Electric heating – Microwave heating – With diverse device
Reexamination Certificate
2003-10-10
2004-09-07
Leung, Philip H. (Department: 3742)
Electric heating
Microwave heating
With diverse device
C219S703000, C219S761000, C219S757000, C244S13400A, C244S13400A
Reexamination Certificate
active
06787744
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a microwave-technical installation for keeping free of ice, and de-icing, form-stable hollow body structures, whose surfaces are exposed to meteorological influences and which must be kept free of ice at least in certain areas which are exposed to flowing air, particularly the leading edges of airplane wings.
The formation of ice on such structures detrimentally affects the airflow and the type of flow which, particularly in aeronautics, may lead to aerodynamically problematic situation and even to uncontrollable airplane behavior.
Countless efforts have been made to keep exposed structures subject to icing ice-free. They include spraying such surfaces or flushing them with a liquid, which inhibits the formation of ice, conducting hot air over the inner surfaces of such structures and electrically heating such areas by way of metal nets installed in the walls of such surfaces.
It is necessary that ice formation on these surfaces be prevented. Deicing by means of liquid is effective only temporarily. The film of deicing liquid adhering to the surfaces is rapidly peeled off with strong airflow around the surfaces. Also rain will wash off de-icing liquid in a short time.
In lightweight construction, increasingly hollow bodies or shell structures of prepreg, CFK and GFK composite parts are used, generally fiber-reinforced materials with additives which improve the material properties for particular applications. However, although these composite materials are rigid and form-stable and also have a high mechanical strength, they have, in comparison with metal, a very low an-isotropic thermal conductivity so that, if heated by exposure to hot air from the inside, they may be over-heated resulting in localized delaminations. As a result, the capability of providing a power density for heating the outer surfaces sufficient to prevent potential icing is highly limited.
DE 100 16 261 discloses a compact microwave system for deicing surfaces or preventing, the formation of ice on surfaces of hollow shell structures which are exposed to meteorological influences. The hollow shell structures consist of cured compounds of thermoplastic or duroplastic materials with dielectric properties. The system includes at least one microwave source whose power output is controllable, and which is operated in a pulsed or continuous manner by way of a hollow conductor and uncoupling system, which is flanged to the microwave source. Energy is radiated out of the microwave source through the conductors monochromatically in the frequency range of 900 MHz to 20 GHz. At least the front area of the respective structure, which is susceptible to icing is of laminated design and consists of a body forming a support structure of dielectric compound material having shear-pressure and torsional stability adapted to the load requirements. In combination with the adjacent structures with metallic surfaces, with which the support structure is electrically connected, a metal-enclosed hollow space is formed.
In the hollow space or in chambers within each of such a formed body an individually operated microwave system is installed which consists of a microwave source with a power supply and an uncoupling arrangement comprising hollow conductors and an uncoupling structure. The uncoupling structure extends within the formed body along the front edge thereof in such a way that the uncoupled microwaves reach the free inner surface of the compound material with a single or almost a single wave front. The microwave than penetrates the compound material and heats the front area of the compound material volume by microwave interaction. Heating occurs in such a way that, under the influence of the microwaves, the compound material temperature remains at any point far below the delamination temperature of 130° C. and can easily withstand a predetermined area power density of up to 60 kW/m
2
at the interface of the formed body and the metal skin when clear ice is present on the surface. As a result, the metal skin can be kept at a predetermined temperature—depending on the meteorological requirements—of 0° C. to 70° C. providing for an ice-melting capability at which no ice can form on the front edges when the microwave de-icing system is energized.
It is the object of the present invention to provide a simple, compact and de-centralized de-icing system for hollow body or shell structures which are exposed to atmospheric air flow.
SUMMARY OF THE INVENTION
A microwave device for de-icing and keeping areas of hollow body structures free from ice keeps atmospherically exposed leading edges and adjacent areas free of ice by means of a coolant circuit. The surface segments between the adjacent areas are kept free from ice as a result of the effects of a microwave device on the wall of the surface segments and the heating that occurs by the exposure to microwave radiation. A series of consecutive microwave-tight chambers is disposed behind the wall of the exposed area. A microwave source supplies microwaves to the chambers with the aid of a decoupling structure disposed therein, resulting in high/multimode excitation. The waste heat of the microwave sources is collected by means of a coolant circuit and transported to the r areas adjacent the leading edge for permanent heating in order to keep the surfaces free from ice. The microwave sources are cyclically operated.
With the surface segments, the ribs and struts in the interior of such a hollow body structure, chambers are formed along the front edge of the body structure, which are sealed with respect to each other in a microwave-tight manner by a metallic skin or microwave-tight metal net or because the rib sections and the respective strut sections are metal-coated or consist of a suitable metal structure such as stainless steel or hard aluminum. The hollow conductor uncoupling structure is attached in each chamber at the inside to the strut so as to extend parallel to the front edge of the hollow body. It is flanged to the respective microwave source through the wall of the strut. The geometry of the chambers and the frequency of the microwave which is between 900 MHz and 25 GHz are so selected that in each chamber, upon energization of the respective microwave source, an electromagnetic field with over-modulation, that is with many possible modes, is generated. As a result, the microwave penetrates, in accordance with the over-modulation, into the wall of the fiber-reinforced compound material CFK or GFK of the surface segment with equal or almost equal area power density and heats the wall in accordance with the electrical conductivity. Because the outer surface segment is shielded by a metal skin, the microwaves cannot escape as the chamber as a whole is microwave tight.
Along the front edges and along the outer hollow body and the end of the surface segment extending therefrom at least up to the strut, metallic double conductors of an electrically well conductive material extending up to at least the strut are installed in the area which is to be kept ice free along the edge exposed to the air. These straight double lines are joined by hoses to the microwave sources or, respectively, the cooling channels thereof so as to form a cooling circuit in such a way, that, within the double conductors, a counter current is established and the microwave sources are subjected to the gas flow one after the other. For the stationary operative of the microwave sources, the temperature along the double lines remains constant the heat being derived solely from the waste heat of the microwaves. Each coolant circuit may be connected to another heat source in order to provide for redundancy of such a system.
The invention also resides in a method of operating a microwave system for a de-icing arrangement according to the invention. One procedure resides in continuously keeping the line structure in the area of the outwardly directed exposed surface of the hollow space structure free of ice by means of the double lines mounted in the wall. With
Feher Lambert
Pabsch Arno
Bach Klaus J.
Forschungszentrum Karlsruhe GmbH
Leung Philip H.
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