The Measurement Of Liauid Diffusion Coefficient And Simulation Of Diffusion Image Based On 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,which is uesd widely in chemical,physical,biological,medicine,environmental protection and other scientific fields.Experimental method is usually used to measure liquid diffusion coefficient because of the difficulty of theoretical analysis.Based on the focal plane imaging principle of a liquid cylindrical lens,the method of the shift of equivalent refractive index(RI)slice(SERIS)has been used to measure the diffusion coefficients D of diethylene glycol and glycine aqueous solution for different concentrations at room temperature(25?).By analyzing the measurement results,the selection principle of RI slice is put forward.Based on the ray tracing principle,the diffusion process is simulated.The main research contents and results are as follows:First of all,the diffusion coefficients D of diethylene glycol and glycine aqueous solution for different concentrations were measured at room temperature by the SERIS.At the same time,the influence of selection of RI slice on diffusion coefficient measurement is studied.The measurement results show that concentration gradient is small when the RI slice is close to the RI of the target solution,and the diffusion coefficient is stable(standard deviation ??0.03×10-5 cm2/s)and accurate(relative error?3%)according to the error function solution which regards the diffusion coefficient as a constant.Secondly,based on the ray tracing principle,the diffusion coefficient is regarded as a constant,the diffusion process of diethylene glycol aqueous solution and glycine aqueous solution with different concentrations is simulated numerically by Matlab.Simulation result shows that the"waist"shift of simulation images over time are well consistent with the experimental images when the RI slice is close to the RI of the target solution,which means the concentration gradient is small.However,when the RI slice deviates from the target solution,the"waist"shift of simulation images over time are inconsistent with the experimental images,and the images are distorted with the increase of the concentration gradient.The simulation results further confirm the selection principle of RI slice when the diffusion coefficient is measured by the SERIS.Finally,based on the experimental diffusion coefficients of diethylene glycol and glycine aqueous solution with concentration,the empirical formulas of the diffusion coefficients with concentration is obtained by fitting analysis,the diffusion process is simulated numerically by the ray tracing method.The simulation result shows that the drift rate of the"waist"is consistent with the experiment whether the selected RI slice closes or deviates from the target solution RI,and the contour of simulation image is also close to the experimental image.This result again shows that diffusion coefficient changes with the concentration,only when the concentration gradient is small,the diffusion coefficient can be calculated as a constant.At the same time,a feasible method for numerical simulation of experimental diffusion image is proposed.