Experimental Characterization of Critical Heat Flux and Minimum Film Boiling Heat Flux for Additively Manufactured Cooling Channels for Liquid Nitrogen Saturated Flow Boiling

Abstract

This work experimentally characterizes the critical heat flux (CHF) and minimum film boiling heat flux (MFBHF) in additively manufactured cooling channels for regeneratively-cooled rocket engines during high pressure saturated internal forced convective boiling of liquid nitrogen (LN2). Three different channels with hydraulic diameters of 1.8 mm, 2.3 mm and 2.5 mm were fabricated by the National Aeronautics and Space Administration (NASA) Marshall Space Flight Center (MSFC). The channels were fabricated using Powder Bed Fusion (PBF) advanced 3D printing of the rocket engine material, GR-Cop42, a copper-chrome-niobium alloy. The fabricated channels were tested using a custom-built cryogenic High Heat Flux Test Facility capable of operating up to 4 MPa of pressure and 10 MW/m2 of heat flux. The channels were asymmetrically heated from the bottom to simulate the performance of the cooling channels of a rocket engine. The high-pressure flow boiling tests were performed at 1.38 MPa with respective saturation temperature of 109 K using LN2 as the working fluid in horizontal orientation of the channels. The volumetric flowrate of LN2 is held approximately constant at 47 cm3/s for all channels. The experiments were performed beyond the CHF to ensure film boiling inside the channels, and then gradually decreased the given power until MFBHF was reached. A CHF of 543 kW/m2 and a MFBHF heat flux of 486 kW/m2 were achieved for the 1.8 mm hydraulic diameter channel. Furthermore, the experimentally measured CHF values were compared with the correlations available in literature. More than 84% increase in CHF has been experimentally measured for the additively manufactured rough cooling channels as compared to the CHF prediction based on literature correlation for smooth channels.

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

“…Cryogenic flow boiling experiments are performed using a high heat flux test facility (HHFTF), shown in Figure 2, capable of operating up to 4 MPa pressure and 755 K temperature using liquid nitrogen (LN 2 ) and liquid methane (LCH 4 ) as the working fluids [26][27][28]. The HHFTF is a thermal concentrator system based on conduction that asymmetrically transfers heat to a horizontal cooling channel resembling regenerative cooling during combustion.…”