MXPA01003371A - Flow modifier for submerged intake screen - Google Patents

Abstract

Improved flow modifier assembly (40, 60) for a water intake system having a cylindrical intake screen (44, 64) prevents damage to fish and other aquatic organisms by providing a controlled velocity profile which causes the average flow velocity (58) to closely approach the peak flow velocity. By extending two or more concentric tubular flow modifiers (42', 52) or (62', 67, 68, 69) into one end of the screen, it is possible to achieve flow uniformities of more than 90%, as compared to a maximum of about 72%for a prior art configuration utilizing a single tube flow modifier (22). In addition, the size, weight and cost of screen required can be greatly reduced for a given peak flow velocity as compared to prior art devices.

Description

FLOW MODIFIER FOR SUBMERGED SOCKETS TECHNICAL FIELD The invention relates to submerged intake meshes, and particularly to internal flow modifiers for said meshes which help to ensure that the maximum flow velocity in the mesh is controlled sufficiently to avoid damage to the fish and at the same time, avoid the accumulation of waste.

BACKGROUND OF THE INVENTION Major manufacturing plants, large cities, irrigation systems and power generation facilities require large quantities of water for their successful operation. For reasons of economy and to facilitate inspection, it is desirable that the length of the collection pipe that must be placed in a body of water such as a lake or a river be minimized. It is also desirable that the mesh assembly that filters the water entering the collection pipeline be as small as possible. However, it is still important, the need to protect fish and other aquatic organisms from damage and prevent the accumulation of debris along the length of the mesh to ensure maximum peak flow velocity through any of the slots of the intake mesh is maintained at 15.5 cm per second or less. A flow modifier of the prior art comprises a single pipe extending within a mesh cylinder. The single pipe flow modifier is typically 50% of the diameter of the mesh cylinder and about 33% of its length. This prior art arrangement is apt to increase flow uniformity, which is the ratio of average to peak flows, approximately 72% compared to just 32% for a cylinder without a flow modifier. Patent A-2 249 960 describes an entry mesh assembly according to the preamble of claim 1.

