Patent Publication Number: US-2023152005-A1

Title: Method of manufacturing heat exchanger pipe

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a Divisional of U.S. patent application Ser. No. 16/858,098, filed on Apr. 24, 2020, which is a continuation-in-part of U.S. patent application Ser. No. 14/373,383, filed on Jul. 21, 2014, which is a National Stage Entry of International Patent Application No. PCT/KR2012/007404, filed on Sep. 17, 2012, which claims the benefit of priority to Korean Patent Application No. 10-2012-0005977, filed on Jan. 19, 2012. The disclosures of the above-listed applications are hereby incorporated by reference herein in their entirety. 
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates to a heat exchanger and, more particularly, to a heat exchanger that enables heat exchange between fluid flowing through a pipe and fluid existing outside the fluid, and a method of manufacturing the heat exchanger. 
     Description of the Related Art 
     In general, a heat exchanger pipe is used for various heating/cooling systems such as a boiler, a heat pump, and an air conditioner and provides not only hot water or heating water, but also hot air and cold air by enabling heat exchange between fluid flowing through the pipe and fluid existing outside the pipe. The fluid flowing through the pipe is gas such as high-temperature combustion gas and the fluid existing outside the pipe is liquid such as raw water. In this case, the high-temperature combustion gas usually exchanges heat with the raw water while flowing through the heat exchanger pipe, thereby providing hot water or heating water, but the fluids existing inside and outside the pipe is not specifically limited and may be liquid or gas. 
     Meanwhile, a ‘heat exchanger tube for heating boilers’ of Korean Patent No. 10-217265, as shown in  FIG.  1   , includes a cylindrical outer tube  1001  and a pair of half shells  1003  and  1004  disposed in the outer tube  1001  in contact with the outer tube  1001 . A plurality of ribs  1005  is disposed in a comb shape in the half shells  1003  and  1004 , thereby increasing the inner surface area. Further, a groove-shaped recess  1007  and a rib-shaped protrusion  1008  that are fitted to each other are formed on the contact-directional edges of the half shells  1003  to increasing the sealing force. 
     However, according to this related art, the lengths of the ribs  1005  are adjusted such that their ends are aligned, so the fluid flowing through the tube makes monotonous flow, and accordingly, there is a problem that the thermal contact amount between the fluid, which is a heat source, and the ribs  1005  is not sufficient. Further, the outer tube  1001  and the half shells  1003  and  1004  are assembled in close contact with each other by uniformly pressing the entire outer circumferential surface of the outer tube  1001 . In this case, the actually applied force acts perpendicularly to the outer circumferential surface of the outer tube  1001 , but the direction of force Fn required to strongly bring the groove-shaped recesses  1007  and the rib-shaped protrusions  1008  in close contact with each other does not coincide with the direction of the actually applied force, so there is a problem that a gap is formed between the groove-shaped recesses  1007  and the rib-shaped protrusions  1008 . 
     Further, since the two half shells  1003  and  1004  are provided as completely separate parts, it is required to separately form the half shells, and then fit them and assemble them in the outer tube  1001  in the manufacturing process. That is, the two half shells  1003  and  1004 , which are completely separated at the groove-shaped recesses  1007  and the rib-shaped protrusions  1008 , are independently formed through extrusion and then need to be combined to face each other and then assembled with the outer tube  1001 . Accordingly, since it is required not only to extrude the two half shells  1003  and  1004 , but also to cut the formed two half shells  1003  and  1004  into predetermined lengths, there is a problem that productivity of the half shells is poor. Further, the two half shells  1003  and  1004  are separately formed and the assembled in the outer tube  1001 , in which it is very difficult to keep the half shells  1003  and  1004  aligned with each other, so there is a problem that productivity of a heat exchange tube is also poor. Further, since the two half shells  1003  and  1004  are completely separately provided, there is a possibility of leakage through the joints at both sides. When sealing is poor, there is a possibility of leakage of condensate water with condensation of high-temperature combustion gas. According to the related art, since there are provided the groove-shaped recesses  1007  and the rib-shaped protrusions  1008 , they are fitted to each other and sealing is somewhat improved, but even in this case, there is a possibility of leakage through the gaps at both sides. 
     On the other hand, a hot water storage type boiler always keeps raw water at an appropriate temperature using a storage type heat exchanger disposed in a hot water tank, so there is the advantage that it is possible to immediately use hot water or heating water and supply a sufficient amount of water in comparison to an instantaneous type. 
