The use of two-phase thermal systems on spacecraft has been greatly hampered by the inability to predict with sufficient confidence their performance at various gravity levels (Earth, Mars, and lunar gravity and low-g). The performance prediction of two-phase systems under these conditions requires a sufficient heat transfer database and reliable models, both of which are not currently available. Although some research in low-gravity adiabatic flows has been performed, very little heat transfer data relevant to advanced space heat exchangers is available and the mechanisms by which heat is removed from the surfaces under varying gravity environments are unclear.

Test conditions include bubbly flow, slug flow, churn flow, annular flow, inverse annular flow, and ultimately dryout. We have performed measurements with infrared thermography in the past, but have recently transitioned to using TSPs since the data interpretation is much easier and the uncertainties are much smaller. Examples of data recently obtained using TSPs are shown along with flow visualization. Current TRL is 4, and it is expected to exit at 4 as well.

At the end of the test campaign, we expect to have completed a preliminary overview of the test matrix for a future ISS experiment.