BRIEF DESCRIPTION OF THE INVENTION Among the objectives of the present invention is provided a flow modifying structure for a cylindrical take-off mesh assembly that will provide a degree of protection to aquatic life as well as the prevention of waste accumulation. Another additional objective is to provide such protection with a structure that allows the use of a mesh assembly of smaller diameter than that previously described. Yet another additional objective is to provide an average flow uniformity across the mesh surface that is very close to the allowable peak flow rate. These and other objects are achieved with the flow modifier and tap screen assembly of the present invention. The mesh is preferably cylindrical and of a length equal to approximately 85-140% of its outer diameter. However, it is highly preferable that the length and diameter of the cylinder be equal to achieve the most desirable flow distribution and minimize the amount of material in the mesh element. Such a shape will more closely approximate the ideal mesh shape that would be spherical, but which would be extremely difficult and costly to manufacture than the wire mesh having a constant slot width. The take-up mesh assembly preferably includes two or more internal flow modifier tubes projecting concentrically towards one end of the axial length of the cylindrical mesh. Proceeding radially inward from the cylindrical mesh surface, each successive tube is somewhat smaller in diameter than the previous one and extends a greater distance in the cylinder of the mesh. Each of the flow modifier tubes has a diameter, the largest of which is about 60% or less of the diameter of the mesh. In addition, preferably they have transverse inflow areas that are approximately equal. The design results in the maximum velocity or peak flow in the mesh at any point along its length that is very close to the average design speed. The average design speed is determined by the volume of water that is expelled by the system pump in the flow modifier tubes divided by the open area of the mesh. For the commonly acceptable peak slot speed of 15.5 cm x second, the improved design can provide an average slot speed of at least 14 cm x second compared to an average slot speed of approximately 11 cm x second for a single tube flow modifier of approximately 4.9 cm x second for a system in where there is no flow modifier tube. The grooves in the mesh comprise the space between the profiled wire covers that form the cylindrical mesh surface. The shape of the wire mesh is important since it has been found that the smooth surface created by a construction with the base of a trapezoid wire facing outwards allows the sliding of debris on the surface of the mesh. Slots can also be formed in the wall of a solid pipe element. In the covered wire mode, the slots can be both transverse and parallel to the mesh axis. In the above arrangement, the covered mesh would have to be cut along its length, flattened, and rolled into a cylinder and welded. For larger sizes, the expense of performance to develop these additional manufacturing steps can often be biased by the reduction in the amount of reinforcement material required to provide the strength needed to withstand a collapse since the mesh bars to which they are attached soldiers the wires will be oriented in circumference where it provides a substantial clamp resistance. Where the flow modifier structure comprises two tubes or pipes, it is preferred that the larger diameter be about 50% of the diameter of the mesh and about 16% of the length of the mesh, while the smaller diameter pipe, which is stacked on the other inside the outer pipe, has a diameter of about 70% of the diameter of the outer pipe and a length that extends approximately 67% of the length of the mesh cylinder. It was found that said arrangement provided a flow uniformity over 90%. Although the modifiers have been referred to as pipes, this term is intended to include hollow shapes made from rolled sheets.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a side view illustrating a prior art intake screen having no flow modifier. Figure 1A is a graph indicating the slot rate versus the distance from the exit end and illustrates the mesh speed profile for the prior art intake screen of Figure 1. Figure 2 is a side view , partially separated, illustrating a prior art intake screen having a single tubular flow modifier. Figure 2A is a graph showing the slot rate versus the distance from the exit end and illustrates the mesh speed profile of the prior art intake screen of Figure 2. Figure 3 is a view side, similar to Figure 2, but illustrating a configuration of the prior art wherein a pair of meshes, each having a simple tubular flow modifier that is attached to a connector element. Figure 4 is a side view, partially broken away, illustrating a preferred embodiment of the improved flow modifier having two flow modifier pipes projecting towards the mesh cylinder. Figure 4-A is a graph indicating the slot velocity versus the distance from the exit end and illustrates the mesh velocity profile, for the take-up mesh of Figure 4. Figure 5 is a partially separated side view. , which illustrates a modality having four flow modifier pipes to cause the uniformity of flow to be further increased compared to the double pipe arrangement shown in Figure 4.

DETAILED DESCRIPTION OF THE DRAWINGS With reference to Figure 1, a prior art intake screen assembly is indicated generally at 10 and includes an outlet pipe portion 12 and a mesh length 14 integrally attached to the outlet pipe portion 12 by a cover of inner end in the form of a portion of an annular flange 15. The mesh 14 is closed at its outer end by an outer end cap or plate 16. The flow enters through the surface of the mesh, as shown by the arrows 17, and exits through the outlet pipe 12. As can be seen in the velocity distribution curve Vpi in Figure 1A, the flow is the highest at points on the mesh that are close to the point of removal of the mesh. Therefore, the actual flow at the left end of the mesh 14 is approximately 6 times the same as the flow at the right end. If the mesh is configured to cause the flow at the far left to have a maximum permissible velocity of 15.5 cm per second, the flow at the far right will be below 3 cm per second and the average flow rate, indicated by the line dotted 18, it will only be around 4.9 cm per second. With reference to Figure 2, a prior art intake screen assembly is shown generally at 20 because it includes an outlet pipe portion 22 and a mesh length 24 integrally attached to the outlet pipe portion 22 by an element. of inner end cap 25 and closed at its outer end by an outer end cap element 26. Flow enters through the surface of the mesh, as shown by arrows 27, and exits through the pipe 22. As can be seen in the velocity distribution curve Vp2 in Figure 1A, when the actual flow velocity of the stream entering the 24 mesh is at a maximum allowable flow rate of 15.5 cm per second, the velocity of flow near the extreme right will be less than 9.2 cm per second and the average flow velocity indicated by dotted line 28 will be 11 cm per second.

