Forced Convection Cooled Thermistors Used as Magnet Lead Flow Sensors

Abstract

Brookhaven National Laboratory (BNL) has developed a simple, inexpensive method for monitoring the flow, which cools the 12×50 Amp corrector power leads for the Relativistic Heavy Ion Collider (RHIC). Since there are more than 500 leads of this type distributed around the 3.8 km circumference accelerator, each requiring flow control and monitoring, the use of conventional mass flow meters is not economically feasible. The device consists of a negative temperature coefficient thermistor mounted inside a tube, through which helium gas flows from the power lead. The helium gas cools the sensor through convection causing a temperature change and therefore a resistance change in the sensor. The electrical circuit reacts by adjusting the current supplied to the sensor to maintain the resistance at a constant value. The change in current is used to calculate the helium mass flow rate. The flow meter monitors flow in the range of .03 to .05 g/s with an accuracy of plus or minus 10%. Presented here are the design calculations as well as the flow meter performance.

Work performed under contract with the US Department of Energy