Method of producing a very light weight finned tube heat exchanger

Abstract

A method and apparatus for producing a finned tube comprises the step of securing a tube to a tube clamping device. The method also comprises the step of arranging a plurality of cutters within the cutter head, wherein the cutters rotate with the cutter head. The method also comprises a step of moving the cutter heads into position around the tube and rotating the cutters around an outside surface of the tube in order to cut fins, via the removal of material, into the outside surface of the tube. The removal of the material also will allow for a very thin inner wall to be arranged underneath the fins being cut therein. This methodology will allow for a very light weight, thermally efficient finned tube to be used to produce a heat exchanger for use in turbine engines or the like.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to a methodology for producing a finned tube for a heat exchanger, and more particularly, relates to the methodology for producing a very light weight finned tube heat exchanger for use in bypass ducts of commercial aircraft engines.

2. Description of Related Art

The manufacture of finned tubes for use in heat exchanger type applications has been known in the art for many years. They are used in the art of aerospace engines and the like to ensure proper and efficient operation of aviation engines, both commercial and military. The prior art generally uses two methods of manufacturing finned tubes with both methods generally resulting in very heavy products and products that may not exhibit heat exchange properties as high efficient as that of the present invention.

One of these prior art methods brazed fins on the outside of a tube thus creating a finned tube that is capable of functioning as a heat exchanger within an aircraft engine. Another prior art method was to roll form the fins on the outside of a thick wall tube. However, in both of these prior art methods, due to the high heat and stresses of the manufacturing processes, the initial and final product has to be very robust to avoid dimensional distortion which would effect the heat transfer rate of the heat exchanger within the turbine engines of airplanes, thus effecting efficiency and overall performance of the engine and aircraft on which the engines were attached thereto. Many of these prior methods of manufacturing finned tubes results in heavy overall designs and tube members for use in heat exchangers and the like. Also, many of these methods required methodologies such as brazing that is very labor intensive and subject to quality problems because the process of brazing fins on to a tube is not easily repeatable in the same manner as required by engine manufacturers of today.

Therefore, there is a need in the art for a new and improved methodology of producing very light weight finned tubes for use in a heat exchanger in aircraft engines. There also is a need in the art for a method of producing very light weight finned tube heat exchangers that is capable of consistently repeating the forming of fins on a tube having very precise dimensions and very small tolerances. Furthermore, there is a need in the art for a method of producing low cost light weight finned tubes for use in a heat exchanger located in the bypass duct of aircraft turbine engines.

SUMMARY OF THE INVENTION

One object of the present invention may be to provide an improved method of producing a finned tube.

Another object of the present invention may be to provide a method and apparatus for producing a very light weight finned tube heat exchanger for use in a bypass duct of an aircraft turbine engine.

Still a further object of the present invention may be to provide a method of fabricating a very light weight finned tube capable of high heat transfer rates.

Still another object of the present invention may be to provide a unique methodology and process along with specific tooling derived from an automatic screw machine to create a light weight finned tube device.

Another object of the present invention may be to provide a methodology for creating a light weight finned tube that is capable of being used with any type of material and that the dimensions of the tubing is only limited by the size of the pipe threading machine/apparatus used during the methodology.

To achieve the foregoing objects, a method for making a finned tube comprises the steps of securing a tube to a tube clamping device. The method also comprises the step of arranging a plurality of cutters within a cutter head, wherein the cutters rotate with the cutter head. The methodology also comprises moving the cutters into position around the tube and rotating the cutters around an outside surface of the tube in order to cut fins on the outside surface thereof. The completion of the steps produce a very light weight finned tube capable of high heat transfer rates for use in a turbine engine or the like.

One advantage of the present invention may be that the method of making a finned tube produces a very light weight finned tube capable of high heat transfer rates.

A further advantage of the present invention may be that the methodology uses a unique process and unique tooling in the form of an apparatus derived from an automatic screw machine.

Another advantage of the present invention may be that the methodology removes material from the tube therefore reducing the weight of the final product.

Another advantage of the present invention may be that having the tube stationary during the methodology allows the cutters to be positioned such that the inner wall may be cut to very thin dimensions under the fins.

Another advantage of the present invention may be that the inner wall may typically have a thickness of approximately 0.013 inches underneath the fins of the tube.

Yet another advantage of the present invention may be that the thin inner wall of the tube results in a very light weight and very high heat transfer rate during operation of the finned tube in a heat exchanger of a turbine engine.

Still another advantage of the present invention may be that the cutters are capable of cutting an entire length of tubing material without causing defects, such as bends, crimps, tears or breaches and fractures in the inner wall of the tube via the cutters.

