9. 2.1 Surface Filters The filter is a membrane(sheet steel, cloth wire mesh, or filter paper) with holes smaller than the dimensions of the particles to be retained
9.2.1 Surface Filters The filter is a membrane (sheet steel, cloth, wire mesh, or filter paper) with holes smaller than the dimensions of the particles to be retained
Although industrial air filters rarely have holes smaller than the smallest particles captured, they often act as if they did. The reason is that, as fine particles are caught on the sides of the holes of a filter, they tend to bridge over the holes and make them smaller. Thus as the amount of collected particles increases, the cake of collected material becomes the filter, and the filter medium (usually a cloth) that originally served as a filter to collect the cake now serves only to support the cake, and no longer as a filter
Although industrial air filters rarely have holes smaller than the smallest particles captured, they often act as if they did. The reason is that, as fine particles are caught on the sides of the holes of a filter, they tend to bridge over the holes and make them smaller. Thus as the amount of collected particles increases, the cake of collected material becomes the filter, and the filter medium (usually a cloth) that originally served as a filter to collect the cake now serves only to support the cake, and no longer as a filter
This cake of collected particles will have average pore sizes smaller than the diameter of the particles in the oncoming gas stream and thus will act as a sieve for them. The particles collect on the front surface of the growing cake. For that reason this is called a surface filter
This cake of collected particles will have average pore sizes smaller than the diameter of the particles in the oncoming gas stream, and thus will act as a sieve for them. The particles collect on the front surface of the growing cake. For that reason this is called a surface filter
One may visualize this situation with a screen having holes 0.75 in(1, 91 cm)in diameter. We could collect a layer of ping Pong balls easily on this screen. Once we had such a layer, we could then collect cherries, which, by themselves, could pass through the holes in the screen but cannot pass through the spaces between the Ping- Pong balls. Once we have a layer of cherries we could put on a layer of peas, then of rice then of sand
One may visualize this situation with a screen having holes 0.75 in. (1,91 cm) in diameter. We could collect a layer of PingPong balls easily on this screen. Once we had such a layer, we could then collect cherries, which, by themselves, could pass through the holes in the screen but cannot pass through the spaces between the PingPong balls. Once we have a layer of cherries, we could put on a layer of peas, then of rice, then of sand
The two most widely used designs of industrial surface filters are shown in Figs 9.13 and 9. 14. Because the enclosing sheet metal structure in both figures is normally the size and roughly the shape of a house this type of gas filter is generally called a baghouse. The design in Fig. 9.13 most often called a shake-deflate filter consists of a large number of cylindrical cloth bags that are closed at the top like a giant stocking, toe upward
The two most widely used designs of industrial surface filters are shown in Figs. 9.13 and 9.14. Because the enclosing sheet metal structure in both figures is normally the size and roughly the shape of a house, this type of gas filter is generally called a baghouse. The design in Fig. 9.13, most often called a shake-deflate filter, consists of a large number of cylindrical cloth bags that are closed at the top like a giant stocking, toe upward