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Deliverables:

Notes from IEEE:

- change in temperature less than 2K across tank [nearly isothermic] 

-24 hour turnover rate of fluid from cryogenic pump

  • Sensors:
    • Static 
    • Floating around 

Would a moving sensor affect the thermodynamics/temperature of the liquid?

Look into: 

  • https://www.realpars.com/blog/thermocouple Thermocoupling 
    • Requires no battery or power draw
  • What homogeneous temperature are we trying to achieve? [so that we know what temperature the sensors have to withstand]
  • Is cost an important factor to the sensor?
  • What is the goal of the sensor suites across the multiple tests? 
    • Is it measuring temperature for all of them?
      • No, look below for the explanation of each test.
  • Optimal Placements for Thermocouplers in the Tank 
    • Other: INSIDE Tank
    • On the baffles 

1. Tank wall thermocouples

Where: Directly on the metal surface of the cryogenic tank itself, under the MLI (multi-layer insulation), touching the tank’s skin.
How many: Often 8–20, spaced around the circumference and length (top, mid, bottom).
Purpose: Detect hot spots, cold spots, and how evenly the tank is cooled.

Think: small metal dots glued right onto the tank’s external shell.

2. Cooling-loop inlet thermocouple

Where: On the tube that carries cold refrigerant into the BAC loop, right before it touches the tank.
Purpose: Measures the temperature of the coolant before it absorbs heat from the tank.

This is the “entry temperature” of the cooling system.

3. Cooling-loop outlet thermocouple

Where: On the tube where the refrigerant exits the BAC loop, right after it has passed along the tank’s surface.
Purpose: Shows how much warmer the coolant got after absorbing heat.

This is the “exit temperature.”

Inlet vs outlet difference = actual heat absorbed from the tank.

4. MLI outer-surface thermocouples

Where: On the outermost layer of the insulation blanket that wraps the tank, fully outside the MLI stack.
Purpose: Shows how hot the outside of the insulation gets from chamber radiation and heaters.

These sit on top of the MLI, not touching metal.

5. Heater / IR panel thermocouples

Where: Stuck directly on the surface of the heater panels or IR lamp housings that are pointed at the tank.
Purpose: Monitor the temperature of the “fake Sun” to confirm your heat input is stable and known.

  • Understand what each test is doing c

Tests our sensor setups have to perform in:

  • Cryocooler Performance Test
  • Baffle & Pump Cryogenic Flow Test 
  • Thermal Subsystem Demo 
  • Mixing Subsystem Demo 


Thermal Subsystem Demo: 

Testing whether a cryogenic tank wrapped in insulation and cooled by a cryocooler can keep its liquid from boiling away in a space-like vacuum environment.

How-to-test:

  • Boil-off flow: mass-flow meter on vent line (gas phase)

  • Mass loss: weigh the filled tank before/after

  • Level sensor (capacitance/RTD stack) to track liquid height over time

  • Temperatures: many thermocouples on tank wall, loop inlet/outlet, MLI outer surface, heater panels

Sensor recommendations:

Mixing Subsystem Demo - Testing that the pump can mix cold fluids with induced heat stratification in low gravity environments. Flight test on parabolic arc with 20 second periods of microgravity, or ground test by spinning the tank to create and artificial gravity and then stopping the tank suddenly.

  • Sensors: thermocouples(mixing of fluid), pressure sensor(LN_2 boils off easily), liquid level sensor(detect sloshing and boil off), flow meter(how much fluid is being moved), IMU/accelerometer(identify periods of microgravity), voltage sensor(how much heat is added for induced stratification)

Baffle and Pump Cryogenic Flow Test - Testing that the pump and baffle system can mix stratified fluid to make it homogenous. Test using liquid nitrogen or oxygen that is allowed to sit(causing the top to warm and create heat stratification), then turn on the pump(and spin the cylinder on a turntable if possible) to measure the temperature equalization.

  • Sensors: thermocouples(prove destratification), pressure transducer(moniters tank pressure for safety), optional flow meter or liquid level sensor to see how other variable are affecting the destratification

Thermal Vacuum Test:

Testing the thermal emissivity (tendency to lose heat energy) and outgassing (escape of boil off through the tank walls in a vacuum environment).

How-to-test:

  • Heat-flux transducers/platinum resistance thermometers (RTDs) placed intermittently along the outer surface to measure thermal flux 
  • thermocouples to measure the temperature of the system in cryogenic conditions
  • quartz crystal microbalances (QCMs)/residual gas analyzers (RGAs)/ion and Pirani vacuum gauges to detect gases escaped through the walls of the tank

Cryocooler Performance Test: Benchmarking the efficiency and endurance of a cooling system at different thermal loads in a a thermal-vacuum chamber. Run neon through a representative tube loop (simulated piping system) to confirm it works.

  • Checking neon gas flow: Coriolis Mass Flow Meter (or/both differential presessure sensor)
  • Checking pressure/drops: pressure transducers
  • Checking temperature: thermocouple along the entire system (cold tip of cryocooler, tube loop)
  • Checking voltage of the cryocooler for efficiency measurements (in IEEE paper it said around 8 We/Wth)
    • For anyone confused...the 8 We/Wth means that per 8 We of power, we reduce the thermal energy by 1 watt of heat
  • We would also need someway to apply a heat load


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