US2754398A - Electrically heated compressor blade - Google Patents

Description

y 1956 H. s. RAINBOW 2,754,398

ELECTRICALLY HEATED COMPRESSOR BLADE med Dec. 12, 1952 2 Sheets-Sheet 1 l 5. Fan/50W July 10, 1956 H. s. RAINBOW ELECTRICALLY HEATED COMPRESSOR BLADE 2 Sheets-Sheet 2 Filed Dec. 12, 1952 United States Patent ELECTRICALLY HEATED COMPRESSOR BLADE Horace Sinclair Rainbow, Coventry, England, assignor lto Armstrong Siddeley Motors Limited, Coventry, Eng

and

Application December 12, 1952, Serial No. 325,527

Claims priority, application Great Britain December 17, 1951 Claims. (Cl. 219-19) The main object of this invention is the protection of aerofoil bodies, disposed in a duct through which an airstream passes, against ice formation thereon, for example, the protection of the inlet guide blades and the early rows of blades of an axial-flow compressor.

The invention is particularly concerned with a method of electrically heating such areofoil bodies.

According to the invention, such an aerofoil body is formed hollow and provided with an internal electrical heating element which is insulated therefrom, the hollow body being filled with an electrically insulating fluid with good heat transmitting properties, and the element having connections to an electrical circuit through means closing the ends of the hollow body.

In this way the electrical heating element (which can be chosen to produce any desired degree of heating) heats the fluid within the hollow body, and the latter itself becomes heated by conduction or convection, or by a combination of the two.

In the accompanying drawings:

Figure l is a sectional elevation showing one construction of inlet guide blade for an axial-flow compressor, according to the invention, with certain parts of the compressor omitted for the sake of clearness;

Figure 2 is a more detailed sectional elevation, and to a larger scale, of a preferred construction according to the invention;

Figure 3 is a transverse sectional elevation taken mainly on the line 3-3 of Figure 2;

Figure 4 is a cross-section taken on the line 44 of Figure 3;

Figure 5 is a fragmentary perspective view, to a still larger scale, showing part of the heating element and the associated insulating support in the interior of the blade; and

Figure 6 is a perspective view of an insulating support at the lower end of the heating element.

In the construction of Figure 1, the hollow blade 11 (representative of any blade in the row) is closed at the ends by plates 12, 13 which are secured thereto in any suitable manner, and each of these plates, round a central opening, is fast with a tubular extension 14, 15 forming the mounting at that end. As more fully described with reference to Figures 2 to 6, the tubular extension 14 at one end of the blade can be square and coact with a hole of the same cross-section in one of the supporting rings (not shown), whereby to locate the blade in its proper angular position but in a manner to accommodate expansion movements of the blade in the radial direction of the supporting ring. The other extension 15 is of circular cross-section for engagement in a circular hole of the other supporting ring, this extension being provided at opposite ends with lateral flanges 17, 18 affording radial location of the blade in the associated ring. The latter, for that purpose, can be formed of two side-by-side ring parts with the division extending axially through all the holes (as shown in Figure 2) Within the tubular extensions at both ends of the blade is a connection 20 for an electrical heating element 21, which latter is supported, with clearance, within the blade, the connections being insulated from the extensions by insulators 22, 22. Each of these elements may be in the form of a wire in which case the ends of the Wire can extend into and be attached to the connections 20 as shown in Figure 1, the connections extending with clearance through the central openings aforesaid. Each connection, axially beyond the ends of the tubular extensions, is fast with terminals 23 or 24 by which the heating elements of adjacent blades can be connected, as desired, in an electrical circuit. These terminals are insulated from the extensions by flanges on the insulators, as indicated at 26, 27.

Preferably the fluid, with which the blade is filled at any appropriate time during its manufacture through one of the central openings in one of the end plates, is a liquid such as an oil of the kind commonly used for cooling electrical transformers. The engagement between the insulators and connections and extensions is such as to prevent escape of the liquid.

In the construction of Figures 2 to 6, the main differences from that of Figure 1 are that the heating element 21a in the interior of a blade 11a is of tortuous shape, and that the two ends of the heating element are fast with connecions 20a which extend through one of the tubular extensions 14a and are secured to terminals 28 by which the heating elements of adjacent blades can be connected, as desired, in an electrical circuit.

