Densities and PVT Data
Densities (T, ρ data) or PVT data for pure components or defined mixtures are needed for various applications as simple volume to mass flow conversations or the development of accurate equations of state. For mixtures the excess volumes are also of interest and can be derived from accurate density measurements. Therefore, a number of different set-ups are available in our laboratory.
- Vibrating tube densimeter for saturated liquid densities (glass type, atmospheric pressure, 278 to 363 K)
- Vibrating tube densimeter for densities and PVT data in the compressed liquid, vapor and supercritical phase (Hastelloy, up to 400 bar, 273 to 423 K)
- Vibrating tube densimeter for densities and PVT data in the compressed liquid phase (DMA-HPM cell, Hastelloy, up to 1000 bar, 273 to 433 K)
- Calibrated glass cylinders for saturated liquid densities (atmospheric pressure, up to 653 K)
- Variable volume cell with sapphire tube for compressed liquid or supercritical PVT data (up to 100 bar, 243 K to 423 K)
- Magnetic suspension balance for compressed liquid and superheated gas phase PVT data and also for simultaneous saturated liquid and vapor density measurements (Hastelloy C-276, up to 200 bar, 233 to 473 K)
- Constant volume cells for gas phase PVT data (up to 100 bar and 473 K)
A computer operated apparatus for the measurement of liquid densities of pure compounds and mixtures in a large temperature and pressure range was developed since 1997 by Dr. Ihmels. A high pressure/high temperature vibrating tube densimeter (DMA-HPT prototype from Labor für Meßtechnik Stabinger (Graz, Austria)) is used for the measurement of density and temperature.
The measuring cell contains an U-tube oscillator (Hastelloy C-276), a thermostat, temperature sensors for control and measurement as well as excitation and measurement coils using permanent magnets. A modified DMA control unit is attached to the measurement cell. The pressure is adjusted with the help of a variable volume connected to a step motor. For pressure measurement a sensor is attached to the variable volume.
The measurement is controlled with the help of the Windows program "AutoTPX – Density Measurement" (Dr. Christian Ihmels). Automatic temperature and pressure programs for the liquid density measurements of compressed pure compounds and mixtures up to 423 K and 40 MPa are possible. The control program is connected to the pure component data bank of the Dortmund Data Bank (DDB). By using the Antoine equation (parameters from the DDB) each isotherm is started slightly above the saturation pressure.
The following figure shows a schematic drawing of the complete setup:
Typical experimental results:
Liquid, vapor or gas phase density data can be measured using a magnetic suspension balance. The set-up was purchased from a commercial source (Rubotherm GmbH) and was equipped with an adapted equilibrium cell with injection valves and sampling ports. By replacing a density sample body with a sample pan, alternatively adsorption isotherms can be determind. The apparatus can be applied at temperatures from about -40 to 200 °C and pressures up to 200 bar. A schematic of the device is shown in the following figure: