High-temperature high-pressure oscillating tube densimeter

We describe an oscillating tube densimeter for use at temperatures up to at least 575 K and at pressures up to 20 MPa. After the densimeter was calibrated under vacuum and filled with water, it was used to measure the density of toluene from 298 to 575 K at 13.8 MPa. The results agree (0.1% rms deviation) with those obtained using other techniques. In the present densimeter, an alternating current is passed through the tube containing the sample to force the tube to oscillate in the field of a permanent magnet. This design avoids the use of electromagnets (with their attendant polymer or ceramic insulations) and does not require attachment of appendages to the oscillating tube. This densimeter oscillates in an overtone rather than in its fundamental mode, thereby achieving improved isolation from environmental noise and a shorter response time. The densimeter is small, weighing 370 g. If transformers are used to couple electrical signals to the oscillating tube, the densimeter itself may be constructed entirely out of metal. (C) 1996 American Institute of Physics.