## 4 Results
### Thermal Insulation
#### 4.2.2 Alternative Concept  
The simulation studies for the alternative concept are--analogous to the reference concept--based on the microporous thermal insulation material, the storage medium solution and the maximum temperature. The inner (\(\Delta s_{1}\)) and outer (\(\Delta s_{2}\)) insulation thicknesses as well as the cooling fluid gap (\(\Delta s_{F}\)) were determined iteratively to fulfil the defined specifications (Table 4) of maximum permitted surface temperature and cooling flow outlet temperatures of each 60 \({}^{\circ}\)C.  
For an example solution (\(\Delta s_{F}\) = 25 mm), the resulting active cooling mass rates (\(\dot{m}_{F,c}\)) are shown in Figure 6 as a function of the insulation thicknesses.  
The results show with smaller thicknesses of the inner thermal insulation (\(\Delta s_{1}\))--due to higher insulation temperatures there--increasing active cooling mass flow rates in order to achieve the specified cooling flow outlet temperatures of 60 \({}^{\circ}\)C. At the same time--despite the increasing active cooling with decreasing inner thermal insulation thickness--higher outer thermal insulation thicknesses (\(\Delta s_{2}\)--colored dots) are required to guarantee the maximum permitted surface temperature of 60 \({}^{\circ}\)C. The reason for this behaviour is associated with increasing heat flow rates by thermal radiation, which leads--despite the existing convective cooling--to an increase in temperatures in the outer thermal insulation. Comparable characteristics can also be seen for other investigated gap thicknesses (\(\Delta s_{F}\)), whereby smaller gap thicknesses lead to lower thermal insulation thicknesses due to higher cooling efficiencies.  
This behaviour is illustrated in the following Figure 7 together with the resulting heat losses and the summed up thermal insulation masses.  
Figure 6: Cooling mass flow rates (\(\dot{m}_{F,c}\)) as a function of inner (\(\Delta s_{1}\)) and outer (\(\Delta s_{2}\)) thermal insulation thicknesses at an exemplarily selected cooling fluid gap (\(\Delta s_{F}\)).  
Figure 7: Total mass of the inner (\(m_{1}\)) and outer (\(m_{2}\)) thermal insulation as well as heat losses (\(\dot{Q}_{loss}\)) and volumetric systemic storage densities of the reference and the alternative concept as a function of the resulting thermal cooling powers (\(\dot{Q}_{F,c}\)).  
As already described above, the results show with smaller gap thicknesses (\(\Delta s_{F}\)) significant lower total thermal insulation masses due to the improved cooling efficiency. This leads at the same time to smaller storage volumes and thus, due to the specified maximum surface temperature of 60 \({}^{\circ}\)C, to lower heat losses (\(\dot{Q}_{\text{loss}}\)--coloured dots). Based on the specified restrictions of a maximum cooling outlet temperature of 60 \({}^{\circ}\)C, the minimum required active cooling mass rates or thermal powers (\(\dot{Q}_{F,c}\)) increase with decreasing gap thicknesses. So, with gap thicknesses of 14 mm minimum active cooling powers of 261.7 W are needed, whereas with gap thicknesses of 45 mm minimum active cooling powers of 123.4 W are reached.  
In addition, the characteristics show, depending on the geometric solution spaces, minima in the summed up thermal insulation masses. The reason for this is the described behaviour in Figure 6 of increasing outer with decreasing inner thermal insulation thicknesses in interaction with the active cooling flow and the thermal radiation.