Thermocouple SUMMARY:
What we need to buy:
Type K
Mineral-insulated (MI)
stainless-steel sheathed
multi-junction (5–10 points inside)
1/8" or 3 mm diameter
length = height of tank + extra
terminated to a connector
Overall Idea of Multi-junction Thermocouple Probe:
Heating/Cooling System
General
https://www.nasa.gov/smallsat-institute/sst-soa/thermal-control/#7.3
Fluid Loops
https://tfaws.nasa.gov/TFAWS04/Website/program/Speakers/TFAWS2004PresentationonMechLoops-v1.pdf
https://apps.dtic.mil/sti/trecms/pdf/AD1195523.pdf
Thermoelectric Coolers
https://spinoff.nasa.gov/Spinoff2009/ip_4.html
https://www.sciencedirect.com/science/article/abs/pii/S1359431123001308
Fluid Loops
- Actively circulate a working fluid (single-phase or two-phase) to transport heat to radiators
- Can move heat over long distances, enabling flexible radiator placement
- Provide strong temperature uniformity across surfaces (especially with two-phase systems)
- Handle variable and transient heat loads effectively by adjusting flow rate
- Mature Technology with extensive spacecraft heritage (CO_2, ammonia, water loops)
- Require pumps, accumulators, and careful fluid management in microgravity
- Add mechanical complexity, mass, and reliability considerations due to moving parts
- Well suited for payloads with continuous or moderate-to-high heat dissipation
Thermoelectric Coolers
- Solid-State devices that move heat via electrical current across a junction
- Compact and mechanically simple
- Provide precise temperature control for small areas or components
- Limited heat transport capacity, efficiency drops sharply with higher loads
- Generate both cold and hot sides, requiring effective conduction and radiator coupling
- Best for localized cooling rather than whole-system thermal management
- Power hungry relative to the amount of heat moved (low coefficient of performance)
- Commonly used for sensors, detectors, or electronics needing fine temperature trimming
Fluid Loops work best for system (optional TEC incorporation for fine trimming)
- Mechanically pumped fluid loop coupling the tank and electronics to a radiator
- Optional TECs for tightly controlled specific sensors or components
- Uniformity across the tank - clamp wall temperatures and minimize gradients to improve homogeneity
- Dynamic load following, adjustable flow tracks pump cycles, frictional heating, and electronics transients without overshoot
- Remote heat rejection - moves heat to radiator efficiently, no radiator placement constraints
- System integration - common thermal bus for tank, pump motor/controller, obc, and sensor electronics
- Microgravity readiness - proven heritage
Cryogenic Liquid Substitute
https://ntrs.nasa.gov/api/citations/20170007274/downloads/20170007274.pdf
Polyalphaolefin
- Stable, non-conductive, low vapor pressure
- Moderate viscosity compatibility with metals
Fluorinated heat-transfer fluid
- Dielectric, low outgassing
- Lower thermal capacity than water
Perfluoropolyether
- Chemically inert, dielectric, very low vapor pressure
- High cost, varying viscosity
Silicone Oils
- Wide temperature range, dielectric, chemically stable
- Higher viscosity than PAO/HFE
Mineral Oils
- Low vapor pressure, decent pumpability
- Can wet surfaces differently
Water-Glycol blends
- High heat capacity, low viscosity
- Electrically conductive, corrosion risks, freeze concerns
Topics of today:
Choosing Fluid for Testing inside the tank: Liquid Nitrogen
- Justification: We need a liquid that does not freeze at -150 C which is space temperature at LEO.
- Liquid Nitrogen: Freezing Temperatures -196 C; Boiling Temperature -210 C
Power Profile: