PDF(Sci-hub)
Abstract：
This study aimed at investigating the performances of air drying of blackberries assisted by airborne ultrasound and contact ultrasound. The drying experiments were conducted in a self-designed dryer coupled with a 20-kHz ultrasound probe. A numerical model for unsteady heat and mass transfer considering temperature dependent diffusivity, shrinkage pattern and input ultrasonic energies were applied to explore the drying mechanism, while the energy consumption and quality were analyzed experimentally. Generally, both airborne ultrasound and contact ultrasound accelerated the drying process, reduced the energy consumption and enhanced the retentions of blackberry anthocyanins and organic acids in comparison to air drying alone. At the same input ultrasound intensity level, blackberries received more ultrasound energies under contact sonication (0.299 W) than airborne sonication (0.245 W), thus avoiding the attenuation of ultrasonic energies by air. The modeling results revealed that contact ultrasound was more capable than airborne ultrasound to intensify the inner moisture diffusion and heat conduction, as well as surface exchange of heat and moisture with air. During air drying, contact ultrasound treatment eliminated the gradients of temperature and moisture inside blackberry easier than airborne ultrasound, leading to more homogenous distributions. Moreover, the total energy consumption under air drying with contact ultrasound assistance was 27.0% lower than that with airborne ultrasound assistance. Besides, blackberries dehydrated by contact ultrasound contained more anthocyanins and organic acids than those dried by airborne ultrasound, implying a higher quality. Overall, direct contact sonication can well benefit blackberry drying in both energy and quality aspects.
摘要：
本研究旨在研究空气超声和接触超声辅助下的黑莓空气干燥性能。干燥实验是在自行设计的干燥机和20kHz超声探头中进行的。考虑温度相关扩散率的非稳态传热和传质的数值模型，应用收缩模式和输入超声能量来探索干燥机理，同时对能耗和质量进行了实验分析。一般来说,空气超声和接触超声都加速了干燥过程，与单独的空气干燥相比，减少了能耗并提高了黑莓花青素和有机酸的保留率。在相同的输入超声强度水平下，黑莓在接触超声处理(0.299W)下接收的超声能量比机载超声处理(0.245W)多，从而避免空气对超声波能量的衰减。建模结果表明，接触式超声比机载超声更能增强内部水分扩散和热传导。以及表面与空气的热量和水分交换。在空气干燥期间，接触超声治疗消除温度和湿度的梯度黑莓比空气中的超声波更容易，导致更均匀的分布。此外，接触超声辅助空气干燥下的总能耗比空中超声辅助低27.0％。此外,接触超声脱水的黑莓比空气超声干燥的黑莓含有更多的花青素和有机酸，意味着更高的质量。总的来说,直接接触超声处理可以很好地有利于黑莓干燥在能量和质量方面。
