Helium Flow Measurement using Ultrasonic Technique
While designing cryogenic instrumentation for the Colliding Beam Accelerator (CBA) helium distribution system it became clear that accurate measurement of mass flow of helium which varied in temperature from room to sub-cooled conditions would be difficult. Full scale differential pressure signals from conventional venturi flow meters would decrease by more than an order of magnitude during cooldown causing unacceptable errors at operating temperature. At sub-cooled temperatures, helium would be pumped around cooling loops by an efficient, low head pressure circulating compressor. Additional pressure drop meant more pump work would be necessary to compress the fluid resulting in a higher outlet temperature. The ideal mass flowmeter for this application was one which did not add pressure drop to the system, functioned over the entire temperature range, has high resolution and delivers accurate mass flow measurement data. Ultrasonic flow measurement techniques used successfully by the process industry seemed to meet all the necessary requirements.
KeywordsHelium Rubber Calorimeter
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