As part of NASA Glenn Research Center’s program in spacecraft fire prevention, detection, and suppression, a numerical model of the ventilation flows in the Destiny laboratory (U.S. segment) of the International Space Station (ISS) was developed. This model facilitates the evaluation of smoke-detector performance, location options, and fire-suppression strategies. The ISS has the means to detect, isolate, and extinguish fires in all locations where this capability may be needed. Fire is detected by smoke detectors in the racks with internal airflow, smoke detectors at the ventilation return air ducts, and by the crew’s sense of smell or other senses. The open area of Destiny is covered by two smoke detectors--one forward-port, the other aft-starboard; both are situated near ventilation return ducts.
Smokeview program showing smoke source on the aft-starboard wall of Destiny (condition 2).
The Fire Dynamics Simulator (FDS) is a computational fluid dynamics model of thermally induced fluid flow that focuses on smoke and heat transport from fires. Smokeview is a three-dimensional visualization program that displays the results of an FDS simulation. These programs were used to determine the smoke density and smoke-detector alarm time for a smoke source in Destiny. The preceding figure shows a Smokeview snapshot of Destiny with an aft-starboard smoke source.
The cabin dimensions, vent locations, and flow rates were obtained from ISS documentation and from conversations with ISS Environmental Control and Life Support System personnel. The smoke source was located along the center of an integrated standard payload rack within the cabin. An aft circumferential profile was constructed by moving the smoke source around the cabin along the four walls. The six air-supply diffusers and ventilation return ducts within the cabin are positioned such that the flow is across the ceiling and down the port wall, establishing a rotational flow pattern (counterclockwise facing forward). Two intermodule ventilation (IMV) diffusers (one aft-port, the other forward-starboard) direct flow along the floor in the forward and aft directions. Three different conditions were investigated: (1) cabin ventilation with aft and forward IMV flow and no cabin obstructions, (2) cabin ventilation with aft IMV flow and no cabin obstructions, and (3) cabin ventilation with aft IMV flow and cabin obstructions (estimated using ISS photographs and located in the aft area of the lab). Condition 1 produced the most symmetric flow, having both IMV diffusers active: one blowing forward, the other aft, in addition to the rotational flow from the supply diffusers. Deactivating the forward IMV produced a fast stream on the port floor, directing flow toward the forward smoke detector. Adding obstructions disturbed the flow field and made the model more realistic.
Results of aft radial smoke source profile showing time and location to first smoke detector alarm.
The bar chart displays smoke-detector alarm time and location for an aft radial profile. For a smoke source located on the starboard wall, eliminating forward IMV flow increased the detection time by 89 percent and changed the detection location. Adding obstructions increased the time34 percent more. Moving the source to the ceiling displayed similar trends. Removing forward IMV flow increased detection time by 133 percent, and adding obstructions an additional 9 percent. A smoke source on the port wall had the overall lowest detection time. A31-percent decrease resulted from turning off the forward IMV flow, and adding obstructions increased the detection time by 21 percent. The lowest detection time (15.3 sec) was obtained when both aft and forward IMV were used and the source was on the floor. It also had the largest increase (414 percent) with just aft IMV flow. Detection time decreased44 percent when obstructions were added. Overall, the addition of obstructions or moderate changes in the ventilation flow can have significant effects on the time required to detect a fire. Careful modeling of the flow in future spacecraft is needed to ensure rapid fire detection.
Find out more about Glenn’s micro-gravity combustion research: http://microgravity.grc.nasa.gov/combustion/
Glenn contacts: John E. Brooker, 216-433-6543, John.E.Brooker@nasa.gov, Dr. David L. Urban, 216-433-2835, David.L.Urban@nasa.govLast updated: December 14, 2007
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