five times the value of the average speed desired on the pasta curtain through the drying chamber; Similarly, the air is taken up at the lower part of the drying chamber 1 through a flat outlet grid 12 and sucked in by a lower outlet corridor 8 at a high speed. The high kinetic energy of the air in the upper corridor 7 combined with the suction of the fan 3 in the lower corridor 8 causes a strong dynamic imbalance which results in a very irregular speed distribution in direction and size on the curtain of pasta. , maximum values of two to three times the expected average value which can appear on the side opposite to the return passage 5, and low speeds and even recirculations from bottom to top which can occur in the upper part of the pasta curtain on the adjacent side in corridor 5. The degree of drying of the pasta obtained is then very uneven and the production of the dryer is reduced, even if the device is used to periodically reverse the direction of air circulation, because the phenomena of drying are not linear over time. We are then led to dispose at the outlet of the drying chambers a retention silo in which the rebalancing of humidity between the different more or less dry pastes occurs.

For simplicity, in FIG. 1, the humid air extraction and dry air intake devices intended to control the average humidity of the drying air have not been shown.

In Figure 2 there is shown in the same schematic form a dryer according to the invention produced so as to obtain a good distribution of the air flow over the pasta. The air from the lateral corridor 5 is introduced into the upper corridor 7 after having been deflected in a conventional manner by a deflecting grid 9. A convergent shape is given to the corridor 7 by means of the upper external wall 10 of the dryer which is arranged obliquely, the law of linearly decreasing section of the channel thus formed being, as it is well known, the theoretical law suitable for ensuring the compatibility of an aerodynamic field of uniform approach in speed and pressure in lane 7 with a sampling uniform flow through the inlet distributor grid 11. Furthermore, at the outlet of the pasta "bed", an outlet or return grille 12, intended to deflect the air by accelerating it, returns it obliquely in the divergent lower corridor 8. This corridor 8 is produced using the lower external wall 13, according to a law of linearly increasing section, suitable for ensuring the regular evacuation of the flow injected uniformly by the grid of so room 12 of room 1.

The velocity and pressure fields in the inlet corridor 7, in the drying chamber on the pasta "bed" and in the recovery corridor 8, are then uniform if the inlet distributor grid 11 deflects the oblique flow of the corridor 7 in a vertical flow at the entrance to the chamber and if the outlet grid 12 ensures a deflection of the vertical flow in an oblique flow at its exit according to a leak angle equal to the angle slope of the oblique panel 13.

The inlet distribution grid 11 shown in FIG. 3 is obtained from a thin stamped panel so as to form corrugations having facing the flow of the roundings 15 arranged in parallel according to a pitch referenced at 14. The roundings 15 are extend by upstream sides 16 and downstream sides 16 ′ with respect to the incident flow represented by an arrow 25. These sides are rectilinear and inclined on the normal to the plane of the panel, so as to form channels 19 which converge slightly towards a bottom 23 comprising perforations 20 leaving spacer tongues 21. The grid 11 is folded at the bottom of the channel 19 in a flat or rounded shape. The width referenced 17, of the perforated bottom 23 is at most equal to 1.5 times the projection of the pitch 14 of the undulations on a plane perpendicular to the generally oblique direction of the incident flow 25. It follows that, for the angle normal incidence of the flow of the fluid to be diverted and distributed over the grid 11, the approach speed of the fluid diverted to the bottom of the channel retains a value close to and at least equal to 0.6 times the value of the speed of incident flow 25.

Air escapes from the grid 11 through the perforations 20 which can be circular, oblong, square or rectangular. The day or rate of perforation created by the perforations 20 does not exceed 85% so as to leave tabs 21 of sufficient width to ensure the mechanical continuity of the corrugations and the good performance of the panel grid.

The day at the bottom of the channel can, however, be reduced to values lower than 85%, for example up to 50%, to improve if necessary the distributing qualities of the grid at the cost of an increased pressure drop. The height of the channel referenced at 26 is between 1.5 and 5 times the width 17 of the bottom 23 of a channel 19. The inclination of the sides 16 and 16 'of the undulations on the normal to the overall plane of the grid is not more than 20 ° angle. The fluid escapes from the perforations 20 in the form of high-speed jets, which after diffusion form a uniform velocity flow which is restored at a distance downstream from the grid of the order of ten times the step 14 of the undulations.