     For example, a hot water storage type heat exchanger including a top end plate having multiple steps  2121   a ,  2121   b , and  2121   c , a bottom end plate  2122  having multiple steps  2122   a ,  2122   b , and  2122   c , and smoke tubes  2130  disposed between the laminas, as shown in  FIG.  2   , has been disclosed in Korean Patent No. 2013-0085090. Accordingly, when high-temperature combustion gas produced by a burner  2151  of a combustor  2150  is discharged through an exhaust port  2140  after passing through the smoke tubes  2130 , low-temperature raw water in a water tank  2110  is heated by the smoke tubes  2130  that function as heat exchanger pipes. 
     However, in the related art shown in  FIG.  3   , the smoke tubes  2130  disposed on steps are all circular tubes having a circular cross-section. Accordingly, many smoke tubes  2130  are required to increase the heat transfer area, which increase the outer diameter of the entire hot water storage type heat exchanger. 
     SUMMARY OF THE INVENTION 
     In order to solve the problems in the related art, an objective of the present invention is to provide a heat exchanger pipe that improves a heat exchange rate by making flow of fluid through the pipe more active and increasing a contact amount when enabling heat exchange between fluid flowing through the pipe and fluid existing outside the pipe, that has an improved contact characteristic and a sealing characteristic between an outer pipe and an insert inserted in the outer pipe in the process of manufacturing, and that is easily manufactured; and a method of manufacturing the heat exchanger pipe. 
     Another objective of the present invention is to provide a heat exchanger fin formed by integrally connecting two half shells to improve productivity by integrally forming the two half shells such that first ends of both ends of the half shells are connected, and a heat exchanger pipe having the heat exchanger fin. 
     Another objective of the present invention is to provide a heat exchanger fin formed by integrally connecting two half shells to be able to completely prevent leakage of condensate water through at least a joint because first ends of the two half shells are integrally formed. 
     Another objective of the present invention is to provide an elliptical exchanger pipe that can increase a heat transfer area in comparison to heat exchanger pipes having the same outer pipe size and another shape by having an elliptical cross-section and that prevents coming-off when a heat exchanger fin is inserted into an outer pipe. 
     Another objective of the present invention is to provide an elliptical heat exchanger pipe that is prevented from deforming and increases a heat exchange rate by configuring some of heat exchanger fins therein in a discontinuous type and configuring the other in a continuous type. 
     Another objective of the present invention is to provide a hot water storage type heat exchanger having an elliptical heat exchanger pipe in which a heat transfer area to the diameter of the entire heat exchanger is increased by arranging an elliptical heat exchanger pipe and a circular heat exchanger pipe in combination in a heat exchanger body. 
     In order to achieve the objectives, a heat exchanger pipe according to the present invention includes: an outer pipe formed in a cylindrical shape; a first half shell and a second half shell each have a semi-cylinder shape having outer circumferential surface being in contact with an inner circumferential surface of the outer pipe when combined to face each other in the outer pipe; and a first rib and a second rib extending internal space from inner circumferential surfaces of the first half shell and the second half shell, respectively, and disposed perpendicular to a virtual interface separating the first half shell and the second half shell, in which the first rib is provided as a plurality of pieces and lengths of the first ribs are adjusted such that an S-shape is formed when ends of the first ribs are sequentially connected by a virtual line; the second rib is provided as a plurality of pieces and lengths of the second ribs are adjusted such that an S-shape is formed when ends of the second ribs are sequentially connected by a virtual line; and the ends of the first ribs and the ends of the second ribs are spaced apart from each other. 
     A first half insert composed of the first half shell and the first ribs and a second half insert composed of the second half shell and the second ribs may be formed in the same shapes by extrusion, and the first half insert and the second half insert may be assembled such that a cross-sectional shape is symmetric left and right. 
     Both ends of the first half shell and both ends of the second half shell may be formed in flat shapes; and first bending portions bending toward the outer pipe may be formed with a predetermined length from the ends of the first half shell, second bending portions bending toward the outer pipe may be formed with a predetermined length from the ends of the second half shell, and when the first half shell and the second half shell are inserted in the outer pipe to face each other and then the outer pipe is pressed, the first bending portions and the second bending portions may be unfolded and the flat ends of the first half shell and the flat ends of the second half shell may be connected in close contact with each other. 
     A plurality of first prominences and recessions may be formed on the ends of the first half shell and a plurality of second prominences and recessions may be formed on the ends of the second half shell, so the first prominences and recessions and the second prominences and recessions may be fitted in close contact with each other when the outer pipe is pressed for assembly. 
