Abstract

The experiments of contact ultrasound intensified heat pump drying (CUHPD) of kiwifruit slices were conducted to investigate the effect of ultrasonic power on dehydration process and water migration of kiwifruit during CUHPD. The results clarified that contact ultrasound (CU) application could reduce the drying time of HPD significantly, and the rise of ultrasonic power had stronger reinforcing effect on dehydration rate. Weibull distribution function could simulate the dehydration process of CUHPD of kiwifruit with high precision, and the β values verified that ultrasonic power improvement could transform the moisture diffusion mechanism of CUHPD from total internal moisture diffusion control to partial internal moisture diffusion control. The D_cal values were 2.304 × 10⁻⁹~4.026 × 10⁻⁹ m²/s and increased as the rise of ultrasonic power. The scanning electron microscopy results illustrated that increasing ultrasonic power could produce more porous and spacious microstructure which was beneficial for water migration. The low-field nuclear magnetic resonance results elucidated that free water, immobilized water, and bound water in kiwifruit migrated and changed during CUHPD. Free water with the highest mobility was the most abundant water in kiwifruit, and was the first kind of water to be completely removed. With drying progressed, the contents of immobilized water and bound water gradually increased and then decreased, but they were not completely removed. The increasing in ultrasonic power was beneficial to promoting internal water migration and shortening the required dehydration time, especially for free water. Proton density images visualized that increasing ultrasonic power could significantly promote the water diffusion from internal kiwifruit outward the surface, and thereby accelerate the rate of water removal. Therefore, CU application is a suitable method to accelerate the water diffusion and moisture migration of HPD process.

中文翻译：

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接触超声强化热泵干燥过程中超声波功率对奇异果片脱水动力学和水分迁移的影响

摘要

进行了猕猴桃片的接触超声强化热泵干燥（CUHPD）实验，研究了超声功率对CUHPD过程中猕猴桃脱水过程和水分迁移的影响。结果表明，接触超声（CU）的应用可以显着减少HPD的干燥时间，并且超声功率的增加对脱水速率具有更强的增强作用。Weibull分布函数可以高精度地模拟奇异果CUHPD的脱水过程，β值证明了超声功率的提高可以将CUHPD的水分扩散机理从总内部水分扩散控制转变为部分内部水分扩散控制。所述d _CAL值分别为2.304×10^-9〜4.026×10 ^-9 米²/ s，并随着超声功率的增加而增加。扫描电子显微镜结果表明，增加超声功率可以产生更多的多孔和宽敞的微观结构，这对水的迁移是有利的。低场核磁共振结果表明，猕猴桃中的自由水，固定水和结合水在CUHPD期间迁移并发生了变化。流动性最高的自由水是猕猴桃中最丰富的水，并且是第一种被完全清除的水。随着干燥的进行，固定水和结合水的含量逐渐增加然后减少，但是没有完全除去。超声功率的增加有利于促进内部水的迁移并缩短所需的脱水时间，特别是对于自由水。质子密度图像可以看出，增加超声功率可以显着促进水分从内部奇异果向外扩散，从而加快除水速度。因此，铜的应用是加速HPD工艺中水扩散和水分迁移的合适方法。