Still another advantage of the present invention may be that the methodology uses a plurality of cutters wherein each of the cutters are offset a predetermined pitch from an adjacent cutter.

Still another advantage of the present invention may be that it allows for each of the cutters to remove ¼ of the material from the tube having the fins arranged thereon.

Still another advantage of the present invention may be that there is no limitation to the type of material that can be processed using the present methodology.

Yet another advantage of the present invention may be the creation of a high pitch count, high aspect ratio fin heat exchanger tubes for applications that require very light weight such as those found in aircraft turbine engines.

Other objects, features and advantages of the present invention will become apparent from the subsequent description and the appended claims, taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a flow chart of the methodology of making a fin tube according to the present invention.

FIGS. 2a through 2c show a cross sectional view of a portion of a finned tube according to the present invention.

FIG. 3 shows a cross sectional view and end view of an apparatus for use with the methodology of creating the finned tube according to the present invention.

FIG. 4 shows a plan view of a portion of a turbine engine using the finned tubes proffered by the present invention.

FIG. 5 shows a partial close up of the finned tubes arranged in a bypass duct of a turbine engine according to the present invention.

DESCRIPTION OF THE EMBODIMENT(S)

Referring to the drawings, a method 10 and apparatus 12 for producing a light weight finned tube 14 for use in a heat exchanger in a bypass duct of an aircraft engine is shown. The light weight finned tube 14 generally may be used in a heat exchanger, wherein the device maybe an oil to air heat exchanger that may be located in the bypass duct 16 of a commercial aviation engine. However, it should be noted that the light weight finned tube 14 can be used in any type of heat exchanger and any type of engine not just those from the aerospace industries, but also those from any other type of industry that needs engines and a highly reliable and effect heat exchanger. This methodology generally will produce a finned tube 14 that has a thin wall. These finned tubes 14 will then be used to make a heat exchanger that is very light weight, thermally efficient and inexpensive to fabricate, thus reducing the cost to the engine manufacturer and engine buyer. It should be noted that in one contemplated embodiment the light weight finned tube 14 is made of a stainless steel material and in particular 300 series stainless steel tubing, however any other type of material is capable of being formed into the finned tubes 14 according to the present invention and is capable of being produced via the methodology described herein. Therefore, while stainless steel is a preferred material any other material, such as but not limited to any metal, aluminum, ceramic, plastic, natural material, etc., may also be used to create the tubes 14 according to the present invention and may also be capable of having the methodology applied thereto to form the finned tubes 14.

As shown in FIGS. 4 and 5, one embodiment in which the very light weight finned tube heat exchanger 18 may be used is that of a turbine engine 20 for use in an aircraft. It should be noted that the light weight finned tube heat exchanger 18 according to the present invention, can be used in any type of engine, however a turbine engine may be one such engine in which they are used. Generally, a bypass turbo fan engine comprises a cylindrical housing, the outer extremity of which defines the outer wall of an annular bypass duct 16. A low pressure spool assembly is rotatable about a central longitudinal access of the engine and comprises a shaft having a fan and a low pressure compressor at the forward end thereof and low pressure turbine at the aft end thereof. If the bypass turbo fan engine is a three spool, an intermediate pressure spool 15 coaxially disposed about the shaft or low pressure spool and comprises a shaft, an intermediate compressor and an intermediate turbine. A high pressure spool assembly is telescoped over the shafts of the low and intermediate pressure spools respectively and comprises a shaft, a high pressure compressor at the forward end thereof and a high pressure turbine at the aft end thereof.

An annular combustor is disposed about the low, intermediate, and high pressure spools and respectively, between the high pressure compressor and high pressure turbine. A combustion gas duct is located aft of the annular combustor and disposed about the high, intermediate and low pressure turbines, respectively. An accessory drive shaft is geared to the shaft of the high pressure spool. Conventional accessories, for example, a starter/generator, are driven by an accessory drive shaft at an RPM directly related to the RPM of the high pressure spool.

A portion of the air induced by the fan flows to the low pressure compressor then to the intermediate and high pressure compressors respectively and a portion flows to the bypass duct 16. The combustion air flows 22 from the exit of the high pressure compressor to the combustor wherein fuel is introduced and burned. Combustion gas is first passed through the high pressure turbine, then through the intermediate and low pressure turbines, respectively. When the engine is operated on the ground and at idle conditions, accessory power is maximized while noise and fuel consumption are minimized by splitting the hot gas stream exiting the high pressure turbine. A portion of the hot gas is diverted readily outwardly and then flows through one or more poppet valves immediately after the high pressure turbine. The poppet valves are disposed in a circumferential spaced array and can be individually or concomitantly opened by computer controlled pneumatic activation. Such an engine may be used with the light weight finned tube heat exchanger 18 produced by the light weight fin tubes 14 of the present invention. FIGS. 4 and 5 show a portion of a turbine type engine relating to where the fin tubes 14 will be arranged in a heat exchanger 18 of an aircraft engine.

