Hockey stick developments extend range, improve accuracy of clamp-on flow measurements

The hockey stick (OKS) buffer waveguide for high-temperature clamp-on flow velocity measurements of hot water, 260°C, first reported in these Proceedings in 1996 and 1997, has evolved in response to the demands of new applications. Accuracy in some cases is needed not just at the temperature extremes but from room temperature to the extreme, requiring dynamic compensation for changes in sound propagation in the buffers. The operation of the OKS can be monitored by sensing overheating, sound speed distribution and coupling efficiency. Couplants for the -150° <;T<;360°C range must satisfy acoustic requirements and safety concerns. Metal foil couplants have been acceptable in most applications. Measurements of secondary flow have been made with clamp-on transducers, even at a location greater than 30 diameters from the nearest flow disturbance.