Evaluation of a Novel Aero-Engine Nose Cone Anti-Icing System Using a Rotating Heat Pipe

Abstract

Preventing ice accumulation on aircraft surfaces is important to maintain safe operation during flight. Ice accumulation on aero-engine nose cones is detrimental as large pieces may break off and be ingested into the engine damaging the compressor blades. Currently, hot bleed air is taken from the compressor and blown over the inside and outside surfaces of the nose cone to prevent ice formation on the surface. Although effective, this technique reduces the efficiency of the aero-engine. This investigation evaluates the performance of a novel anti-icing system that uses a rotating heat pipe to transfer heat from the engine to the nose cone. Rotating heat pipes are effective two-phase heat transfer devices capable of transporting large amounts of heat over small temperature differences and cross-sectional areas. In this system, waste heat that is generated in the engine would be transferred to the rotating heat pipe at an evaporator and then transferred into the critical areas of the nose cone at a condenser preventing ice accumulation on the outside surface. In this investigation, the heat is transferred into the heat pipe from a fluid heated by the engine that would pass through a small annular gap between the rotating heat pipe and a stationary wall. The heat transfer for this configuration and the effect of passive heat transfer augmentation on the outside of the rotating heat pipe in the jacket was investigated experimentally for a range of Taylor numbers of 10^6 < Ta < 5x10^7 and for axial Reynolds numbers of 900 < Re_x < 2100, characteristic of this configuration when engine lubricant was used as the working fluid. It was found that by using an array of three-dimensional cubical protrusions, the heat transfer in the evaporator could be increased by 35% to 100%. This result was better than that found using two-dimensional rib roughness. It was also found that the evaporator performance was a limiting factor in the heat transfer performance of the system under most conditions, so further optimization of the evaporator is important. In the proposed condenser design, the condenser section of the rotating heat pipe would be encased in a lightweight, high conductivity polycrystalline graphite or similar composite material and the end of the heat pipe would be in direct contact with the nose cone. It was found that the end-wall of the heat pipe was not a source of high heat transfer, however it provided an effective means for heating the tip of the nose cone. The effect of using heating channels on the inside of the nose cone was also considered. Here, the condensate from the rotating heat pipe was driven through small radially spaced channels on the inside surface of the nose cone. The heating channels were found to be ineffective due to the small contact area that could be made with the nose cone. This was a result of the limited condensate flow that occurs in rotating heat pipes. The heat transfer through the proposed system was 700W to 1100W using water and 400W to 800W using ethanol in the heat pipe. It was found that 50% to 75% of the arclength of the nose cone could be maintained above 0°C using water in the heat pipe at an ambient temperature of -30°C and an airplane speed of 300 km/h. This arclength decreased to approximately 25% when ethanol was used as the working fluid. An increase in airplane speed reduced this arclength maintained above 0°C significantly.