FIG. 4 shows a heat exchanger 18 connected to a turbine engine 20 via a bypass valve assembly 24. The heat exchanger 18 includes an exhaust duct attachment face 26 that is used to attach to a portion of the turbine engine body. The heat exchanger 18, according to the present invention, will have a drive motor 28 that is used to activate the bypass valve assembly 24 thus allowing air to flow into the light weight fin tube heat exchanger 18 and out of the heat exchanger 18 to any predetermined number of areas within the turbine engine or aircraft. The bypass valve assembly 24 may have a shuffle seal package 30 arranged between it and the pre-cooler assembly 18. The pre-cooler assembly 18 generally includes the fin tubes 14 produced by the methodology described herein wherein the finned tubes 14 generally are made of a stainless steel material, however any other material as noted above may also be used for the finned tubes 14. The finned tubes 14 make a heat exchanger 18 that is very light weight, thermally efficient and inexpensive to fabricate, thus allowing for the engine to reduce weight and also reduce costs in having the manufacturing process easier to perform. The diversion of air, via the bypass valve assembly 24, allows for either heating or cooling of the air within the heat exchanger 18 depending on the need of the customer using the engine. The tubes 14, as shown in FIGS. 4 and 5, generally are assembled into a multi tube heat exchanger 18 and may be installed in the bypass duct 16 of a gas turbine engine. The heat exchange rates have been demonstrated to meet and exceed the expected rates and the finned tubes 14 of the current invention have been shown to be mechanically robust and free from failure during simulated operational tests within a turbine engine. The heat exchanger 18 generally is used when the aircraft is on the ground and tarmac, allowing for cooled air to be sent to predetermined parts of the aircraft As shown in FIG. 5 the air flow 22 enters the bypass duct 16 and then is passed over the finned tubes 14 and into a duct 32 that the customer has control over. The cooled or heated air is then passed on to a predetermined part of the aircraft or engine. The core flow 22 does not effect the air being passed over the finned tubes 14 and hence, does not effect the overall efficiency of the engine during use or while on the tarmac during bypass use. It should be noted that the finned tubes 14 may have arranged therein a fluid or gas thus allowing for the finned tubes heat exchanger 18 to either cool the air entering the bypass duct 16 or heat the air to a predetermined temperature as it comes through the bypass duct 16. The air then enters a customer duct for use in the aircraft or in other portions of the aircraft as deemed necessary by the customer. As shown in FIG. 5, a plurality of tubes 14 generally are arranged side by side and held together side by side to create a heat exchanger finned tube assembly 18. Any known methodology for securing the finned tubes 14 into the circumferential shape as shown in the Figures, or any other known shape, may be used along with any known connecting methodology to connect the finned tubes 14 to the exhaust duct attachment face 26.

FIGS. 1 through 3 generally show the methodology and apparatus to produce the finned tubes 14 for use in the finned tube heat exchanger 18 as shown in FIGS. 4 and 5, according to the present invention. Generally, the apparatus 12 used in the methodology for producing the very light weight finned tube 14 and heat exchanger 18 according to the present invention is a standard pipe threading machine with adaptations thereto. Generally, a standard pipe threading machine is well known in the art and as such, is not shown or described in detail in the present application. The modified pipe threading machine of the present invention includes a tube clamping device 34 that will fix the tube 14 in a stationary position relative to a rotating cutter head 36. This allows the fabrication process on the tube 14 to occur in a precise and predetermined manner. The tube clamping device 34 may have any shape. One embodiment of the tube pipe threading machine 12 used herein has the tube clamping device 34 fixed or secured to the ground and hence, will not allow for any lateral or axial movement of the tube 14 with respect to the tube clamping device 34 and with respect to the cutter head 36 and cutters 38 of the apparatus 12 for use in producing a very light weight finned tube 14. The machine 12 also, according to the present invention, includes a cutter head 36 which rotates and moves or translates motion in a lateral or axial direction relative to the axis of the tube 14 being held in the tube clamping device 34. The cutter head 36 rotates at any speed necessary around the outside surface of the tube 14. The cutter head 36 may also move in an axial direction relative to the axis of the tube 14. This movement allows the cutter head 36 to place the cutters 38 at a predetermined position relative to the outside surface of the tube 14 being processed therein. The cutter head 36 generally has a wheel like or cylindrical shape with a predetermined thickness and a predetermined diameter wherein that diameter generally is much greater than the diameter of the tube 14 being processed therein. The necessary clamps, chucks, fasteners, pins and rods connect the cutter head 36 to the other components of the threading machine 12 to ensure proper rotation and axial movement of the cutter head 36 with respect to the tube 14 being held in the tube clamping device 34.