     A heat exchange groove for increasing a surface area may be formed on a surface of the outer pipe. 
     A locking protrusion protruding inward may be formed at each of portions corresponding to both longitudinal ends of the first half shell and the second half shell on the outer pipe, thereby preventing separation of the first half shell and the second half shell from the outer pipe. 
     A method of manufacturing the heat exchanger pipe according to the present invention includes: an insert preparation process of placing the first half shell and the second half shell on ends on an upper bed having the same diameter as the first half shell and the second half shell combined to face each other; an outer pipe preparation process of placing the outer pipe on end on a lower bed having a larger diameter than the upper bed and supporting a bottom of the upper bed such that the first half shell and the second half shell are inserted in the outer pipe; a pressing-preparation process of disposing a dice mold having a tapered portion at a lower portion therein and having a pressing portion over the tapered portion therein-a diameter of a lower end of the tapered portion is the same as an outer diameter of the outer pipe and a diameter of the pressing portion is the same as a diameter of an assembly of the first half shell and the second half shell-over the outer pipe; and a pressing process of pressing the outer pipe with the pressing portion such that the inner circumferential surface of the outer pipe comes in close contact with the outer circumferential surfaces of the first half shell and the second half shell by moving down the dice mold such that the outer pipe is fitted in the dice mold and then by further moving down the dice mold. 
     A heat exchange fin formed by integrating two half shells according to the present invention includes: a first half shell formed in a semi-cylinder shape; a first rib extending toward an inner space from an inner circumferential surface of the first half shell; a second half shell formed in a semi-cylinder shape, forming a cylindrical shape through which fluid flow when combined with the first half shell to face each other, and having a circumferential end integrally connected to the first half shell; and a second rib extending toward an inner space from an inner circumferential surface of the second half shell. 
     The first rib may be provided as a plurality of pieces and lengths of the first ribs may be adjusted such that an S-shape is formed when ends of the first ribs are sequentially connected by a virtual line; the second rib may be provided as a plurality of pieces and lengths of the second ribs may be adjusted such that an S-shape is formed when ends of the second ribs are sequentially connected by a virtual line; and the ends of the first ribs and the ends of the second ribs may be spaced apart from each other. First prominences and recessions may be formed at an end of the first half shell where the first half shell and the second half shell are not integrally connected, second prominences and recessions may be formed at an end of the second half shell where the first half shell and the second half shell are not integrally connected, and the first prominences and recessions and the second prominences and recessions may be fitted in close contact each other. 
     The first half shell and the second half shell may be integrally connected through a bridge, and a bending groove guiding the first half shell and the second half shell such that the first half shell and the second half shell are closed may be formed at the bridge. 
     A heat exchanger pipe according to the present invention has the heat exchanger fin described above and a cylindrical outer pipe, in which the cylindrical heat exchanger fin is assembled in contact with an inner circumferential surface of the outer pipe. A locking protrusion protruding inward may be formed at each of portions corresponding to both longitudinal ends of the heat exchanger fin on the outer pipe, thereby preventing separation of the heat exchanger fin from the outer pipe. 
     An elliptical heat exchanger pipe according to the present invention includes: a pipe-shaped heat exchanger tube having an elliptical cross-section and having a hollow portion for flow of a heat source; and a plurality of heat exchanger fins protruding from an inner circumferential surface of the heat exchanger tube. 
     The heat exchanger fins may be disposed on a line extending from a side to the other side of the inner circumferential surface of the heat exchanger tube and may be spaced in the direction of the apsidal line of the heat exchanger tube; some of heat exchanger fins may be discontinuous type heat exchanger fins that are disconnected at middle portions in a longitudinal direction thereof and the others except for the discontinuous type heat exchanger fins may be continuous type heat exchanger fins that are entirely continuous in a longitudinal direction thereof. 
     A continuous fin group in which one or more continuous type heat exchanger fins are continuously disposed may be included in the heat exchanger fins. 
     One or more continuous fin groups may be provided and the continuous fin groups may be disposed between sections composed of the discontinuous type heat exchanger fins. 
     Lengths of ends of the discontinuous type heat exchanger fins in a section divided by the continuous fin group may be adjusted such that an S-shape is formed when ends thereof are sequentially connected by a virtual line. 
