The Measurement Of Concentration-dependent Liquid Diffusion Coefficients Of Three Nitrogen Fertilizers Based On A Liquid-core Cylindrical Lens

Diffusion coefficient(D)is a fundamental data in study of mass-transfer process,the calculation of mass-transfer rate,the design and development of chemical engineering.Which is uesd widely in the physical,chemical,biological,medicine,environmental protection and other scientific fields.Generally speaking,the liquid diffusion coefficient is a function of the solution concentration D(C),which is measured by a large number of different concentration pairs diffusion experiment.In this paper,an asymmetric liquid cylindrical lens is applied as the diffusion cell and imaging element.Based on the principle of focal plane imaging,the CMOS detector is used to collect experimental diffusion images.The experimental concentration spatial profiles(C~r(z,t)s)of three different nitrogen fertilizer aqueous solutions are obtained from the relation among image width,refractive index and solution concentration.The finite difference method(FDM)is applied to solve numerically Fick diffusion equation,and a series of concentration spatial distribution functions(C~m(z,t)s)were calculated at the same time as the experiment.Finally,the polynomial expressions D(C)of three different nitrogen fertilizer aqueous solutions were obtained quickly by comparing(C~r(z,t)s)with(C~m(z,t)).The main research contents and results are as follows:Firstly,Measuring the(C~r(z,t)s),calculated the(C~m(z,t)),the polynomial expressions D(C)were obtained by comparing the(C~r(z,t)s)with(C~m(z,t)).Using this method,the liquid diffusion coefficients of three nitrogen(urea,ammonium chloride,ammonium sulfate)aqueous solutions were measured at room temperature(298.15K).The results show that the polynomial expression D(C)obtained by the method is accurate and stable,short measuring and small measuring workload.Secondly,Based on the principle of ray tracing,numerical simulation was carried out on the polynomial expressions D(C)of three nitrogen fertilizer aqueous solutions by Matlab.The simulation results show that the simulation image and the“waist”shift of simulation image over time is consistent with the experimental images well,and the contour of the image is close to each other basically.Thirdly,The polynomial expression D(C)of ammonium chloride solution at the temperature between 288.15K to 313.15K were measured by finite difference method(FDM).The polynomial expression D(C)of ammonium chloride solution and Arrhenius formula is applied to measure the diffusion activation energy with the concentration-dependent between288.15K to 313.15K temperature.The measured results show that the liquid diffusion coefficient increases with the increase of temperature,and the measured results conform to the Arrhenius formula.Diffusion activation energy decreases with increasing concentration.