Analysis of the diffusion characteristics and activation energy of rice drying using low‐field nuclear magnetic resonance

Abstract

Abstract This research was conducted to determine the effective moisture diffusion coefficient and activation energy of rice using low‐field nuclear magnetic resonance (LF‐NMR). The results showed that the evaporable water was rapidly removed under high‐temperature drying in the early stages of drying. The diffusion rate of evaporable water at different temperatures in the later stages of drying was not significant. Besides, the activation energy in rice was divided into the activation energy of the conversion of the chemically bound water (15.04–25.69 kJ/mol) to evaporable water and the activation energy of the diffusion of evaporable water from rice (6.42–16.42 kJ/mol), indicating that more energy was needed to dry the chemically bound water from rice. A new method for obtaining the effective moisture diffusion coefficient and the activation energy was proposed based on the relaxation time distribution profiles, revealing the internal relationship between various phase moisture and activation energy. These results will provide a theoretical guidance for the drying process. Practical applications The moisture diffusion characteristics and activation energy of rice were determined using low‐field NMR signal quantities, which were important parameters for optimizing the drying process. In addition, the variable temperature drying method was conducive to the rapid diffusion of moisture in the rice. The chemically bound water within rice required more energy to diffuse than other forms of water components. An internal relationship between moisture content and the activation energy was established to provide a theoretical reference for high‐quality drying techniques.