Environmental Engineering Reference
In-Depth Information
(5.5) a th it is defined as the root of the product of thermal conductivity λ , density
of the storage medium ρ SM and specific heat capacity c p .
a
=
λ
ρ
c
(5.5)
th
SM
p
Table 5.2 Parameters of different storage materials (standard values)
Density Specific heat
capacity
Thermal pene-
tration coeffi-
cient
Maximum
temperature
Thermal
conductivity
in kg/m 3
in Ws 1/2 /Km²
in °C
in W/(m K)
in J/(kg K)
970 a
Silicone oil
400
0.1
2,100
450
900 a
Mineral oil
300
0.12
2,600
530
Molten sodium
chloride
927 b
450
0.57
1,500
890
Approx.
1,000 d
0.9 c
Insulating bricks
700
950
925
Reinf. concrete 400 1.5 2,500 850 1785
Construction steel 700 40 7,900 430 11,700
Spec. Specific; Reinf. Reinforced; Approx. approximately; a at 20 °C; b at melting point;
c 0.18 to 1.6 W/(mK); d between approximately 800 to 1,200 kg/m³.
5.1.4 Thermodynamic cycles
The exergy of heat can be utilised by closed or open cycles. In these processes a
working medium undergoes a series of state changes which are either caused by
heat exchange or performance of work.
- If the initial state is identical to the final state, so that the working medium
could undergo the same process again, the process is referred to as a "closed
cycle" (Fig. 5.4).
3
3
3
3
2
2
2
2
T
T
T
T
4
4
4
4
Reservoir
Reservoir
1
1
1
1
5 = 1
5 = 1
(a)
(a)
(b)
(b)
s
s
s
s
Fig. 5.4 Temperature/entropy-diagram ( T,s -diagram) of a closed (left, (a)) and an open
cycle (right, (b)) (the arrows refer to the direction the cycles performed)
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