# Thermal Effusivity Tester (TET)--A New Device to Determine Thermal Effusivity of Textiles
## 4 Discussion  
The results shown in Table 3 reflect the calculated means of various single measurements grouped in several temporally independent measurement batches. Robustness of the TET's effusivity measurement (temporal stability, respectively batch-to-batch variation due to uncontrolled factors) was evaluated by calculating batch standard deviations between each of the nine different samples by means of single factor ANOVA. The results of the ANOVA calculations, summarized in Table 5, illustrate that there is no significant batch-to-batch variation, except for samples 1 and 6. In case of sample 1, where the most repetitions were made, an erroneous data set was discovered and consequently left out of account, leading to a slight change in the main value (sample 1a). For sample 6, no explanation could be found, but irregularities in the fabric surface could be the reason. As for all other samples, there was hardly any batch-to-batch variation detected; as such, effusivity measurement with TET can be regarded as robust and very stable. Figure 4 shows a comparison of thermal effusivity as measured on nine fabric samples. For the first four samples, a comparison of Alambeta, TCi and TET is given. For all the samples, a comparison of Alambeta and TET is given. Except for fabric 1, wide agreement was observed among the three devices, and the correlation factor among the three methods was between 0.86 and 0.92 (see Table 6). Figure 4: Thermal effusivity as measured with Alambeta, TCi and TET; mean values \(\pm\) standard deviation. \begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline
**Sample No.** & **1** & **1-a** & **2** & **3** & **4** & **5** & **6** & **7** & **8** & **9** \\ \hline Batches (N) & 5 & 4 & 4 & 3 & 4 & 2 & 2 & 2 & 2 \\ Single measurements (n) & 32 & 25 & 24 & 18 & 24 & 12 & 12 & 12 & 12 \\ mean & 161 & 164 & 232 & 216 & 174 & 181 & 195 & 136 & 187 & 148 \\ RSD\({}_{\text{within batch}}\) & 4.6 & 4.9 & 4.6 & 4.8 & 3.1 & 3.5 & 4.0 & 4.5 & 3.1 & 5.1 \\ RSD\({}_{\text{batch-to-batch}}\) & **4.2** & 1.8 & 0.9 & 0.0 & 0.0 & 0.0 & **4.0** & 2.1 & 0.9 & 0.0 \\ RSD\({}_{\text{measurement}}\) & 6.2 & 5.2 & 4.6 & 4.8 & 3.1 & 3.5 & 5.6 & 5.0 & 3.2 & 5.1 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Summarized ANOVA results. Bold indicates significant variations. A closer look was taken at the correlation of Alambeta's and TET's effusivity results. \(t\)-tests were applied to check whether the respective means are comparable. Prior to the \(t\)-tests, F-tests were performed to check for comparability of variances, and the pooled standard deviations for the respective data sets were calculated. The \(t\)-tests revealed differences for five samples at the 5% significance level; however, at the 1% significance level, only three samples turned out to give different effusivity results (samples 1,4 and 8 in Table 7 and Figure 5). The different results obtained on fabric 1 (cotton interlock knit) and the smaller differences between TET and Alambeta on other fabrics (Table 7) can be explained by the differences in the applied pressure on the compressible fabrics, as these fabrics show some 3D (vertical) structure with a resilient character. The effect of applied pressure on thermal \begin{table}
\begin{tabular}{c c c} \hline \hline \multicolumn{3}{c}{**Correlation Factors**} \\ \cline{2-3}  & **Effusivity** & **Conductivity** \\ \hline TET/Alambeta & 0.86 & 0.24 \\ \hline TET/TCi & 0.92 & 0.92 \\ \hline TET/Kawabata & 0.92 & - \\ \hline TCi/Alambeta & 0.81 & 0.44 \\ \hline \end{tabular}
\end{table} 
Table 6: Pearson correlation of results of TET with results from Alambeta, TCi and Kawabata, and the correlation of thermal effusivity and conductivity between Alambeta and TCi. Figure 5: Effusivity correlation between Alambeta and TET.