The Study On Measuring Temperature-dependent Liquid Diffusion Coefficient Based On A Liquid-core Cylindrical Lens

Liquid diffusion coefficient(D)is a fundamental parameter in the study of mass-transfer process,which is uesd widely in chemical,medical and environmental protection fields.Temperature is an important factor that affects the liquid phase diffusion coefficient.In order to measure the temperature-dependent liquid phase diffusion coefficient accurately and quickly.In this paper,temperature control device has been designed to adjust the diffusion solution temperature conveniently,which has a wide temperature control range and high accuracy based on semiconductor refrigeration.The diffusion coefficients of β-alanine and vitamin C aqueous solution at different temperatures were measured based on the temperature control device and liquid cylindrical lens.The main research contents and results are as follows:First of all,the temperature control device of liquid phase diffusion coefficient measuring instrument was designed by semiconductor refrigeration chip and temperature control module.The temperature control range is 283.15 K to 323.15 K,and the temperature control accuracy is ± 0.1 K,which solves the problems of small temperature range(288.15 K to 303.15 K)and low accuracy(± 2.0 K)of the air conditioning device.Secondly,the concentration-dependent diffusion coefficients of β-alanine aqueous solution were measured in the temperature range of 288.15 K to 318.15 K using the methods of “equivalent refractive index(RI)of thin liquid layer method” and “measurement of concentration-dependent diffusion coefficients based on finite difference method”.The measurement results D(C)of the two methods are consistent to each other.The measurement results show that the diffusion coefficient decreases with increasing concentration at the same temperature;the measurement results of the diffusion coefficients of the same concentration at different temperatures satisfy the Arrhenius relationship.Based on the ray tracing method,the numerical simulation of the diffusion images were carried out.The simulated images are close to the experimental images,which verifies the correctness of the D(C)relationship and the measurement result of the diffusion activation energy.Finally,based on the temperature-controlled liquid phase diffusion coefficient measuring instrument,the diffusion coefficient of vitamin C aqueous solution under infinitely dilute conditions was measured in the temperature range of 288.15 K to 318.15 K.The results show that the diffusion coefficients increase firstly and then decreases with increasing temperature.The diffusion coefficient is the largest at 313.15 K,and the variation law of the diffusion coefficients with temperatures does not follow the Arrhenius relationship.Using the "heating and cooling" and "liquid chromatography" methods,the liquid phase diffusion coefficients of the vitamin C aqueous solution were measured under the same conditions.The structural change at high temperature may be the reason of the vitamin C diffusion coefficient does not satisfy the Arrhenius relationship.