Improving the thermal insulation capacity of wood shaving insulation mats through the addition of carbon black (Part 2): Thermal conductivities of full-scale mats and the mechanisms of performance improvement
2017
Sekino, N. | Sasaki, S.
In order to decrease the thermal conductivity of mats made from wood shavings, a simple manner of adding carbon black (CB) to wood shavings was tried in the previous study, Part 1, with the use of laboratory-made wood shavings. The results showed that a small addition rate of CB, less than 2%, was enough to decrease the thermal conductivity of the mats. In the present study, full-scale wood shaving mats with or without additions of CB were made with real wood shaving waste material from a wood processing factory and the mat thermal conductivities were measured in order to confirm the performance improvement. It was found that the addition of CB with a rate of only 0.25% reduced the thermal conductivity of the mat by 14 % on average and this performance improvement was greater than that found in the previous study, Part 1. Also, it was found that the hygroscopicity of wood shavings was almost the same before and after CB addition, which suggests that CB addition does not encourage moisture uptake that reduces thermal insulation capacity. Furthermore, the mechanisms behind the reduction of thermal conductivity were discussed based on aspects of the mode of heat transfer in the mat. There were three types of heat transfer, namely, conduction through an individual wood shaving, conduction at connecting points between wood shavings, and convective and radiant heat transfer in the space surrounded by wood shavings (coarse p-ores). A calculation of the apparent thermal conductivity of coarse pores revealed that the addition of CB significantly reduced the heat transfer in coarse pores, which suggests that a new wood shaving's surface developed by CB addition reduces both the degree of convection and the radiation factor.
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