Simultaneous measurement of density and viscosity of n-pentane from 298 to383 K and up to 100 MPa using a vibrating-wire instrument

Experimental results of density and viscosity of n-pentane are reported at temperatures from 303 to 383 K and pressures up to 100 MPa. The two propert ies were measured simultaneously using one single vibrating-wire sensor, wh ich is composed of a sinker suspended from a thin metallic wire, both of wh ich are immersed in the sample fluid. The oscillation characteristics of th e wire are obtained by means of an electromagnetic coupling. The response o f the wire is related to the density of the fluid mainly through the buoyan cy force acting upon the sinker, whereas the viscosity of the fluid affects the damping of the oscillations. The technique is based on a rigorous theo retical framework and thus, once all of the sensor parameters are known, ei ther by independent means or from a single reference experiment, no extensi ve calibration procedures are required for measurements at high pressure or at temperatures away from ambient conditions. The present results of densi ty exhibit a precision of +/-0.04% and an estimated accuracy of +/-0.2%. Th e viscosity measurements exhibit a precision of +/-0.5% and are judged accu rate within +/-2.5%. Tests of the instrument with gaseous nitrogen are repo rted in order to assess the performance of the technique when measuring in a fluid of low viscosity. (C) 2001 Elsevier Science B.V. All rights reserve d.