Evolution and Modelling of the Moisture Diffusion in Walnuts during the Combination of Hot Air and Microwave–Vacuum Drying

Xiaolan Man, Long Li, Xiuwen Fan (), Hong Zhang, Haipeng Lan, Yurong Tang and Yongcheng Zhang
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Xiaolan Man: College of Mechanical Electrification Engineering, Tarim University, Alar 843300, China
Long Li: College of Mechanical Electrification Engineering, Tarim University, Alar 843300, China
Xiuwen Fan: College of Mechanical Electrification Engineering, Tarim University, Alar 843300, China
Hong Zhang: College of Mechanical Electrification Engineering, Tarim University, Alar 843300, China
Haipeng Lan: College of Mechanical Electrification Engineering, Tarim University, Alar 843300, China
Yurong Tang: College of Mechanical Electrification Engineering, Tarim University, Alar 843300, China
Yongcheng Zhang: College of Mechanical Electrification Engineering, Tarim University, Alar 843300, China

Agriculture, 2024, vol. 14, issue 2, 1-18

Abstract: To understand the moisture transfer mechanism of walnuts during the combination of hot air ( HA ) and microwave–vacuum ( MV ) drying ( HA-MVD ) process, the drying characteristics and moisture diffusion characteristics of walnut during HA-MVD were investigated. The results indicated that the HA-MVD of walnuts occurred mainly in the falling-rate stage. The value of effective moisture diffusivity ( D eff ) dropped continuously with the decrease in moisture content ( MC ) during the HA drying, while switching to MV drying could truncate the decrease in D eff and still maintain a high value until the end of drying. The HA temperature, MC of the transition point, microwave power, and MV thermostatic temperature have significant effects on the moisture diffusion characteristics of walnuts. The values of D eff for walnuts ranged from 2.33 × 10 −9 m 2 /s to 6.89 × 10 −8 m 2 /s. The third-order polynomial prediction model of D eff related to the sample MC and drying conditions was established to describe the dynamic change in the D eff of walnuts during the HA-MVD process. The application of MVD in the final stage of drying could rapidly increase the internal vapor pressure of the walnuts, accelerate the diffusion speed of the internal moisture, and re-enhance the drying rate. The findings have practical value for the development of efficient and energy-saving drying methods in the walnut industry.

Keywords: walnut; combined drying; hot air drying; microwave–vacuum drying; moisture diffusion; model (search for similar items in EconPapers)
JEL-codes: Q1 Q10 Q11 Q12 Q13 Q14 Q15 Q16 Q17 Q18 (search for similar items in EconPapers)
Date: 2024
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