Li Sanping, Qi Jiamei, Wu Liguo, Wei Xinlong, Yuan Longqiang, Lin Haibin
School of Mechanical and Electrical Engineering, Northeast Forestry University, Harbin, 150040, China.
Harbin Institute of Forestry Machinery, State Forestry and Grassland Bureau, Harbin, 150086, China.
Heliyon. 2024 Jan 22;10(3):e24931. doi: 10.1016/j.heliyon.2024.e24931. eCollection 2024 Feb 15.
The moisture content of freshly picked walnuts is very high. In order to facilitate storage and transportation, it needs to be dried to prevent mildew. In this study, the pre-drying simulation and experimental study were carried out on the walnut drying equipment made by the research group to determine the optimal drying parameters. The effects of different inlet temperatures (353K, 373K, 393K), drying wind speeds (1.1 m/s, 1.4 m/s, 1.7 m/s) and drying time (30min, 45min, 60min) on the temperature and velocity fields of fluid and walnuts in the drying device were investigated by using the orthogonal test method of three factors and three levels. FLUENT software was used to simulate the drying process of open walnuts under hot air heating, and the distribution of fluid temperature field and velocity field in the drying device and the temperature change law of walnuts were obtained. The results show that when the inlet temperature is 393K, the inlet velocity is 1.7 m/s, and the drying time is 45min, the temperature field distribution of fluid and walnut in the drying device is the best and the change is the most uniform. In addition, the temperature change of the simulation results is consistent with the test results through experiments, which verifies the reliability of the simulation results. In order to more accurately simulate the change law of temperature and humidity transfer in hot air drying of walnuts, the walnut was modeled as a sphere consisting of three layers: walnut shell, air gap and walnut kernel. The reliability of the parameters was verified by surface response analysis. Taking inlet temperature, velocity and drying time as influencing factors and temperature change rate as evaluation index, the determination coefficient of regression model was R = 0.9966, and the correction determination coefficient Adj. R = 0.9922, indicating three influences. This study provides a theoretical basis for determining the optimum operating parameters of open walnut pre-drying, and has application value for walnut food processing.
刚采摘的核桃含水量很高。为便于储存和运输，需要进行干燥处理以防止霉变。本研究针对课题组自制的核桃干燥设备进行了预干燥模拟及实验研究，以确定最佳干燥参数。采用三因素三水平的正交试验方法，研究了不同进口温度（353K、373K、393K）、干燥风速（1.1m/s、1.4m/s、1.7m/s）和干燥时间（30min、45min、60min）对干燥装置内流体及核桃温度场和速度场的影响。利用FLUENT软件模拟热风加热下开口核桃的干燥过程，得到了干燥装置内流体温度场和速度场的分布以及核桃的温度变化规律。结果表明，当进口温度为393K、进口风速为1.7m/s、干燥时间为45min时，干燥装置内流体和核桃的温度场分布最佳且变化最为均匀。此外，通过实验验证了模拟结果的温度变化与试验结果一致，验证了模拟结果的可靠性。为更准确地模拟核桃热风干燥过程中温度和湿度传递的变化规律，将核桃建模为由核桃壳、气隙和核桃仁三层组成的球体。通过表面响应分析验证了参数的可靠性。以进口温度、风速和干燥时间为影响因素，温度变化率为评价指标，回归模型的决定系数R = 0.9966, 校正决定系数Adj. R = 0.9922，表明三者具有显著影响。本研究为确定开口核桃预干燥的最佳运行参数提供了理论依据，对核桃食品加工具有应用价值。
