Electric heating – Microwave heating – With diverse device
Reexamination Certificate
2002-09-24
2003-08-26
Leung, Philip H. (Department: 3742)
Electric heating
Microwave heating
With diverse device
C219S761000, C219S703000, C244S13400A, C244S13400A
Reexamination Certificate
active
06610969
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a microwave system for the deicing of front areas of hollow spaces forming shell structure which are exposed to air flows and, as a result, subjected to meteorological influences and which are therefore subject to icing.
The formation of ice on such structures detrimentally affects the air flow around the structures which results, particularly in aeronautics, to problematic aerodynamic behavior.
Many efforts have been made to keep the front edges of such structures, which are at the greatest risk of icing, free of ice. The exposed surfaces of the front areas of such surfaces are for example sprayed or flushed with liquids which prevent the formation of ice, hot air is conducted across the inner surface areas or the areas are heated electrically by resistance heating systems. De-icing by liquids is limited by the liquid reservoir required and, furthermore, is considered to be unreliable.
It is necessary to suppress the conditions under which ice can form on the respective surfaces. This is possible with liquids only for a limited time, particularly with the use of deicing liquids on the ground before the start. The anti-icing film is torn off already during the starting phase and provides during the passage of an airplane through cloud formations in which the surfaces are subject to icing, only a relatively small time safety window. Rain washes such an anti-icing film off already on the ground relatively soon.
In aeronautics, it is common practice to blow hot air taken from the engines at the inner surfaces of the wings or, respectively, the aerodynamically important slats, that is the exposed front surfaces, particularly the wing tips. The heat transfer to the slats depends on the thermodynamic flow conditions and the meteorological circumstances and also on the travel height, the outside temperature, the travel speed, the droplet size, the lateral cloud formation, the water content of the air etc. Taking these parameters into consideration, the efficiency of a hot air anti-icing system is estimated to be about 30-40%.
Such a system results in a high power consumption and also in high losses in the supply ducts to the endangered areas of the airplane. In aeronautics, particularly in connection with modern engine technology, there are furthermore limits to the removal of sufficient amounts of hot air from the bypass flow of the engines so that it is not always possible to withdraw a sufficient amount of hot air.
In another technique, metallic nets or heating mats are disposed in the wall or on the inside wall of such structures which nets or mats can be electrically heated so that, by resistance heating, the respective surface areas can be heated or kept warm as desired. Because of the high power requirements, the electric supply lines from the onboard generator to the connecting points of the nets or heating mats, have to have a large cross-section. A homogeneous heating, that is avoiding excessive local heating, particularly in the area of the contact bars is always problematic when electric power is to be supplied to an extended area and must be carefully observed. In addition, the heat transfer to the problem areas is generally difficult.
DE 197 45 621 C1 discloses a de-icing procedure wherein a thin layer with hydrophobic properties of diamond-like carbon/amorphous hydrocarbon is deposited on the surfaces to be de-iced and, upon the formation of ice, the surface areas are irradiated by an outer infrared radiation source or are heated by a heating mat which is in contact with the surface areas and are excited and heated thereby.
DE 197 50 198 C2 discloses a technique for de-icing airplanes by microwaves wherein the microwaves are fed to the areas to be de-iced from a remote source disposed in the airplane fuselage. Fluid dynamically important areas of an airplane, which are sensitive to icing, consist of compound materials whose dielectric areas are permeable for microwaves above 20 GHz. For conducting the microwaves, suitable hollow conductors comparable to present hot air pipes, extend in the airplane fuselage within the wings from the microwave generator up to those areas where the microwaves are then uncoupled and keep these areas free of ice by heating the dielectric areas. Ice already formed is rapidly removed by heating of the interface area of the ice and the surface on which the ice has formed.
In lightweight body construction, increasingly hollow body or shell structures including pre-formed, CFK and GFK composite components are used. Although such composite materials are very form-stable and rigid and have a high mechanical strength in comparison with metal, they have, in comparison with metal, a relatively low an-isotropic thermal conductivity. As a result, heat can build up and the structure may overheat whereby local delaminations may occur when they are exposed to hot air. Concerning the flight safety the capability of supplying a sufficient power density to the surface area adjacent the air flow, which surface area is potentially coated with ice, is highly limited.
It is the object of the present invention to provide a compact de-centralized de-icing system for hollow or shell body structures which are exposed to atmospheric air flow and which are therefore subject to the formation of ice thereon.
SUMMARY OF THE INVENTION
In a microwave de-icing system for the front areas of exposed shell structures, at least one independently operable microwave generator is disposed in each shell structure closely adjacent the surfaces of the shell structure to be de-iced or kept free of ice and uncoupling means are flanged to the microwave generators with uncoupling openings disposed along the area of the shell structure to be heated so as to provide a microwave wave front directed toward this area. The area subjected to the wavefront includes a wall of a dielectric composite material with a metallic skin whereby the microwave front penetrates the wall and at least partially is converted into heat within the wall of the composite material thereby providing for a rapid and effective heat supply to the wall area of the shell structure to be kept free of ice.
To this end, a microwave source whose power output is controllable by way of pulse width control is disposed in the interior of the hollow or shell body structure and an uncoupling arrangement is flanged to the exit of the microwave source directly behind, or as close as possible behind, the front area which, on the outside, may be subject to ice formation thereon or which his to be kept free of ice. The mechanically stable hollow or shell body structures consist of CFK materials or of GFK materials or of pre-preg compound materials or a composition thereof. The outer surface of the structure consists of a metal film or a metal skin; at least the aerodynamically exposed outer surface is covered by such a film or skin which is connected along the whole edge thereof with adjacent metallic structures/surfaces, so that these hollow or shell body structures are microwave or high-frequency tight and do not permit electromagnetic radiation to be radiated out into the ambient area.
By way of the uncoupling structure, the microwave radiation is directed onto the front whereby the irradiated compound material volume is heated. Within this material, after startup, a temperature gradient is established which becomes smaller toward the outer skin. The microwave radiates controllably up to such a power level that, on one hand, at each location of the irradiated compound material volume a temperature-based safety distance of between 35 and 75° C. from the delaminating temperature of T
DL
≈130° C. of the compound material can be maintained and, on the other hand, there is, at the interface with the metal skin, a thermal surface area power density of up to 46 kW/m
2
, whereby ice formed on the surface of the structure can be melted so that it is released from the surface and fully ripped off by the air flow.
The uncoupling structure of the uncoupling arrangement is a hollow conduct
Bach Klaus J.
Forschungszentrum Karlsruhe GmbH
Leung Philip H.
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