Mathematical model of water sorption isotherms of UBC

Mathematical models for sorption isotherms were investigated as for UBC (Upgraded Brown Coal) and its feedstock coals, dried and not dried. Studies on classic models proved that: (1) Characteristic curves of Polanyi plot showed that UBC is more hydrophobic than its dried feedstock coal. (2) BET model is applicable in the range of 5 to 40% relative humidity and can provide a rough estimation of the heat of adsorption. Among modern models, Henderson model showed the best fitting but several other models gave satisfactory results when regression constants were properly adjusted. The fact that different models based on different theories describe a phenomenon, depending on regression constant values, implies that a reasonable interpretation of the constants is essential in understanding the phenomena through models. This is normally difficult but the constant of Henderson model was successfully interpreted through analogy to application of Weibull function to reliability engineering. Furthermore, it was proved that the constants of this model do not depend on temperature when moisture is non-dimensionalized.