production of selected secondary metabolites in transformed ...

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