Figure 3 shows another prior art assembly 30 illustrating a pair of take-up mesh assemblies 34 that can be joined together in a T-shaped configuration that allows the diameters of the mesh to be reduced compared to the only mesh configuration shown in Figures 1 and 2. Figure 4 shows a preferred embodiment of the present invention wherein a take-up mesh assembly indicated generally at 40 includes an outer pipe portion 42 and a mesh length 44 integrally joined thereto by means of the inner end cap member 45. The right end of the mesh 44 is closed by the outer end cap member 46. Preferably, the primary flow modifier portion 42 'of the outlet pipe 42 has a length to the right of the end cap member 45 which is about 16% of the length of the mesh surface 44 between the end cap member 45 and the end cap member 46 although its diameter is about 50% of the diameter of the mesh 44. The right end of the secondary flow modifier portion 52 extends to approximately 67% of the length of the mesh surface 44 between the end cap member 45 and the end cap member 46. The diameter of the secondary flow modifier portion 52 is preferably about 60% of the diameter of the primary flow modifier portion 42 'to cause the annular flow area Ai between the flow modifier portions 42 'and 52 are equal to the flow area A2 defined by the open right end of the flow modifier portion 52. The portion mo Secondary flow feeder 52 may be mounted within the primary flow modifier portion 42 'by any suitable means, such as a variety of radially spaced and radially spaced rod elements (not shown). Figure 4A shows the velocity distribution curve Vp4 illustrating the actual flow velocity at various points along the length of the mesh 44 in Figure 4. The average flow velocity indicated by the dotted line 58 is 14 cm per second, and is very close to the maximum allowable slot speed of 215.45 cm per second. Therefore, the flow uniformity is 92% with the two improved pipe flow modifiers, compared to 72% for a pipe of the prior art design shown in Figure 2a and just 132% for the design of the prior art shown in Figure 1A that has no flow modifier. Fig. 5 shows an alternative mesh assembly 60 which is similar to Fig. 4 in that it includes elements 62, 64, 65 and 66 corresponding to the elements 42, 44, 45 and 46. However, the design includes 4 modifying portions flow 62 ', 67, 68 and 69 whose diameters are configured to provide equal flow areas Bi, B2, B3 and B4. Each of the four flow modifier portions are preferably of a length such that their right end will come placed at the same distance from the previous flow modifier or, in the case of the first flow modifier 62 ', from the cover element of the flow modifier. end 65. The major flow modifier pipe 62 'is preferably separated from the outlet end of the mesh 64, as defined by the end cap member 65, by a distance equal to 1 / (2 (N + 1)) times the mesh length, where N is the number of flow modifier pipes. Therefore, in the four-pipe system shown in Figure 5 the pipes 62 ', 67, 68 and 69 will be extended 1/10, 7/20, 3/5 and 17/20 times the length of the mesh . Similarly, in a three pipe system, the pipes will extend 1/8, 11/24 and 19/24 times the mesh length outside the outlet end of the mesh. Table 1 shows several parameters for several water intake systems that are based on the number of flow modifiers associated with them. Assuming a typical flow rate of 7.570 per minute, a mesh with a slot width opening of 2 mm would need to have a length and a diameter of 137 cm for the prior art construction shown in Figure 1 which does not include flow modifier The use of a single flow modifier pipe in the prior art construction shown in Figure 2 will allow the mesh size to be reduced to 91 cm in length and 91 cm in diameter. By providing two flow modifier pipes 42 'and 52, as shown in Figure 4, the mesh size can be reduced to just 76 cm long and 76 cm in diameter. The design of Figure 4 produces a flow uniformity of 92% compared to 32% and 72% for the prior art embodiments shown in Figures 1 and 2, respectively. Although the use of more and more flow modifier pipes, such as the four shown in Figure 5, would produce slightly greater flow uniformities, their use would produce higher pressure drops and higher pumping and material costs.

