Phase Change Material Thermal Storage Medium
Eutectic Salt / Paraffin / Engineered-Lunar-Composite PCM Mass
Mass of phase-change material (PCM) — molten-salt eutectic mixtures, paraffin waxes, or engineered lunar-regolith composites — that stores thermal energy as latent heat of fusion during charge, releasing it during discharge at near-constant temperature.
Purpose
Capture surplus waste heat from the reactor/Stirling converters and solar concentrators during lunar day for later release during the lunar night, providing both habitat heating and Stirling-conversion energy with high volumetric energy density.
Context
Stored in L3-ESS-THRM-TANK insulated vessels, charged/discharged through L3-ESS-THRM-HEX heat exchangers, circulated by L3-ESS-THRM-PUMP, converted to electricity (when needed) by L3-ESS-THRM-CONV Stirling engine. Supervised by L3-ESS-THRM-CTRL.
Principles
- ▸Phase change at constant temperature absorbs/releases the latent heat of fusion (e.g., NaCl 482 kJ/kg, paraffin ~200 kJ/kg, LiH ~2880 kJ/kg)
- ▸Choose PCM with melting point matching desired operating temperature (e.g., 250 °C for Stirling integration)
- ▸Volumetric heat storage of PCM is much higher than sensible heat — water 80 °C ΔT stores 0.34 MJ/L, NaNO3 at melting point stores 0.6 MJ/L
- ▸Engineered Lunar Composites (ELC) with paraffin + carbon microfibers achieve >100× thermal conductivity vs. bare regolith
- ▸Eutectic mixtures (e.g., NaNO3/KNO3 60/40, LiF/CaF2) have sharply-defined melting points and low corrosion
- ▸Encapsulated PCM prevents leakage during phase change and improves heat-transfer surface
Typical implementations
- ▸Concentrated Solar Power (CSP) molten-salt storage: Andasol-1 Spain, Solar Two USA, Solana USA (terrestrial)
- ▸Cryogenic thermophysical property measurements of engineered lunar regolith composites (ScienceDirect 2025): >101× conductivity increase, >27× thermal inertia
- ▸Two-dimensional solidification simulation of PCM molten salt for Stirling engine TES (Wiley 2024)
- ▸NASA's Sunflower power module concept with PCM thermal storage
- ▸ESA studies on lunar surface PCM thermal storage
- ▸Recent (2024) review on molten salt as TES medium for solar Stirling engine systems (ScienceDirect)
Lunar considerations
- ▸Lunar regolith is an abundant ISRU material — engineered lunar composites (ELC) avoid Earth-sourced PCM mass
- ▸Choice of melting temperature must match available heat source (reactor coolant, Stirling, solar concentrator)
- ▸Cycle durability >5000 melt-freeze cycles required for 100-year lunar mission (each day-night = 1 cycle)
- ▸Long-term phase-segregation in eutectic mixtures may degrade performance — encapsulation mitigates
- ▸Lunar dust contamination of PCM during ISRU processing must be controlled
- ▸Vacuum environment eliminates convective heat loss from tank but increases reliance on radiative shield
Specifications
Functional
| primary function | Store/release thermal energy via phase change |
| inputs | Heat from L3-ESS-THRM-HEX during charge, Mass of PCM material (one-time ISRU/Earth-supplied) |
| outputs | Heat to L3-ESS-THRM-HEX during discharge, Stored energy reservoir at melting temperature |
| pcm type baseline | NaNO3/KNO3 eutectic (60/40) |
| pcm type alt | LiH (high T), Engineered Lunar Composite (paraffin+regolith), LiF/CaF2 |
| melting temperature c | 220, 240 |
| latent heat kj per kg | 105 |
| specific heat kj per kg k | 1.5 |
| thermal conductivity w per mk | 0.5 |
| density kg per m3 | 1900 |
| total mass tonnes | 5 |
| stored energy kwh thermal | 1500 |
| cycle life min | 5000 |
Physical
| mass kg | 5000 |
| dimensions | Contained in L3-ESS-THRM-TANK |
| materials | NaNO3/KNO3 60/40 eutectic salt (baseline), Paraffin + carbon microfiber + lunar regolith composite (alternative), Encapsulation: 316L stainless steel macro-capsules or graphite shells, Optional Cu/Al fins for heat transfer enhancement |
| operating temperature c | 220, 240 |
| storage temperature c | 200, 260 |
Operational
| power consumption w | 0 |
| thermal range c | 200, 260 |
| lifetime years | 25 |
| mtbf hours | passive |
Interfaces
Provides
- Stored latent + sensible heat at ~230 °C
Requires
- Heat input during charge
- Insulated containment vessel
Cite this entry
Lunar Ark Codex. "Phase Change Material Thermal Storage Medium" (L3-ESS-THRM-PCM). Retrieved 10 September 2026, from https://lunarark.com/entry/L3-ESS-THRM-PCM
Licensed CC-BY-SA 4.0. You may reuse and adapt this entry with attribution, under the same licence.