Chemistry Reference
In-Depth Information
s
p
Fig. 4.2
The temperature change in the block during the linear pyrolysis of PMMA (
m
0
= 3
.
93 g)
and at thermal relaxation for the bottom section (
1
), the middle section (
2
), and the top section (
3
)
to occur in the so-called
regular
mode. In this case, the average temperature in the
block longitudinal section is close to its volumetric mean value.
The expression for
Q
∑
calculation is
Q
Σ
=
(
Σ
MC
)
cal
Δ
T
0
,
(4.1)
m
0
με
where (
Σ
MC
)
cal
is the effective heat capacity of the calorimeter,
Δ
T
0
is the calcu-
lated (see below) change in the middle (
l
/
2) block section,
0
/
2) is the cor-
μ
= cos(
ν
=
exp
[
(Bi+ν
0
/
2
)
τ
p
]
−
1
β
rection for the heat transfer through the Dewar vessel bottom,
ε
0
/
2
)
τ
p
is the correction for the heat transfer through the Dewar vessel walls during pyrol-
ysis [Bi =
(Bi+
ν
β
αδ
/
λ
is the Bio number, 4
δ
=
d
is the block diameter,
β
=
l
/
δ
is the
2
geometrical block parameter,
τ
p
=
at
p
/
δ
is the dimensionless time (Fourier num-
ber) of linear pyrolysis,
ν
0
is the minimum eigenvalue for
ν
0
=
β
Bi
/
tg
ν
0
,
α
is the
factor for heat transfer through the Dewar vessel walls,
and
a
are the thermal con-
ductivity and the temperature diffusivity of the block material, and
t
p
is the duration
of linear pyrolysis].
Δ
λ
T
(Fig. 4.3) by extrapolating
the straight line corresponding to a “regular” mode to
t
= 0. In the case of
T
0
is determined from the time dependence of lg
Δ
ε
≈
1
(fast pyrolysis, good thermal insulation of the block), the expression
Q
Σ
=
(
Σ
MC
)
cal
Δ
T
0
.
5
,
(4.2)
m
0
μ
where
T
0
.
5
is determined by the same extrapolation method to
t
= 0
.
5
t
p
, can be
used instead of Eq. (4.1).
Δ
