Experimental measurement of thermal conductivity of wood species in india: effect of density and porosity,International Journal of Science, Environment and Technology4(5), 1360-1364. In the actual measurement, since the measurement theory assumes that the specimen is an infinite body, the dimensions of the specimen and the heating time tmax must be set so that the probing depth dp (mm), which represents the reach of the heat from the sensor, is less than the distance between the boundary of the specimen and the sensor: The hot-disk method for anisotropic materials is also established when the surface in contact with the sensor is an isotropic surface [7, 9]. The heat conductivity of wood at climatic temperature differences,Heating, Piping, and Air Conditioning5, 313-323. Part I,Wood and Fiber Science37(4), 699-711. Article 12). A combination of small pieces of air-dried wood was used as the test set, and the thermal conductivity in three directions was measured by the steady-state method. In other words, when the sensor is in contact withthe xyplane, this theory is applicable when the thermal properties alongxandydirections are equal (Fig. 12 of 1405J/kgK. On the other hand, in the transient method, the thermal diffusivity is determined from the temperature change when a sample is heated. YT substantively revised this work. wheretis the time from the start of the measurement,R0 is the initial resistance of the sensor,resistance is the temperature coefficient of resistivity, andTi is the temperature change inside the insulation film. hRT, hLR, and hLT are the thermal conductivities measured by the hot-disk method when the sensor was in contact with the cross section (RT plane), radial section (LR plane), and tangential section (LT plane), respectively. Front page | puutieto | Wood as a material | Thermal properties of wood. Vay, O., De Borst, K., Hansmann, C., Teischinger, A., and Mller, U. The thermal conductivity obtained by this method was close to that measured by the steady-state method in the longitudinal direction, and approximately 20% larger in the radial and tangential directions. Therefore, in order to utilize the thermal diffusivity obtained by the hot-disk method, it is necessary to pay attention to the detailed test conditions. Figure 2 presents the relation between thermal conductivity and density of the tested woods.
evaluated the relationship between the thermal conductivity, moisture content, and density of seven Chinese wood species and lauan wood [12], and Williams et al. (MPEs are in parentheses), Relationship between the thermal diffusivity measured by the hot-disk method and that calculated from Eq.
Skaar C (1988) Equilibrium moisture content of wood. According to Eq. The thermal conductivity of Indian timbers, in:Proceedings of the Indian Academy of Sciences-Section A, Springer, 300-315. 7, greater thermal conductivity in the hot-disk method means that \(\Delta \overline{T\left(\tau \right)}\) is smaller. (2012) presented a thermal conductivity of 0.111 W/mK, which is almost the same as the value obtained here, for samples with 0.388 g/cm3density. Schematic diagram of the water movement and the heat transfer on the air-dried wood during the hot-disk measurement.
Table 2. (2015). The advantage of this calculation method is that special equipment, which was employed by Adl-Zarrabi et al. The oven-dry density and moisture content of the specimens are shown in Tables 1 and 2. 16 and that measured by the steady-state method are shown in Figs. (2012). The studies by Willams et al. For example, Skaar [26] showed that when measuring the thermal conductivity of wood under a steady-state temperature field, the thermal conductivity of the wood immediately after the temperature distribution ceases to change; it is theoretically higher by the amount of the Dufour effect, which is the heat flow induced by the concentration gradient [27].
In order to realize measurements using the radial and tangential sections, it is essential to clarify the relationship between the measurement results of the hot-disk method and existing thermal properties by accumulating experimental results such as the above-mentioned study [16]. Tmaxwas measured from the temperature change of the water. The specimen was vacuumed and sealed with 0.2g of a polyolefin film, and then placed in an oven set at 94C. 3). There wasnt much information available about thermal conductivity of the species studied; however some authors reported comparable thermal conductivities for some of them. The two parallel plates, one on either side of the specimen, establish a steady state one-dimensional heat flux through the pine disk, at constant but distinct temperatures (ex: 10 C and 30 C). Effects of ThermoWood process combined with thermo-mechanical densification on some physical properties of scots pine (Pinus sylvestrisL.),BioResources9(3), 4552-4567.
