Accuracy improvement of a flowmeter for steam and air to be set on the outside of a pipe utilizing a circumferential heater

摘要

A clamp-on type flowmeter for steam and air, which does not require pipe-cutting for installation, is needed for diagnosing performance and saving energy in facilities such as factories and power plants. Therefore, in our previous study we devised a heater method for measuring steam and air flow, in which a circumferential heater was attached to the outside of a pipe and then the axial temperature distribution on the outside of the pipe was measured by thermocouples. Steam velocity was analyzed on the basis of the temperature distribution in the pipe axial direction, considering heat transfer inside the pipe and thermal conductivity in the steel pipe-wall. Thus, we determined a thermal boundary layer coefficient, which is the ratio of the thermal boundary layer flow rate to the flow rate in the whole pipe cross section, and two kinds of thermal transfer coefficient depending on position, which were that upstream of the heater and that at the middle of the heater. In the present study, we conducted further experiments under various steam pressures, calibrated the reference fluid flowmeter under supervision of the National Institute of Advanced Industrial Science and Technology, and reconsidered the fluid pressure values. Using the experimental data obtained, we could decide the parameters more precisely compared with in the previous study, and thus improved the accuracy of the heater method.