The large-volume Ti-autoclave, which is designed to allow for quasi-isobaric sampling of coexisting liquid-vapour pairs, has a total volume of 500 cm3 and the sample volume is about 0.2 % of the total volume. Experiments are performed along particular isotherms at different pressures. The runs always start in the one-phase field above the critical pressure for the particular fluid composition. Evacuation of part of the charge results in a pressure drop and the two-phase field is reached. The system is then hold horizontally to allow for equilibration. Sampling is done in a vertical position with the liquid phase sampled at the lower and the vapour phase at the upper sampling line. Subsequent evacuation through the vapour line results in a further pressure drop and sampling is repeated at lower pressure.
is measured online using a transducer gauge with a sensitivity of about 0.5 mV/bar that is calibrated at the liquid-vapour equilibrium of pure H20 and has a pressure uncertainty of ± 1 bar.
Heating is with three independently controlled furnaces. The temperature inside the autoclave is measured online with three Ni/CrNi thermocouples placed at different positions and shielded by a Ti-capillary. The thermal gradients inside the autoclave are < 1 °C.