Int J Thermophys 23:843853, Skaar C (1988) Irreversible thermodynamics and nonisothermal diffusion. Dotted line: the specific heat of wood with 5% moisture content obtained from Eq. Springer Nature. 2 and 13 as follows: The equation for obtaining the thermal conductivity in the longitudinal direction is the same method used to calculate L from hRTusing Eq. The thermal conductivities in the radial and tangential directions calculated from Eq. With regard to anisotropic materials, a theory to apply the hot-disk method was established [7]. All rights reserved. Increasing the moisture in the wood also increases its thermal conductivity. The Heat Flow Meter is capable of measuring the steady-state heat transfer properties of foams, solids, and textiles. 11). Springer-Verlag, Berlin, In Wood-Water Relations. In this study, the measured thermal conductivity was expressed by the geometrical average of that in x-direction and y-direction. DOI: 10.13073/0015-7473-61.2.130. These results agreed with the measurement results reported by Maku [22]. Springer-Verlag, New York, In Wood-Water Relations. Rev Sci Instrum 71:24522455, We would like to thank Editage [http://www.editage.com] for editing and reviewing this manuscript for English language. 
The insulation performance of wood and wood materials is an important property of building materials, affecting the thermal comfort of living spaces and the efficiency of heating and cooling. On the other hand, the variation was larger than that in the case of the thermal conductivity. The thermal conductivity was calculated from the temperatures when the change in temperature at each point became 0.1C or less within 30min after 1h from the start of the measurements. 2820 Faucette Dr., Campus Box 8001Raleigh, NC 27695. Thermal properties of wood measured by the hot-disk method: comparison with thermal properties measured by the steady-state method. In addition to this assumption, if it is considered that Eq. The wood samples came from various lumber sales sites, in Izmir City, Turkey. The results that did not show any difference between the two thermal conductivities in the longitudinal direction on the kiri and sugi specimens (Fig. Dndar, T., Kurt, ., As, N., and Uysal, B. Holzforschung 67:437445, Yu Z, Xu X, Fan LW, Hu YC, Cen KF (2011) Experimental measurements of thermal conductivity of wood species in China: effects of density, temperature, and moisture content. The MPEs in each direction shown in Fig. Left: test specimens for the hot-disk measurement. Mason, P. E., Darvell, L. I., Jones, J. M., and Williams, A. Although the size of the HFM chamber can accommodate for a sample as large as 12 X 12 X 4, the heat flux transducers are positioned in the center of the upper and lower plates, allowing for any sample shape and a size as small as 6 X 6 X 0.4. measured the thermal conductivities of end grain and straight grain boards by both the hot-disk method and the comparative method, which is one of the steady-state methods. We hope that future studies will solve the problems presented in this paper and thus, the hot-disk method may be considered as a reliable measurement method for the thermal properties of wood. Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The second method was proposed to calculate the specific heat and thermal conductivities in three directions from the results of the cross section, radial section, and tangential section measurements. (2008).
It was found that this difference could be explained both by the heat loss from the hot-disk sensor and the electrical lead and by the transfer of water vapor produced by the heating of the sensor.
Fire Mater 30:359369, Lagela S, Bison P, Peron F, Romagnoni P (2015) Thermal conductivity measurements on wood materials with transient plane source technique.
16 were approximately 20% larger than those measured by the steady-state method. Thermal conductivity and diffusivity of wood,Wood Science and Technology33(6), 465-473. In Eq.
16. Thermochim Acta 600:4551, Maeda K, Shida S, Tsunetsugu Y, Miyamoto K, Shibusawa T (2020) Comparison of thermal conductivities of wood determined by hot disk technique and plate comparison method (In Japanese). R. Soc. 2022 BioMed Central Ltd unless otherwise stated. The thermal conductivity obtained by the hot-disk method was larger than that obtained by the steady-state method.
