This invention relates to vanes of the type positioned in a moving fluid stream and used to turn and spread or contract the moving fluid. The fluid may be liquid or gaseous. The concept disclosed in this application has particular reference, for illustrative purposes, to the turning and/or spreading of a moving stream of air laden with particulate matter in order to introduce the moving stream into a filter. The vanes are constructed and positioned in the moving stream of air so that entrained particulate matter does not catch on the upstream surface of the vane.
Fluid flowing in a straight line tends to resist deflection from the path of flow. When the fluid is forceably deflected, as by passing it through a right angle turn in a duct or other enclosed structure, turbulence results. Turbulence causes noise, vibration and increased energy consumption. Therefore, it is well known in the prior art to position turning vanes in fluid ducts at a point of deflection in order to decrease turbulence. Vanes can also be used to decrease turbulence and to improve flow distribution when passing the moving fluid from a relatively small duct into a relatively large one, or vice versa. Both of these procedures are often necessary during the process of filtering particulate matter from a moving fluid stream.
For example, air filtration often takes place through a drum-type filter. A rotatable drum is covered with a fluid permeable filter medium and is positioned for rotation within a housing. Filtration takes place by passing air laden with particulate matter from the upstream to the downstream side of the drum through the filter medium. The particulate matter is trapped on the upstream side of the filter medium and forms an overlying porous layer of particulate matter which is often referred to as a "mat" or "cake". The mat then serves as an additional filter medium of enhanced filtering capacity. Recent developments have improved the efficiency of certain types of filters to the point where the underlying filter medium now serves primarily as a filter support. In order to filter large quantities of air during a given period, drum filters are many axial feet in length. However, the fluid is conveyed to the filter in ducts which may have interior dimensions only a fraction of the length of the filter drum itself. Furthermore, in order to save space, ducts often approach the filter closely adjacent the filter housing and in axial alignment with the drum. This requires that the moving air stream be turned 90.degree. within a relatively short distance while at the same time being spread so that it enters the filter at substantially right angles along the entire length of the drum. Both of these procedures are particularly important in building a mat which is to serve as a primary filter medium, as described above. The flow of air through the filter medium must be free of turbulence which can tear sections of the mat away from the drum. Bare sections cause further unevenness in filtration and also permit particulate matter to pass through the clean filter medium which would otherwise be trapped in the overlying mat. Futhermore, in order for the mat to filter at maximum efficiency, it must be formed evenly across the entire axial length of the drum.
Accomplishing all of these tasks has been a particular problem in the past since known vanes present an upstream face which is perpendicular to the air flow and typically extend from one side of the duct to the other. Fibers and clumps of particulate matter snag on the vanes and are held there. This increases drag within the moving air stream requiring additional horsepower to move the air at its desired velocity. Other material in the air stream is trapped by the projecting clumps causing a decrease in velocity and an increase in fluid turbulence. If the clump eventually breaks loose it can enter the filter and impact the mat with such force that a portion of the mat is torn away, thereby causing an immediate decrease in filter efficiency. If the clump does not tear loose it can eventually cause a choke by blocking all or part of the duct. This can require a shutdown of the equipment while the choke is removed.
Therefore, a vane has been developed which, when positioned in a stream of moving fluid, can be used to turn and contract or spread the fluid without turbulence and without the accumulation of particulate matter on the vane.