Roughness Augmented High Pressure Flow Boiling Heat Transfer Enhancement using LN2 on Additively Manufactured Rocket Engine Regenerative Cooling Channels

摘要

This work experimentally characterizes the flow boiling heat transfer performance of a regenerative cooling channel using liquid nitrogen as the working fluid. The high-pressure flow boiling tests were conducted using a state-of-the-art diagnostic system, the High Heat Flux Test Facility, designed and developed to investigate the steady state heat transfer of cryogenic propellants at the NASA MIRO Center for Space Exploration and Technology Research at the University of Texas at El Paso. This facility was designed to capture the one dimensional and asymmetric heat flow performance as experienced in the regenerative cooled liquid rocket engine channels. For this specific study, a 3.2 mm × 3.2 mm × 50.8 mm Inconel 625 channel of 0.8 μm surface roughness was tested at 1.28 MPa pressure, and 2487 kg/m~2-s mass flux. The test was conducted up to the film-boiling regime, and corresponding heat transfer coefficients (HTC) were calculated from measured wall-superheat. A comparison of experimental critical heat flux and predicted from literature models has been made in this work. The critical heat flux value of 551 kW/m~2 at 162 K wall superheat has been achieved for the lowest mass-flux and smoothest channel wall conditions. This is more than 300% enhancement as compared to the literature prediction. The maximum heat transfer coefficient of 3500 W/m~2-K has been determined at the critical heat flux condition with exit vapor quality of 0.18. Moreover, the minimum film boiling heat flux value of 177 kW/ra~2 at wall superheat of 252 K has been achieved in this work.