Another method is to calculate the thermal conductivity in three directions and the specific heat only from the measurement results of the hot-disk method on the three surfaces. Table 1 presents the results of the variance analysis of thermal conductivity made on the 31 different wood species. They found that the thermal conductivity obtained by measuring straight grain boards using the hot-disk method was expressed in the form of the product of the thermal conductivity in the longitudinal and radial directions [16].
It should also be noted that the present results obtained by assuming Eq. Standard test method for determination of thermal conductivity of soil and soft rock by thermal needle probe procedure, ASTM International, West Conshohocken, PA. Buar, B., and Strae, A. 16 for each species and each used thermal conductivity. The thermal conductivities in the longitudinal, radial, and tangential directions were also measured by the comparison method using the same specimen. The relationship between thermal conductivity (W/mK), thermal diffusivity (m2/s), specific heat C (J/kgK), and density (kg/m3) can be expressed by the following equation: This equation indicates that all thermal properties can be calculated in one measurement of the hot-disk method for isotropic materials with a known density. Subsequently, water evaporation in the vicinity of the sensor occurs which causes an increase in the humidity (Fig. Therefore, the thermal diffusivity should reflect a subtle difference near the sensor, such as the difference between earlywood and latewood, the smoothness of the contact face, and stability in the contact state. Because the desorption of water may occur near the measurement surface as described above, the slight difference in the specific heat may be due to the desorption energy of water. The heat storing capacity of wood depends on its density, moisture content, temperature and the direction of the grain. The difference in tendency between the thermal conductivity and thermal diffusivity measured by the hot-disk method may be attributed to the fact that the effect of the heat loss and the transfer of water vapor was more pronounced in measurements of the thermal conductivity than those of the thermal diffusivity, according to the characteristics of the sensitivity coefficient of the hot-disk method [30]. 13 is not an exact solution of the hot-disk method for anisotropic materials. In the steady-state method, the thermal conductivity (W/mK) is determined from the temperature gradient of a material, dT/dx (K/m), given a steady-state heat flow J (W/m), according to Fouriers law (Eq.
The average specific heat value of pine and spruce at +0 100 C is 2,300 J/kgoC. The analysis using the hot-disk method for three-dimensional anisotropic materials (Eq. This may be due to heat dissipation from the calorimeter to the insulation tank. Considering Makus result that the apparent thermal diffusivity when wood with water was heated initially increased with the heating time (because water moved from the heated surface into the wood with the temperature gradient) [22], the increase of thermal properties by water movement is expected to be greater after an elapsed time than immediately after heating, that is, when the temperature change is small. The thermal conductivity of fir and beech wood heat treated at 170, 180, 190, 200, and 212C,Journal of Applied Polymer Science121(4), 2473-2480. As described by Kollmann [21], the thermal conductivity measured in the longitudinal direction by the steady-state method (L) was higher than that in the other directions, and the thermal conductivity in the radial direction (R) was slightly higher than that in the tangential direction (T). Wood Ind 75:29, Gustafsson SE, Gustavsson M, Gustavsson J (2000) Method of Measuring Thermal Properties of Materials with Direction Dependant Properties. Narayanamurti, D., and Ranganathan, V. (1941). Theoretical considerations. 16 was large, regardless of the tree species. In this study, we considered that the hot-disk method, one of the transient methods, could be applied to measure the thermal properties of wood and wood materials. Measurements were carried out using a TPS 500S Thermal Constant Analyzer (Hot-disk AB, Sweden) and a hot-disk sensor with a diameter of 12.8mm at ambient conditions of 25C and 30%RH. 16 was large, the value was larger than that obtained by the steady-state method. Thermal Conductivity Variance Analysis. Rowley, F. B. ISO 554. An increase in moisture improves the specific heat of the wood, because the specific heat of the water is greater than that of the wood. Vasubsbu, M., Nagaraju, B., Kumar, J. V., and Kumar, R. J. 16 was greater than that obtained by the mixing method (Fig.
