Patent Publication Number: US-2011061846-A1

Title: Method of producing a very light weight finned tube heat exchanger

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. 2   a  through  2   c  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.