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Figure 4 illustrates the typical dependencies <strong>of</strong> the thermophysical parameters <strong>of</strong> PMMA<br />
on the heat energy for the heat power 1.75 W. This figure shows that thermal diffusivity <strong>of</strong><br />
PMMA slightly decreases with the <strong>in</strong>creas<strong>in</strong>g temperature as well as thermal conductivity. On<br />
the contrary, the specific heat <strong>in</strong>creases with the <strong>in</strong>creas<strong>in</strong>g temperature <strong>of</strong> measured sample.<br />
CONCLUSIONS<br />
This paper presents the results <strong>of</strong> the measurements <strong>in</strong> optimal experimental conditions and<br />
<strong>of</strong> the study <strong>of</strong> the dependency <strong>of</strong> the thermophysical parameters on the temperature <strong>of</strong><br />
studied specimen that were obta<strong>in</strong>ed on PMMA. The measurements were made <strong>in</strong> air. To<br />
<strong>in</strong>terpret the outcomes, the simplified heat conductivity model is used [3]. Results show the<br />
image <strong>of</strong> heat distribution <strong>in</strong> the specimen, <strong>in</strong> various time <strong>in</strong>tervals after the heat supply from<br />
the source.<br />
The analysis <strong>of</strong> experimental data measured by the pulse transient method for various heat<br />
power and pulse width <strong>of</strong> measurement was performed on polymethyl methacrylate (perspex).<br />
The optimization <strong>of</strong> the procedure <strong>of</strong> conditions meter<strong>in</strong>g was used to f<strong>in</strong>d the optimal range<br />
<strong>of</strong> measur<strong>in</strong>g process at 25 °C where data stability <strong>in</strong>terval exists, e.g. the values <strong>of</strong><br />
thermophysical parameters are reliable. The value <strong>of</strong> thermal diffusivity calculated from the<br />
data stability <strong>in</strong>terval was determ<strong>in</strong>ed as 0.115 m 2 s –1 , 1428.2 J kg –1 K –1 for the specific heat<br />
and the value <strong>of</strong> thermal conductivity was calculated as 0.195 W m –1 K –1 and they are close to<br />
the recommended values; see Table 2. The pulse transient method gives data with<strong>in</strong> the<br />
experimental error less than 4.35 % for thermal diffusivity, less than 1.20 % for specific heat<br />
and 3.59 % for thermal conductivity. These evaluations could be used for more accurate<br />
determ<strong>in</strong>ation <strong>of</strong> the thermal parameters <strong>of</strong> studied (homogeneous and heterogeneous)<br />
matters.<br />
Data measured on PMMA clearly show difference <strong>of</strong> thermophysical parameters measured<br />
<strong>in</strong> different temperatures for the same specimen and experimental conditions. Thermal<br />
diffusivity <strong>of</strong> PMMA slightly decreases with the <strong>in</strong>creas<strong>in</strong>g temperature as well as thermal<br />
conductivity. On the contrary, the specific heat <strong>in</strong>creases with the <strong>in</strong>creas<strong>in</strong>g temperature.<br />
ACKNOWLEDGEMENTS<br />
This work was supported by the Grant Agency <strong>of</strong> the Czech Republic, contract No.<br />
2239/2006/G1.<br />
REFERENCES<br />
[1] Steiger T., Pradel R.: Update on COMAR – the Internet Database for Certified<br />
Reference Materials. Journal <strong>of</strong> Metrology Society <strong>of</strong> India. Vol. 19. No. 4. 2004.<br />
p. 203-207.<br />
[2] Boháč V., Kubičár L.: Investigation <strong>of</strong> Surface Effects on PMMA by Pulse<br />
Transient Method. In Thermophysics 2001, Meet<strong>in</strong>g <strong>of</strong> the Thermophysical<br />
Society, Work<strong>in</strong>g Group <strong>of</strong> the Slovak Physical Society. Račkova dol<strong>in</strong>a. October<br />
23, 2001. p. 21-27. ISBN 80-8050-491-1.<br />
[3] Stefkova, P., Zmeskal, O., Capousek, R. Study <strong>of</strong> Thermal Field <strong>in</strong> Composite<br />
Materials. In Complexus Mundi. WS. London, World Scientific. 2006. p. 217 –<br />
224. ISBN 981-256-666-X.<br />
[4] Vohlídal J., Julák A., Štulík K.: Chemické a analytické tabulky. Grada Publish<strong>in</strong>g<br />
1999; 1. vydání; Praha 1999; 652 s. ISBN 80-7169-855-5.<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 237