ESA Document - Emits - ESA

s
equivalent efficiency
9.0E-03
8.0E-03
7.0E-03
6.0E-03
5.0E-03
4.0E-03
3.0E-03
2.0E-03
1.0E-03
0.0E+00
5 10 15 20 25 30 35 40 45 50
MLI number of layers (DAM + Gold ext layer)
Figure 4-41: Equivalent efficiency and boil-off
Boil off [kg/mth]
HMM
Assessment Study
Report: CDF-20(A)
February 2004
page 290 of 422
10.0
9.0
8.0
7.0
6.0
5.0
4.0
3.0
2.0
1.0
0.0
0.0E+00 1.5E-03 3.0E-03 4.5E-03 6.0E-03 7.5E-03 9.0E-03
MLI equivalent efficiency
Hydrogen Oxygen
The number of tanks and their diameter shall be traded off so that despite possible boil off (BO
dependent of the diameter), the required capacity is reached at the end of the 24 months. Within
that hypothesis, the following figures indicate the relationship between tank diameter, number of
tanks and BO when no cooling capability is provided. Although acceptable for oxygen, it is not
manageable for hydrogen (diameter and BO too high) and will require a cooling capability.
number of tanks
10
9
8
7
6
5
4
3
2
1
Hydrogen (22.9K, 0.2MPa, 250K)
0
0
0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5
tank diameter [m]
nbr of tnk BO
150
135
120
105
90
75
60
45
30
15
boil off rate per month
and per tank [%/mth]
number of tanks
10
9
8
7
6
5
4
3
2
1
Oxygen ( 97.2K, 0.2MPa, sink 250K)
0
0.0
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2
tank diameter
nbr of tanks BO
Figure 4-42: Number of tanks and boil-off as function of tank diameter for LOx and H2
The thermal design for hydrogen tanks is a hybrid solution combining cryocooling technology
and passive insulation. For the hydrogen tanks, the required heat lift from the cryocooler is
indicated in Figure 4-43. The dotted line indicates an ideal solution (heat lift exactly
compensates heat losses through MLI) and the others lines where heat losses exceed heat lift,
solution possible with a tolerance on the BO.
5.0
4.5
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
boil off rate per month
and per tank [%/mth]