A systematic theoretical investigation has been carried out to study the effect of viscosity of the pressure-transmitting fluids on the measurement of pressure up to 1 GPa using piston gauges. The fluid flow equation is modified to determine the fall rate (v) with pressure (P), taking the pressure-dependent viscosityη(P) and clearance between piston and cylinder [H(P)] terms into account. Above 0.4 GPa, the fall rate curve shows the tendency to be pressure independent. The near-constancy ofv withP can be avoided with less viscous fluid or by increasingH(P). Finally. the initial clearance obtained from the experimental data of fall rate, shows a weak dependence of pressure, although theoretically it is assumed to be independent of pressure. This weak pressure dependence is attributed to the effect of viscosity of the pressure transmitting fluid.
Volume 94, 2019
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