The strength of wood chips attachment to storage walls cause by freezing
Mattsson, J.E.
In cold climates, wet comminuted wood fuels sometimes freeze to walls and other surfaces during cold storage. This is well known. However, few studies have examined the relationship between the strength of attachment caused by freezing and factors such as temperature, fuel moisture content (MC), and surface type. The freezing of wood chips to three different surfaces (smoothed concrete, urethane rubber, and coated plywood) was studied on a laboratory scale with equipment designed for the study. Six plastic pipes embedded in thick insulation and filled with wood chips (15% to 155% MC, dry basis) were kept in direct contact with the surfaces that were mounted on a cold wall (-25 degrees C). This allowed the freezing of wood chips to six circular sections of the wall surfaces. The strength of the attachment caused by freezing was defined as the force parallel to the wall needed to loosen the wood chips. The force needed to loosen the wood chips was exponentially related to the MC of the chips. It was 4.3, 17.6, and 40.4 kN per m2 of contact area at MCs of 50, 100, and 150 percent, respectively. There was no significant difference in attachment between the three wall surfaces. The strength of attachment caused by freezing was influenced by the way the wall was kept cold. Because the study only included three surfaces and used wood chips with a very low proportion of fines and oversized particles, more surfaces and kinds of comminuted wood fuel ought to be studied.
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