Abstract:
NASA explored the idea of nuclear thermal rockets in the 1950's and 60's and has recently shown interest in reviving the nuclear rocket program in an attempt to reach manned mission to Mars by 2035. One problem with nuclear rockets is finding ways to test them inside the atmosphere. NASA's Stennis Space Center has considered using a non-nuclear device to simulate a nuclear reactor during testing. The reactor is responsible for heating the propellant to over 1,922 K (3,000 °F), so the reactor simulator should be capable of heating to this temperature. A pebble-bed heater at Glenn Research Center was used for nuclear rocket testing in the past; however, the device no longer exists. This particular pebble-bed heater used hot gases to heat the pebble bed made of high melting temperature ceramics and was able to reach 2,755 K (4,500 °F) but could only sustain the temperature for 30 seconds at most. If the pebbles were heated by magnetic induction, then heat would consistently be generated within the heater, and tests could run longer. Magnetic induction heats a ferrous metal by inducing a current on its surface and by rapidly reversing a magnetic field surrounding the metal. Unfortunately, it was found that a magnetic induction pebble-bed heater using steel could not reach 1,922 K (3,000 °F) due to the Curie and melting temperatures. However, the device could be used if a higher melting temperature metal was found that was also magnetic. A small-scale pebble-bed heater heated by magnetic induction was designed, built, and tested to analyze its behavior at 27 different combinations of flow rates, pebble sizes, and power levels. The temperature changes were recorded for each test. With this data, a relationship between dimensionless heat transfer, dimensionless power, and Reynolds number was found.
