Frequency Response Analysis for the Determination of Thermal Conductivity and Water Transport in MOF Adsorbent Coatings for Heat Transformation

In this paper we focus on the differentiation and quantification of different heat and mass transfer phenomena governing the overall sorption dynamics, for the example of a binder-based aluminium fumarate (Alfum) coating for heat transformation applications with water as refrigerant. The methodological emphasis is on extending the volume swing frequency response (FR) method to problems with strong heat transfer limitation. The heat and mass transfer parameters are mapped to the sample temperature and loading state, in order to be able to reproduce the strongly non-linear behaviour exhibited under application conditions. Based on a model with discretised heat transfer and linear driving force (LDF)-simplified micropore diffusion, the thermal conductivity of the samples was identified as about 0.07 W/(m K), and the LDF time constant between 0.1 and 3 s-1 at 40°C with a U-shaped loading dependency and an Arrhenius-type temperature dependency. The method is validated by comparing a measured large temperature jump experiment to the results from a non-linear simulation informed solely by these parameters obtained from the new FR-based method.