烟草加料过程中双流体喷嘴雾化粒径的研究

【作者】 王宇；

【导师】 李晓；

【作者基本信息】 郑州轻工业学院 ， 食品科学与工程， 2018， 硕士

【摘要】 加料是烟草生产加工中的重要工序之一,而加料过程中雾化粒径及其分布均匀性会直接影响到料液的均匀性及有效利用率。本文利用双流体喷嘴雾化系统,开展了烟草加料过程中双流体喷嘴雾化粒径的研究。对影响双流体喷嘴雾化粒径大小及分布均匀性的因素进行了分析,同时运用数值分析和量纲分析研究了不同截面粒径大小及其分布规律,并建立了索特尔平均直径D32的模型。结果表明:(1)自主设计并搭建出双流体喷嘴雾化系统。本系统可以实现水蒸气和压缩空气的自由切换,并对工况参数进行精确控制,关键参数的控制精度在2%以内;建立了图像采集系统,图像精度可达2.28 μm/pixel;建立了图像处理系统,雾化粒径测试误差在1.1%以内。(2)调节雾化介质流量、料液流量、料液温度及料液类型可以实现对雾化液滴粒径大小及其分布均匀性的控制。研究表明:①雾化介质流量或液路流量恒定时,增大气液比,雾化粒径D32减小,液滴分布更加均匀。②其他条件相同,水的温度对雾化粒径大小及均匀性没有显著影响;提高料液温度,雾化粒径D32减小,雾化液滴的分布均匀性没有显著变化。③提高料液的运动黏度,雾化粒径D32增大;引射介质使用压缩空气相比水蒸气,其雾化液滴分布更加均匀。(3)调节雾化截面距离喷嘴的位置,可以实现对雾化粒径大小及其均匀性的整体控制。研究表明:①沿X轴线方向,首先液滴碰撞、融合效应占主导,其后重力发挥主要作用,导致液滴雾化粒径沿轴线方向呈现先增大后减小的趋势;随着轴线距离的增加,液滴整体分布更加均匀。②沿Y轴方向,下部区域液滴粒径明显大于上部区域;上部区域液滴分布均匀性明显优于下部区域。(4)建立了双流体喷嘴雾化粒径模型Ln(SMD/d)=lnK-aln(Re)-bln(We)+hlnf,根据预测模型得到的计算值和实际值拟合良好,方程决定系数均大于0.87,标准化残差均小于±2;模型与实测值之间平均相对误差2.3%-3.9%,最大相对误差15.2%,能够满足工程应用要求。更多还原

【Abstract】 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 μm/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:① 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.② 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.③ 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:① 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.② 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.更多还原