The Study On Measuring Liquid's Diffusion Coefficient By Equivalent Observation Altitude And Water Absorption By Liquid Based On Double Liquid-core Cylindrical Lens

Liquid diffusion coefficient(D)is a fundamental data that is widely used in the fields of Physics,Chemistry,Biology,Medicine,Environmental protection and other scientific fields,and that has important significance for mass transfer process,mass transfer rate calculation and chemical design and development.The liquid diffusion coefficient mainly depends on the experimental method.The coefficient is calculated based on the second law of Fick by measuring the diffusion-induced concentration change with time and space.In this paper,we introduce a new method(Equivalent Observation Altitude Measurement Method)to calculate the liquid diffusion coefficient by using double liquid-core lens(DLCL)as both diffusive pool and imaging element.The DLCL can eliminate the spherical aberration at a specific refractive index or reduce the spherical aberration over a wide refractive index range.The diffusion coefficients of0.33 mol/L KCl aqueous solution and different concentrations' NaCl aqueous solution have been measured by equivalent observation altitude measurement method.Then,based on the spatial resolving ability of double liquid-core cylindrical lens for measuring refractive index,a preliminary analysis and research about the water-absorption of ethylene glycol(EG)also have been made in this paper.The main contents and research results are as follows:Firstly,a method to calculate liquid diffusion coefficient: equivalent observation altitude measurement method is introduced in this paper.By the method,observe the change of the width of the diffusion image at a certain fixed position and solve the corresponding concentration change.Then,Solve the minimum sum of squares of experimental concentration distribution and theoretical concentration distribution calculated by Fick's second law Gaussian error function solution,So we can get the diffusion coefficient D.The diffusion coefficients of 0.33 mol/L KCl solution and NaCl solutions at different concentrations were measured by this method at room temperature(25 ?).The measurement results show that the method has the advantages of stable and accurate diffusion coefficient(relative error less than 3%),short measuring time(about70 min)and visualization of diffusion process.Secondly,based on the spatial resolution of refractive index of liquid core column lens and the changes of the image width,a method to measure the water absorption of EG was proposed.The method was used to measure the water absorption of different concentrations' EG in the period of 20 h-30 h.A control group was used to compare with it which measured water absorption by digital balance under the same experimental conditions.The relative errors between the two methods were less than 5%.Our method of measuring the water absorption is characterized by real-time observation and visualization of water absorption process.Thirdly,The diffusion of EG during water absorption process was simplified to Semi-infinite diffusion.Then,the diffusion coefficients of water and different concentrations of ethylene glycol were measured by the equivalent refractive index of thin liquid layer method.The experimental results show that the larger diffusion coefficient,the faster diffusion of water to ethylene glycol,and the morewater-absorption in the same time.