     A hot water storage type heat exchanger according to the present invention includes: a top end plate having a first top stage disposed at a center of a disc and a second top stage disposed around the first top stage; a bottom end plate having a first bottom stage disposed at a center of a disc and a second bottom stage disposed around the first bottom stage; a plurality of circular heat exchanger pipe having upper ends passing through the first top stage, having lower ends passing through the first bottom stage, and having a circular cross-section; and the elliptical heat exchanger pipes having upper ends passing through the second top stage and lower end passing through the second bottom stage. 
     The elliptical heat exchanger pipes may be circumferentially arranged along the second top stage and the second bottom stage. 
     According to the heat exchanger pipe of the present invention described above, since the lengths of the ribs are adjusted such that the ends of the ribs of the first half shell and the second half shell form S-shapes, the heat exchanger pipe improves a heat exchange rate by making flow of fluid through the pipe more active and increasing a contact amount. 
     Further, according to the method of manufacturing the heat exchanger pipe, since there are bending portions that are bent in the same direction as an actually applied force when the outer pipe is pressed, it is possible to improve a contact characteristic and a sealing characteristic between the outer pipe and an insert. Further, the outer pipe and the insert are brought in close contact with each other only by fitting and pushing down a dice mold, so manufacturing becomes easy. 
     Further, an end of the first half shell and an end of the second half shell are integrally connected. Accordingly, productivity of not only the heat exchanger fin, but also the heat exchanger pipe is improved. 
     Further, since ends are integrally formed, sealing is secured at the portion. Accordingly, leakage of condensate water through at least the ends is completely prevented. 
     Further, the elliptical heat exchanger pipe provides a heat exchanger pipe having an elliptical cross-section. Accordingly, a heat transfer area is increased in comparison to heat exchanger pipes having the same size of outer pipe and different shapes. Further, separation between the outer pipe and the heat exchanger fin is prevented when the heat exchanger fin is inserted into the outer pipe to be in close contact therewith. 
     Further, some of the heat exchanger fins of the elliptical heat exchanger are discontinuous type heat exchanger fins and the others are continuous type heat exchanger fins without disconnection, thereby providing a complex configuration. 
     Accordingly, the heat exchange rate is increased by the discontinuous type heat exchanger fins and deformation of the heat exchanger tube is fundamentally prevented by the reinforcing force provided by the continuous type heat exchanger fins, so it is not required to improve the processes or add processes in order to prevent deformation, thereby improving productivity. 
     Meanwhile, in the hot water storage type heat exchanger of the present invention, elliptical heat exchanger pipes having a large heat transfer area is disposed at the outer portion in the end plate having a large circumference and the circular heat exchanger pipes having a small heat transfer area are disposed at the center of the end plate having a small circumference, thereby providing a complex array of heat exchanger pipes. Accordingly, it is possible to considerably increase the heat transfer area by the heat exchanger pipe to the outer diameter of the entire heat exchanger and a relatively small number of heat exchanger pipes are used to provide the same thermal efficiency, so it is possible to reduce the size of the heat exchanger. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a cross-sectional view showing a heat exchanger pipe (heat exchanger tube) according to the related art; 
         FIG.  2    is a front cross-sectional view showing a hot water storage type boiler according to the related art; 
         FIG.  3    is a view showing the hot water storage type boiler according to the related art; 
         FIG.  4    is a perspective view showing a heat exchanger pipe according to a first embodiment of the present invention; 
         FIG.  5    is a cross-sectional view showing the heat exchanger pipe according to a first embodiment of the present invention; 
         FIG.  6    is a cross-sectional view showing a heat exchanger pipe according to a second embodiment of the present invention; 
         FIGS.  7 A and  7 B  are cross-sectional views showing a heat exchanger pipe according to a third embodiment of the present invention; 
         FIG.  8    is a partial cross-sectional view showing a heat exchanger pipe according to a fourth embodiment of the present invention; 
         FIG.  9    is a perspective view showing a heat exchanger pipe according to a fourth embodiment of the present invention; 
         FIG.  10    is a perspective view showing a heat exchanger pipe according to a sixth embodiment of the present invention; 
         FIGS.  11 A to  11 E  are views showing a method of manufacturing the heat exchanger pipe according to the first embodiment of the present invention; 
         FIG.  12    is a perspective view showing a heat exchanger pipe according to a seventh embodiment of the present invention; 
         FIGS.  13 A and  13 B  are front views showing a heat exchanger fin formed by integrally connecting two half shells for the heat exchanger pipe according to the seventh embodiment of the present invention; 
         FIGS.  14 A to  14 E  are views showing a method of manufacturing the heat exchanger pipe according to the seventh embodiment of the present invention; 
         FIG.  15    is a perspective view showing an elliptical heat exchanger pipe according to an eighth embodiment of the present invention; 
         FIGS.  16 A to  16 C  are plan views showing the elliptical heat exchanger pipe according to the eighth embodiment of the present invention and an another-shaped heat exchanger pipe; 
         FIGS.  17 A and  17 B  are plan views showing other examples of the heat exchanger pipe according to the eighth embodiment of the present invention; 
         FIG.  18    is a perspective view showing a hot water storage type heat exchanger having the elliptical heat exchanger pipe according to the eighth embodiment of the present invention; 
         FIG.  19    is a plan view showing the hot water storage type heat exchanger having the elliptical heat exchanger pipe according to the eighth embodiment of the present invention; and 
         FIG.  20    is a front view showing the hot water storage type heat exchanger having the elliptical heat exchanger pipe according to the eighth embodiment of the present invention; 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Hereafter, a heat exchanger pipe according to embodiments of the present invention and a method of manufacturing the heat exchanger pipe are described in detail with reference to the accompanying drawings. 
