Environmental Engineering Reference
In-Depth Information
Fig. 6.5 Example of a magnetocaloric material embodied within Peltier thermal diodes. CHEX
and HHEX represent the heat-source and heat-sink exchangers, respectively
electric power P el (i.e. pure exergy). Because of the low exergy ef
ciency of the
Peltier module, most of this exergy will be destroyed and will represent an
additional anergy
ow to the cold magnetocaloric material. Only a small portion of
exergy from P el will be added to the exergy
fl
E H and therefore the exergy
fl
ux
fl
ux
from the Peltier element to the working
fl
uid will be larger than the exergy
fl
ux
from the cold magnetocaloric material to the Peltier element (i.e. E C [ E H ).
Now, according to the diagram in Fig. 6.4 and the data obtained from the
commercial programme [ 7 ], each of the thin-
lm Peltier modules A, B and C will
provide 4 kWm 2 of cooling. Note that these are not optimal conditions, but just an
example to demonstrate the difference between the Peltier module and the thermal
diode ef
ciency.
Let us consider the temperature of the ambient (not to be misunderstood as the
heat-sink temperature of the Peltier) is 303 K. The COP of the Peltier module under
these conditions is COP = 160.8 (note that the COP depends on the temperature
difference between the heat source and the heat sink of a device, which in our case
is 0.1 K for the Peltier modules).
The speci
c exergy
fl
ux which exits selected Peltier modules equals:
_
T amb
T C
303
273
439 kW/m 2
e CA ¼
_
1
q C ¼
1
4
¼
0
:
ð 6 : 1 Þ
q C ¼
T amb
T C
303
288
208 kW/m 2
e CB ¼
1
1
4
¼
0
ð 6 : 2 Þ
:
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