云南小粒种咖啡热风干燥特性及其数学模型

Hot Air Drying Characteristics of Yunnan Small Seed Coffee and Its Mathematical Model

以云南小粒种咖啡为原料,探究小粒种咖啡热风干燥特性及最佳数学模型,为咖啡热风干燥工艺提供参考。对小粒种咖啡湿豆进行热风干燥,用正交试验的方法研究其在不同热风温度、风速、铺装厚度和搅拌转速下的热风干燥特性,比较10种数学模型在热风干燥特性中的适用性。结果表明:热风风速在干燥实验中对传热传质有催进作用;搅拌可加快热传递提高热效率,减少干燥时间;铺装厚度主要影响干燥用时,铺装厚度与干燥速率变化成反比;咖啡干燥以降速干燥为主,无明显恒速干燥阶段,热风温度对热风干燥的干燥特性影响最大;对正交试验进行极差、方差分析可知,温度40℃,风速1 m/s,搅拌转速2 r/min为最优热风干燥方案,最佳数学模型为Logarithmic模型,热风温度、热风风速与搅拌转速3个因素对热风干燥总时长影响的极差值为19、6.67、5.5,3个因素在95%置信区间下P值为0.011、0.082、0.391。主次顺序为热风温度A>热风风速B>搅拌转速C;由评价指标R2、SSE、残差均方及对比实验数据与常用干燥模型进行非线性回归拟合分析,结果显示Logarithmic模型拟合度最好,其中R2为0.986444、SSE为0.021734、残差均方为0.002075。该数学模型可预测云南小粒种咖啡湿豆的热风干燥特性曲线,也为实际的生产与加工提供依据和参考。

Yunnan small seed coffee was used to explore the characteristics and optimal mathematical model of hot air drying.The hot air drying characteristics of the coffee beans under different circumstances were studied by an orthogonal experiment with wind speed,pavement thickness and stirring speed,and the applicability of 10 mathematical models in hot air drying characteristics was compared.The results showed hot air velocity could promote the heat and mass transfer in the drying process.The mixing process not only could accelerate heat transfer,but also improve heat efficiency and reduce drying time.Coffee bean pavement thickness mainly affected the drying time.The pavement thickness was inversely proportional to the change of drying rate.Data analysis revealed the drying was mainly characterized by decreasing drying speed,and there was no obvious constant speed drying stage,and the hot air temperature had the greatest influence on the drying characteristics of hot air drying.According to the range and variance analysis of the orthogonal experiment,the optimal hot air drying scheme was temperature 40℃,wind speed 1 m/s and stirring speed 2 r/min.The optimal mathematical model was an logarithmic equation.The range values of the influence of hot air temperature,hot air speed and stirring speed on the total hot air drying time was 19,6.67,5.5,respectively.P value of the three factors under 95%confidence interval was 0.011,0.082 and 0.391 respectively.The primary and secondary order was hot air temperature A>hot air speed B>stirring speed C.Logarithmic model was analyzed by the nonlinear regression fitting of evaluation index R2,SSE,mean square of residual and comparison experimental data with commonly used drying model.According to the date analysis,the results showed that the best-fitting degree of Logarithmic model,R2 is 0.986444,SSE is 0.021734,mean square of residual is 0.002075.Taking all the factors into conclusion the mathematical model not only can predict the hot air drying characteristic curve of Yunnan arabica wet beans,but also provide a theoretical basis and reference for the actual production and processing of small seed coffee.