production of selected secondary metabolites in transformed ...

MEASUREMENT OF THERMOPHYSICAL PROPERTIES OF PMMA
BY PULSE TRANSIENT METHOD
Ing. Pavla Štefková
Supervisor: Prof. Ing. Oldřich Zmeškal, CSc.
Institute of Physical and Applied Chemistry, Faculty of Chemistry, Brno University of
Technology, Purkynova 118, 612 00 Brno, Czech Republic, email: stefkova@fch.vutbr.cz
INTRODUCTION
Polymethyl methacrylate (PMMA) is the synthetic polymer of methyl methacrylate. This
thermoplastic and transparent plastic was developed in 1928 in various laboratories and was
brought to market in 1933 by the German Company Rohm and Haas. This material is used as
the standard reference material for thermal conductivity measurements in metrology.
Chemical analysis and materials testing are becoming ever more important as science,
trade and society are getting more complex worldwide. The number and significance of
decisions based on the results of chemical analysis and materials’ testing is ever increasing in
all spheres of life. For this purpose results of analysis and testing have to be reliable and
comparable as well as acceptable worldwide. The use of certified reference materials is an
efficient and proper tool to achieve these goals [1].
Measurement of the thermophysical properties of PMMA shows that some effects
influencing the measurement process have to be known when one want to use it as laboratory
reference or standard reference material (SRM). This material should be used for validation of
apparatuses upon well-known experimental conditions, to obtain reliable data [2].
The pulse transient method allows investigating the thermal diffusivity, specific heat and
thermal conductivity within single measurement. The principle of this method and the
arrangement of the measured sample are shown in Figure 1. The heat pulse is generated by
the passing of the electrical current through the plane electrical resistor made of metallic foil.
A sensor measures the time development of the temperature field (temperature response) in a
point of the tested body. Then the temperature is characterized by a function [3]
⎟ 2
Q S ⎛ h ⎞
ΔT =
⋅ exp ⎜
⎜−
. (1)
( E−
D)
/ 2
cp
ρ ( 4π
at
) ⎝ 4a
t ⎠
The thermophysical parameters are calculated from the characteristic parameters of the
temperature response (time and the maximum of temperature response to the heat pulse).
The thermal diffusivity is given by
2
h
a =
2tmax f a
the specific heat by
2
h
=
2(
E − D)
tmax
, (2)
Q
cp = ⋅
ρ ΔTmaxh
and thermal conductivity by
f c
=
2π exp( 1)
Q
E−
D
ρ ΔTmaxh
( E −D
) / 2
⎛ E − D ⎞
⋅ ⎜
2 exp( 1)
⎟
⎝ π ⎠
(3)
Q
λ = cp ρ a =
E−
D−2
2(
E − D)
ΔTmaxt
maxh
( E −D
) / 2
⎛ E − D ⎞
⎜
2 exp( 1)
⎟ .
⎝ π ⎠
(4)
Sborník soutěže Studentské tvůrčí činnosti Student 2006 a doktorské soutěže O cenu děkana 2005 a 2006
Sekce DSP 2006, strana 233