The flow in centrifugal fan and 90° bend pipe was simulated numerically by the RNG k-turbulent model in software Fluent, and obtained the distribution diagram of the pressure and velocity. From the distribution diagram of the pressure and velocity, for measurement, three measurement points must be chosen, and two of them should be closed to the wall of pipe. However, in order to insure the measure accuracy, five or six measure points should be chosen. In addition, the velocity distribution of pipe bending reaches well-distibuted at the 1000 mm away from pipe exports. That is fluid flowing after through the flow field of bending section tends to uniform soon, so for the greater curvature bend pipe, measurement is more convenient.
As the development of pipe industry, pipe and pipe fittings, including pipe coupling, pipe tee, pipe elbow are more and more widely use in industrial area. There are four types of welded steel pipe that are mostly used:
1. Welded steel pipe: it is also called welded pipe. It is shaped by steel plate or steel strip through bending and then welding. It is divided into seam welded pipe and spiral welded pipe. According to the application, it is divided into general welded pipe, galvanized welded pipe, oxygen blowing metric welded pipe, welded pipe, wire casing, roller tube, deep well pump pipe, auto tube, transformer, electric welding thin wall pipe, welded pipe and spiral welded pipe.
2. General welded pipe: general welding work for low pressure liquid. It uses Q195A, Q215A, Q235A steel and adopt other mild steel welding for manufacturing. Steel pipe needs to be tested through pipe pressure, bending, flattening and some experiments, and there are some specific requirements for the surface quality. Usually the delivery length is for 4 to 10m. Welded pipe wall thickness is divided into two kinds: thread steel pipe and threadless steel pipe.
3. Seamless pipe: with increasing tube welding technology and simple processing, now seamless pipe has been replaced by welded pipe. Welded pipe producing capacity has been more than 219 mm (8 inches).
4. Oxygen tube welding: it is used for steelmaking oxygen tube. It generally uses small diameter welding pipe. Its specifications range from 3/8 inch to 2 inch. The welding is made of With 8, 10, 15, 20, or Q195 steel strip. For corrosion protection, some of them need aluminized processing.