The Measurement Of Liquid's Diffusion Coefficient Based On A Double Liquid-core Cylindrical Lens And Image Feature Extraction Method

Liquid diffusion coefficient(D)is a fundamental parameter in the study of mass-transfer process,the calculation of mass-transfer rate,the design and development of chemical equipment,which is uesd widely in the physical,chemical,medicine,food,biological,environmental protection and other scientific fields.The D value depends mainly on experimental methods,by measuring the distribution of solution's concentration with space and time,then the D value can be calculated by Fick's law.Using the double liquid-core cylindrical lens(DLCL)as both diffusive pool and imaging element,we measure the liquid D value by the focal plane imaging method and the image feature extraction method.The D value of different concentrations of sucrose solution at room temperature(25?)have been measured by two methods(the equivalent refractive index(RI)of thin liquid layer method and the instantaneous diffusion image analyzing method).The main research contents and results of the dissertation are as follows:First of all,based on the focal plane imaging method,the main parameters that affect the measurement results of diffusion coefficient are introduced.They are RI sensitivity(?f),the measurement error of focal length(?f),minimum resolution of RI change(?n)and spherical aberration(SA).The DLCL has a high RI sensitivity and a smaller minimum resolution of RI change,which can reduce the spherical aberration at the thin layer of the specific liquid and in a certain refractive index.Secondly,based on the focal plane imaging method,we measured D value by analysing the characteristic parameters of the diffusion image.In order to improve the measurement accuracy of D value,it is important to extract the characteristic parameters of diffusion image accurately.In this paper,image enhancement method is used to improve the image quality,and then the diffusion image's characteristic parameters are analyzed,which include the position of the "waist" and the width of the image.Finally,using the DLCL and combining with the method of image feature extraction,the D value of different concentrations of sucrose solution at room temperature(25?)were measured by the two methods(the equivalent RI of thin liquid layer method and the instantaneous diffusion image analyzing method).Both methods have the characteristics of high measurement accuracy.The experimental results show that using DLCL and the image features extraction method to measure D value is accurate and the measurement system is stable and reliable.