       FIG.  4    is a perspective view showing a heat exchanger pipe according to a first embodiment of the present invention and  FIG.  5    is a cross-sectional view showing the heat exchanger pipe according to a first embodiment of the present invention. 
     First, a heat exchanger pipe  20  according to a first embodiment of the present invention, as shown in the perspective view of  FIG.  4    and the cross-sectional view of  FIG.  5   , includes an outer pipe  21  formed in a cylindrical shape, a first half insert  22 ,  23  and a second half insert  24 ,  25  that are inserted in the outer pipe  21 . For example, the outer pipe  21  may be made of a metal material such as steel, and the first half insert  22 ,  23  and the second half insert  24 ,  24  may be made of an aluminum material. 
     The first half insert  22 ,  23  is composed of a first half shell  22  formed in a semi-cylinder shape obtained by longitudinally cutting a cylinder, and a plurality of first ribs  23  disposed in the first half shell  22  and having long fin shapes. Similarly, the second half insert  24 ,  25  is composed of a second half shell  24  and a plurality of second ribs  25 . 
     Ends F of the first half shell  22  and ends F′ of the second half shell  24  are flat surfaces, so when the first half shell  22  and the second half shell  24  are disposed to face each other and assembled such that the ends are strongly brought in surface contact with each other, fluid flowing through the first half shell  22  and the second half shell  24  is prevented from leaking through gaps between the first half shell  22  and the second half shell  24 . 
     The first ribs  23  spaced a predetermined gap from each other extend toward the inner space from the inner circumferential surface of the first half shell  22  and the second ribs  25  spaced a predetermined gap from each other extend toward the inner space from the inner circumferential surface of the second half shell  24 . The first ribs  23  and the second ribs  25  are arranged perpendicular to a virtual interface that separates the first half shell  22  and the second half shell  24 . 
     In particular, the lengths of the first ribs  23  and the second ribs  25  are adjusted to each make an S-shape when the ends of the first ribs  23  and the ends of the second ribs  25  are sequentially connected by virtual lines, respectively, and the facing ends of the first ribs  23  and the second ribs  25  are spaced not to be in contact with each other. 
     For example, the first ribs  23  include first-first rib  23   a  to sixth-first rib  23   f  sequentially from the left in the figure, in which the second-second rib  25   b  is longer than the first-first rib  23   a  and the third-first rib  23   c  is shorter than the second-first rib  23   b.    
     Further, the fourth-first rib  23   d  is longer than the third-first rib  23   c , the fifth-first rib  23   e  is shorter than the fourth-first rib  23   d , and the sixth-first rib  23   f  is shorter than the fifth-first rib  23   e , that is, the lengths of the ribs are adjusted in this way. 
     Therefore, when the ends from the first-first rib  23   a  to the sixth-first rib  23   f  are sequentially connected by a virtual line, two S-shapes overlapping each other appear (indicated by dotted lines in  FIG.  5   ). 
     The second ribs  25  also include six ribs, similar to the first ribs  23 , in which when the ends from the first- to sixth-second ribs  25  are sequentially connected, two S-shapes overlapping each other appears. The first ribs  23  and the second ribs  25  are spaced not to be in contact with each other. 
     Accordingly, as compared with a heat exchanger tube of the related art in which flow of fluid in the tube is monotonous because the ends of ribs (see  1005  in  FIG.  5   ) are aligned to form a comb shape, the present invention further have an S-shaped passage, so the fluid flowing through the first half shell  22  and the second half shell  24  fluctuates much, whereby the thermal contact amount between the fluid and the first ribs  23  or the second ribs  25  increases. 
