NONLINEAR AND UNSTEADY-FLOW ANALYSIS OF FLOW IN A VISCOUS FLOWMETER

An experimental and theoretical investigation has been undertaken on a viscous flowmeter, with both steady and unsteady flow. The steady flow analysis quantifies the non-linear effects of entry and exit losses, development length effects and compressibility effects. The steady flow analysis and experiments show that the pressure drop has a quadratic response to flowrate, but that for practical applications a linear approximation will lead to an error of less than 1%. The unsteady flow experiments show that it is necessary to integrate the instantaneous flow over a whole number of cycles, in order to obtain reliable values of the mean flow. An analysis of unsteady viscous flow has been used to show how the instantaneous pressure difference measured across the viscous flowmeter can be analysed to give the instantaneous volume flow rate.