Corrections of gradiomanometer data for volume fractions in two-phase flows

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Abstract
For typical applications of the gradiomanometer in laboratory two-phase flows, we analyse major contributions to the measured differential pressure. Application for estimation of the fluid-phase volume fraction is valid only when terms representing friction and differential momentum flux (acceleration) are negligible or can be corrected for. The importance of friction is commonly recognized, but that of acceleration in developing flows is less so. Order-of-magnitude estimates of friction and acceleration are given for typical cases of (i) air/water and (ii) kerosene/water two-phase flows. We point out that the acceleration term could be significant in developing liquid/liquid flows of weak density contrast. For the liquid/liquid case, it is therefore important that measurements be made in a fully developed region of the flow. Results for several multi-phase flows are compared with data from local optical fibre probes in a series of companion articles.