Method and apparatus useful for rapidly determining the molecular weight of a flowing gaseous material

In a method of operating a vortex tube by feeding a gas under pressure to an inlet of the tube and expanding the same in a vortex generation chamber to form hot and cold fractions, and wherein said fractions are separately removed from the tube, the improvement comprising determining the molecular weight of said gas by the aid of said tube and by means of the following steps:

• pressurizing the inlet gas,
• sensing the temperature of the gas in said inlet by means of a temperature sensor to produce an e.m.f., designated V.sub.i,
• sensing the temperatures of the hot and cold fractions as they emerge from the tube by means of temperature sensors to produce e.m.f.'s respectively designated V.sub.h and V.sub.c,
• obtaining a first differential e.m.f. V.sub.h -V.sub.i, designated delta V.sub.h that is representative of the temperature difference between the hot fraction and the inlet gas,
• obtaining a second differential e.m.f. V.sub.i -V.sub.c, designated delta V.sub.c, that is representative of the temperature difference between the inlet gas and the cold fraction,
• forming a ratio of the delta V's,
• and employing said ratio in a pre-established ratio-molecular weight converter relationship to convert the ratio to the molecular weight of the gas.