Experimental Investigation of Cryogenic Convection and Boiling in Traditionally and Additively Manufactured Rocket Engine Cooling Channels

The Center for Space Exploration and Technology Research at the University of Texas at El Paso, has designed, built, and optimized an experimental high heat flux test facility to investigate the heat transfer coefficient of liquid methane and other cryogenic propellants for regenerative cooled rocket engine design. The system is composed of a copper conduction based thermal concentrator that delivers heat flow into a single sub-scaled cooling channel (test article). This study focuses on optimizing this design of the high heat flux test facility to develop a more accurate method for measuring the conductive heat flow going into the cooling channel by adding an aluminum wafer between the copper block and test article, that will act as a thermal resistance of known geometry. Experimental repeatability for the upgraded set-up is validated based on previous experimental data collected for one copper test article with a 3.2 mm 3.2 mm squared cross-section geometry and a 0.8 μm surface roughness. It is important to note that this study uses LN2 as its working fluid, and because the data used for comparison used LCH4 as its working fluid, a non-dimensional number analysis was done prior to the present test in order to develop a test matrix that yields the necessary LN2 flow rates and inlet properties. Moreover, this study will also provide a comparison of cooling effectiveness between traditionally manufactured and additively manufactured Inconel 625 squared cooling channels with different surface roughness. Data suggests that subcooled film-boiling phenomena is present in all channels tested, and film-boiling onset at critical heat flux (CHF) was correlated to the boiling number Bo ~ 0.056. Moreover, the convective Nusselt Number follows predicted trends for Reynolds Number with a wall temperature correction for both boiling and nonboiling regimes. Nusselt Number trends also suggest a higher heat transfer coefficient for channels with rougher surface finish. Nusselt number ranges are between 350 and 1450, while the Reynolds number ranges are between 195,000 and 245,000