US3759580A

US3759580A - Structure for transporting fluid-entrainable material

Info

Publication number: US3759580A
Application number: US00255700A
Authority: US
Inventors: D Ott; I Reba
Original assignee: Crown Zellerbach Corp
Current assignee: James River Corp of Nevada
Priority date: 1972-05-22
Filing date: 1972-05-22
Publication date: 1973-09-18
Anticipated expiration: 1990-09-18
Also published as: NL7306912A; JPS5342956B2; SE401159B; DE2326011A1; CA975823A; FR2185569A1; FR2185569B1; JPS4949384A; GB1406951A

Abstract

Fluid-entrainable material is transported along a first flow path and then around a bend or corner to a second flow path. In order to minimize impingement of the particles against a surface defining the outer radius of the corner, means, in the form of a Coanda nozzle which is further described in the specification, is arranged in the corner to increase the downstream flow velocity along a downstream surface in the second flow path leading from the inner radius of the corner as compared to downstream flow velocity along the surface defining the outer radius of the corner. Further, means are provided cooperating with the Coanda nozzle in the corner to remove some entraining fluid from the first flow path before the particles reach the corner to slow them down, and then reintroduce the removed entraining fluid into the second flow path. Because auxiliary fluid is added at the corner, vent means are provided to remove this fluid downstream of the corner and structure is disclosed which permits reintroduction of the vented fluid into the corner.

Description

United States Patent. 1 ()tt et al.

[111 3,759,580 Sept. 18, E973 STRUCTURE FOR TRANSPORTING FLUlD-ENTRAINABLE MATERIAL [57] ABSTRACT [75] Inventors: 3 22 gig zggg f Reba Fluid-entrainable material is transported along a first n ouver O o S flow path and then around a bend or corner to a second [73] Assignee: Crown Zellerbach Corporation, flow path, In order to minimize impingement of the San Francisco, Calif. particles against a surface defining the outer radius of 7 W the corner, means, in the form of a Coanda nozzle [2-2] Filed May 1972 which is further described in the specification, is ar- [21] Appl. No.: 255,700 ranged in the corner to increase the downstream flow velocity along a downstream surface in the second flow path leading from the inner radius of the corner as [a] 302/64, 302/29 compared to downstream flow velocity along the sub fuss! "i; "6 face f g the outer radius of the comer. Further, l e o 3 2/29 2 means are provided cooperating with the Coanda noz- 02/17 64 zle in the comer to remove some entraining fluid from the first flow path before the particles reach the comer [56] Cited to slow them down, and then reintroduce the removed UNITED STATES PATENTS entraining fluid into the second flow path. Because auxl,5l2,322 10/1924 Wallace 302/23 X iliary fluid is added at the corner, vent means are pro- 3,205,0l6 9/1965 Panning... 302/23 vided to remove this fluid downstream of the corner 3,321,251 5/1967 Reitere r 302/23 and structure is disclosed which permits reintroduction of the vented fluid into the corner. Primary Examiner'-Evon C. Blunk Assistant ExaminerH. S. Lane 12 Claims, 4 Drawing Figures Attrney-J0hn O. Reep et al.

w L ll w l W i 68 l 62 I6 IO 6 52 42 II I.

24- 26 2 11. o a i 74 t h 76 4o t H i STRUCTURE FOR TRANSPORTING FLUID-ENTRAINABLE MATERIAL BACKGROUND OF THE INVENTION The present invention relates to structure for transporting fluid-entrainable material in an entraining fluid.

Particulate material, such as wood chips, sand, grain, or other fluid-entrainable material, is often conveyed through pipes by entraining this material in an entraining fluid, such as air, and rapidly moving the material with the fluid by aid of fans, blowers or the like from a zone at the inlet of the pipe to a remotely located outlet zone. It is often necessary to provide bends or corners in the conveying pipe so that the material is turned from a first flow path to a second flow path extending in a different direction. Providing bends or corners in the pipe introduces problems because therapidly moving material, in negotiating the corner, tends to impinge against the surface defining the outer radius of the corner, causing erosion of the pipe surface and damage to entrained materialas a result of such impingement.