In Figures 2 and 3 the tubular extension 140, fast with the end plate 12a closing the adjacent end of the blade, is of rectangular section, whilst the tubular extension 15a, fast with the other closing end plate 13a, has flanges 17a, 1811 providing radial location in a supporting ring. This supporting ring is built up of two separate portions 30, 31 which are secured to one another as by studs and nuts 32, the division being through the holes 33 (for the extensions 15a) provided jointly by the two portions. The tubular extension 15a has a filling passage 35 provided in it, this passage being closed by means of a soft plug 36 held in position by a hard plug 37 which, in "its turn, is located by the metal of the tubular extension being peened over it, as shown at 38 in Figure 2.

On the other hand, the tubular extension 14a is a sliding fit in a corresponding hole of rectangular section provided in a ring 39 which is supported in any convenient manner by a structural member 40 of the compressor. A clearance to allow for radial expansion is shown at 41. The connectors 20a to the ends of the heating element pass through insulating bushes 42, 42 located in the end plate 12a and its associated extension 14a, and also through an insulating washer 43 below the end plate 12a. The free interior of the tubular extension, round the terminals 28, is filled with an insulating resin 44.

It will be seen that the heating element is substantially symmetrical about the line 3-3 in Figure 2, being supported at its lower end, and having its two halves 45, 46 held separated from one another, by an insulating member 47. This member has legs 48 which rest upon the adjacent end plate 13a, and end faces 49, 49 which engage the adjacent internal surfaces of the blade. A clearance is shown at 50 to allow for expansion of the heating element when starting up.

In addition, each of the halves 45, 46 of the heating element is formed as an open loop having between its two limbs an insulating strip 51. Each of these strips, at intervals along its length, has integrally formed side faces 53, 53 which engage the adjacent internal faces of the blade, and two slit supports 54, 54 which receive the respective runs of the associated half of the heating element.

In this way the heating element is firmly supported against contact with the interior of the blade, and it offers a substantial heating area whereby to heat the liquid enclosed in the interior of the blade.

What I claim as my invention and desire to secure by Letters Patent of the United States is:

1. An axial flow compressor blade comprising means for protecting against ice formation thereon, said blade being open-ended, hollow, of aerofoil cross-section, and said means including plates secured to and closing the ends of the blade, said plates carrying mounting means for the blade, electric terminals extending through and insulated from said mounting means and extending from the exterior to the interior of said blade, an electric heating element spaced interiorly from the walls of said blade and interconnecting said terminals whereby said element will be heated when said terminals are connected in an electric circuit, and an insulating liquid having good heattransferring properties substantially filling the rest of the interior of said blade.

2. A hollow, open-ended axial compressor blade of aerofoil cross-section comprising means secured to and closing the open ends of said blade, electric terminals extending from the exterior to the interior of said blade, said terminals insulated from said blade and for incorporation into an electrical circuit, an electrical heating element in said blade extending between and secured to said terminals, said heating element extending substantially throughout the length of the interior of said blade, and an electrically insulating and heat-transmitting fluid in said blade in contact with the interior walls thereof and with said heating element.

3. A hollow, open-ended blade of aerofoil cross-section and for use in an axial flow compressor, means secured to and closing the open ends of said blade, electric terminals extending from the exterior to the interior of said blade, said terminals insulated from said blade and for incorporation into an electrical circuit, an electrical heating element in said blade extending between and secured to said terminals, and an electrically insulating and heat transmitting liquid in said blade in contact with the interior walls thereof and with the heating element, in which said heating element is of tortuous form and rigid insulating means are included between the heating element and the wall of the blade.

4. A hollow, open-ended blade of aerofoil cross-section and for use in an axial flow compressor, means secured to and closing the open ends of said blade, electric terminals extending from the exterior to the interior of said blade, said terminals insulated from said blade and for incorporation into an electrical circuit, an electrical heating element in said blade extending between and secured to said terminals, and an electrically insulating and heat transmitting liquid in said blade in contact with the interiorwalls thereof and with the heating element, in which said heating element is of tortuous form and rigid insulating means are included between the heating element and the wall of the blade, and in which said heating element comprises two generally similar open loops connected to one another.

5. A hollow, open-ended blade of aerofoil cross-section and for use in an axial flow compressor, means secured to and closing the open ends of said blade, electric terminals extending from the exterior to the interior of said blade, said terminals insulated from said blade and for incorporation intoan electrical circuit, an electrical heating element in said blade extending between and secured to said terminals, and an electrically insulating and heat 7 References Cited-in ,the'file of this patent UNITED STATES PATENTS 664,776 Porter Dec. 25, 1900 1,705,126 Lee Mar.'12,1929 1,750,777 Ingram Mar. 18, 1930 2,269,566 Van Daam Ian. 13, 1942 2,402,770 Poekel June 25, 1946 2,418,205 Taylor Apr. 1, 1947 2,591,757 Young Apr. 8, 1952

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