Thermal Storage Heat Exchanger
Plate-Fin / Shell-and-Tube HEX for Molten Salt Charge-Discharge
Compact plate-fin or shell-and-tube heat exchanger transferring heat between an external loop (reactor coolant, Stirling working fluid) and the PCM mass within the thermal storage tank, sized for several hundred kW peak heat transfer.
Purpose
Provide the physical interface between the thermal storage medium and the rest of the Ark thermal system — must work across the wide temperature range of charge/discharge cycles and resist long-term corrosion by molten salt.
Context
Bridges L3-ESS-THRM-TANK (containing PCM) with L3-ESS-THRM-PUMP (circulating heat-transfer fluid) and indirectly with L3-ESS-THRM-CONV (Stirling engine) on the discharge side. Charges via reactor primary loop or solar concentrator heat.
Principles
- ▸Compact heat exchangers (plate-fin, microchannel) achieve high U·A (overall coefficient × area) per unit volume
- ▸Molten-salt corrosion of stainless steels manageable below 600 °C; above that requires nickel alloys (Hastelloy, Inconel)
- ▸Heat-transfer fluid on the salt side: liquid sodium, NaK, or molten salt itself; high-temperature gas alternative possible
- ▸Fouling and salt-precipitation mitigated by maintaining flow velocity above critical threshold
- ▸Charge mode reverses heat flow vs. discharge mode — symmetric HEX design preferred
- ▸Differential thermal expansion across operating range must be accommodated by floating-tube or bellows construction
Typical implementations
- ▸CSP molten-salt steam generators (Andasol-1, Solana, etc.)
- ▸Nuclear reactor secondary loop heat exchangers (heritage)
- ▸Compact plate-fin HEXs by Heatric, Vahterus (terrestrial)
- ▸NASA Glenn lunar thermal storage demonstrator HEX designs
- ▸Stirling engine hot-side heat exchanger heritage (Sunpower, Infinia)
Lunar considerations
- ▸Lunar dust must be excluded from HEX surfaces — hermetic primary loop
- ▸Vacuum environment eliminates convective heat loss to atmosphere but increases radiative loss requirement
- ▸Differential thermal cycling across day/night drives thermal fatigue of HEX joints — design for 5000+ cycles
- ▸Inspection access for in-situ tube leak detection challenging — leak-before-break design philosophy
- ▸Material selection (Inconel 625 / 800H) drives both performance and cost; ISRU production not feasible — Earth-supplied
Specifications
Functional
| primary function | Transfer heat between PCM tank and external thermal loops |
| inputs | Hot side: heat input from reactor / Stirling / solar concentrator, Cold side: heat extraction by Stirling working fluid or coolant |
| outputs | Heat into PCM during charge, Heat out of PCM during discharge, Temperature and flow telemetry |
| rated heat transfer kw | 300 |
| design temperature c max | 400 |
| design pressure bar | 20 |
| u a kw per k | 8 |
| minimum approach t c | 10 |
| thermal cycles min | 5000 |
Physical
| mass kg | 80 |
| dimensions | 800 × 400 × 200 mm |
| materials | Inconel 800H or 625 tubes/fins, Stainless 316L shells (for moderate temperatures), Welded plate-fin geometry with offset-strip fins, Bellows-type expansion joints |
| operating temperature c | 50, 400 |
Operational
| power consumption w | 0 |
| thermal range c | 50, 400 |
| lifetime years | 25 |
| mtbf hours | 200000 |
Interfaces
Provides
- Heat exchange surface in contact with PCM
- Heat output during discharge (Stirling hot side)
Requires
- Circulation of heat-transfer fluid
- Reactor primary-loop heat for charging
- Mounted within or adjacent to PCM tank
Cite this entry
Lunar Ark Codex. "Thermal Storage Heat Exchanger" (L3-ESS-THRM-HEX). Retrieved 10 September 2026, from https://lunarark.com/entry/L3-ESS-THRM-HEX
Licensed CC-BY-SA 4.0. You may reuse and adapt this entry with attribution, under the same licence.