Environmental Engineering Reference
In-Depth Information
TABLE 7.1
Physical Properties of Sensible Storage Materials
Average
Heat
Conduc-
tivity
Volume-
Specific
Heat
Capacity
Average
Heat
Capacity
Temperature
(°C)
Average
Density
Media
Cost
Media
Cost
Storage
Medium
Cold
Hot
(kg/m
3
)
(W/mK)
(kJ/kgK)
(kWh
t
/m
3
)
($/kg)
($/kWh
t
)
Solid media
Sand-rock-
mineral oil
200
300
1,700
1.0
1.30
60
0.15
4.2
Reinforced
concrete
200
400
2,200
1.5
0.85
100
0.05
1.0
Solid NaCl
200
500
2,160
7.0
0.85
150
0.15
1.5
Cast iron
200
400
7,200
37.0
0.56
160
1.00
32.0
Cast steel
200
700
7,800
40.0
0.60
450
5.00
60.0
Silica fire
bricks
200
700
1,820
1.5
1.00
150
1.00
7.0
Magnesia
fire bricks
200
1,200
3,000
5.0
1.15
600
2.00
6.0
Liquid media
Mineral oil
200
300
770
0.12
2.6
55
0.30
4.2
Synthetic oil
250
350
900
0.11
2.3
57
3.00
43.0
Silicone oil
300
400
900
0.10
2.1
52
5.00
80.0
Nitrite salts
250
450
1,825
0.57
1.5
152
1.00
12.0
Nitrate Salts
265
565
1,870
0.52
1.6
250
0.70
5.2
Carbonate
salts
450
850
2,100
2.0
1.8
430
2.40
11.0
Liquid
sodium
270
530
850
71.0
1.3
80
2.00
21.0
Source:
Hermann, U., Geyer, M., and Kearney, D. 2002.
Overview of Thermal Storage Systems
.
With permission.
attractive for materials that undergo a significantly high change in internal
energy during a phase change.
Latent Heat Storage via Phase Change Materials
The phase change energy (heat of fusion or vaporization) of a material
determines its thermal storage capacity as a phase change material (PCM).
Molecular bonds of a PCM are broken when sufficient heat is applied. Their
bonding energy gives PCMs their exceptional heat capacity. To be appropri-
ate for latent heat storage, materials must exhibit a high heat of transition,
high density, appropriate transition temperature, low toxicity, and long-term
performance at low cost. For example, paraffin waxes and salt hydrates have
