Cryogenic Flow Boiling Heat Transfer on Additively Manufactured Liquid Rocket Engine Cooling Channels
The enhancement of flow boiling heat transfer is critical because it can solve thermal management issues seen across all engineering and manufacturing applications. Even though advancements are being made, more studies are needed to understand the behavior of forced convective boiling further. Currently, there are four major issues in the field of regenerative cooling of liquid rocket engines. 1. The cooling channels are typically manufactured using conventional machining, while aerospace industries are currently exploring the additive manufacturing approach. 2. The experimental critical heat flux values for cryogenic fluids are either lower or very close to the model predictions; however, the effect of roughness and the associated heat flux enhancement is not considered in the models. 3. Cryogenic flow boiling experiments are typically performed in symmetrically heated channels; however, rocket engine cooling channels experience asymmetric heating. 4. Although the chill-down experiments can measure temperature-controlled minimum film boiling, the throat section of the cooling channels experiences heat flux-controlled minimum film boiling, yet almost no literature data is available for this phenomenon. The focus of this research is to demonstrate some potential solutions to the issues above. It will begin by investigating the flow boiling heat transfer performance of additively manufactured rocket engine cooling channels during asymmetric heating. Then, the research will identify the critical heat flux (CHF) and the minimum film boiling heat flux (MFBHF) for various channels at various pressures, degree of subcooling, flow rates, and working fluids for a cooling channel in a regeneratively-cooled rocket engine. Lastly, the research will compare the experimental results with literature models to identify the heat transfer enhancement. The research detailed here is based on a cooling channel’s flow boiling heat transfer analyses using three cooling channel hydraulic diameters – 1.8 mm, 2.3 mm, and 2.5 mm (0.07”, 0.09”, 0.097”), three pressures – 0.89 MPa, 1.37 MPa, and 1.58 MPa (130 psi, 200 psi, 230 psi), two degrees of sub-cooling – 0 K and 5 K, three cryogenic flow rates – 32 cm3/s, 47 cm3/s, 57 cm3/s (0.5 gpm, 0.75 gpm, and 0.9 gpm), and two different cryogenic fluids – liquid nitrogen (LN2) and liquid methane (LCH4). The analyses were completed with a thermal concentrator setup known as the High Heat Flux Testing Facility (HHFTF) at the University of Texas at El Paso’s Aerospace Center. The testing of the HHFTF was performed in conjunction with a methane condensing unit for the provision of LCH4. The results for the single-phase forced convection showed a 200% enhancement from values found in the literature, which can be attributed to the higher surface roughness due to additive manufacturing. The results for the forced convective boiling show that while using the three additively manufactured samples, the one with the greatest CHF and MFBHF was the sample with a hydraulic diameter of 1.8 mm (0.07”), seeing a positive trend with increasing mass flux with a maximum value of 14,295 kg/m2s. Another finding was that as pressure increases, CHF decreases, and as the subcooling degree increases, so does the CHF. These trends revealed that a balance between pressure and subcooling degree is needed to increase the heat flux. Finally, after comparing the results with the experimental data with the literature models, a 98% enhancement for CHF was determined. Additionally, an enhancement of 13 times the model values for MFBHF was found.
Aerospace engineering|Fluid mechanics|Mechanical engineering
Ortega, Debra Jazmin, "Cryogenic Flow Boiling Heat Transfer on Additively Manufactured Liquid Rocket Engine Cooling Channels" (2022). ETD Collection for University of Texas, El Paso. AAI30000395.