FLOW SIGNAL CHARACTERISTICS OF AN ULTRASONIC TRANSDUCER AT A HIGH TEMPERATURE

The exact measurement of feed water flow is the major factor in nuclear power plant efficiency. However, due to the fouling problem, the venturi nozzle used in feed water measurement frequently causes a decrease in the efficiency of the nuclear power plant. To avoid this problem, ultrasonic technology is a reasonable candidate. The temperature of the feed water is about 300 degrees C. The commercial piezoelectric element used in an ultrasonic transducer preserves its characteristics up to a temperature of 120 degrees C. This problem must be overcome in order to use an ultrasonic flowmeter to measure the feed water flow. To address this issue, we designed a thermal block to insulate the high temperature from the pipe line. The method we used included a clamp-on type transducer and a driving circuit with a transit time difference method. The signals from the driving circuit were measured and the ultrasonic transducer assembly was tested at room temperature and at a high temperature of 300 degrees C. The test results revealed that the transit time difference was reasonably proportional to the flow velocity at room temperature, and the signals of the transducer installed on the pipe line were the same at 300 degrees C as those at room temperature. This result confirmed that the ultrasonic pulse was working well through the thermal block and in the high temperature fluid.