Monitoring Dynamic Moisture Gradients in Wood using Inserted Relative Humidity and Temperature Sensors

Journal article, 2016

To be able to combine the preservation of wooden objects of cultural significance with energy efficiency measures it is important to develop our knowledge of the relation between the rate of change of relative humidity and temperature, moisture content gradients and the resulting dimensional change of wood. The work presented here introduces and evaluates a method for monitoring dynamic moisture content gradients, mainly for research applications. Relative humidity and temperature were measured by miniature sensors, placed in drilled holes at different depths in wood samples to monitor the moisture transport. The data was used to calculate moisture content and the results could hence be compared with the results from a commercial resistance moisture meter, monitored at the same depths. The results of the two methods did not coincide. A Fickian model for moisture diffusion was chosen to verify the monitored results. It showed poor fit with the commercial resistance method and a reasonably good fit with the new method using relative humidity and temperature sensors. We concluded that the new method provides reliable and consistent data suitable for monitoring moisture content at different depths under unsteady state conditions, while the data generated by the resistance method in our set-up was inconsistent with the model and with our understanding of the moisture transport process.