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Title: Calibration Of Volume Standards For Flow Rates Of Hot Water Up To 120 m/h At Temperatures Up To 180 C
Author: J.-F. March
Source: 2002 International Symposium on Fluid Flow Measurement
Year Published: 2002
Abstract: Heat district suppliers demand carefully constructed and calibrated flow sensors of heat meters at temperatures above 100 C. For this reason a test facility for hot water flows had been installed at PTB generating volume flow rates up to 120 m/h at temperatures up to 180 C. The fundamental mass-time method (gravimetric standard method 1) is available only below 80 C because of the losses in mass due to evaporation. Above this temperature only closed test facilities operating under pressure are therefore suited. Because of the large technical difficulties encountered at high temperatures a test facility using the gravimetric standard method is not yet available. For the determination of the flow rates above 100 C in such test facilities, neither primary nor calibrated reference flow rate standards are known up to now. The aim of this work was to calibrate a secondary volume standard, serving in the PTB hot water test facility for the determination of the volume with a relative uncertainty of less than 0.2 % in the temperature range between 20 C and 180 C and at the flow rates between 50 m/h and 120 m/h. The relative uncertainty of 0.2 % is the upper limit according to DIN EN 1434 2 for the volume uncertainty of test facilities for class 2 heat meters. Numerous investigations of flow meters have shown that the 4 AOT 1) turbine flow meters have the best measuring performance. The relative uncertainties concerning volume measurements with these flow meters, proved in a test facility with the mass-time method in the temperature range from 20 C to 80 C and at flow rates between 50 m/h and 180 m/h amount to less than 0.1 % 3. It will be shown, that the aim of calibrating an AOT flow meter, called AOT #1, as a secondary standard had been reached at temperatures above 80 C by determining the relative variations of the calibration factors using a laser Doppler velocimeter (LDV) combined with a novel one-point relative method discussed in detail in 4.

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