Heat exchange – With coated – roughened or polished surface
Reexamination Certificate
2000-11-09
2003-02-11
Leo, Leonard (Department: 3743)
Heat exchange
With coated, roughened or polished surface
C165S154000, C165S169000, C165S179000, C060S267000
Reexamination Certificate
active
06516872
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method of manufacturing a high heat flux regenerative circuit comprising a structure having an inner functional surface in contact with a first fluid and a set of channels formed in the body of the structure for conveying a second fluid in heat exchange relationship with the first fluid, the method consisting in using thermal spraying and machining operations around a reusable support core to build up the structure from said inner functional surface.
The invention also relates to a high heat flux regenerative circuit obtained by the method, such as the rocket engine combustion chamber.
Structures constituting high heat flux regenerative circuits are used in various contexts, for example in heat exchangers, in turbine blades cooled by a circulating liquid, or in the walls of combustion enclosures.
Thus, combustion enclosures, such as the combustion chambers and nozzles of rocket engines, in particular engines using liquid propellants, have walls which are in contact with combustion gases that constitute a high temperature medium, and such walls are generally cooled while they are in operation.
A common cooling technique consists in providing the walls of such enclosures with cooling channels. This applies in satellite launchers and space planes, and also in satellite thrusters, nuclear reactors, and high efficiency boilers, and it can also apply to heat shields or to the nose cones of vehicles traveling at very high speed.
Specifically in the context of rocket engines, various methods have already been proposed for manufacturing the walls of combustion chambers to enable cooling channels extending in a longitudinal direction to be included therein, which channels convey a cooling fluid that may be one of the propellant components used for feeding the rocket engine, so that the cooling system thus constitutes a regenerative system.
The techniques for manufacturing such combustion chambers are nevertheless difficult to implement, lengthy, and expensive.
In certain particular applications, it is also useful to be able to heat up an enclosure that is cold, by causing a hot fluid to circulate via passages formed in the wall of the enclosure, which thus also constitutes a regenerative circuit.
Prior Art
In a first technique for manufacturing regeneratively-cooled combustion chambers for liquid propellant rocket engines, cooling channels are machined in an inner base body formed as a single piece of a metal that is a good conductor of heat, such as copper. The cooling channels are thus separated from one another by partitions of the base body, and an outer cover is made by electrodeposition of multiple layers of nickel alternating with machining corrections that are necessary between each of the electrodeposition passes. The channels are closed prior to electrodeposition by applying a conductive resin.
FIG. 14
shows an example of a combustion chamber wall made using that technique.
An inner jacket
104
that is made by forging, e.g. out of a metal material such as Narloy Z, has cooling channels
105
that are made by machining.
A layer
107
for closing the channels
105
is made by electrodeposition and is itself covered in nickel that is likewise deposited by electrodeposition. Various elements of the outer shell
109
made of a superalloy such as Inconel-718, for example, are assembled together via joins
110
by means of electron beam welding.
The operations of forming the inner jacket
104
of the combustion chamber and of closing the channels
105
by electrodeposition constitute major drawbacks of that method. Those operations are lengthy and expensive. Furthermore, each of the welds
110
used for final assembly of the components of the chamber constitutes a potential risk of breakage. In a second prior art technique of combustion chamber manufacture, attempts have been made to eliminate those disadvantages by using the plasma-forming methods.
FIG. 15
shows an example of a combustion chamber wall made using that second manufacturing technique which consists in making all or part of the structure of the combustion chamber by thermally spraying powders of defined alloys.
In an example of such a method in which the wall of the combustion chamber is made starting from the inside and going towards the outside of the chamber, a spraying core
1
is made out of mild steel machined to the inside dimensions of the combustion chamber that is to be obtained.
First spraying under a partial vacuum then serves to use copper alloy (Narloy Z, . . . ) to make the jacket
4
of the future chamber on the surface of the core
1
. The following operation consists in machining the cooling channels
5
and in inserting a consumable filler material therein. After excess filler has been removed by machining, a second operation of spraying the copper alloy under partial vacuum enables a layer
7
to be formed for closing the channels. Immediately thereafter, the superalloy shell
8
is built up directly on the copper jacket by thermal spraying. The final operation consists in chemically eliminating the filler material so as to open up the channels
5
, and also so as to remove the spraying core
1
.
Proposals have also been made to provide a support core built up from a plurality of parts, thus making it possible to reuse the core. By way of example, a core can be constituted by two stainless steel cones that are separated from each other by a washer of mild steel, with the assembly being covered in a deposit of steel. Once the combustion chamber has been made, the dissolving of the inserts placed in the cooling channels is accompanied by dissolving the washer and the steel deposit. The two cones can then be removed and recovered.
Nevertheless, known methods remain relatively unsatisfactory, in particular because of the slowness of the process whereby the inserts are dissolved and the temporary layers are eliminated, and because of difficulties in making structures that are of large dimensions in satisfactory manner.
OBJECT AND BRIEF SUMMARY OF THE INVENTION
The object of the invention is to remedy the above-specified drawbacks and to enable regenerative circuit structures to be manufactured in a manner that is more convenient than in prior art methods while also making it possible to optimize the characteristics of the manufactured structures, even when the structures are of large dimensions and are subjected to high heat flux densities.
According to the invention, these objects are achieved by a method of manufacturing a high heat flux regenerative circuit comprising a structure having an inner functional surface in contact with a first fluid and a set of channels formed in the body of the structure for conveying a second fluid in heat exchange relationship with the first fluid, the method consisting in using thermal spraying and machining operations around a reusable support core to build up the structure from said inner functional surface, the method being characterized in that it comprises the following steps:
a) placing a support core representing the inner profile of the structure about an axis of rotation, the support core being made of a material whose coefficient of thermal expansion is very close to or slightly greater than that of the body material of the structure;
b) making an intermediate layer on the support core out of a material that is different from that of the support core and that of the body of the structure;
c) forming a series of channels regularly spaced apart around the core and opening out to face said intermediate layer, each of the channels being provided with a soluble insert comprising a mixture of organic binder and metal powder;
d) preheating the support core to a temperature greater than about 850° C. and making the body of the structure by thermal spraying under a vacuum or low pressure by means of a plasma torch, while maintaining the temperature of the support core at said temperature greater than 850° C.;
e) without dismantling the support core, machining channels in the form of grooves in the outside of
Coddet Christian
Cornu Daniel
De Monicault Jean-Michel
Verdy Christophe
Leo Leonard
Societe Nationale d'Etude et de Construction de Moteurs d&a
Weingarten Schurgin, Gagnebin & Lebovici LLP
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