TABLE 1 Number of modifiers None One Two flow Fig. 1 Fig. 2 Fig. 4 Tap flow (liters per minute) 7,570 7,570 7,570 Slot opening (mm) 2 2 2 Peak slot speed (cm by 15.5 15.5 15.5 second) Speed slot average 4.9 11 14 (cm per second) Uniformity of flow 32% 72% 92% Required mesh diameter 137 91 76 (cm) Required mesh length (cm) 137 91 76 Open area of the mesh (cm2) 14,104 9,794 Dimensions of internal flow modifiers-diameter (cm) Length (cm) - 51 Area (cm) 222 Dimensions of the modified 46 38 external flow-diameter (cm) Length (cm) 30.5 12.7 Area (cm2) - 1, 639 - 1,136 Annular area (cm2) 568 Although the invention has been shown and described particularly with reference to the preferred embodiments thereof, those skilled in the art will understand that various alterations may be made in form and detail without departing from the spirit and scope of the invention.

Claims (5)

NOVELTY OF THE INVENTION CLAIMS

1. - An input mesh assembly (40, 60) for a water intake system comprising a mesh element (44, 64) having a cylindrical mesh surface, said mesh element being closed at its outer end by a outer end cap element (46, 66), said mesh element is partially closed at its inner end by an inner end cap element (45, 65), said inner end cap element has a tubular element of outlet pipe (42) attached thereto for transporting water that has passed through said mesh surface, said outlet pipe element having a diameter that is substantially less than the diameter of the mesh surface, and flow modifying means ( 42 ', 52, 62', 67, 68, 69) positioned within said cylindrical mesh surface to direct water to said outlet pipe element and comprise a cylindrical pipe element whose portion communicates with the element of outlet pipe and extends from the inner cover element, characterized in that the flow modifying means causes the flow to enter the mesh surfaces along the entire length of the same so that it has a flow uniformity exceeding 75% where flow uniformity is defined as the average flow velocity across the mesh surface divided by the peak velocity at any point along its length; said flow modifier means comprises at least two portions of cylindrical pipe element (42 ', 52, 62', 67, 68, 69) extending axially along a portion of the axial length of said mesh element (44, 64), each of these two mentioned cylindrical pipeline portions are radially spaced from each other and the innermost portion (52, 69) of said cylindrical pipeline portions at least extends axially towards the element mesh (44, 64) in the direction away from the inner lid element (45, 65) compared to the pipe element portion (42 ', 68) that is radially adjacent thereto.

2. The input mesh assembly for a water intake system according to claim 1, further characterized in that the diameter of the innermost pipe element portion (52) is such that its internal cross-sectional area (A2) is approximately the transverse area (Ai) of the portion of the pipe element (42 ') radially adjacent thereto.

3. The input mesh assembly for a water intake system according to claim 2, further characterized in that the innermost pipe element portion (52) extends approximately 2/3 of the length of the mesh cylinder (44) and the portion of the outermost pipe element (42 ') that extends approximately 1/6 of the length of the mesh cylinder.

4. The input mesh assembly for a water intake system according to claim 1, further characterized in that it consists of multiple pipes (62 ', 67, 68, 69) further characterized in that the diameters of the pipes are such that the internal transverse area (B4) of the smaller pipe (69) and of the cross-sectional area (B2, B2, B1) in which the radially adjacent pipes (68, 67, 62 ') are essentially equal to the others.

5. The input screen assembly for a water intake system according to claim 4, further characterized in that the ends of the successive pipes (62 ', 67, 68, 69) are still separated from each other and the pipeline of longer length (62 ') is separated at a distance equal to 1 / (2 (N + 1)) x the length of the mesh away from the outlet end (65), where N is the total number of pipes.