Liquid Nitrogen Flow Boiling Critical Heat Flux in Additively Manufactured Cooling Channels

This paper presents an experimental characterization of liquid nitrogen (LN2) flow boiling in additively manufactured minichannels. There is a pressing need of concerted efforts from the space exploration and thermal transport communities to design high-performance rocket engine cooling channels. A close observation of the literature gaps warrants a systematic cryogenic flow boiling characterization of asymmetrically heated small (<3 mm) non-circular channels fabricated with advanced manufacturing technologies at mass flux > 3000 kg/m(2)s and pressure > 1 MPa. As such, this work presents the LN2 flow boiling results for three asymmetrically heated additively manufactured GR-Cop42 channels of 1.8 mm, 2.3 mm, and 2.5 mm hydraulic diameters. Twenty different tests have been performed at mass flux similar to 3805-14,295 kg/m(2)s, pressures similar to 1.38 and 1.59 MPa, and subcooling similar to 0 and 5 K. A maximum departure from nucleate boiling (DNB)-type critical heat flux (CHF) of 768 kW/m(2) has been achieved for the 1.8 mm channel. The experimental results show that CHF increases with increasing LN2 flow rate (337-459 kW/m(2) at 25-57 cm(3)/s for 2.3 mm channel) and decreasing channel size (307-768 kW/m(2) for 2.5-1.8 mm channel). Finally, an experimental DNB correlation has been developed with 10.68% mean absolute error.