Experimental Study On Fluid Velocity Measurement In Microchannels Based On Temperature Cross-correlation Method

"Difficult fluid"flow rate measurement is a fundamental topic in many industrial tieids such as fluid machinery,clean energy utilization,and petrochemical industry.However,It is difficult for conventional flow rate measuring instruments to function in this field,especially for "difficult fluid" flow rate measurements in some micro-sized devices.In recent years,the rapid development of test technology has provided new ideas for the measurement of flow rate of"difficult fluids"in microchannels.This paper first reviews the"difficult fluid"flow measurement technology,combs the basic theory of the relevant flow measurement technology;uses the temperature cross-correlation method to conduct flow measurement experiments on the high pressure water and high temperature and high pressure water vapor in the micro tube.The main work and research results include:(1)A set of high-temperature and high-pressure fluid flow rate test platform based on temperature cross-correlation method was built.The pulse heating system,temperature signal acquisition system and related flow rate measurement system were designed.Two kinds of pulse heating systems,internal heating and external heating,are established.The external heating method realizes pulse heating with periodic time controllable,and the internal heating mode shows better heating effect.When calculating the cross-correlation delay,the Matlab delay time calculation program is written,which avoids the use of cumbersome and complex common correlation algorithms.This test can quickly perform data acquisition and calculation of delay time with strong timeliness(2)The effects of pulsating heating method,sensor spacing,sampling frequency and other factors on the velocity measurement of temperature cross-correlation method are studied The results show that the internal heating method is placed inside the flow field,the heating effect is better,and the delay time is more accurate.The sensor spacing has the best value.The result shows that the upstream signal distortion is aggravated and the correlation is reduced.Too small a pitch will also cause a decrease in the maximum correlation coefficient,which will affect the accurate acquisition of the delay time.In this test,the best thermocouple distance in the internal heating mode is 13cm,and the best distance in the external heating mode is 8cm;the sampling frequency has a weak influence on the signal correlation,and the sampling number has a strong influence on the test.The pulse signal is generated in the external heating mode,and the correlation of the signal is related to the on-off time of the heating.Generally,the heating mode of the 4s is used,and the heating mode of the 6s is high,and the measurement error is small;the flow state of the fluid can affect the average flow rate correction.The size of the factor,in the internal heating mode,the average flow rate correction factor of the fluid under laminar flow in the test basically meets the theoretical value of 0.5(3)The uncertainty of the method for measuring the relevant flow rate in this test is 1.79%,and the repeated measurement deviation is within 3%.After analysis,the measurement error of the relevant flow rate in the external heating mode is about 20%,and the average flow velocity correction factor which is in line with the theoretical value is obtained under the internal heating mode.