There are structural arrangements which have been previously suggested for minimizing the erosion problem caused by impingement of the particles at the surfaces defining the corner. Prior structural arrangements are exemplified by such patents as US. Pat. Nos. 584,968 and 3,149,885; German Pat. Nos. 584,852 and 598,363; and British Pat. Nos. 731,646 and 11,590 (1915). While the patents just mentioned suggest supplying auxiliary fluid at the bend or comer to aid the entrained material in negotiating the turn, none has suggested the desirability of'or provided means for purposely increasing the velocity of the entraining fluid along the surface leading downstream of the inner ra- SUMMARY In accordance with one aspect of the present invention, means are provided'deflning flow paths for fluid entrainable material wherein the material flows in and with the entraining fluid along a first flow path, turns a corner, and then continues along a second flow path extending in a different direction from the first flow path. Structural means, such as a Coanda nozzle, is positioned in the vicinity of the corner to increase the flow velocity of the entraining fluid along the surface in a downstream direction forming a continuation of the inner radius of the comer as compared to the downstream flow velocity along the surface in the second flow path forming a continuation of the outer radius of the comer.

Another aspect of the present invention resides in taking advantage of theentrainment properties of Coanda nozzles to remove a portion of the entraining fluid from the first flow path to slow the particles prior to reaching the corner and then reintroducing this ,removed entraining fluid into the second flow path.

Yet other aspects reside in provision of vent means for venting or removing auxiliary entraining fluid from the flow path downstream of its introduction and recirculating this removed fluid into the system.

' BRIEF DESCRIPTION OF THE DRAWINGS Embodiments of the present invention are illustrated in the accompanying drawings in which:

FIG. 1 is a side sectional view through a structure of one embodiment of the present invention;

FIG. 2 is a sectional view taken on line 22 of FIG.

FIG. 3 is a side sectional view through a structure fonning another embodiment of the present invention; and

FIG. 4 is a diagrammatic sectional view to illustrate dimension and flow velocities obtained under specified operating conditions of a structure made in accordance with the present invention.

GENERAL DESCRIPTION Because reference has been made previously, and will hereinafter be made, to a phenomenon known as the Coanda effect," it will be useful to provide a description thereof. This phenomenon has been known for many years, as exemplified by US. Pat. No. 2,052,869 Coanda, and can be described as the tendency of a fluid, which emerges from a slit under pressure, to attach itself or cling to and follow a surface in the form of an extended lip of the slit, which lip recedes from the flow axis of the fluid as it emerges from the slit. This creates a zone of reduced pressure in the region of the slit and so air or any other entrainable material which is in the zone will become entrained and flow with'the fluid which has attached itself to the extended lip. A Coanda nozzle may, therefore, be defined as a device which utilizes this phenomenon.

Referring now to FIGS. 1 and 2, there is disclosed structure comprising means defining a first flow path 10 which leads, in the direction of arrows as illustrated in the drawing, around a comer 12 into a second flow path 14 which extends in a different direction from the first flow path.

Upstream of the comer 12, the first flow path 10 is generally rectangular'in cross-sectional configuration, and the flow path is enclosed by bottom wall 16, top wall 18 and opposed

side walls

20 and 22. Downstream of the corner 12, the second flow path is also generally rectangular in cross-sectional configuration and is defined by bottom wall 24, top wall 26 and opposed

side walls

28 and 30.

' The top wall 18 has a portion 32'which diverges upwardly in a direction leading into the corner to provide an enlarged zone in the corner which is capable of receiving a Coanda nozzle 34 having a curved upper sur- I I under pressure from a compressor or pump 40, having a duct 42 leading to the chamber. There are lips 44 and 46 defining a slit 48 leading from chamber 38, and one of the lips 46 is extended and recedes from the flow axis of fluid as it emerges from the slit to provide a flow attachmen surface 50 for this fluid so that it operates in accordance with the aforementioned Coanda effect.

" The bottom surface 52 of the nozzle 34 is flat, and the nozzleis so positioned in the enlarged corner zone so that the surface 52 provides an upper boundary for particulate material being entrained along a substantially straight line in the first flow path 10. The upper curved surface 36 of the nozzle 34 provides a lower boundary for a secondary path 54 which is in communicationwith the first flow path 10 through opening 56.

A screen 58 extends across the opening to this secondary path 54, and the mesh size of the screen is chosen so as to prevent entrained particulate material from entering this secondary flow path while permitting entraining fluid to pass therethrough.

The bottom surface 52 of nozzle 34 is slanted in such a manner that the cross-sectional area of the first flow path decreases in a downstream direction starting from an area adjacent upstream end 60 of the nozzle surface 52 toward downstream end 62 of the nozzle surface 52. This reduction in the cross-sectional area of the flow path is desirable to aid in assuring that the entraining fluid has sufficient velocity while passing through this region of decreased area to maintain entrainment of the particles, taking into account the fact that some of the entraining fluid has been removed through secondary path 54.

