Preventing vibration induced by flow instability in a tube-containing duct conveying a gaseous stream

摘要

821,473. Steam superheaters; feed water heaters. COMBUSTION ENGINEERING Inc. Feb. 26, 1957 [March 28, 1956], No. 6410/57. Classes 64(3) and 123(3) In a steam generator comprising a furnace 10 from which gases flow through a lateral pass 16 locating a secondary superheater 24 into a downpass 18 locating a primary superheater 22 and an economizer 44, the superheaters and economizer consist of platens of multiple-bend U-tubes spaced apart across the width of the passes, the limbs of the U-tubes, instead of being parallel to those of the adjacent platen, being set at an angle # thereto, the angle being approximately equal to tan-SP1/SPK(x-d), L where L is the length of the tube run across the pass, # is the outside diameter of the tubes, x is the distance between the platens and K is unity. If the tube limbs are parallel, severe vibration and intense noise occurs in operation if the laterally-directed gas pulsations which develop at the same frequency across the width of the pass as a result of gas flow instability occurring as the gas passes around the tubes, are in acoustical reson. ance with the chamber formed by the gas pass due to the establishment of a standing wave across the pass. With the adjacent tubes set at the angle the instability generated pulses at any particular frequency do not reach a sufficient energy level to establish a standing wave and the noise and vibration are prevented.