     Further, the thermal contact amount of fluid, which is a heat source such as high-temperature combustion gas, with the first ribs  23  or the second ribs  25  increases, the amount of heat transferring to the outer pipe  21  being in contact with the first half shell  22  and the second half shell  24  also increases, whereby it is possible to increase the heat exchange efficiency with raw water, etc. outside the outer pipe  21  can be increased. However, the first half insert  22 ,  23  is formed by integrally extruding the first half shell  22  and the first rib  23  and the second half insert  24 ,  25  is formed by integrally extruding the second half shell  24  and the second ribs  25 , and in this case, if the same mold is used regardless of the first half insert  22 ,  23  and the second half insert  24 ,  25 , it would be possible to reduce the manufacturing cost. 
     Obviously, in this case, the first half insert  22 ,  23  and the second half insert  24 ,  25  should be assembled such that the cross-sectional shapes are symmetric left and right. 
     Hereafter, a heat exchanger pipe according to a second embodiment of the present invention is described with reference to the accompanying drawings. 
       FIG.  6    is a cross-sectional view showing a heat exchanger pipe according to a second embodiment of the present invention. 
     As shown in  FIG.  6   , a heat exchanger pipe  30  according to a second embodiment of the present invention includes an outer pipe  31  formed in a cylindrical shape, and a first half insert  32 ,  33  and a second half insert  34 ,  35  that are inserted in the outer pipe  31 . 
     The first half insert  32 ,  33  is composed of a first half shell  32  and a plurality of first ribs  33  and the second half insert  34 ,  35  is composed of a second half shell  34  and a plurality of second ribs  35 . This configuration is the same as that of the first embodiment of the present invention described above. 
     However, in the heat exchanger pipe according to the second embodiment of the present invention, the first ribs  33  include a first-first rib  33   a  to a fifth-first rib  33   e  sequentially from the left in the figure and the second ribs  35  also include five ribs. When the ends of the five first ribs  33  are sequentially connected by a virtual line, one S-shape is obtained and, similarly, another S-shape is obtained from the second ribs  35 . 
     That is, the ribs of the first embodiment of the present invention described with reference to  FIG.  5    each include six ribs (see  23  and  25  in  FIG.  5   ), while the ribs of the second embodiment of the present invention each include five ribs  33  and  35 , that is, the numbers of ribs are different, so the S-shapes may be slightly changed, but the present invention can increase the heat exchange rate by increasing flow of fluid. 
     Hereafter, a heat exchanger pipe according to a third embodiment of the present invention is described with reference to the accompanying drawings. However, the third embodiment of the present invention is fundamentally based on the first embodiment of the present invention, so only different configurations are shown and described. 
       FIGS.  7 A and  7 B  are cross-sectional views showing a heat exchanger pipe according to a third embodiment of the present invention. 
     As shown in  FIGS.  7 A and  7 B , a heat exchanger pipe according to a third embodiment of the present invention includes a first half insert  22 ,  23  and a second half insert  24 ,  25  that are inserted in an outer pipe (see  21  in  FIG.  2   ) formed in a cylindrical shape. The first half insert  22 ,  23  is composed of a first half shell  22  and a plurality of first ribs  23  and the second half insert  24 ,  25  is composed of a second half shell  24  and a plurality of second ribs  25 . This configuration is the same as that of the first embodiment of the present invention described above. 
     However, the third embodiment of the present invention has a different in that first bending portions  22   a  and second bending portions  24   a  for assembly are respectively formed at both end portions of the first half shell  22  and at both end portions of the second half shell  24 , and the first bending portions  22   a  and the second bending portions  24   a  are bent outward respectively from first bending surfaces  22   a ′ and second bending surfaces  24   a′.    
     That is, both ends of the first half shell  22  and both ends of the second half shell  24  are formed in flat shapes, in which, as shown in  FIG.  7 A , the first bending portions  22   a  bending toward the outer pipe  31  are formed with a predetermined length from the flat ends of the first half shell  22  and the second bending portions  24 a bending toward the outer pipe  31  are formed with a predetermined length from the flat ends of the second half shell  24 . 
     Accordingly, as shown in  FIG.  7 B , when the outer pipe  21  is pressed and compressed to come in close contact with the outer circumferential surfaces of the first half shell  22  and the second half shell  24  in the assembling process, the first bending portions  22   a  and the second bending portion  24   a  are pressed and unfolded inward and the flat ends of the first half shell  22  and the flat ends of the second half shell  24  are slightly pressed and deformed, whereby the ends are strongly brought in surface contact with each other. 
