Measuring Diffusion Coefficient In The Ethylene Glvcol-Water System By Imaging Method Under Different Temperature

The mass transfer process occurs on account of asymmetrical distribution of concentration, which is associated with physic, chemistry, biology and medical science and plays an important role in these fields. Diffusion process leads to the mass transfer process, then diffusion process is divided into molecular diffusion and convection diffusion, the latter is associated with the situation of the system’s bulk flow so that it’s difficult to research it qualitatively. Generally, we study molecular diffusion which result from the random thermal movement of molecules. The diffusion coefficient is the essential key parameter to describe diffusion process, but it’s difficult to describe liquid diffusion process with mathematic model. Hence liquid diffusion coefficient is acquired by experiment and the data of it is lacking.The methods to measure the liquid diffusion coefficient include Diaphragm-cell method, Taylor dispersion method, Holographic interferometry method, Chemical color reaction in micro-channels method and so on. These methods have respective advantages and disadvantages, but the common disadvantage is time consuming. This paper mainly studies the change rule of diffusion coefficient with the change of temperature by measuring the diffusion coefficient in the Ethylene Glycol-Water system using an asymmetric liquid-core cylindrical with imaging method under different temperature. The specific works are as flows:First, the solution layers with different refractive index are observed to measure the diffusion coefficient respectively when EG and water are the diffusion system. It’s found that the experimental value is close to the diffusion coefficient of the EG in infinite solution when the refractive index of the layer is close to that of water. So the experimental procedure is determined that the layer which refractive index is close to that of water is observed to record the change rule of the layer’s position over time after injecting the two liquid of the diffusion system and to calculate the diffusion coefficient with the second Fick’s law and linear regression of the change rule of the layer’s position over time.Second, the diffusion coefficients of EG in the infinite solution under different temperature(15℃,20℃,25℃,30℃,35℃,40℃) are measured. And the results from25℃to40℃are ideal with lesser error. It’s indicated that the higher the temperature is, the higher the diffusion coefficient is. Meanwhile, the diffusion coefficient is associated with temperature with the relationship,"Arrhenius relationship", which diffusion activation energy is calculated basing on. Compared with the literature value, the relationship between diffusion activation energy and temperature is discussed.Finally, the diffusion coefficient of EG in the ethylene glycol aqueous solution with different mass fraction is measured basing on the conclusion from the verification experiment, which indicates that the denser the ethylene glycol aqueous solution is, the diffusion coefficient of EG in it is higher.