A microfluidic oscillating tube densitometer

This article discusses a microfluidic oscillating tube densitometer with an internal volume of approximately 20 μl. Accuracy better than +/−0.5% in density is demonstrated over a range of temperatures (50 °C–150 °C) and pressures (150–15 000 psi) by prior calibration with air and water. The flexibility of the tubing facilitates use of a novel actuation and detection system that greatly simplifies the fabrication. Two simple and automated calibration methods are discussed using measurements performed with an evacuated and a water-filled tube. Measurements show that the effective spring constant of the tube is strongly affected by temperature and is largely insensitive to pressure. The tube volume, on the other hand, is strongly affected by pressure.