     Therefore, it is possible to solve the problem in the related art that the force that is actually applied for assembly acts perpendicular to the outer circumferential surface of the outer tube  1001  in the related art but the force for strongly bring the groove-shaped recesses  1007  and the rib-shaped protrusions  1008  in close contact with is not actually applied in the direction of the above force, thereby causing gaps between the groove-shaped recesses  1007  and the rib-shaped protrusions  1008 . 
       FIG.  8    is a partial cross-sectional view showing a heat exchanger pipe according to a fourth embodiment of the present invention. 
     Referring to  FIG.  8   , in a fourth embodiment of the present invention, a plurality of first prominences and recessions  22   b  is formed on flat ends of the first half shell  22  and a plurality of second prominences and recessions (not shown) is formed on flat ends of the second half shell  24 , so the first prominences and recessions  22   b  and the second prominences and recessions are fitted to each other when the entire outer pipe  21  is uniformly pressed for assembly, thereby being able to further increase the sealing force. 
     Obviously, a cut groove  22   c  is formed on the bending surfaces of the first bending portions  22   a  and the bending surfaces of the second bending portions  24   a , so when the entire outer pipe  21  is pressed for assembly, the first bending portions  22   a  and the second bending portions  24   a  are guided to be unfolded, whereby assembly can be achieved more easily. 
     Hereafter, a heat exchanger pipe according to a fifth embodiment of the present invention is described with reference to the accompanying drawings. 
       FIG.  9    is a perspective view showing a heat exchanger pipe according to a fourth embodiment of the present invention. 
     As shown in  FIG.  9   , a heat exchanger pipe according to a fifth embodiment of the present invention includes an outer pipe  41 , and, as described above, an insert  42  composed of a first half insert and a second half insert. This configuration is the same as the above description. 
     However, in the fifth embodiment of the present invention, heat exchange grooves  41   a  for increase the surface area is formed on the surface of the outer pipe  41 , so the heat of fluid (i.e., high-temperature combustion gas, etc.) flowing through the outer pipe  41  can more efficiently transfer to fluid (i.e., raw water, etc.) existing outside the outer pipe  41 . 
     However, it is exemplified that a plurality of heat exchange grooves is longitudinally formed on the outer pipe  41  and arranged around the outer pipe  41  in  FIG.  9   , but the heat exchange grooves circularly arranged around the outer pipe  41  may be longitudinally arranged with predetermined gaps on the outer pipe  41  or may be spirally formed on the outer circumferential surface of the outer pipe, and other various patterns may be possible. Hereafter, a heat exchanger pipe according to a sixth embodiment of the present invention is described with reference to the accompanying drawings. 
       FIG.  10    is a perspective view showing a heat exchanger pipe according to a sixth embodiment of the present invention. As shown in  FIG.  10   , a heat exchanger pipe  50  according to a sixth embodiment of the present invention includes an outer pipe  51 , and, as described above, an insert  52  composed of a first half insert and a second half insert. 
     In particular, a locking protrusion  51   a  protruding inward where the insert  52  is inserted is formed at both end portions of the outer pipe  51 , that is, the locking protrusions  51  are formed at portions corresponding to both longitudinal ends of the insert  52  on the outer pipe  51 . 
     Accordingly, the insert  52  is firmly fixed without moving toward an end or the other end of the open outer pipe  51 , so after the outer pipe  51  and the insert  52  are assembled by pressing the entire outer pipe  51  such that the inner circumferential surface of the outer pipe  51  and the outer circumferential surface of the insert  52  are brought in contact with each other, separation of the insert  51  from the external pipe  51  is prevented. 
     Hereafter, methods of manufacturing the heat exchanger pipes according to the above embodiments of the present invention are described hereafter. 
       FIGS.  11 A to  11 E  are views showing a method of manufacturing the heat exchanger pipe according to the first embodiment of the present invention. 
     A method of manufacturing the heat exchanger pipe according to the first embodiment of the present invention described with reference to  FIG.  4    is exemplified hereafter. First, as shown in  FIG.  11 A , a bed T, T′ is prepared to manufacture a heat exchanger pipe according to the present invention. The bed T, T′ is composed of a lower bed T and an upper bed T′ fixed on the lower bed T. 
     The upper bed T′ has a size that is the same as the diameter of the assembly of the first half shell  22  and the second half shell  24 , so the first half shell  22  and the second half shell  24  can be stably placed thereon. Further, the lower bed T is larger in diameter than the upper bed T′, so the outer pipe  21  can be placed thereon. 
