Study On Flow Rate Measurement System In Small Pipes Based On Five-electrode Capacitively Coupled Contactless Conductivity Detection Technique

Flow rate is one of the most important process parameters in many industries. Currently, with the development of new technologies, the industrial devices and equipments present a trend of miniaturization. However, the existing flowmeters are commonly used in the normal scale pipes and the applications of existing flowmeters in the small pipes are limited. So, it has important theoretical and practical values to implement the flow rate measurement in small pipes.Capacitively Coupled Contactless Conductivity Detection (C4D) is a new conductivity detection technique. It has advantages of contactless detection and low cost. Unfortunately, up to date, C4D is mainly studied and applied in the research field of analytical chemistry in capillary. Few researches concerning the application of C4D to the flow rate measurement in small pipes have been reported.Combining C4D technique and the principle of cross correlation flow measurement, a new method for flow rate measurement in small pipes is presented, and a flow rate measurement system in small pipes is designed in this work. Main works and innovation points are listed as follows:(1) Combining C4D technique and the principle of cross correlation flow measurement, a new flow rate measurement method in small pipes(inner diameter:0.5mm-4mm) is presented.(2) A new five-electrode C4D sensor, which is suitable for the flow rate measurement in small pipes, is developed. Comparing with the conventional C4D sensor, the conventional current measurement way has been changed to the voltage measurement way. Thus, in the new five-electrode C4D sensor, the unfavorable influence of the coupling capacitances on conductivity detection can be decreased. Two independent conductivity signals of fluid can be obtained by measuring the differential voltage signals, and then the flow rate measurement can be implemented according to the principle of cross correlation flow measurement. With the new five-electrode C4D sensor, conductivity measurement experiments are carried out in five small pipes with different inner diameters of0.5mm,0.8mm,1.8mm,3.0mm and3.9mm respectively. The experimental results show that the developed five-electrode C4D sensor is successful.(3) A flow rate measurement system in small pipes base on C4D technique is built. Flow rate measurement experiments are carried out in five small pipes with different inner diameters. The experimental results show that the proposed method and system could implement flow rate measurement in small pipes, and the maximum relative difference of the flow rate measurement between the reference flow rate and the measured flow rate is less than5%.