黑莓微波真空干燥传热特性

摘要

对黑莓进行微波真空干燥,研究不同微波功率和真空度对黑莓干燥过程中温度的影响,观察样品整个温度场的分布规律.采用数值模拟的方法,建立电磁与传热耦合模型,经过2 min的微波真空加热,得出不同微波功率、不同真空度下黑莓的仿真温度场分布图.选取微波功率为400 W,真空度为一60 kPa的条件进行试验,对数值模拟的结果进行分析和评定.仿真的意义在于规避加热区域的冷点位置,同时选取合适的微波功率和真空度以降低热点区域的温度差异性,保证实际加热时同一批次的样品加热效果基本一致.结果表明:黑莓在微波功率为400 W,真空度为一80 kPa的条件下加热2 min后,热点的温度维持在60℃左右,温度差异性为0.27,在样品热点区域加热温度高度一致性的前提下,保证了合适的加热温度,满足黑莓的干燥要求.%Microwave vacuum drying of blackberry was carried out to investigate the effect of microwave power and vacuum degree on the temperature of blackberry during drying process,and the distribution law of the whole temperature field was observed.Using numerical simulation method,the coupling model of electromagnetic and heat transfer was established.After two minutes of microwave vacuum heating,the simulation temperature field distributions of blackberry under different microwave power and vacuum degree conditions were obtained.The experiment was carried out under the condition of microwave power of 400 W and vacuum degree of-60 kPa,and the experiment and simulation results were compared to analyze and e valuate the results of numerical simulation.Simulation can observe and avoid the hot and cold spots.The appropriate microwave power and vacuum were also selected by simulation to reduce the temperature difference and ensure heating uniformity.The results showed that blackberry under the condition of the microwave power of 400 W and vacuum degree of-80 kPa after heating 2 min,the temperature of the hot spot was maintained at about 60 ℃,with the temperature difference about 0.27.The heating uniformity was consequently ensured to meet the drying requirements of the blackberry.