Wall 26 which defines one boundary of second flow path 14 provides a first surface portion 64 which extends in a direction intersecting the first flow path downstream in continuation of the outer radius of the corner between the first and second flow paths. Wall 24 which defines another boundary of second flow path 14 provides a second surface portion 66 which extends downstream of the corner 12 in continuation of the inner radius of the corner.

The flow attachment surface 50 of nozzle 34 is positioned so as to direct a curtain of entraining fluid moving at high velocity in a direction extending across the path of flow of entrained material traveling along the first flow path 10. The curtain is directed toward surface 66. This high velocity curtain follows surface 66 so that the velocity of entraining fluid flowing in a downstream direction along second surface 66 is substantially increased as compared to the flow velocity extending downstream along first surface 64. This increased velocity along surface 66 has a rapid turning effect on the entrained material and has been found to substantially reduce impingement of the entrained material against surface 64, and, therefore, reduces erosion of this surface. Stated another way, this increased velocity flow along surface 66 tends to re-entrain the entraining fluid in a direction away from the outer surface 64 and, in turn, carries the material in a direction away from wall 64 which minimizes direct impingement of material against surface 66.

Operation of the structure thus far described can best be understood by referring to FIG. 4 in connection with the following description. A device, as illustrated at FIG. 4, was constructed with the following dimensions:

Dimension A 3 inches Dimension B 3 34 inches (width of wall 18) Dimension "C" inches Dimension D 28 inches Dimension E" 4 inches Dimension F 3 V: inches Dimension G 2 V4 inches Dimension H" 2 A: inches Dimension 1" 4 inches Dimension K 3 inches Dimension L 3 .4 inches (width of wall 26) Dimension M 2 inches Air was supplied to chamber 38 under a pressure of 5.0 psig, and the width (distance between lips 44 and 46) of slit 48 was 0.050 inch. A pitot tube was inserted through small openings in the walls at various points in the system to obtain velocity profiles of air moving through various parts of the system, and velocities (in feet per minute) are indicated at FIG. 4.

Still referring to FIG. 4, when air exits from slit 48 it attaches itself to and follows flow attachment surface 50 at substantial velocity due to the aforementioned Coanda effect. This curtain of air is directed downstream along surface 66 so that the flow velocity about one-eighth inch from surface 66 and about one-fourth inch downstream from the corner 12 is about 3,600 feet per minute in a downstream direction. With the conditions just described, there is no downstream flow velocity at a point about one-eighth inch from surface 64 directly across from the point where the aforementioned 3,600 feet per minute reading was obtained; in fact, as indicated in the drawing, a back-flow was created, causing a velocity along surface 64 of about 1,300 feet per minute in an upstream direction.

Still referring to FIG. 4, when air exits at high velocity from slit 48, a zone of reduced pressure is created in the region of the slit which causes entrainment of a substantial volume of air into the system through inlet 68. With about 60 SCFM (standard cubic feet per minute) of air supplied to chamber 38, the induced air flow was about 220 SCF M in the first flow path 10 upstream of opening 56, 150 SCFM in

secondary path

54, 70 SCFM in the flow path 10 downstream of opening 56, and 280 SCFM in the second flow path 14. The side walls of the system were made of rigid, transparent plastic so that the extent of direct impingement of material exiting from flow path 10 against surface 64 could be observed visually. When wood chips were fed to the inlet and propelled therethrough by entrained flow, the chips rapidly turned the corner and very little impingement of the chips against the surface 64 was observed. It will, of course, often be desirable to utilize additional pipe section both upstream and downstream of the system illustrated at FIG. 4, and in such instances it will be desirable to utilize sources for supplying entraining fluid to the system in addition to the Coanda nozzle located in the corner.

As regards values for pressure supplied to chamber 38 and for the width of slit 48, these values may be chosen over a rather broad range depending on such factors as the size of the pipes in the system and the velocity with which it is desired to move the entrained material through the system. Thus, the width of the slit 48 is preferably selected to be between about 0.001 to 0.150 inch. The cross-sectional area of the slit opening should preferably be between about 0.1 percent and 10.0 percent of the cross-sectional area in the duct between comer l2 and downstream end 62 of the nozzle. Pressures supplied to chamber 38 may be between 1 psig and 400 psig. For a given slit width, an increase in the pressure of fluid that is supplied to the slit will increase the velocity of the fluid as it exits from the slit and moves over attachment surface 50 and, therefore, the velocity imparted to the material being entrained will increase.