Arranged within the cutter head 36 are a plurality of cutters 38, also known as chasers, that are rotatably fixed with respect to the cutter head 36, but are capable of translating or moving in a radial direction with respect to the cutter head 36. Therefore, the cutters 38 rotate when the cutter head 36 rotates, but are also capable of moving in a radial direction with respect to the cutter head 36 at the same time. This will allow for the cutters 38 to be moved a predetermined distance into the outer surface of or toward the axis of the tube 14 being held in the tube clamping device 34 while the cutters 38 are being rotated about the outer surface of the tube 14 via the rotation of the cutter head 36. Any known fastening methodology or technique which allows for the radial movement of the cutter 38 with respect to the cutter head 36 is used to attach the cutters 38 to the cutter head 36. It should be noted that the cutters 38 generally are offset longitudinally ¼ pitch relative to an adjacent cutter 38, however any other pitch offset or no offset may also be used. In one contemplated embodiment four cutters are spaced at approximate 90° intervals from one another around the outer surface of the tube 14 which is stationary. It should be noted that any other number of cutters spaced at any known interval may also be used with the present invention. The cutters 38 may have a plurality of teeth or a single cutting tooth thereon. In the embodiment shown each chaser or cutter 38 has three or four cutting teeth and will use the same or a different cutting pattern. Each chaser is offset or advanced ¼ pitch forward of its adjacent cutter 38. As an example, the offset for a twenty eight pitch fin would be approximately 0.0089 inches. Therefore, with four cutters 38 being arranged within the cutter head 36 each cutter 38 will remove and cut approximately ¼ of the material from the outside surface of the tube 14 being finned.

The process of manufacturing the very light finned tube 14 according to the present invention occurs by removing material from the outside diameter of a thick walled tube 14 leaving the heat exchanger finned shape on the outer surface thereof. This material removal is accomplished using the special set of cutters 38 described above that have been adapted to a standard pipe threading machine 12 as described above. The threading machine 12, according to the present invention, holds the tube 14 stationary while the cutting head 36 rotates around the tube 14. The cutters 38 are positioned in a manner that allows the removing of the material without damaging or deforming the product during the cutting operation and allows for extremely thin inner wall 42 thicknesses at the base of the fins 44. It should be noted that standard thread cutting heads may be used to position the cutters 38 according to the present invention. Furthermore, due to the nature of the process and methodology described herein, adjustments to the speed and feed of the tube 14 are critical to fabricating a defect free product and must be adapted to individual tubing materials. However, it should be noted that there is no known limitation to the types of materials that may be processed using the methodology herein and that the dimensions of the tubing 14 that may be processed is limited only by the size of the pipe threading machine 12 used according to the present invention. This new methodology of creating a finned tube 14 by removing material reduces the weight of the final product. The positioning of the cutter 38 with respect to the stationary tube 14 allows the inner wall 40 to be cut to very thin dimensions under the fin 44 and in one embodiment typically 0.013 inches for the inner wall 40 of the tube 14. It should be noted that smaller and larger thicknesses for the inner wall 40 are also possible. This inner wall 40 dimension is very small compared to other prior art methodologies and results in a very light weight and very high heat transfer rate for the heat exchanger made of these fin tubes 14 after the manufacturing process.

