Seite - 94 - in Intelligent Environments 2019 - Workshop Proceedings of the 15th International Conference on Intelligent Environments

Fig. 3. Experimental and expected density versus Fe2O3 content of the studied samples. 3.3. Thermal conductivity The kinetics of the heat flux for samples with different Fe2O3 content is shown in Figure 4. The temperature of the hot plate was set to 61.2 oC at t = 0 and the heating was switched off at t = 23 hrs. Room temperature was around 15 oC during all tests. According to this experimental protocol, three clearly defined stages are observed in the heat flux kinetics. In the first stage, during the first 8 hours, samples heat up from room temperature to an equilibrium value, thus reaching the steady state regime. During the second stage, between 8 and 23 hours, the system is in stationary conditions. After switching off heating of the hot plate at t = 23 hrs the samples are cooled down to room temperature. Figure 4(a) shows that, in the steady state regime, the temperature difference between the hot and cold sides increases progressively with iron (III) oxide content. Small fluctuations of cold side temperatures observed in this regime could be due to the small changes of the room temperature during the test. The cold side temperatures of each sample used for the later calculations is an average of measured temperatures in the steady state regime between 8 and 23 hours of the test. More specifically, the values of temperatures at the cold side for the two extreme compositions M-0 and M-20 were 30.5 oC and 23.7 oC, respectively. Taking into account that room temperature during the test was 15±1 oC, these data mean that the increase of temperature for M-0 and M-20 are 15.5 oC and 8.7 oC respectively, thus the temperature increase for M-0 is twice that for M-20. As far as the length of all samples was kept similar (less than 2.5% difference), the measured temperatures on the cold side give an intuitive idea of the different efficiency of thermal isolation of both materials. Heat flux-time diagram in figure 4(b) shows the same tendency as cold side temperature-time dependence. In fact, there exist a direct relation between both parameters. Heat flux arriving at the cold side of the sample contributes to heating up the material on this side. Experimental and theoretical thermal conductivities are compared in Fig. 5. The data show a progressive essentially linear drop of both experimental and theoretical thermal conductivities with the increase Fe2O3 content. For sample without iron (III) oxide, M-0, experimental conductivity results are very close to the theoretical one. However, as the Fe2O3 content B.Alordaetal. /OverheatingMitigationStrategiesAnalysis: AMediterraneanCaseStudy94