In practice, a distributing grid with a given profile retains its deflecting and distributing qualities for a large incidence range of the fluid to be distributed, from an angle of approach normal to the grid to a maximum value of the angle of approach in oblique attack of the panel all the higher as the ratio of the space 17 at the bottom of the channel to the pitch 14 is low. For angles of approach that are too small relative to the plane of the grid, the flow takes off on the rounded edges 15 ′ in order to abut and rebound on the downstream flank 16 ′ of the channel 19, disposed opposite the incident flow, the outlet jets can even be returned in a direction opposite to the direction of flow approach.

To improve the functioning of the grid at large angles of approach, auxiliary perforations 24 can be provided in the downstream sides 16 ′ at the limit of the rounding 15 of the wave, on the side opposite to the oblique impact of the fluid to deviate. The fluid sucked in by the auxiliary perforations 24 results in the resorption of the release pockets and at the same time causes the correct rounding of the roundness 15 of the corrugation.

It further results that the fluid sucked through the perforations 24 serves to supply the downstream flow through the dead space located under the grid 11 and thus improves the uniformity of the flow of the fluid downstream of the panel. The perforated auxiliary surface 24 can be at most equal to the normal perforation 20 of the bottom 23 of the channels 19.

The essential qualities resulting from the distribution grid according to FIG. 3 are aerodynamic, technical and economic.

On the aerodynamic level, the grid adapts to a very variable angle of incidence of the approach flow up to a high limit angle depending on the perforations and the profiling of said grid, this good ability being linked to the presence rounding 15 of the ripple to the flow and to the converging shape of the channels 19 comprised between the flanks 16 and 16 'of the rounded, the flow being deflected and traversing said channels practically without slowing down or losses. The pressure drop of the grid is weakly dependent on the approach angle up to the limit angle of use, the loss being practically only constituted by the diffusion of the jets from the perforations 20 by sudden widening at the outlet. The grid thus has practically the minimum loss for deviating and distributing the fluid in an oblique approach.

On the technical level, by the manufacturing principle, by stamping, a very regular, rigid and light grid is obtained, without welding or gluing, which allows it to be used at high temperature if it is metallic. In addition, the grid is not very sensitive to the fouling phenomenon due to its rounded shape facing the flow and the absence of re-entrant angles, where particles could be deposited.

The manufacture of these grids according to the methods of manufacturing conventional corrugated perforated sheets, while saving labor costs, makes these grids particularly economical.

The ripple pitch is chosen to be less than 1/10 of the distance between the grid 11 and the pasta plies 18 so as to ensure uniform flow at the level of these plies.

The use of the distributing grid according to the invention is not limited to the sole case of the general oblique approach at a constant angle of the fluid flow to be diverted and distributed, but can be extended to the case of fluids approaching from different angles in space.

In the embodiment of the cylindrical chamber 1 of FIG. 4, the use of two grids 11 and 11 ′, arranged in series in parallel planes so that their rounded edges 15 and 15 ′ are oriented perpendicular to each other others, destroys all components tangentials of the upstream flow and restore a downstream speed perfectly oriented according to the normal to the plane of the grids.

FIG. 5 shows an embodiment of the outlet grid 12 from the chamber 1 and of entry into the exit corridor.

The purpose of the outlet grille 12 is to deflect the air and return it at an oblique exit angle by accelerating it, the directions of incidence and emergence being represented by the arrows 25 'and 42' respectively. The grid 12 consists of a thin-walled panel from which perforations 33 have been previously cut. The panel is then pleated by stamping so as to form blades 30 parallel to each other, at the step referenced at 29. The blades 30 are inclined on the overall plane of the grid 12 with a setting angle referenced at 31 the smaller the greater the deflection of the desired flow. The blades 30 are mechanically joined together by tabs 32 remaining after perforation of the panel.

The fluid which passes through the grid 12 abuts against the blades 30 and passes after separation of the flow on the upstream lip 34 of the blade 30 in the perforations 33 released by cutting between the tongues 32. These perforations 33 can be square or rectangular , or even oblong or circular.

