BUFFER WAVE-GUIDES FOR FLOW MEASUREMENT IN HOT FLUIDS

To obtain reliable ultrasonic flow measurements in the 200-300 degrees C range continuously, with possible excursions to 450 degrees C, buff er waveguides can be used to separate the piezoelement from the hot fl uid. It is important that the buffer waveguides do not corrupt the sig nals. Until recently, this goal has been elusive because of dispersion , multipaths. mode conversion and beam spread (diffraction loss) in th e buffer(s). In this paper, we describe two buffer constructions that avoid these problems. The buffers can be made of virtually any standar d engineering material, provided the material is compatible with the p ipe or fluid. One design, primarily intended for clamp-on applications , guides shear waves at oblique incidence relative to the radiating fa ce. The other design, primarily intended for wetted applications, guid es compressional waves at normal incidence to the radiating face. Once the piezoelement is far enough from the heat, it becomes an easy matt er to enclose it in an explosion-proof housing. That housing can be ma de separable and removable from the clamped-on or permanently installe d buffer. This removability feature simplifies transducer repair. reca libration or replacement in the field. Laboratory and field test resul ts are presented for liquid and gas flowmeter applications in the 200- 300 degrees C range. (C) 1998 Elsevier Science B.V.