| Casing is one of the important processes in tobacco production,While Sauter mean diameter and uniformity index during the feeding process will directly affect the uniformity and effective utilization of feed liquid.We use the two-fluid nozzle atomization system to study the atomized particle size during tobacco casing.The effects of atomizing medium'stype,vapor liquid ratio,temperature and properties of casing solution on the droplet size distribution of two-fluid spay were investigated.Moreover,an empirical model of Sauter mean diameter(D32)of two-fluid spay was established based on the dimensional analysis method.The main conclusions were as follows:(1)We design and build a two-fluid nozzle atomization system independently.The system can free switch water vapor and compressed air.It accurately can control the working parameters such as temperature,pressure,flow rate of compressed air,water vapor and feed liquid,and the control accuracy of key parameters is within 2%;The laser image acquisition system with solid laser source and high-speed CCD camera imaging can achieve an image accuracy of 2.28 ?m/pixel.An image processing system based on the grayscale threshold is established,whose error of atomization particle size measurement is within 1.1%.(2)Adjusting the flow rate of the atomizing medium,the flow rate of the material and the liquid,the temperature of the liquid and the type of the liquid can realize the control of the size and distribution uniformity of the atomized liquid droplets.The conclusion were as follows:? When the flow rate of atomization medium or casing solution was constant,D32 decreased gradually and the uniformity index(N)increased slightly with a rising temperature of vapor liquid ratio.? With the same other parameters,there was no obvious change of D32 and N when the water temperature rose.However,D32 decreased gradually and N had no obvious change when the temperature of casing solution increased.? As the feed liquid viscosity rose,D32 had a trend of decreasing with the same other parameters.Compared with that of water,N of various casing solutions had no significant change by using compressed air as the atomizing medium.However N of various casing solutions were obviously smaller than that of water when the steam was used as an atomizing medium.(3)Adjusting the position of the atomizing section from the nozzle can achieve overall control of the size and uniformity of the atomized particle size.The research shows that:? Along the X-axis direction,the collision and fusion effects of droplets are dominant,and gravity plays a major role in it.As a result,the particle size of the droplets first increases and then decreases along the axial direction;along the axis With the increase,the overall droplet distribution is more uniform.? In the Y-axis direction,the droplet size in the lower region is significantly larger than that in the upper region;the uniformity of droplet distribution in the upper region is significantly better than that in the lower region.(4)The model Ln(SMD/d)=lnK-aln(Re)-bln(We)+hlnf is established for two-fluid nozzle atomized particle size.The calculated and actual values obtained from the prediction model are well-fitted,and the equation is determined.The coefficients are all greater than 0.87,and the standardized residuals are all less than ±2.The atomizing medium of compressed air or steam and the liquid of water or various casing solutions,the average relative error and the maximum relative error of D32's predicated values and the measured values were respectively 2.3%?3.9%&15.2%,which have been satisfied with the engineering application requirements. |
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