Again referring to FIG. I, it is to be understood that additional fluid is introduced into the system via nozzle 34. In order to eliminate the necessity for enlarging the pipelines downstream of the nozzle, especially when additional, relatively long sections of pipes are utilized downstream of the comer, it is desirable to remove the auxiliary entraining fluid introduced through nozzle 34 from the system downstream of the corner. To accomplish this removal of air, a venting chamber 70 may be provided in the second flow path 14 downstream of corner 12. This venting chamber can lead through a valve 72 to an outlet 74. Optionally, the outlet 74 may be connected to an inlet pipe 76 leading to compressor or pump 40 so that vented fluid can be continuously recirculated through the system.

Now, turning to the embodiment illustrated at FIG. 3, there is illustrated a pipe 80 defining a first flow path 82 for entrained material, and the material passes around corner 84 to a second flow path 86 defined by a pipe 88. A first downstream surface portion 90 in the second flow path extends in a direction intersecting the first flow path downstream in continuation of the outer radius of the corner 84, and a second downstream surface portion 92 extends downstream of the corner in continuation of the inner radius of corner 84. Actually, the surface portion 92 forms a flow attachment surface for fluid exiting from slit 94 in Coanda nozzle 96, the fluid being supplied from pump or compressor 98 via chamber 100.

It is to be understood that the velocity of the fluid moving along surface 92 in a downstream direction is substantially greater than the velocity of the fluid moving along surface 90 in a downstream direction. The flow entrainment caused by this high velocity movement along surface 92 causes the entrained material to rapidly turn the corner and follow second flow path 86.

Because a reduced pressure zone is created in the region of the slit, this region seeks" additional fluid for entrainment. It is, therefore, desirable to provide an opening 102 through the outer bend of surface 90 to provide a source for this additional fluid. This opening 102 could be in communication with the atmosphere, or, optionally, and as shown in FIG; 3, it may be in communication with a venting chamber 104 downstream of this corner via auxiliary duct 106 to recirculate vented fluid. As in FIG. 1, an additional venting duct 108 with valve 110 may be provided, and, if desired, this venting duct 108 may be attached in fluid flow communication to an inlet 112 to compressor 98.

While the foregoing specification has set forth specific embodiments of the invention in detail for purpose of making a complete disclosure, other embodiments will occur to those skilled in the art, but will fall within the spirit and scope of the invention defined in the following claims.

What is claimed is:

1. Structure for transporting and turning material entrained in an entraining fluid from a first flow path around a corner to a second flow path extending in a different direction from the first flow path, including:

means defining said first flow path;

means defining said second flow path, including a first downstream surface portion which extends in a direction intersecting the first flow path downstream in continuation of the outer radius of the comer, and said means defining the second flow path further including a second downstream surface portion which extends downstream of the corner in continuation of the corner; and

means for increasing the flow velocity of the entraining fluid in a downstream direction along said second downstream surface as compared to the flow velocity along said first downstream surface comprising a nozzle having a chamber for receiving fluid under pressure, pump means for supplying fluid to said chamber, means defining an exit slit leading from said chamber, and a curved fluid flow attachment surface leading in a downstream direction from said slit, said fluid flow attachment surface being positioned to utilize the Coanda effect to direct the fluid attached thereto in a downstream direction along said second downstream surface portion whereby a turning of said entrained material is facilitated and impingement of the entrained material against the first downstream surface portion is reduced.

2. The structure as set forth in claim ll wherein said fluid flow attachment surface leading from said slit is spaced from said second downstream surface portion and is positioned to direct a curtain of fluid across the flow path of the entrained material traveling along said first flow path.

3. The structure as set forth in claim it wherein said flow attachment surface forms a part of said second downstream surface portion.

4. The structure as set forth in claim 3 which further includes means defining an opening through said first downstream surface portion to permit entry of fluid through said opening toward a zone of reduced pressure caused by fluid exiting from said slit.

5. The structure as set forth in claim 4 which further includes an auxiliary duct connecting said opening in fluid flow communication with a zone downstream of said first down-stream surface portion to cause removal and re-entrainment of entraining fluid passing downstream of said comer.

6. Thestructure as set forth in claim 1 which further includes means defining a vent for removing entraining fluid supplied to the material flow path from said chamber at a position downstream of said corner.

7. The structure as set forth in claim 6 wherein said 7 vent means is connected in fluid flow communication with said pump means whereby fluid removed from said vent is recirculated through said chamber.

