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:

Source: https://www.emerson.com/documents/automation/product-data-sheet-rosemount-multipoint-thermocouple-rtd-profiling-sensors-type-tx-mtx-wx-mwx-en-88382.pdf

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