Intl. J. of Molecular Zoology, 2012, Vol.2, No.8, 62
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69
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66
temperatures of every slot. Our observations and our
data (Figure 1 and Figure 2) suggest that the smoking
of the bush meat with the help of the fire of wood is
associated to two types of heat transfer: a transfer of
heat by radiance and a transfer of heat by convection.
In what milked to the first fashion the equation used to
value the energy radiated by the incandescent wood
coals to dry or to smoke meat on the hurdle is: H
r
=e σ
(
T
2
4
-
T
1
4
),
the temperature being expressed in Kelvin.
T
1
is the temperature of the home and T
2
,
the
temperature measured on the cut of meat put down on
the metallic hurdle since the beginning of the
operation. So, is its raised value to the thermocouple
in this survey 20°C, either T
1
=293 K.
The surface of the home is estimated to S
f
=S
F
-
S
t
,
where S
F
,
surface of the stock, is equal to π D
2
/4
≈2042
cm
2
and S
t
,
surface of the hole, equal to
h
f
×l
f
≈1449
cm
2
.
Therefore, the surface of the home is: S
f
=593
cm
2
.
According to opinions of people investigated on
features of the smoking fire, the half of topics
estimated that the intensity of fire was strong for a
middle quantity of 7.8 kg wood (Figure 1). As for the
firepower it relates to the middle power (in watts)
during smoking to high power or low power (Bailis et
al., 2007; Vita, 1985). It is given by the F
pc
expression=f
cm
×Pc÷60×(t
cf
-
t
ci
),
où f
cm
,
where f
cm
is
the equivalent of the coal clear soup and t
cf
-
t
ci
the
variation of temperature at the time of the operation of
smoking. The calorific power (Pc) of the fuel (coal of
wood) is the free energy quantity for every unit of
mass (or of volume) burnt. Of the writing inventory
one assigns fluently to the coal of wood a calorific
power of about 25 000 kJ/kg to 26 750 kJ/kg, either 6
000
kcal/kg to 6 400 kcal/kg (
Rossier
and
Micuta
,
2005),
or even 7 500 kcal/kg (Keita, 2007). However,
considering an elevated enough relative humidity, we
estimate that values of Pc can be lower. Can one
therefore apply for a "valued fire power" to 2 000 W
(
Hr), for a coefficient of broadcast (e) of the coal of
equal ardent wood to 0.95 (Kieffaber, 1982). Knowing
that
σ=5.67×10
-3
W·m
-2
·
K
-4
(
Rozis, 1995), it follows
that the T
2
value of the home for such an intensity can
be calculated from: T
2
4
-
T
1
4
=Hr÷eσS
.
What gives,
after calculations and simplification, a value of T
1
that
adds up to 1.01×10
3
K. The temperature of the home is
therefore 1 000K, either about 707°C, value that
adjoins the one brought back by the FAO (2005). Of
the stock, the hot air flux takes place inside of the
home toward the hurdle by convection, in accordance
with the equation: H
cv
=h S
f
(
T
2
－
T
1
),
where h is the
coefficient of air convection, valued to 29W·m
-2
·
°C
for a speed of the air of 2m/s (middle value recorded
by anemometric in our shops). In these conditions, if
one relates to data of faces 2 and 3, the loss of heat by
convection can be estimated on average, for a middle
mass of bush meat eviscerated of 3.5 kg of African
brush-tailed porcupine or blue duiker exposed above
to 50cm fire, to: H
cv
= -272.2W.
So, as smoking is achieved (in the first 3 hours), the
temperature adjoins 1 100°C, value brought back by
the literature (FAO, 2005), in relation with losses in
grease contributing to revive fire. Had consideration to
the convection, this temperature decreases the hurdle
at the level. These evaluations seem to agree therefore
with our data, as for the downward and decreasing
phase of temperature curves (Figure 1 and Figure 2).
Indeed, a reduction of the fire intensity is started after
3
at 4 o'clock in order to avoid the formation of crusts
on meat. In relation with the operator's cleverness,
the regulating of fire, the restraint of the heat and
smoke determines the quality of the bush meat
otherwise, in end of smoked. However, changes of
wind direction participate in the disruption of the
working of the oven; what makes difficult the
regulating of fire and the restraint of the heat.
If the height of the hurdle proves to be weak, it is
necessary that fire is slightly back the product; what
entails a bigger dwindle of heat and smoke. Besides,
when it blows in the middle, the quality of the product
is affected, especially if the smokehouse is not
covered. To have a smoking uniform necessitate to
return and to change the site of the product regularly
during smoking. While taking opinions of
transformers interrogated as a basis, two main factors
contribute to the obtaining of a better quality of meat
smoke. It is on the one hand preferentially about its
coloration golden. On the other hand, another factor is
the disposition of meat to smoke on hurdles
superimposed on the oven or the smokehouse. The
configuration of hurdles is effectively function of the
measurement of the smokehouse (notably in relation