The Measurement, interpretation and use of unsteady momentum fluxes in two-phase flow.

Abstract

The steady and unsteady components of the momentum flux in a two-phase flow have been measured at the exit of a vertical pipe by means of an impulse technique using a turning tee and beam. Different electrical filters have been tried in the recording circuit for eliminating the signals around the natural frequency of the beam system. A special filter set has been designed to approximate the inverse of the transfer function of the beam system. Thus the signals recorded after passing through the beam-filter combination can be considered as the excitation times a constant. Two different analog methods have been used to analyze the random signals for obtaining some statistical quantities such as the predominant frequency and the rms value of the unsteady momentum flux. These quanities are useful in some applications involving two-phase flow. In the preliminary measurements of the unsteady momentum flux for the adiabatic up flow of an air-water mixture in a 5/8 inch pipe, the greatest unsteadiness of momentum flux appeared in the quality range of one per cent to six per cent. Above ten per cent quality no appreciable fluctuation has been detected. In an example problem, using the preliminary results, the effect of the unsteady momentum flux on a fuel rod has been studied. The amplitude of the vibrations resulting from the two-phase excitation has been found. In addition it has also been found that there is a possibility of unstable vibrations due to a nonlinear restoring force on the fuel element. This nonlinearity is due to the unsteady component of the momentum flux in the flow past the rod.