Measurements of lithium flow with an EM flow meter in LIMITS

A simple electromagnetic flow meter was constructed and used in the one-inch thick-walled 316 L stainless steel tubing (20.6 mm i.d.) of LIMITS, an experimental lithium flow loop at Sandia National Laboratories. (A parallel paper in this conference by Tanaka et al describes LIMITS.) The flow meter uses a pair of NdFeB permanent magnets (57.2 mmW /spl times/ 48.3 mmD /spl times/ 76.2 mmH) mounted on an iron yoke producing a field of about 0.5 Tesla. This paper describes the field measurements, calibration and use of the flow meter in experiments with flowing lithium. Initial calibration of the meter was done as lithium was moved using gas pressure from a transfer tank to the lithium furnace. In this calibration, we monitored the signal from the flow meter and the signal from a previously uncalibrated level meter in the lithium furnace. The reference for the calibration was the change in weight of the transfer tank, which we measured using a set of load cells under the sled supporting the tank. The flow meter signal ranged from 0 to about 6 mV for flow speeds of 0 to about 1 m/s. There was, as expected, some noise with the mV signal, but use of a running average essentially eliminated the noise. The signal was quite linear with flow as judged by the correspondence between the integrated flow signal and the weight of lithium transferred. We also have used the flow meter in lithium flow experiments in LIMITS and these data and the calibration procedure will be reported in the paper. Among the observed effects during the flow tests was a difficulty in interpreting the signal whenever vibration of stainless steel tubing occurred due to the (usually smooth running) pump or changes in the valve positions, for example, opening a valve with the pump running.