Improving RF heating performance for granular products through vibration assistance

Abstract

Non-uniform heating remains a major obstacle hindering the large-scale industrial application of radio frequency (RF) technology. For improving RF heating performance, a vibration-assisted RF heating system was applied, using mung beans as a model granular product, to systematically investigate effects of electrode gap and vibration frequency on RF heating rate and uniformity (λ). The relationship between vibration frequency and RF heating performance was explored using a coupled simulation model by integrating Multibody Dynamics (MBD) and Discrete Element Method (DEM). Experimental results demonstrated that the electrode gap of 130 mm achieved the optimal balance between heating rate (2.5 °C/min) and uniformity (λ = 0.036). As vibration frequency increased, the λ value initially decreased and then stabilized, showing an 80 % reduction compared to static conditions. The lowest λ value was obtained when the vibration frequency was greater than 15.0 Hz. A strong positive correlation (r = 0.997) was identified between the single circular motion time (ST) of particles and λ, indicating that increased particle kinetic energy and decreased ST, resulting in three-dimensional motion patterns, were critical factors for achieving uniform energy absorption. Conversely, the reduction in contact points (r = 0.918) was identified as the primary reason contributing to the decreased heating rate. This study may provide both theoretical insights and technical support for the industrial application of vibration-assisted RF heating in achieving uniform thermal processing of granular agricultural products.