Cross-Correlation Techniques Applied to Pulsating Flow Measurement

Abstract

A new method for measuring pulsating flow has been devised in which the mean flow velocity is derived from the transit time of temperature fluctuations between two points in a pipe. The transit time is determined from the cross-correlation of the temperatures at these points. The method has been tested with water and linear calibrations have been obtained in the laminar (Re. < 2000) and turbulent (Re. > 3000) regions, however it is non-linear in the transitional region (2000 < Re. < 3000). Tests with steady flow and pulsating flow with pulsation frequencies between 1 Hz and 5 Hz give very similar calibrations. In the worst case, on/off pulsations at 5 Hz, the deviation from the steady flow reading is only 8 per cent. The process transducers are robust thermocouples. The cross-correlation function can be computed by an on-line digital computer, alternatively one of the commercially available cross-correlators can be used.