惰性粒子流化床干燥玉米膏的体积传热系数

Volumetric heat transfer coefficient of drying corn paste in fluidized bed with inert particles

为考察及提升玉米膏在惰性粒子流化床中的干燥体积传热系数,在利用现代计算流体动力学模拟技术对床内流场进行初步分析的基础上,改用自设计的新型波纹气分板替代了传统的直孔平板气分板。通过实测体积传热系数与进风速率、进风温度等参数间的对应关系曲线,获知了体积传热系数的若干变化规律。借助极差分析的正交实验设计,开展了体积传热系数的参数影响水平及取值优化研究,并基于因次分析建立了相应的模型表达式。结果发现:体积传热系数随进风速率、进料质量流量或惰性粒子静床高的提高而增大,随惰性粒子粒径的提高而减小,随进风温度的提高而先增大后减小;另与传统的直孔平板气分板相比,新型波纹气分板将更有助于提升操作的体积传热系数。同时,各参数对体积传热系数的影响作用强弱依次为进风速率>进风温度>惰性粒子静床高>进料质量流量>惰性粒子粒径,且优化工艺组合为进风速率6.5 m/s、进风温度90℃、惰性粒子粒径1.5 mm、进料质量流量11.5 g/s及惰性粒子静床高40mm,对应的体积传热系数可约达2.76 kW/(m3.℃)。此外,构建得到的关联模型也适于体积传热系数的估算,其预测值与实验值吻合良好。

To investigate and improve the volumetric heat transfer coefficient index of drying corn paste in fluidized bed with inert particles,the flow field in bed is preliminarily analyzed by means of the modern simulation technique of computational fluid dynamics,and as a result,a novel corrugated gas distributor designed in our lab is recommended to replace the traditional flat plate distributor with a straight hole structure.The relative change laws concerning the volumetric heat transfer coefficient are acquired and summarized by testing the effect relationship curves of volumetric heat transfer coefficient with respect to gas intake rate,gas intake temperature and etc.Based on the orthogonal experiment design with range analysis,the effect degrees of different operational factors on volumetric heat transfer coefficient are discussed and the relevant parameter optimization work is performed,and a calculation formula of volumetric heat transfer coefficient is subsequently constructed via dimensional analysis.The study results show: the volumetric heat transfer coefficient increases with the increase of gas intake rate,feed mass flow or inert particle static bed height,and decreases with the increase of inert particle diameter,and increases firstly and decreases later with the increase of gas intake temperature.Moreover,compared with the traditional flat plate distributor,the novel corrugated gas distributor can bring higher volumetric heat transfer coefficient.Meanwhile,the effect degree order of operational factors on volumetric heat transfer coefficient is gas intake rate>gas intake temperature>inert particle static bed height>feed mass flow>inert particle diameter,and the optimum technological combination is gas intake rate at 6.5 m / s,gas intake temperature at 90 ℃,inert particle diameter at 1.5 mm,feed mass flow at 11.5 g / s and inert particle static bed height at 40 mm,while the value of volumetric heat transfer coefficient can reach about 2.76 kW /(m 3·℃).Besides,the constructed correlation formula is also suitable for the calculation and estimation of volumetric heat transfer coefficient,and its predicting values are in good agreement with the experimental data.