Microwave measurement of phase equilibria

An apparatus for measuring the phase behaviour of a fluid, the apparatus comprising:

• an electromagnetic resonant cavity, operating at frequencies up to and including microwave frequencies, said cavity being formed with a reentrant geometry having at least two utilised resonant frequency modes in which one resonant mode is employed to facilitate the detection of the onset of formation of a new phase;
• a probe for exciting and monitoring the electromagnetic resonances of the cavity;
• a pressure sensor and temperature sensor for sensing the pressure and temperature respectively of fluid in the cavity;
• and,
• a signal processing means operatively connected to said pressure and temperature sensors and said probe for calculating a phase transition in the fluid within the cavity based on detected changes in the resonant properties of the cavity.

A method of measuring the phase behaviour of a fluid, the method comprising the steps of:

• detecting changes in the resonant properties of an electromagnetic resonant cavity containing a fluid under various conditions of pressure and temperature;
• varying the volume of a pressure chamber in fluid communication with said resonant cavity and/or the temperature of the entire apparatus;
• sensing the pressure and temperature of the fluid in the cavity;
• and,
• calculating a phase transition of the fluid within the cavity based on the detected changes in the resonant properties of the cavity.