Abstract:
A heat exchange tube is constructed by forming, on a cylindrical tube peripheral wall, a plurality of projecting portions which project to an inside of the tube peripheral wall, and which are formed by pushing. The plurality of projecting portions are formed, respectively, into conical shapes across a tube axis, and are arranged along virtual spirals on the tube peripheral wall. Accordingly, it is possible to provide a heat exchange tube which facilitates formation of a plurality of projecting portions with the thickness hardly changed and without formation of protruded portions, and which is capable of contributing to enhancement of heat exchanging efficiency.

Description:
TECHNICAL FIELD 
     The application discloses an improvement of a heat exchange tube constructed by forming, on a cylindrical tube peripheral wall, a plurality of projecting portions which project to an inside of the cylindrical tube peripheral wall, and which are formed by pushing. 
     BACKGROUND OF THE INVENTION 
     A heat exchange tube is already known, as disclosed in, for example, Japanese Patent Application Laid-open No. 2004-85142. The heat exchange tube disclosed in Japanese Patent Application Laid-open No. 2004-85142 will be described based on  FIGS. 7 to 9 . 
     There is a conventional heat exchange tube  014  in which a plurality of projecting portions  031  are arranged in a zigzag form along an axis of the tube as shown in  FIG. 7 . In this case, there are the projecting portions  031  as shown in  FIG. 8  and  FIG. 9 . In  FIG. 8 , the projecting portion  031  is formed so that its ridge becomes linear, and a peripheral wall  030  of the portion other than the projecting portion  031  is not deformed. In  FIG. 9 , the projecting portion  031  is also formed so that the ridge becomes linear, but the peripheral wall of the portion other than the projecting portion  031  is deformed so that opposite end portions in the peripheral direction of the projecting portion  031  are protruded. 
     Incidentally, the projecting portion shown in  FIG. 8  is unfavorable in workability since the thickness of the ridge portion of the projecting portion  031  inevitably increases more than the thickness of it before formation of the projecting portion, and due to the linear ridge of the projecting portion  031 , the peripheral length of the tube in the projecting portion  031  decreases more than that before formation of the projecting portion, and sufficient increase in the surface areas of the inside and outside of the tube cannot be desired due to the projecting portion. Further, in the projecting portion shown in  FIG. 9 , increase in the plate thickness of the ridge portion of the projecting portion  031  can be suppressed, but protruded portions  031   a  are formed at opposite ends in the peripheral direction of the projecting portion  031 . Therefore, when the tube is inserted into the hole of another member, the protruded portions  031   a  inhibit or interfere with insertion of the tube, and have an adverse effect on the assembly property. 
     Further, as shown in  FIG. 7 , the height of each of the projecting portions  031  is set to be lower than the radius of the tube  014 , and therefore, a linear main flow path F with which a plurality of projecting portions  031  do not interfere is formed inside the tube  014 , which makes agitation of a fluid inside the tube  014  difficult, and inhibits enhancement of efficiency of heat exchange. 
     SUMMARY OF THE INVENTION 
     A heat exchange tube facilitates formation of a plurality of projecting portions with the thickness hardly changed and without formation of protruded portions, and further is capable of contributing to enhancement of heat exchanging efficiency. 
     According to a first feature, there is provided a heat exchange tube constructed by forming, on a cylindrical tube peripheral wall, a plurality of projecting portions which project to an inside of the cylindrical tube peripheral wall, and which are formed by pushing, wherein the plurality of projecting portions are formed, respectively, into conical shapes across a tube axis, and are arranged along virtual spirals on the tube peripheral wall. 
     On the tube peripheral wall, a plurality of projecting portions which project to the inner surface side of the tube peripheral wall, and are formed by pushing, are formed into conical shapes across the tube axis, and therefore, the thickness of each of the projecting portions hardly differs from the thickness of the original peripheral wall. Accordingly, forming by pushing of each of the projecting portions can be easily performed, and workability is favorable. In addition, the surface areas of the inside and outside of the tube can be effectively increased by the conical projecting portions. 
     Further, a plurality of projecting portions are arranged along the virtual spirals on the tube peripheral wall, whereby the spiral flow path is formed in the tube. In addition, the sectional area of the flow path changes to become the minimum at the position of the vertex of each of the projecting portions, and become the maximum at the intermediate position between the adjacent projecting portions, and the gas which flows in the above described spiral flow path is effectively agitated by repeating expansion and contraction while turning, whereby heat exchange can be efficiently performed between the fluids inside and outside the tube. 