Therefore, the methodology as described herein will develop a high pitch count, high aspect ratio fin 44, that produces heat exchanger tubes 14 for applications that require very light weight. This creates a completely different tube 14 than those made by conventional prior art fin tubed methodologies that generally use a rolling operation to generate the fins and hence, result in heavy heat exchangers that are not competitive with other heat exchanger technologies. Therefore, the present inventions unique manufacturing process enables the heat exchanger 18 to be used in a turbine engine such as described above. It should be noted that two of the traditional methods of manufacturing finned tubes both resulted in a much heavier product wherein that first method had brazing of the fins onto the outside surface of the tube while another method used roll forming as described above onto the outside of a thick wall tube. Both of these prior art methodologies due to the high heat and stresses of their manufacturing processes ensure that the initial and final product had to be very robust to avoid dimensional distortion, but with both of these heavy designs the heat transfer rates were not as high as those of the present invention and both of those methodologies were very labor intensive and subject to quality problems because of the difficulty in recreating the steps in a highly repeatable manner for each finned tube made. As shown in FIG. 1, generally the methodology in box 46 secures a tube 14 into a tube clamping device 34 which is fixed to the ground or fixed with respect to the cutter head 36 to any other type of machine or component. Next, in box 48 the methodology arranges a plurality of cutters 38 within a cutter head 36 wherein the cutters 38 are capable of radial movement with respect to the cutter head 36. Next, in box 50 the methodology moves the cutter 38 to the outer surface of the tube 14 and then in box 52 the cutter head 36 starts to rotate, the cutters 38 are moved radially as the cutter head 36 is rotated, thus allowing for a predetermined amount of material to be removed from the outside surface of the tube 14 in order to create a thin inner wall 40 as described above. Once the depth of the fins 44 have been achieved, via the cutters 38 moving radially inward to a predetermined depth, the cutters 38 will be moved in a radial outward direction and then repositioned via the cutter head 36 moving in an axial direction with respect to the axis of the tube 14 and the next set of fins 44 are then cut therein via the cutters 38 being moved in a radial direction toward the outer surface of the tube 14. It should be noted that fins 44 may be arranged along the entire length of tube 14 or only on a predetermined portion thereof. The methodology may also include the step of adjusting the speed of rotation of the cutter head 36 and adjusting the speed of the feed mechanism for the tube 14 depending on the material being processed. It should be noted that it is also contemplated to have the tube clamping device 34 move relative to the cutter head 36, thus allowing for the tube 14 to move in an axial direction with relation to the cutter head 36 in another contemplated embodiment.

Therefore, the methodology and apparatus described herein will allow for the production of very light weight finned tubes 14 for use in a heat exchanger 18 which may be used in bypass ducts 16 of aviation engines. This methodology and apparatus will allow for these light weight and thermally efficient tubes 14 to be made with a cost effective methodology thus reducing the costs to the manufacturer of building the engine and the cost to the airlines using the engines via the reduction in weight, thus reducing fuel costs for the aircraft using such heat exchangers having the light weight finned tube 14.

The present invention has been described in an illustrative manner. It is to be understood that the terminology which has been used is intended to be in the nature of words of description rather than of limitation.

Many modifications and variations of the present invention are possible in light of the above teachings. Therefore, within the scope of the appended claims, the present invention may be practiced otherwise than as specifically described.

Claims

1. A method of making a finned tube, said method comprising the steps of:

securing a tube to a tube clamping device;

arranging a plurality of cutters within a cutter head, said cutters rotate with said cutter head;

moving said cutters into position around said tube;

rotating said cutters around an outside surface of said tube in order to create fins on said outside surface of said tube.

2. The method of claim 1 wherein said tube is stationary.

3. The method of claim 1 wherein said plurality of cutters comprises four cutters.

4. The method of claim 3 wherein each of said cutters are offset longitudinally ¼ pitch relative to adjacent said cutters.

5. The method of claim 3 wherein said four cutters are arranged at 90° intervals within said cutter head.

6. The method of claim 3 wherein said cutters move radially with respect to said cutter head and said tube.

7. The method of claim 1 wherein said cutter head moves in an axial direction with respect to said tube.

8. The method of claim 1 further comprising the step of securing said tube clamping device to a predetermined position on a ground.

9. The method of claim 1 wherein said tube having a thick wall.

10. The method of claim 9 wherein said wall of said tube initially before processing is approximately 0.05-0.09 inches thick.

11. The method of claim 10 further comprising a step of removing material from an outside surface of said tube to create a light weight finned tube.

12. The method of claim 11 wherein said fins having a height of approximately 0.03-0.08 inches.

13. The method of claim 11 wherein an inner wall of said tube after processing having a thickness of approximately 0.012-0.017 inches.

14. The method of claim 13 wherein said thin inner wall and said fins result in a lightweight tube with high heat transfer rates.

15. The method of claim 1 wherein each of said cutters has at least three teeth.

16. The method of claim 1 wherein said tube is stainless steel.

17. The method of claim 1 further comprising the step of adjusting the speed of rotation of said cutter head.

18. The method of claim 1 further comprising the step of adjusting a speed of a feed mechanism for said tube.

19. The product produced by the method of claim 12.

20. The product produced by the method of claim 1.