Thermal oxidation deposition characteristics of RP-3 kerosene in serpentine tubes under supercritical pressure

Abstract Kerosene is in increasing demand as a coolant in advanced aircraft to cool aircraft subsystem and engine. Unfortunately, during fuel heated process, thermal oxidation deposition accumulates on the surface of cooling channels attributed to the participation of trace species via autoxidation chain reactions. The deposition can weaken heat transfer, block flowing passageway, and even cause the catastrophic aircraft failures. However, most investigations have only considered straight tubes, although more compact serpentine tubes are more practical for applications in aircraft cooling system to save space and enhance heat transfer. In this work, deposition and heat transfer behaviors in straight tube and serpentine tubes with 2, 3 and 4 bending sections were firstly compared. Then, the deposition characteristics in 4-Bend serpentine tubes were analyzed at different outlet fuel temperatures of 400–800 K, mass flow rates of 0.5–1.5 g/s and supercritical pressures of 3–7 MPa. The experimental results indicated that the application of serpentine tubes not only effectively inhibited deposition, but also remarkably enhanced heat transfer. In 4-Bend serpentine tube, the total deposition amount was approximately 24.8% less than that in straight tube. The deposition rate achieved a peak value at bending section because of the strong mass transfer caused by secondary flow. The fuel temperature, which was the dominant factor in thermal oxidation deposition process, influenced the deposition distribution and morphology. As temperature increased from 400 to 800 K, deposition exhibited five main morphologies, ranging from small particles through clusters to dented block deposition. The total deposition amount was directly proportional to the mass flow rate. High system pressure slightly inhibited deposition formation, but resulted in a more dramatic decrease in outlet fuel temperature. Overall, a relatively low supercritical pressure was preferable, considering the deposition and heat transfer performance.