Pressure Effect on the Surface Deposition of Aviation Fuel in a Heat Exchange Tube

Abstract

The surface deposition of aviation fuel is a crucial and challenging issue in the application of air-to-fuel heat exchangers in aero-engines. The present study investigated the effect of pressure on the surface deposition of aviation fuel in a horizontal tube. Surface deposition distributions of aviation fuel RP-3 under different pressures (from 1.5 to 5.5 MPa) and different heat fluxes (from 0.08 to 0.4 MW/m2) were measured. Some experimental cases were numerically simulated to analyze the intrinsic mechanism of pressure affecting deposit formation. It was shown that pressure affects oxidative and pyrolytic deposition differently. Elevated pressure promotes the formation of pyrolytic deposits, whereas the oxidative deposition rate increases as pressure decreases. Pressure affects surface deposit formation via the physical properties of aviation fuel, especially density. The phase transition of fuel from liquid to vapor greatly accelerates the precipitation and deposition of insoluble substances under subcritical pressure. The deposition acceleration mechanism caused by the radial density gradient also plays a role under supercritical pressures, especially when pressure approaches the critical value. In addition, surface deposition depends more strongly on wall temperature than on bulk temperature.