The Study On Measuring Diffusion Coefficient Of Liquid Based On Double Liquid-core Cylindrical Lens

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.Its accurate measurement has importantly scientific significance and applicable value in Physics,Chemistry,Biology,Medicine,Environmental protection and other scientific fields.To improve measurement accuracy and shorten the measurement time,a double liquid-core cylindrical lens(DLCL)is first designed and produced in this doctoral thesis.The optical measuring system consists of a DLCL has high refractive index(RI)sensitivity,very high minimum resolution of RI change.The DLCL consists of two parts,the front lens and the rear lens.The front lens of DLCL is used as diffusion cell and key imaging element,the RI of liquid filled in its core can be measured in the way of spatial resolution;The rear lens of the DLCL is used as an aplanatic component,either the RI position of spherical aberration(SA)or the SA in a range of RI caused by the front lens can be regulated by selecting liquid,of which RI is known and filled in the rear liquid core.In this paper,based on the focal plane imaging principle of DLCL,several measurement methods for liquid diffusion coefficient are proposed and studied when the liquid diffusion coefficient is constant or varies with the concentration.The main research contents and results of the dissertation are as follows:1.When the diffusion coefficient is measured by the focal plane imaging method,the main parameters that affect the measurement results are introduced.They are RI sensitivity(?f),the measurement error of focal length(8f),minimum resolution of RI change(?n)and aberration.In order to solve the problems existing in asymmetric liquid-core cylindrical lens(ALCL),a DLCL was designed,and the parameters of DLCL were analyzed.In terms of RI measurement,the RI sensitivity of the DLCL is increased by 4 times and the minimum resolution of RI change in DLCL is increased by 2 times.Under the condition of eliminating the SA,either the RI position of SA or the SA in a range of RI caused by the front lens can be regulated by selecting liquid,of which RI is known and filled in the rear liquid core.2.Based on the focal plane imaging principle of DLCL,the liquid diffusion coefficient of 0.33Mol/L KCl aqueous solution,infinitely dilute BaCl2 aqueous solution and heavy water diffusion in light water at temperature 298.15K have been measured by the equivalent RI of thin liquid layer method.These demonstrate the rule in selecting liquid thin layer and the effect on the measurement results when the liquid diffusion coefficient is measured by the method of equivalent RI of thin liquid layer.The diffusion coefficient between heavy water and light water was measured in the temperature range of 293.15K-313.15K according to the thin layer selection rule.The measured diffusion coefficients at different temperatures are in good consistent with the Arrhenius equation.3.Fixed observation height method for measuring the liquid diffusion coefficient is proposed.When measuring the liquid diffusion coefficient by this method,it is only need to select a certain position on the diffusion image as the observation height.With the diffused image reflecting the time-varying concentration information at the observation position,the liquid diffusion coefficient can be calculated by the least squares fitting method.Diffusion coefficients of 0.33 Mol/L KCl aqueous solution and infinitely dilute BaCl2 aqueous solution were measured at 298.15K by the fixed observation height method.The method has the characteristics of accurate measurement(relative error less than 2%)and fast measurement(-60min).4.Instantaneous diffusion image analyzing method for measuring the liquid diffusion coefficient is proposed.When measuring the liquid diffusion coefficient by the instantaneous diffusion image analyzing method,it is only necessary to select a certain position on the diffusion image as the observation height.The instantaneous diffusion image analyzing method is based on the concentration information which is changed with the position reflected by the transient diffusion image above the "waist",and the liquid diffusion coefficient can be calculated by the least squares fitting method.This method can greatly shorten the measurement time from the traditional method of a few hours or even longer time to the time that shoot a transient diffusion image(?17ms).Diffusion coefficients of 0.33 Mol/L KCl aqueous solution and infinite dilute BaCl2 aqueous solution were measured at 298.15K by the analyzing an instantaneous diffusion image method.The measurement results are very similar to the literature values.5.When the diffusion coefficient is not constant but varies with the concentration function,Bolzmann-Matano and Sauer-Freise methods,which are usually utilized to measure the solid diffusion coefficients,are used to measure the liquid D values that are dependent on solution concentration.Similarly,these methods require that DLCL can reduce SA in a wide range of RI.The diffusion coefficients for the different concentrations of KCl and BaCl2 aqueous solutions are measured by these methods at 298.15 K.These methods not only can shorten the measurement time of diffusion coefficient from the traditional method of dozens of hours or even longer to the time that shoot a transient diffusion image(?17ms),but also,only one transient diffusion image can simultaneously measure the diffusion coefficient of multiple concentrations.This truly realizes the transient measurement for the diffusion coefficient varied with solution concentration.