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Title: Quantifying and reducing errors in equilibrium moisture content measurements with dynamic vapor sorption (DVS) experiments

Source: Wood Science and Technology. 52(4): 909-927.

Author(s)Glass, Samuel V; Boardman, Charles R.; Thybring, Emil Engelund; Zelinka, Samuel L.

Publication Year: 2018  View PDF »

Category: Journal Articles
Associated Research Project(s):   FPL-4716-3A

Abstract: Dynamic vapor sorption (DVS) measurements are widely used to collect water vapor sorption isotherms for wood and other cellulosic materials. Equilibrium moisture content (EMC) is typically assumed to have been reached when the rate of change in moisture content with time (dM∕dt) drops below a certain value. However, the errors associated with determining EMC in this manner have never been characterized. Here, an operational defnition of equilibrium for DVS measurements is provided, and twenty test cases over four cellulosic materials are presented where the relative humidity was stepped up or down and then held constant until equilibrium was reached. Then, both the time to reach various dM∕dt “stop criteria” and the errors in EMC associated with those stop criteria are quantifed. The errors in the EMC from the widely used 0.002% min−1 stop criterion are found to be as large as 1.2% MC, and the average error for 20 test cases is 0.5% MC, which are much larger than the 0.1% MC error claimed in the literature. Longer data collection times are recommended, and a more stringent dM∕dt criterion (0.0003% min−1, using a 2-h window) for cellulosic materials is proposed. The errors with this criterion are less than 0.75% MC, and the average error is 0.3% MC. Furthermore, it is shown that the errors for a given stop criterion are systematic and can be fairly well characterized with a simple linear regression. Finally, a correction for systematic error is proposed that results in more accurate EMC values with shorter hold times.

Keywords: Dynamic vapor sorption (DVS); wood-moisture relations; sorption isotherms; experimental methods; equilibrium moisture content

Publication Review Process: Formally Refereed

File size: 2,048 kb(s)

Date posted: 09/14/2018

This publication is also viewable on Treesearch:  view
RITS Product ID: 91830
Current FPL Scientists associated with this product (listed alphabetically)
Glass, Samuel V.
Research Physical Scientist
Zelinka, Samuel L.
Materials Research Engineer
 

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