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刘云宏,孙畅莹,曾雅.直触式超声功率对梨片超声强化热风干燥水分迁移的影响[J].农业工程学报,2018,34(19):284-292.DOI:10.11975/j.issn.1002-6819.2018.19.036
直触式超声功率对梨片超声强化热风干燥水分迁移的影响
投稿时间:2018-05-02  修订日期:2018-08-14
中文关键词:  干燥  水分  超声    低场核磁共振  磁共振成像  水分迁移
基金项目:国家自然科学基金资助项目(U1404334);河南省高校创新人才资助项目(19HASTIT013);河南省高校青年骨干教师资助项目(2015GGJS- 048)
作者单位
刘云宏 河南科技大学食品与生物工程学院洛阳 471023 
孙畅莹 河南科技大学食品与生物工程学院洛阳 471023 
曾雅 河南科技大学食品与生物工程学院洛阳 471023 
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中文摘要:为探讨直触式超声对梨片热风干燥过程的水分迁移强化效应,在不同超声功率下进行梨片超声强化热风干燥试验,应用低场核磁共振(low-field nuclear magnetic resonance,LF-NMR)技术的自旋-自旋弛豫时间T2反演图谱及磁共振成像(magnetic resonance imaging,MRI)技术分析超声功率对梨片干燥过程中内部水分状态与迁移变化的影响。结果表明:梨片热风干燥属于内部扩散控制,在梨片热风干燥过程中施加超声有利于增强内部传质、加快干燥进程;干燥温度为45?℃时,超声功率升至12、24、36、48 W时,对应平均干燥速率比0 W时分别提高了13.1%、49.1%、83.6%、139.34%,表明提高超声功率有利于提高脱水速率。扫描电镜(scanning electron morphology, SEM)观察发现,施加超声会导致梨片组织微细孔道的增大与增多,从而有利于水分迁移。LF-NMR结果表明,超声功率越大,自由水、不易流动水和结合水的峰面积A值变化越显著,表明提高超声功率有利于提高水分流动性;结合干燥特性可以看出,干燥过程中首先除去的是自由水,超声功率由0 W升至48 W,自由水完全被脱除时间由720 min缩短至360 min,表明超声在自由水存在的情况下能实现较好的声波能量传递及内部水分湍动,进而产生显著的水分迁移强化效果;超声功率越大,不易流动水和结合水的脱除速率加快,表明提高超声功率可增强超声的高频振动和扩张作用,有利于减弱组织结构对水分的束缚力并增强水分流动性。MRI图像直观显示出梨片干燥过程中水分减少和水分空间分布变化规律,超声功率越大,H+质子密度图红度值下降越快,说明提高超声功率有利于加快水分迁移速率。研究结果可为超声强化热风干燥的理论研究及技术应用提供参考。
Liu Yunhong,Sun Changying,Zeng Ya.Effect of contact ultrasound power on internal moisture migration of pear slices during ultrasound enhanced hot air drying[J].Transactions of the Chinese Society of Agricultural Engineering (Transactions of the CSAE),2018,34(19):284-292.DOI:10.11975/j.issn.1002-6819.2018.19.036
Effect of contact ultrasound power on internal moisture migration of pear slices during ultrasound enhanced hot air drying
Author NameAffiliation
Liu Yunhong Henan University of Science and Technology, Luoyang, 471023, China 
Sun Changying Henan University of Science and Technology, Luoyang, 471023, China 
Zeng Ya Henan University of Science and Technology, Luoyang, 471023, China 
Key words:drying  moisture  ultrasonics  pear  low-field nuclear magnetic resonance  nuclear magnetic resonance imaging  moisture migration
Abstract: Ultrasound strengthening technology has gained more and more attention in drying research, however, the strengthening mechanism of ultrasound on water status and moisture migration during drying has been unclear until now. In order to investigate the strengthening effect of contact ultrasound on moisture migration of pear slices during hot air drying process, the experiments of ultrasound reinforced hot air drying on pear slices were conducted with different ultrasound powers. The scan electric microscope was used to observe the surface microstructure of dried pear slices at different ultrasound powers. The low-field nuclear magnetic resonance (LF-NMR) technology and nuclear magnetic resonance imaging (MRI) technology were applied to analyze the influence of ultrasound power on internal water state and moisture migration of pear slices during hot air drying. The results showed that hot air drying of pear slices belongs to internal diffusion control, and the reduction ratios of drying time were 60.0%, 58.3% and 57.8% when contact ultrasound of 48 W was applied in hot air drying of pear slices at 35, 45 and 55 ℃, respectively, which indicated that the application of contact ultrasound could significantly accelerate drying process. The drying time reduced from 1440 min to 1260, 960, 780, 600 min when contact ultrasound assistance at 12, 24, 36, 48 W was applied in hot air drying of pear slices at 45 ℃, which showed that higher ultrasound power could lead to higher water removal rate and shorter drying time. The results of scan electric microscope showed that the application of ultrasound could improve the number of micro-capillaries as well as enlarge the size of micro-capillaries, and higher ultrasound power produced looser microstructure of pear surface that was contacted with ultrasound radiation board, which was favorable to moisture migration and water diffusion. The LF-NMR results showed that the peak amplitudes of inversion spectrum kept decreasing during the drying process and higher ultrasound power led to faster decreasing rate of the amplitudes, which represented that free water, immobilized water and bound water inside pear slices changed and migrated during drying process, and higher ultrasound power could accelerate the migration of the 3 kinds of water. Free water, with the greatest mobility and the highest content, was the first kind of water for total removal. The removal time of free water was 720, 660, 600, 480 and 360 min at ultrasound powers of 0, 12, 24, 36 and 48 W, respectively. Ultrasound showed great strengthening effect on free water removal, which indicated that ultrasound could achieve good energy transmission and strong water turbulence at the existence of free water. The contents of immobilized water and bound water decreased during the drying, however, the immobilized water and bound water inside pear slices could not be removed completely. The peak areas became smaller with the increase of ultrasound power, which indicated that the increase in ultrasound power could improve water mobility and reinforce moisture migration. The MRI results showed the change of moisture content and water distribution at different ultrasound powers during the drying process, and higher ultrasound power caused faster moisture reduction, which indicated that the MRI images could visually illustrate the change and transformation of water inside pear slices and the application of ultrasound could accelerate internal moisture migration significantly and increase drying rate. The research can present reference to the theoretical study and technical application of ultrasound enhanced hot-air drying technology.
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