【摘要】 在油菜籽干燥过程中,干燥工艺(热空气温度、速度和油菜籽初始含水率)主要影响着恒速干燥阶段的传热、传质系数,为此该文基于恒速干燥阶段,借助流化床干燥试验装置,试验分析了油菜籽初始含水率、热空气温度、热空气流速对油菜籽流化床干燥对流传热、传质系数的影响,结果表明:各影响因素的敏感性主次顺序为油菜籽初始含水率>热空气温度>热空气流速,其中油菜籽初始含水率为29.72%的对流传热、传质系数约为含水率14.41%的1.9倍,2.25 m/s热空气流速的对流传热、传质系数约为1.75 m/s的1.2倍,65℃热空气温度的对流传热、传质系数分别约为45℃的1.2倍和1.4倍。为此,以对流传热、传质系数为性能指标,根据Box-Behnken试验设计原理,应用Design-Expert 8.0.6软件,建立了影响因子与性能指标的回归模型,通过验证发现对流传热、传质系数两个模型预测值与试验值的最大相对误差仅为4.83%和4.79%,表明该两个回归模型拟合度较好,可靠性较高。研究结果可为强化传热传质提高油菜籽流化床干燥效率提供理论依据,同时也为生产工艺条件选择和干燥设备设计提供理论支撑。更多还原

【Abstract】 The rapeseed oil is one of the main edible vegetable oils in China and the third largest edible vegetable oil all over the world.It is easier to mold under the high temperature and humidity because the rapeseed has more protein and very small porosity.Therefore,the fresh rapeseed is hard to be safely stored.At present,the traditional solar drying method of rapeseed can hardly meet the requirements of rapeseed drying in China.For the timely safe storage,artificial drying methods must be employed,among which the hot-air fluidized-bed drying is commonly applied.The principle of the rapeseed fluidized-bed drying is extremely sophisticated because it is often associated with impaired heat transfer,mass transfer,and momentum transfer.The convective heat and mass transfer coefficient are key influence factors to the drying efficiency and the drying quality of rapeseed fluidized-bed drying.In brief,the changing regularity of convective heat and mass transfer coefficient,and the measures on improving convective heat and mass transfer have become the vital problems concerning the timely safe storage of fresh rapeseed.In order to investigate the changing regularity of convective heat and mass transfer of the rapeseed fluidized-bed drying,the influence of the initial moisture content,the hot air temperature,and the hot air velocity on the convective heat and mass transfer coefficient was analyzed by using experiment equipment of rapeseed fluidized-bed drying.The results showed that the convective heat and mass transfer coefficient increased with the increase of the initial moisture content,the hot air temperature,and the hot air velocity.And the primary and secondary order of the factor influencing the convective heat and mass transfer coefficient was:the initial moisture content,the hot air temperature,and the hot air velocity.The convective heat transfer coefficient and the convective mass transfer coefficient of the rapeseed with 29.72%initial moisture content were both 1.9 times that with 14.41%initial moisture content.The convective heat transfer coefficient and the convective mass transfer coefficient of the rapeseed with 2.25 m/s hot air velocity were both 1.2 times that with 1.75 m/s hot air velocity.At the same time,the convective heat transfer coefficient and the convective mass transfer coefficient of the rapeseed with 65℃hot air temperature were 1.2 and 1.4 times thatwith 45℃hot air temperature,respectively.On the basis of these,a second orthogonal rotation combination test was executed through the Design-Expert 8.0.6 software.The initial moisture content,the hot air temperature,and the hot air velocity were selected as influencing factors.The convective heat and mass transfer coefficient were response indices.Then the regression models of the convective heat and mass transfer coefficient were established.For the 3 groups of experiment results,the maximum relative errors of the convective heat and mass transfer coefficient between the model prediction values and the corresponding experimental values were 4.83%and4.79%,respectively.It was proved that the regression models had higher precision.The results may provide the theoretic basis for improving convective heat and mass transfer,which effectively improves the drying efficiency and the drying quality of rapeseed fluidized-bed drying.更多还原