     Furthermore, by the inward conical projecting portions, outward projections are not formed on the tube peripheral wall, and therefore, interference with the other members of the tube is avoided, which can contribute to improvement in assembly property of the heat exchanger. 
     According to a second feature, in addition to the first feature, the tube peripheral wall is divided into a plurality of axial areas and the plurality of projecting portions are arranged along the virtual spirals which are drawn in respective adjacent axial areas and have their turning directions inversed from each other. 
     According to the second feature, when the fluid flowing in the flow path in the tube while turning moves from one axial area to the other axial area, the fluid inverses the turning direction. Therefore, agitation of the fluid can be performed more effectively, and the aforementioned heat exchange can be performed more efficiently. 
     According to a third feature, in addition to the second feature, a distance along a direction of the tube axis between centers of the adjacent projecting portions in each of the regions is set to be smaller than a major diameter of each of the projecting portions. 
     According to the third feature, the spiral flow path in the tube can be reliably formed in each of the axial areas, and the agitation effect of the fluid can be enhanced. 
     The above description, other objects, characteristics and advantages will be clear from detailed descriptions which will be provided for the preferred embodiment referring to the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The advantages of the invention will become apparent in the following description taken in conjunction with the drawings, wherein: 
         FIG. 1  is a longitudinal cross-sectional view of a heat exchanger for a gas cogenerator according to an embodiment of the present invention; 
         FIG. 2  is a cross-sectional view taken along line  2 - 2  in  FIG. 1 ; 
         FIG. 3  is a perspective view of a heat exchange tube in the heat exchanger; 
         FIG. 4  is a side view of the heat exchange tube; 
         FIG. 5A  is a cross-sectional view taken along line  5 A- 5 A in  FIG. 4 ; 
         FIG. 5B  is a cross-sectional view taken along line  5 B- 5 B in  FIG. 4 ; 
         FIG. 5C  is a cross-sectional view taken along line  5 C- 5 C in  FIG. 4 ; 
         FIG. 5D  is a cross-sectional view taken along line  5 D- 5 D in  FIG. 4 ; 
         FIG. 5E  is a cross-sectional view taken along line  5 E- 5 E in  FIG. 4 ; 
         FIG. 5F  is a cross-sectional view taken along line  5 F- 5 F in  FIG. 4 ; 
         FIG. 6  is a view explaining a method to form by pushing a projecting portion in the heat exchange tube; 
         FIG. 7  is a longitudinal cross-sectional view of a conventional heat exchange tube; 
         FIG. 8  is a cross-sectional view taken along line  8 - 8  in  FIG. 7 ; and 
         FIG. 9  is a view showing another conventional heat exchange tube and corresponding to  FIG. 8 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     An embodiment will be described below on the basis of the attached drawings. 
     First, based on  FIGS. 1 and 2 , a heat exchanger  1  for gas cogenerator using the heat exchange tube  14  of the present invention will be described. 
     The heat exchanger  1  for cogenerator has an outer barrel  2 , and upper and lower end plates  3  and  4  which are connected to opposite upper and lower ends of the outer barrel  2 . An exhaust gas inlet pipe  7 , to which an exhaust pipe  6  of a gas engine is connected, is connected to a center portion of the upper end plate  3 . A catalyst converter  8  for purifying exhaust gas, which communicates with the exhaust gas inlet pipe  7  is placed at the center portion of the outer barrel  2 . 
     A spiral exhaust gas flow path  10  which communicates with a lower end of the catalyst converter  8  is formed around the catalyst converter  8 . The exhaust gas flow path  10  communicates with an annular upper exhaust gas chamber  11  which is formed at an upper portion of the inside of the outer barrel  2 . The upper exhaust gas chamber  11  communicates with a lower exhaust gas chamber  12  which is formed at a lower portion of the inside of the outer barrel  2  through a plurality of heat exchange tubes (hereinafter, simply called tubes)  14  according to the present invention. 
     These tubes  14  are arranged in the annular form to surround the spiral exhaust gas flow path  10 , and are supported by an upper support plate  15 , an intermediate support plate  16  and a lower support plate  17  which are connected to the outer barrel  2 . 