(MPEs are in parentheses). Results show that wood species have a significant effect on thermal conductivity, establishing once more that it is important to select the right wood species for application to building construction. Error bars represent the standard errors of the specific heat. 12 can be explained by the fact that the Dufour effect is smaller in the longitudinal direction because water vapor can move more easily in the longitudinal direction than in the radial and tangential directions. Siau JF (1984) Steady-state moisture movement. Graduate School of Agricultural and Life Sciences, The University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo, 113-8657, Japan, Forestry and Forest Products Research Institute, 1 Matsunosato, Tsukuba, Ibaraki, 305-8687, Japan, You can also search for this author in DOI: 10.1007/s00226-015-0716-x, Yapici, F. I., Ozcifci, A., Esen, R., and Kurt, S. (2011). 14c). Maeda, K., Tsunetsugu, Y., Miyamoto, K. et al. Test specimens and a silicon rubber plate with known thermal conductivity were placed between a hot plate and a cold plate. Experimental measurements of thermal conductivity of wood species in China: Effects of density, temperature, and moisture content,Forest Products Journal61(2), 130-135. Therefore, only the thermal conductivity may become larger than that obtained by the steady-state method. A comparison between the thermal properties was made based on the assumption that the thermal conductivity in the contact surface of the hot-disk sensor is equivalent to the geometric mean of the thermal conductivity in the two main directions on the surface. Terms and Conditions, cm C). This device consists of a copper calorimeter, a stirrer, and an insulation tank. Because of good heat capacity, a heavy-duty log wall is a relatively good external wall structure, although the heat insulation capacity of mineral wool, for example, compared to the thermal conductivity of wood is about three times as great. J Soc Inorg Mater 14:489495, CAS Both thermal diffusivities were almost constant with the density, and the thermal diffusivity of the low-density specimen was slightly larger than that of the other specimens. Wood Ind 75:286291, JIS A 1412-2 (1999) Test method for thermal resistance and related properties of thermal insulationspart 2: heat flow meter apparatus. Suleiman, B. M., Larfeldt, J., Leckner, B., and Gustavsson, M. (1999). 13 may contain errors, in principle, because Eq. (2010). Some studies treated similar tendency about thermal property.
(1976). Specimens were made from kiri (Paulownia tomentosa), sugi (Cryptomeria japonica), hinoki (Chamaecyparis obtusa), yachidamo (Fraxinus mandshurica), and buna (Fagus crenata). For example, Harada et al. Springer-Verlag, New York. Note: L, R, and T are the thermal diffusivities in the longitudinal, radial, and tangential directions calculated from L, R, and T, respectively. See the literature [5, 6, 19] for details ofD() and how to derive it. Oxford Science Publications, New York, Carslaw HS, Jaeger JC (1986) Instantaneous line, plane, and spherical surface sources, In Conduction of Heat in Solids, 2nd edn. Previous studies applying the hot-disk method for anisotropic materials [14, 15] have shown that the thermal conductivity in the longitudinal direction obtained by the hot-disk method was larger than the values found in literature, while that in the fiber orthogonal direction was similar to the ones in literature. Because the heat flow through the test specimen and the silicon rubber plate equalized after these temperatures became constant, the thermal conductivity of the specimen(W/mK) was calculated using the following equation: wherel(mm) is the thickness of the test specimen,l0 (mm) is the thickness of the silicon rubber plate which is 19.9mm, and0 (W/mK) is the thermal conductivity of the silicon rubber plate as shown in the following equation: This equation is a calibration line created from the thermal conductivities of the silicon rubber plate measured by the heat flux method in accordance with JIS A 1412-2 [17], which can be used for an average material temperature range of approximately 1050C. The specific heat obtained by Eq. Another problem is that the measurement results for the radial and tangential sections as the measurement planes have not been sufficiently analyzed. 13 may change depending on the measurement conditions such as the degree of material anisotropy and the size of the sensor. Furthermore, Dupleix et al. The present study proposed two methods for calculating the thermal properties of wood from the hot-disk method were proposed, and it was found that the errors between the obtained thermal properties and those obtained by the steady-state method differed depending on the calculation method. Wood Sci Technol 33:465473, Dupleix A, Kusiak A, Hughes M, Rossi F (2012) Measuring the thermal properties of green wood by the transient plane source (TPS) technique. 
