Anti-icing apparatus and method for aero-engine nose cone

#The present invention relates generally to aero-engines and, more particularly, to an anti-icing scheme for an engine nose cone.

#Icing occurs when airplanes move through clouds of suspended water droplets that remain liquid at sub-zero temperatures. While smaller droplets follow the flow around the nose cone into the engine, the larger droplets tend to impact on the cone surface and freeze forming an undesirable layer of ice. Icing is typically prevented on small turbofan engines by blowing hot bleed air from the compressor into and over the nose cone to maintain it above the critical icing temperature. Although this method is effective, increased draw of compressor air reduces the thermodynamic performance of the gas turbine engine. It is an object of the present invention to provide an improved anti-icing system.

#In one aspect the present invention provides an anti-icing apparatus for a aero-engine nose cone, the nose cone connected for rotation with a central shaft of the engine, the apparatus comprising: a heat pipe mounted for rotation inside the central shaft with an end of the heat pipe adjacent a central portion of the nose cone, the heat pipe containing a working fluid; a heat input apparatus adapted to provide heat to an opposite end of the heat pipe; and a condenser assembly (20) mounted intermediate the heat pipe and the nose cone, the condenser assembly (20) including a plurality of concentric annular condensing surfaces (44, 44′) adapted to condense working fluid thereon.

#FIG. 1: Prior art nose cone anti-icing concepts.

#FIGS. 2a and 2b: a typical gas turbine engine incorporating the present invention.

#FIG. 3: The rotating heat pipe nose cone anti-icing concept may be conceptualized as a series of thermal resistances where the difference between the hot engine source and the ambient is the potential.

#Referring to FIGS. 2a and 2b, a new aero-engine nose cone anti-icing system 10 using a rotating heat pipe 12 is shown. As will be described in more detail below, the rotating heat pipe 12 transports engine heat, provided to the heat pipe 12 through an evaporator 14, interiorly through an aero-engine central shaft 16 to the engine's nose cone 18 to maintain it above a critical icing temperature, and a condenser apparatus 20 is provided to assist in distributing heat from the heat pipe 12 to the nose cone surface. The aero-engine 22 in this embodiment is a gas turbine turbofan engine, having a fan 24 mounted for rotation on the central shaft 16, the central shaft 16 being driven by a low pressure turbine 26, while a high pressure turbine 28 drives a high pressure compressor 30, both turbines 26, 28 being driven as a result of the combustion of a fuel-air mixture in a suitable combustor 32. Referring to FIG. 1, in use as the aero-engine passes through air with suspended water-vapour, in certain conditions the water vapour will undesirably freeze on the nose cone.

#Referring now to FIG. 4, the invention employs preferably waste engine heat which is transported along the rotating heat pipe 12 through the central fan shaft 16 to the engine nose cone 18 to maintain the outer nose cone surface above the critical icing temperature. In addition, the rotating heat pipe 12 can be used for engine thermal management while eliminating the use of prior art compressor bleed air for anti-icing, as will be discussed further, below.

#The rotating heat pipe 12 is preferably a closed hollow cylinder containing a charge of working fluid 34 and is conceptually divided into three sections along its length (see FIG. 5), namely an evaporator portion 14 in contact with the heat source 36, an adiabatic transport section (referred to herein as the “heat pipe”), and condenser portion. For analysis and design purposes, the anti-icing system 10 may be modelled as a thermal resistance network as shown in FIG. 3, or in any other suitable manner. The temperature difference between the hot source 36 in the engine Thot source and the ambient air Tinf defines the overall heat transfer driving potential. The thermal resistance of each component determines the intermediate temperatures throughout the system 10 and in combination the system heat transfer. One general constraint on the anti-icing system 10 is that the overall heat transfer must be sufficient to prevent ice accumulation over the critical area of the nose cone 18 given feasible heat sources in the aero-engine 22. For the preferred embodiments described herein, the engine heat source is preferably about Thot source ˜100° C. and the ambient air may be as low as Tinf ˜40° C., yielding a system temperature difference on the order of 140° C. Nose cone surface temperatures of 3° C.-10° C. are typically required to ensure prevention of icing on a body in all environmental conditions. This temperature range constrains the minimum nose cone surface temperature. Hence, the total system heat transfer required or the heat load can be determined according to known techniques from knowledge of the boundary layer flow over the nose cone 18.