     The upper support plate  15  has a plurality of support holes  15   a  in which the upper end portions of the tubes  14  are fitted, and defines a bottom wall of the upper exhaust gas chamber  11 . The upper end portions of the tubes  14  are welded  18  to peripheral edge portions of the support holes  15   a  to be liquid-tight. The intermediate support plate  16  has a plurality of support holes  16   a  in which the intermediate portions of the tubes  14  are fitted, and the intermediate portions of the tubes  14  are welded  19  to peripheral edge portions of the support holes  16   a . The lower support plate  17  has a plurality of support holes  17   a  in which the lower end portions of the tubes  14  are fitted, and the lower end portions of the tubes  14  are welded  28  to peripheral edge portions of the support holes  17   a.    
     A heat receiving chamber  20  which houses a plurality of tubes  14  by being sandwiched by the outer barrel  2  and the spiral exhaust gas flow path  10  is defined between the upper exhaust gas chamber  11  and the lower exhaust gas chamber  12 . A water inlet pipe  21  and a water outlet pipe  22  which open respectively to a lower portion and an upper portion of the heat receiving chamber  20  are provided at the outer barrel  2 . A water supply source  23  such as a water line is connected to the water inlet pipe  21 , and a hot water supply part  24  such as a hot water storage tank and a heater is connected to the water outlet pipe  22 . A number of through-holes  25  which allow water to flow in the heat receiving chamber  20  are provided in the aforementioned intermediate support plate  16 . An exhaust gas outlet pipe  26  which opens to the lower exhaust gas chamber  12  is provided in the lower end plate  4 , and an exhaust pipe  27  which is opened to the atmosphere is connected to the exhaust gas outlet pipe  26 . 
     Thus, when an exhaust gas G of the gas engine enters the exhaust gas inlet pipe  7 , HC, CO 2  and the like are removed from the exhaust gas G while the exhaust gas G passes through the catalyst converter  8 . Subsequently, the exhaust gas G rises in the spiral exhaust gas flow path  10  to move to the upper exhaust gas chamber  11  and lowers while splitting into a plurality of tubes  14 . The split exhaust gas merges in the lower exhaust gas chamber  12 , after which, the exhaust gas is released to the atmosphere through the exhaust gas outlet pipe  26  and the exhaust pipe  27 . 
     During this time, water W which is supplied to the heat receiving chamber  20  from the water inlet pipe  21  receives heat from the exhaust gas G through the exhaust gas flow path  10  and the tubes  14 , and becomes hot water to be supplied to the hot water supply part  24  from the water outlet pipe  22 . Thus, the exhaust heat of the gas engine is effectively used for hot water supply, and the exhaust gas G can be discharged into the atmosphere by being reduced in temperature. 
     The aforementioned tube  14  will be described with reference to  FIGS. 3 to 6 . 
     As shown in  FIGS. 3 to 5A  to  5 F, the tube  14  is made of a stainless steel pipe as a raw material, and in a cylindrical tube peripheral wall  30 , a plurality of projecting portions  31 ,  31  which are projected to the inside of it and formed by pushing are formed as follows, and arranged. 
     First, each of the projecting portions  31  is formed into a conical shape which projects to the inside of the tube peripheral wall  30  to be across a tube axis Y, and the vertex portion of the projecting portion  31  forms a substantially semicircular shape. Specifically, a height H of each of the projecting portions  31  is larger than a radius of the tube peripheral wall  30 . On forming the projecting portion  31 , the periphery of the element pipe of the tube  14  is held with upper and lower two-part molds  33  and  34  as shown in  FIG. 6 . A punch  36  is slidably inserted in a guide hole  35  which is provided in one mold  33 . The punch  36  is in a tapering shape having a substantially semispherical tip end portion, and by pushing the punch  36  into the tube peripheral wall  30  by its radius r or more, the projecting portion  31  projecting across the axis Y is formed inside the tube  14 . Specifically, the height of the projecting portion  31  is set to be larger than the radius r of the tube  14 . 
     The tube peripheral wall  30  is divided into a plurality of axial areas A 1  and A 2 , a first area A 1  and a second area A 2  in the illustrated example. A plurality of the aforementioned projecting portions  31  (three in the illustrated example) are arranged along a first virtual spiral S 1  and a second virtual spiral S 2  with the turning directions opposite from each other which are drawn in the first and the second axial directions, and in each of the areas A 1  and A 2 , a distance P along the direction of the tube axis Y between the centers of the adjacent projecting portions  31  is set to be smaller than a long diameter D of each of the projecting portions  31 . 
