DEVELOPMENT OF THE MICRO-ICE-LENS MODEL

摘要

The micro-ice-lens model describes the abnormal contraction during freezing after the first ice formation (frost shrinkage) and the equivalent expansion during heating. The chemical and mechanical stability criteria are developed from surface thermodynamics. Microscopically, the model points to a redistribution of water in the pore space from gel to larger pores during cooling and a water uptake from external sources during heating. The moving boundary condition given by the progressing ice front (cooling) and melting front (heating) enhances this. A short description of the stresses caused by the formation of micro-pore-ice in the gel at very low temperatures is also given. The model provides a basis for understanding frost suction over a freeze-thaw cycle. If a critical degree of saturation is exceeded the well-known damage models can be applied. This knowledge is essential for accurate testing methods and simulation of practice conditions.