Experimental and numerical study of microwave heating in sand columns: Water saturation effects on temperature profiles and heat transfer mechanisms

• Microwave heating with an embedded coaxial antenna in a 220 L sand column. • Water saturation > 10% allows reduced-gradient temperature profiles. • Logarithmic temperature profiles and 2D modeling suggest a small dielectric source term. • Power conversion improvements could expand use at contaminated sites. Subsurface heating finds applications in soil remediation and enhanced resource recovery, with microwave heating offering advantages over conventional methods (conductive heating, hot vapor injection). However, the transition from laboratory-scale studies conducted in microwave ovens to in situ applications using embedded antennas in relevant environments remains poorly studied. This study investigates microwave heating mechanisms of a 2.45 GHz coaxial antenna in sand across varying water saturation levels. Results reveal that the reported advantages of microwave heating—rapid and homogeneous temperature rise—require a critical water content. For near-dry sand (<5% water saturation), temperature increased but exhibited steep, non-constant radial gradients. Conversely, at higher saturation levels (14% and 22%), temperature profiles rapidly developed near-constant, reduced gradients. Despite these differences, modeling indicates that thermal conduction, rather than direct absorption, remains the dominant heat transfer mechanism across all tests. Furthermore, the study identifies a significant discrepancy between nominal power and actual absorbed power, highlighting a low conversion efficiency. These results suggest that while microwave heating is effective for moderately saturated soils, further optimization of power and heat delivery is essential to promote its applicability to thermal desorption of polluted soil.