     It should be noted that an upper end portion, an intermediate portion (boundary portion of the areas A 1  and A 2  in the first and second axial directions) and a lower end portion of the tube  14  keep the circular sectional shapes of the original tube element pipe so as to be closely fitted in the support holes  15   a ,  16   a  and  17   a  of the aforementioned upper support plate  15 , intermediate support plate  16  and lower support plate  17 . 
     Next, an operation of this embodiment will be described. 
     Since in the tube peripheral wall  30 , a plurality of projecting portions  31  which project to the inner surface side and formed by pushing are formed into the conical shapes across the tube axis Y, each of the projecting portions  31  is analogous to the shape of a part of the tube peripheral wall  30  being inversed inward, as a result of which, the thickness of each of the projecting portions  31  hardly differs from the thickness of the original peripheral wall  30 , or rather decreases. Accordingly, forming of each of the projecting portions  31  by pushing can be easily performed. In addition, the conical projecting portion  31  contributes to effective increase of the surface area of the inside and outside of the tube  14 . 
     Further, a plurality of projecting portions  31  are arranged along the virtual spirals S 1  and S 2  on the tube peripheral wall  30 , whereby, a spiral flow path  32  is formed by a plurality of projecting portions  31  inside the tube  14 , and in addition, the sectional area of the flow path  32  changes to be the minimum at the position of the vertex of each of the projecting portions  31  and becomes the maximum at the intermediate position between the adjacent projecting portions  31 . 
     When a high-temperature exhaust gas G passes inside the tube  14  having a plurality of projecting portions  31 , the exhaust gas G is effectively agitated by repeating expansion and contraction while turning, whereby every portion of the exhaust gas can be brought into contact with the wide inner surface of the tube  14 . Therefore, heat exchange between the exhaust gas G and the water W of the heat receiving chamber  20  can be efficiently performed, and heating of the water W of the heat receiving chamber  20  can be effectively performed. 
     Furthermore, since by the inward conical projecting portions  31 , the outward projections are not formed on the tube peripheral wall  30 , the tube  14  is easily inserted through the support holes  15   a  to  17   a  of the aforementioned upper support plate  15  to the lower support plate  17 , for example, and the gaps between them can be closed easily and reliably by welding, which can contribute to enhancement in assembling property of the heat exchanger  1 . 
     Further, the aforementioned plurality of projecting portions  31  are arranged along the first and the second virtual spirals S 1  and S 2  which are drawn in the first and the second axial areas A 1  and A 2  of the tube peripheral wall  30 , and have the turning directions opposite from each other. Therefore, the turning direction of the spiral flow path  32  formed in the tube  14  become opposite in the first and the second axial areas A 1  and A 2 . As a result, the exhaust gas G flowing in the flow path  32  in the tube  14  while turning reverses the turning direction when moving to the second axial area A 2  from the first axial area A 1 . Therefore, agitation of the exhaust gas G can be performed more effectively, and the aforementioned heat exchange can be performed more efficiently. 
     Further, the distance P along the direction of the tube axis Y between the centers of the adjacent projecting portions  31  in each of the axial areas A 1  and A 2  is set to be smaller than the long diameter D of each of the projecting portions  31 . Therefore, the aforementioned spiral flow path  32  is reliably formed, and the agitation effect of the exhaust gas G can be enhanced. 
     The present invention is not limited to the above described embodiment, and various design changes can be made within the scope without departing from the gist of the present invention. For example, the number of divisions of the tube  14  when the tube  14  is divided into a plurality of the axial areas A 1  and A 2 , and the number of the projecting portions  31  in each of the axial areas can be properly set in accordance with the demand characteristics of the heat exchanger  1 , and the tube  14  can be applied to the heat exchange tubes of the heat exchangers other than those for gas cogenerators. 
     Although a specific form of embodiment of the instant invention has been described above and illustrated in the accompanying drawings in order to be more clearly understood, the above description is made by way of example and not as a limitation to the scope of the instant invention. It is contemplated that various modifications apparent to one of ordinary skill in the art could be made without departing from the scope of the invention which is to be determined by the following claims.