Investigation Of Measurement Principle And Methods For Measuring Minute Fluid Flow Under Unsteady Flow Condition

Accurate minute flow measurement is widely required along with fluidic systems grow smaller in size. The minimum flow may be ml/min in medical devices, leak detection of hydraulic components, tolerance check for irregular shape, study of flow characteristics of MEMS, micro tube or capillary tube diameters measurement and biochemical defense. Nowadays, minute flow measurement is under the condition of steady flow and it requires precise hydraulic constant pressure instrument. This will cause the complexity of measuring system. Besides, it is obvious that conventional flow meter is difficult to be used in minute flow measurement for great measuring errors and high pressure loss.In this dissertation, unsteady flow measuring principle is proposed and the applications of this method are developed.Based on unsteady flow Bernoulli equation, three typical models of outflow through minute flow paths are established for round corner thin-wall hole, sharp corner thin-wall hole and long hole respectively. Then corresponding flow formulas and elevation conditions for application (ECA) of the method are deduced. Nonlinear differential equations are built for unsteady minute flow under inconstant pressure. Theoretical measuring errors are computed and analyzed. Experimental instrument for unsteady minute flow measurement is established. Test results prove the correction of the theoretical analysis. For measuring the regurgitant volume of artificial mechanical cardiac valve prosthese, an unsteady flow measuring instrument is developed. This device has been industrialized. For flow check of intra-vein catheter, an unsteady flow measuring instrument is designed, which is multi-pieces marked. For valve plate couples of water axial piston pump, clearance leak flow measuring instrument is studied and manufactured. With this instrument, the clearance of the couples can be obtained.The thesis contains 6 chapters.In chapter 1, the objective and significance of the study are stated. Current research situations of minute flow measurement are analyzed and the main contents of the study are introduced.In chapter 2, under the condition of steady flow, three typical models of outflow through minute flow paths are established for minute round corner thin-wall hole, sharp corner thin-wall hole and long hole respectively. Based on steady flow Bernoulli integral equation, correspondent flow formulas are deduced. According to the characteristics of minute flow, four measuring methods are proposed,named static mass memthod,static volume method, dynamic mass method and dynamic volume method,and corresponding instruments are designed.Meanwhile,the existing problems for steady minute flow measurement are pointed out.In chapter 3,unsteady minute flow measuring principle is proposed.Based on unsteady flow Bernoulli imegral equation.three models are established for typical free outflow through minute flow paths.Then,corresponding flow formulas and elevation conditions for application(ECA)of the method are deduced.Theoretical measuring errors are analyzed.In chapter 4,experimental instrument of unsteady flow measurement is established. Unsteady flow and steady flow measuring methods are both applied to standard flow check block and the results are compared.The test results show that measuring errors will increase with the ratio of flow seetion area of tested component(a)to that of measuring instrument(A). This proves the coffeetion of the theoretical analysis.The causes of measuring errors are analyzed and error compensation methods are proposed.In chapter 5,specified measuring instrument is studied and manufactured for regurgitant volume in artificial mechanical cardiac valve prosthese.Unsteady flow measuring principle is applied in the device thus proved correct.In chapter 6,an unsteady flow measuring instrument,which is multi-pieces marked,is designed for flow check of intra-vein catheter.Clearance leak flow measuring instrument is studied and developed for valve plate couples of water axial piston pump.With this instrument,the clearance of the couples can be obtained.At last,the main results and conclusions of this work are summarized,and further research plan is brollght forward.This research is initiative as follows:(1) Unsteady minute flow measuring principle and the realization are proposed.It puts forward a new way for minute flow measurement.(2) Based on unsteady flow and Bernoulli integral equations,the elevation conditions for applications(ECA)of this method are deduced.(3)Unsteady flow measuring instrument for regurgitant volume of artificial mechanical cardiac valve prosthese is developed and industrialized.