The Mesoscopic Risk Hypothesis: Structural Failure Mechanisms of Microwave Dehydration in Heritage Conservation

[Background]Current microwave dehydration techniques in heritage conservation primarily rely on macroscopicsurface monitoring, such as Infrared Thermography (IRT). However, these methods fail to accountfor localized thermodynamic transitions occurring at the mesoscopic scale (100 μm) within porousmasonry.[Hypothesis & Modeling]This study proposes the "Mesoscopic Risk Hypothesis," asserting that 100 μm cracks act as "thermodynamiclocks" that spontaneously capture moisture via Young-Laplace pressure and Kelvin effects.We demonstrate that fluidic resistance in these cracks is approximately 1,538 times higher than inmillimeter-scale channels, severely impeding vapor discharge.[Quantitative Results]Simulations show that 0.524 mg of internal moisture can undergo complete phase change in approximately0.28 seconds under 5W effective power. This process triggers a 1,600-fold volumetricexpansion. We identify a critical "Exhaust Lag" and a "Condensation-Re-evaporation" loop that sealsexhaust paths, causing internal pressure to surge. Even at 3% vaporization, localized stress at conicaltips can reach 2.3 GPa, far exceeding the structural capacity of historical red brick.[Conclusion]The hypothesis further unveils the "Thermal Desorption Avalanche," where high-pressure vaportriggers a chain reaction of adsorbed water desorption, leading to a secondary "step-like" pressurespike. This study concludes that the high efficiency of microwave dehydration masks severe risks ofirreversible microstructural damage, occurring within a "monitoring vacuum" that transcends currentempirical observations.