The deviation sought is all the more easily obtained and for a pressure drop all the lower the greater the projection referenced at 38 of the blade 30 on the plane of the panel of the grid 12 compared to the pitch referenced at 29, the projection referenced at 37 of the tongue 32 being reduced to the minimum compatible with the requirements for folding the tongue 32. The gap 37 is approximately equal to twice the minimum internal radius of folding of the sheet. This radius is therefore worth approximately five times the thickness of the sheet forming the panel.

The outlet grid 12 according to the invention can be attacked by the fluid at an angle deviating from the normal to the grid. It then transforms the tangential component normal to the generators of the blades and keeps the tangential component parallel to the generators and restores the component normal to the plane of the grid after diffusion of the output jets.

In its most frequent and most interesting use, the grid 12 will be used without approach component parallel to the generatrices of the blades 30. For a given grid, the exit angle of the speed varies as a function of the angle of approach with normal to the grid. For sufficiently deviating grids, more than 70 °, this exit angle varies however quite small for an oblique attack not deviating by more than 20 ° from the normal attack, and the same grid can be used in this range, which allows it to be placed obliquely if necessary at the outlet of the drying chamber.

The outlet grids according to the invention have deflecting and distributing qualities, in particular in association with a divergent return passage 8 which brings their performance closer to that which could theoretically be achieved with a grid of the turbine blade type, while keeping the qualities of simplicity and economy of construction, robustness and the advantage of a large format.

Claims (8)

1 / Fluid current deflection grid for receiving an incident fluid current arriving in an incidence direction (25, 25 ') and forming an emerging fluid current flowing in a substantially uniform manner over its entire section at distance from the grid in an emergence direction (42, 42 ') differing by more than 45 ° from the direction of incidence, this grid having orifices distributed over its entire surface, characterized in that it has the shape general of a panel (11, 12) consisting of at least one thin corrugated and perforated sheet, the direction of the waves being perpendicular to both the directions of incidence and of emergence, each wave forming at least two bands (23 , 16, 16 ') (30, 32, 33) substantially planar, the lengths of which extend in this direction of the waves, the perforations (20, 24) (33) of this sheet forming said orifices and some of them ( 20) (33) at least being produced in strips (23) (32, 33) where the sheet metal st substantially perpendicular to the direction of emergence. 2 / deflection and distribution grid according to claim 1, this grid having the form of a panel (11) perpendicular to the direction (42) of emergence of the fluid and being characterized in that each wave of the sheet starting from the emergence side, - a substantially flat bottom strip (23) parallel to the mean plane, with a width at most equal to 1.5 times the projection of the undulation pitch on a plane perpendicular to the direction of incidence (25), and with main perforations (20), - two substantially flat side strips (16, 16 ') located on either side of this bottom strip and diverging from it, - And a curved top strip (15) connecting one of the flank bands of this wave to a flank band of the adjacent wave, the concavity being arranged on the side of the emerging fluid. 3 / Grid according to claim 2, characterized in that the auxiliary perforations (24) are formed astride the top strip (15) and the side strip (16 ^* ) located downstream of the top strip by compared to the incident flow. 4 / grid according to claim 3, characterized in that the height of the waves is between 1.5 and 5 times the width of the bottom strip (23). 5 / Grid according to claim 1, this grid having the form of a panel (12), characterized in that each wave of the sheet is made up of: - a substantially flat guide strip (30) which deflects the incident flow towards the perforations (33), - a perforated strip (32, 33) substantially perpendicular to the plane of the panel, - the perforations (33) extending over the entire width of this perforated strip so that the fluid emerges from said perforations (33) in oblique jets detached from the panel, these jets reconstituting after diffusion a uniform downstream flow strongly inclined on the plane of the sign. 6 / grid according to claim 5, characterized in that the angle (31) of inclination of the guide blades (30) on the plane of the panel is at most equal to 45 °. 7 / A device for circulating a fluid to make an object interact with a fluid in uniform flow in a chamber (1), characterized in that it comprises an inlet grid according to claim 2 and means for placing said object (18) downstream of this grid (11) a distance at least equal to 10 times the undulation pitch of the latter. 8 / Device according to claim 7, characterized in that the chamber (1) is arranged between a grid inlet (11) according to claim 2 and an outlet grille (12) according to claim 5 opposite the inlet grille.

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