Heat treatment changes the chemical, physical, and mechanical properties of wood. The properties of heat-treated wood have been researched considerably, but the thermal conductivity of heat-treated wood in various conditions has not been reported. In this study, the thermal conductivity of heat-treated fir and beech wood at temperatures 170, 180, 190, and 212 C for 2 h with ThermoWood method were investigated. The results were compared with industrially kiln-dried reference samples. The results show that heat treatment caused an important reduction on thermal conductivity of wood, the extend of which is depend upon temperature and wood species. Considering all heat treating temperatures, generally by increasing heat treatment temperature the thermal conductivity of wood decreased. The effect of heat treating temperature on thermal conductivity was identical for fir and beech wood. The highest decrease in thermal conductivity occurred at 212 C for both wood species. When compared with untreated wood, the decreases in thermal conductivity at 170 C, and 212 C for fir and beech wood were 2%, 9 and 2%, 16% respectively. Depending on heat treatment temperature, the decrease found out beech in high temperature is higher than that of fir.
Thermal conductivity is a very important parameter in determining heat transfer rate and is required for the development of drying models and for the industrial operations such as adhesive cure rate. The objective of this research was to investigate the effects of impregnation on the thermal conductivity of six-layered laminated veneer lumber (LVL) made of beech and pine. Boric acid, zinc chloride, and ammonium sulfate were used as impregnation chemicals and poly(vinyl acetate) (PVAc) and melamine-formaldehyde (MF) adhesives as bonding agent were used to produce LVLs. The veneers were impregnated by using the vacuum-pressure method. The thermal conductivity test was performed based on ASTM C 1113-99 hot-wire method. Results showed that the impregnation chemicals increase the thermal conductivity. As impregnation chemicals the highest values were obtained with boric acid and zinc chloride. In addition, the thermal conductivity of LVL made of beech was higher than that of LVL made of pine. The thermal conductivity of LVL bonded with PVAc was absolutely higher than LVL bonded with MF in both wood species.
Thermal conductivity values for ash, oak, silver wattle, poplar, and beech were measured. Thermal conductivity coefficients of the wood species were determined for radial and tangential directions at four different moisture conditions, ranging from 0 to 22 percent moisture content (MC). Equations predicting thermal conductivities of the wood species according to the MC are proposed in the tangential and radial directions. The thermal conductivity test was performed with a quick thermal conductivity meter based on the ASTM C1113-99 hot-wire method, and measurements were carried out at a room temperature of 20°C to 24°C. The effect of density and porosity on thermal conductivity was also investigated. Results showed the behavior of all wood species studied is quantitatively similar. Thermal conductivity increased with increasing MC. Tangential thermal conductivity values within the MC range of 0 to 22 percent changed from 0.089 to 0.147 W/m-K for poplar, 0.127 to 0.222 W/m-K for beech, 0.113 to 0.202 W/m-K for ash, 0.142 to 0.290 W/m-K for silver wattle, and 0.130 to 0.219 W/m-K for oak. Tangential thermal conductivity was similar to radial thermal conductivity. Radial thermal conductivity was 1.08 times tangential thermal conductivity for poplar, 1.01 times for beech, 1.06 times for ash, 0.95 times for silver wattle, and 1.03 times for oak, respectively. The data are useful when calculating the energy required to kiln-dry lumber and predicting the thermal insulating qualities of log homes made from the species.
In this paper, the thermal conductivity and dielectric parameters for pine [Pinus sylvestris (L.)] woods were determined in transverse directions for moisture conditions from oven-dry to 22 percent at a room temperature of 22 to 24 °C. Results indicate that the behaviors of thermal conductivity and dielectric parameters with moisture content and structural directions were similar. In general, the properties increased within the range studied with increasing moisture content. The radial values were similar to tangential values for both thermal conductivity and dielectric properties. The data presented here should be useful in most design problems where pine wood is subjected to microwave electric fields and heat changes.
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