Boundary Conditions in Hygrothermal Measurements of Biobased Material

Biobased materials have a significant appeal in the construction industry because of their sustainability. The hygroscopic properties of these materials play a very important role in various applications as they affect the mechanical properties, durability, and indoor environmental quality. The hygrothermal behavior of biobased construction and textile materials is influenced by various environmental factors such as temperature, relative humidity, airflow, and exposure to liquid water. In this context, precise management of boundary conditions is crucial for accurately forecasting the internal mass transport (specifically, bound water absorbed at the nanoscale within the amorphous regions of cellulose) and heat flow. To understand the intricate dynamics of heat and moisture transfer within dry cellulosic materials, our study delves into the temperature distribution throughout the sample over time. We examine how these materials respond when subjected to controlled dry airflow at a temperature different from the initial homogeneous temperature of the sample. We show that one can deduce the boundary conditions from the knowledge of the heat distribution in the sample. A similarity approach shows that they may be described by an expression involving a single unknown parameter (boundary layer thickness). On another side we carry out experiments now with a sample initially saturated with bound water and submitted to a dry air flux of the same temperature. We show the consistency of the two similarity approaches (for the mass and for the heat transport) by comparing the values of the boundary conditions in each case.

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