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The typical time responses <strong>of</strong> temperature for the rectangle (Dirac) pulse <strong>of</strong> different <strong>in</strong>put<br />
power <strong>of</strong> heat with various pulse widths are presented <strong>in</strong> Figure 2. The heat power and width<br />
<strong>of</strong> pulse were changed for f<strong>in</strong>d the optimal measurement conditions and subsequently<br />
determ<strong>in</strong>e the reliable data <strong>of</strong> thermal diffusivity, specific heat and thermal conductivity <strong>of</strong><br />
studied material. These results are summarized <strong>in</strong> Table 1.<br />
Table 1 Thermophysical parameters <strong>of</strong> PMMA measured <strong>in</strong> optimum exp. conditions.<br />
Q/S (J m –2 ) P (W) ΔTmax (°C) tmax (s) a (m 2 s –1 ) cp (J kg –1 K –1 ) λ (W m –1 K –1 )<br />
13 069 0.58 0.307 144 0.113 1425.0 0.190<br />
17 325 0.67 0.398 146 0.110 1457.1 0.190<br />
17 267 0.67 0.397 148 0.109 1456.9 0.188<br />
19 789 0.76 0.460 144 0.112 1440.5 0.190<br />
17 990 0.92 0.424 148 0.113 1420.0 0.190<br />
20 197 1.21 0.477 141 0.120 1419.1 0.202<br />
23 753 1.75 0.563 139 0.124 1414.1 0.207<br />
28 706 2.88 0.680 141 0.123 1415.2 0.207<br />
40 081 2.88 0.955 148 0.115 1405.6 0.192<br />
(0.115 ± 0.005) (1428.2 ± 17.8) (0.195 ± 0.007)<br />
The thermophysical parameters were calculated from the parameters <strong>of</strong> the temperature<br />
response to the heat pulse. Typical temperature <strong>in</strong>creases for reliable data were between<br />
0.3 °C and 1.0 °C that were equivalent to the heat powers <strong>of</strong> 0.58 W up to 2.88 W and to the<br />
heat energies <strong>of</strong> 13000 J m –2 up to 40000 J m –2 .<br />
The pulse transient method gives data with<strong>in</strong> the experimental error less than 4.35 % for<br />
thermal diffusivity, less than 1.25 % for specific heat and 3.59 % for thermal conductivity.<br />
Average values a = 0.115 m 2 s –1 , cp = 1428.2 J kg –1 K –1 and λ = 0.195 W m –1 K –1 are <strong>in</strong><br />
reasonable co<strong>in</strong>cidence with the recommended values, see Table 2.<br />
Table 2 Recommended values <strong>of</strong> thermophysical parameters <strong>of</strong> PMMA at 25 °C [4].<br />
D (–)<br />
ρ (kg m –3 ) a (m 2 s –1 ) cp (J kg –1 K –1 ) λ (W m –1 K –1 )<br />
3.0<br />
2.5<br />
2.0<br />
1.5<br />
1.0<br />
0.5<br />
0.0<br />
1188 0.112 1450.0 0.193<br />
0 50 100 150 200 250<br />
t (s)<br />
15065 J m<br />
20197<br />
23753<br />
28706<br />
40081<br />
-2<br />
J m -2<br />
J m -2<br />
J m -2<br />
J m -2<br />
Figure 3 Fractal dimension <strong>of</strong> the heat distribution <strong>in</strong> the specimen determ<strong>in</strong>ed from<br />
<strong>in</strong>creased part <strong>of</strong> characteristics.<br />
Sborník soutěže Studentské tvůrčí č<strong>in</strong>nosti Student 2006 a doktorské soutěže O cenu děkana 2005 a 2006<br />
Sekce DSP 2006, strana 235