8. Structure for transporting fluid-entrainable material entrained in an entraining fluid from a first flow path around a corner to a second flow path extending in a different direction from the first flow path, said structure including:

v Surface portions defining said first and second flow paths for said material;

Means comprising nozzle structure within said corner for removing entraining fluid from said entrainable material passing through said first flow path and for redirecting the removed entraining fluid into the second flow path, said nozzle structure including a chamber for receiving fluid under pressure and pump means for supplying fluid to the chamber,

means defining a slit leading from said chamber, and a curved fluid flow attachment surface leading from said slit, said fluid flow attachment surface being positioned to utilize the Coanda effect to direct entraining fluid exiting from said slit across the first flow path in a direction leading downstream of said second flow path along a predetermined sur-' face portion of said second flow path whereby the fluid attached thereto re-entrains material exiting from said first flow path into said second flow path and reduces impingement ofsaid material against a surface portion of said second flow path. 9. Structure as set forth in claim 8 wherein said nozzle structure includes surface portions which define 12. The structure as set forth in claim 8 wherein the cross-sectional area of the slit leading from the chamber is between about Oil percent and 10.0 percent of the cross-sectional area defined by the surface portions in the immediate vicinity of the downstream extent of the fluid flow attachment surface.

t I i i

Claims

1. Structure for transporting and turning material entrained in an entraining fluid from a first flow path around a corner to a second flow path extending in a different direction from the first flow path, including: means defining said first flow path; means defining said second flow path, including a first downstream surface portion which extends in a direction intersecting the first flow path downstream in continuation of the outer radius of the corner, and said means defining the second flow path further including a second downstream surface portion which extends downstream of the corner in continuation of the corner; and means for increasing the flow velocity of the entraining fluid in a downstream direction along said second downstream surface as compared to the flow velocity along said first downstream surface comprising a nozzle having a chamber for receiving fluid under pressure, pump means for supplying fluid to said chamber, means defining an exit slit leading from said chamber, and a curved fluid flow attachment surface leading in a downstream direction from said slit, said fluid flow attachment surface being positioned to utilize the Coanda effect to direct the fluid attached thereto in a downstream direction along said second downstream surface portion whereby a turning of said entrained material is facilitated and impingement of the entrained material against the first downstream surface portion is reduced.

2. The structure as set forth in claim 1 wherein said fluid flow attachment surface leading from said slit is spaced from said second downstream surface portion and is positioned to direct a curtain of fluid across the flow path of the entrained material traveling along said first flow path.

3. The structure as set forth in claim 1 wherein said flow attachment surface forms a part of said second downstream surface portion.

5. The structure as set forth in claim 4 which further includes an auxiliary duct connecting said opening in fluid flow communication with a zone downstream of said first down-stream surface portion to cause removal and re-entrainment of entraining fluid passing downstream of said corner.

6. The structure as set forth in claim 1 which further includes means defining a vent for removing entraining fluid supplied to the material flow path from said chamber at a position downstream of said corner.

7. The structure as set forth in claim 6 wherein said vent means is connected in fluid flow communication with said pump means whereby fluid removed from said vent is recirculated through said chamber.

8. Structure for transporting fluid-entrainable material entrained in an entraining fluid from a first flow path around a corner to a second flow path extending in a different direction from the first flow path, said structure including: Surface portions defining said first and second flow paths for said material; Means comprising nozzle structure within said corner for removing entraining fluid from said entrainable material passing through said first flow path and for redirecting the removed entraining fluid into the second flow path, said nozzle structure including a chamber for receiving fluid under pressure and pump means for supplying fluid to the chamber, means defining a slit leading from said chamber, and a curved fluid flow attachment surface leading from said slit, said fluid flow attachment surface being positioned to utilize the Coanda effect to direct entraining fluid exiting from said slit across the first flow path in a direction leading downstream of said second flow path along a predetermined surface portion of said second flow path whereby the fluid attached thereto re-entrains material exiting from said first flow path into said second flow path and reduces impingement of said material against a surface portion of said second flow path.

9. Structure as set forth in claim 8 wherein said nozzle structure includes surface portions which define boundaries for said first flow path and a path for the entraining fluid removed from the first flow path.

10. The structure as set forth in claim 9 which further includes a screen separating the path for the removed entraining fluid from the first flow path.

11. The structure as set forth in claim 8 wherein the slit leading from said chamber has a substantially uniform width in the range of 0.001 to 0.150 inch.

12. The structure as set forth in claim 8 wherein the cross-sectional area of the slit leading from the chamber is between about 0.1 percent and 10.0 percent of the cross-sectional area defined by the surface portions in the immediate vicinity of the downstream extent of the fluid flow attachment surface.