For future spacecraft thermal control architectures, an alternative heat sink technology is being developed at the NASA Glenn Research Center, a spray-cooling concept similar to the current space shuttle flash evaporator system (FES). In the compact FES (CFES) concept, the vehicle’s primary heat transfer fluid flows inside a flat-plate heat exchanger while water is sprayed against the outside. The steam is then exhausted to space. Design, fabrication, and testing of the CFES have culminated in the successful delivery of the development unit.
The space shuttle orbiter's FES cannot be scaled from its heat-rejection capability of 38 kW to the 4.5 kW required for the Orion Crew Exploration Vehicle (CEV) spacecraft. A completely new design is needed to meet the Orion’s requirements. The CFES takes advantage of new spray nozzle designs and increased knowledge of spray cooling. An earlier CFES concept was based on the Cray X-1 supercomputer spray nozzle hardware made by Parker Hannifin Corporation’s Gas Turbine Fuel Systems Division in Mentor, Ohio.
During mission phases when the CEV Service Module (SM) radiator is inadequate or unavailable (after SM and Crew Module separation), the CEV may use an open-loop evaporative cooling system to reject heat. The advantages of a spray concept are
The principal disadvantage is that ice formation may occur for off-nominal conditions, such as changes in water feed pressure or sudden reductions in heat load that lead to the deposition of excess water onto the heat exchanger. This failure condition is unrecoverable in a short amount of time since it takes several minutes for the ice to melt after it has formed.
Heat exchanger CFD analysis.
CFES hardware was developed using computational fluid dynamics (CFD) tools, standard computer-aided design (CAD) software (see the preceding figure), specialized control and diagnostics software, and experience gained from drop tower work. The electrical discharge machining (EDM) tools at Glenn were critical for fabrication of the unique minichannel high-heat-flux heat exchanger. Glenn’s Vacuum Facility 12 was used in conditions beyond its design requirements: it was able to maintain vacuum, even with water being evaporated into the chamber (see the following photographs).
Single nozzle spray in a vacuum at 10-3 torr.
Glenn's Vacuum Facility 12 with CFES test rig.
With the successful development of this hardware, quantifiable performance data under a realistic flightlike environment is now possible. Comparison of these data with similar data for the other two evaporative heat sinks will allow NASA to be better prepared in choosing options for future spacecraft thermal control architectures.
Golliher, Eric, et al.: Development of the Compact Flash Evaporator System for Exploration. SAE Technical Paper No. 2007-01-3204, 2007.
Golliher, Eric L.; Zivich, Chad P.; and Yao, S.C.: Exploration of Unsteady Spray Cooling for High Power Electronics at Microgravity Using NASA Glenn’s Drop Tower. ASME Summer Heat Transfer Conference, HT2005-72123, 2005.
Glenn Contact: Eric L. Golliher, 216-433-6575, Eric.L.Golliher@nasa.govLast updated: October 31, 2008
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