# Non-Destructive Infrared Evaluation of Thermo-Physical Parameters in Bamboo Specimens
## 6 Estimation of Thermo-Physical Properties of Bamboo Using Experimental Data
\(\sigma_{y}\) is the standard error of the fit that exhibits higher values at the beginning of the heating. This bias is due to the over estimation of the prediction model. However, \(\sigma_{y}\) is still low. The overestimated temperature data reflects in the histogram of residuals showed in Figure 10a. Even though this distribution is biased toward right, it is still a normal distribution, which is a desirable property that guarantees no systematic error. \begin{table}
\begin{tabular}{c c c c|c c} \hline \hline
**Bamboo Category** & \(h\) [W/m\({}^{2}\cdot\)K] & \(p_{fit}\) [W/m\(\cdot\)K ] & \(\tilde{\sigma_{p}}\) & \(\mathbf{R^{2}}\) \\ \hline \multirow{3}{*}{unpreserved} & 15 & [0.109 & \(4.200\times 10^{6}\)] & [0.0010 & 0.1476] & 0.98 \\  & 25 & [0.154 & \(6.744\times 10^{6}\)] & [0.0004 & 0.0644] & 0.99 \\  & 35 & [0.215 & \(9.020\times 10^{6}\)] & [0.0006 & 0.0874] & 0.99 \\ \hline \multirow{3}{*}{preserved} & 15 & [0.111 & \(4.274\times 10^{6}\)] & [0.0008 & 0.1148] & 0.99 \\  & 25 & [0.168 & \(7.175\times 10^{6}\)] & [0.0005 & 0.0738] & 0.99 \\ \cline{1-1}  & 35 & [0.233 & \(9.100\times 10^{6}\)] & [0.0008 & 0.1162] & 0.98 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Average parameter estimates (obtained by using the LM algorithm) for unpreserved and preserved bamboo samples. Ten bamboo samples were used to estimate \(p_{fit}^{\gamma}\) which is the average of the optimal estimates of each bamboo sample. The two columns in both \(p_{fit}\) and \(\sigma_{p}\) refer to \(k\), \(\rho c_{p}\), respectively. Figure 8: \(k\) and \(\rho c_{p}\) estimates for unpreserved (**a**) and (**b**) and preserved (**c**) and (**d**) bamboo samples as the convective coefficient of air \(h\) varies. Figure 9: Thermal diffusivity estimates for unpreserved (**a**) and preserved (**b**) bamboo samples. The curves were obtained by dividing thermal conductivity and volumetric heat capacity curves displayed in Figure 3.  
In this work, furthermore, the bamboo preservation process is based on a diffusion treatment with a combination of borax and boric acid. In this process, molecules of the preservative migrate through a porous medium, bamboo [30]. According to our experiments, the differences between thermal properties of preserved and non-preserved bamboo samples are not significant to conclude about the quality of preservation based on thermal parameters. A reason for this result is that the temperature evolution on the external face of the bamboo is not sensitive enough to variations of density and porosity generated by treatment process. Furthermore, bamboo is a non-homogeneous material and is seldom totally saturated with water when treated and dried causing a non-uniform distribution of preservant across the specimen. In a similar work carried out on laminated veneer lumber, the authors have found that thermo-physical properties such as the thermal conductivity \(k\) and volumetric heat capacity \(\rho c_{p}\) of materials may vary after preservation process [28], although they manifest that further studies have to be done to corroborate whether these variations are a consequence of chemical interactions of preservatives with the wood or with the adhesives that join the wood laminates.