ATCS means coolant loops. A vehicle will typically have one or more hydraulic (liquid) coolant loops to transport waste heat from equipment and the cabin out to radiators or other heat sinks. A coolant loop is very similar to a hydraulic power loop (like the brake system in your car or the hydraulic aerosurfaces in an airplane) except it is optimized to transport heat power instead of mechanical power.

Typical heat sources to the loop:

• heat exchangers
• coldplates

Typical heat sinks:

• radiators
• evaporators
• sublimators

Typical coolant types:

• water, propylene glycol (antifreeze) or some mixture
• ammonia
• HCFC’s (“freon” & the like)

Sometimes a vehicle will have separate internal & external loops. The internal loop will use a non-toxic coolant (water, etc) and goes inside the pressure vessel to pull heat from internals, like the cabin, etc. Using a fluid-to-fluid heat exchanger (HX) it dumps its heat to a colder external loop which uses a more exotic but typically toxic coolant which also cools other more external equipment and dumps to the external heat sinks. Loops are usually redundant, i.e. two parallel internal and/or external loops in case of failure to one. Sometimes a loop will have more than one pump for redundancy.

Since each loop is self-contained fluidically, we usually make a separate network drawing for each loop to reduce node count in each network.

ATCS tech includes liquid lines, mixing, flow & temperature control valves, pumps, accumulator bottles & pressurant, heat exchangers & coldplates and various heat sinks.

The main thing we use GUNNS for is to model the heat transfer to & from the fluid and its sources/sinks. Important parameters are the fluid temperature at various locations, the heat transfer coefficients that govern how effective each interface is, pump performance. Users are typically interested in how well the system can maintain equipment & cabin temperatures in various nominal & off-nominal situations.

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