Research On Key Technologies Of On-line Metering System For Partially Filled Pipe’s Wastewater

The partially filled pipe is a state in which the fluid is not filled with a cross section of the pipe.Since the liquid level of the fluid under the condition of partially filled pipe is instantaneously changed,it is difficult to accurately measure the liquid level height value.Due to the electromagnetic flowmeter has the advantages of corrosion resistance,high measurement accuracy and small flow field distribution in the tube,the electromagnetic flow method is generally used to measure the flow of partially filled pipe sewage.However,since the measuring electrode must be immersed in the fluid to obtain the measurement signal,it is difficult to collect the measurement signal when the fluid level is lo、wer than 0.1D(10%of the pipe diameter).There are multiple pairs of electrodes in the flowmeter,once a problem occurs in one of the electrodes,the entire flowmeter needs to be replaced,which increases the cost.In order to solve the problem that it is difficult to accurately measure the flow when the fluid level is lower than O.1D,a new method of partially filled pipe flow measurement is been proposed:based on the theory of communicating pipe,the height value of the fluid level was been measured by a high-precision pressure sensor.The precise flow value flowing through the pipe to be tested was been obtained by the liquid level-flow function model.Before the experiment,a U-shaped communicating pipe was externally been connected at the appropriate position of the pipe to be tested.Based on the computer fluid dynamics(CFD)simulation technology,the flow state of the gas-liquid two-phase flow in the pipeline was been simulated,the diameter and the best installation location of the U-shaped communicating pipe were been selected.Selected 100mm as the measured pipe diameter.According to the simulation results,the pipe diameter of the U-shaped communicating pipe should be 0.02m,and the installation position of the communicating pipe should be selected at the position of the pipe from 1m to 2.5m.Built The experimental platform by the simulation results,the liquid level-flow model has preliminarily been established based on the hydraulic method,and the model has been corrected by experiments.The flow result output by the system has been compared with the electromagnetic flow meter measurement result.The results show that when the liquid level of the fluid is not higher than 10%of the pipe diameter,the measurement error is less than 2%and the repeatability error is 1.45%,which verifies the reliability of the measurement method.The measurement method proposed in this paper breaks through the limitation of the traditional partially filled pipe flowmeter,which is difficult to be measured the fluid flow value below 0.1D,and it avoids the problem of large loss of precision and low wear caused by the built-in level gauge.The liquid level measuring device has been placed outside the U-shaped,so the replacement is simple and easy to be maintained.The cost is greatly reduced,and the measurement method in this paper has certain significance on the flow rate of partially filled pipe sewage’s research.