     Next, as shown in  FIG.  11 B , the first shell  22  and the second half shell  24  combined to face each other are placed on ends on the upper bed T′. That is, the first half insert  22 ,  23  and the second half insert  24 ,  25  are prepared (insert preparation step). 
     Next, as shown in  FIG.  11 C , a prototypal outer pipe  21 ′ is placed on end on the lower bed such that the first half shell  22  and the second half shell  24  are positioned inside the outer pipe  21 ′ (outer pipe preparation step). The prototypal outer pipe  21 ′ not machined yet is larger in diameter than the assembly of the first half shell  22  and the second half shell  24 , so the outer pipe can be fitted over the first half shell  22  and the second half shell  24  from above. 
     Next, as shown in  FIG.  11 D , a dice mold D having a tapered portion, which gradually decreases in width upward, at a lower portion therein, having a pressing portion over the tapered portion therein is prepared over the outer pipe  21  (pressing-preparation step), in which the diameter of the lower end of the tapered portion is the same as (or may be slightly larger than) the outer diameter of the outer pipe  21  and the diameter of the pressing portion is the same as (or may be slightly smaller than) the diameter of the assembly of the first half shell  22  and the second half shell  24 . 
     Next, as shown in  FIG.  11 E , the dice mold D is moved down such that the prototypal outer pipe  21 ′ is inserted into the dice mold D, and in this state, the dice mold D is further moved down such that the pressing portion presses the prototypal outer pipe  21 ′, whereby the inner circumferential surface of the outer pipe  21  obtained by compression of the prototypal outer pipe  21 ′ is pressed to come in close contact with the outer surfaces of the first half shell  22  and the second half shell  24  (pressing step). Accordingly, it is possible to conveniently and simply manufacture a heat exchanger pipe. 
     Hereafter, a heat exchanger pipe according to a seventh embodiment of the present invention is generally described with reference to the accompanying drawings. 
       FIG.  12    is a perspective view showing a heat exchanger pipe according to a seventh embodiment of the present invention. 
     As shown in  FIG.  12   , a heat exchanger pipe according to the present invention includes an outer pipe P formed in a cylindrical shape and a heat exchanger fin  20  formed by integrally connecting two half shells inserted in the outer pipe P (hereafter, referred to as a ‘heat exchanger fin’). 
     The heat exchanger fin  20  and the outer pipe P are assembled such that the outer circumferential surface of the heat exchanger fin  20  and the inner surface of the outer pipe P are completely in close contact with each other. The outer pipe P is made of a metal material such as steel and the heat exchanger fin  20  is made of a metal material such as aluminum. Accordingly, heat is exchanged between first fluid flowing through the heat exchanger fin  20  and second fluid flowing on the surface of the outer pipe P. 
     For example, when high-temperature combustion gas produced by burning fuel with a burner (not shown) flows through the heat exchanger fin  20  and low-temperature raw water comes in contact with the surface of the outer pipe P, heat exchange occurs between the high-temperature combustion gas and the raw water. The heated raw water is used as hot water, heating water, or the like. 
     In the entire length of the outer pipe, a locking protrusion G protruding inward is formed at portions corresponding to both longitudinal end of the heat exchanger fin  20 . Accordingly, separation of the heat exchanging fin  20  from the outer pipe P is separated. This is for preventing separation of the heat exchanger fin  20  due to vibration of its own weight in long-time use. 
       FIGS.  13 A and  13 B  are front views showing a heat exchanger fin formed by integrally connecting two half shells for the heat exchanger pipe according to the seventh embodiment of the present invention. 
     As shown in  FIGS.  12 ,  13 A, and  13 B , the heat exchanger fin  20  according to the present invention includes a first half shell  21  and a second half shell  22  integrally connected to the first half shell  21 . First ribs  21   a  are formed on the inner circumferential surface of the first half shell  21  and second ribs  22   a  are formed on the inner circumferential surface of the second half shell  22 . 
     The first ribs  21   a  are integrally formed on the inner circumferential surface of the first half shell  21  and the second ribs  22   a  are integrally formed on the inner circumferential surface of the second half shell  22 . In particular, the first half shell  21  and the second half shell  22  are integrally formed with first ends thereof are connected to each other. As a forming method, extrusion is usually used. 
     The first half shell  21  and the second half shell  22  function as a body, and the first ribs  21   a  and the second ribs  22   a  are used for the purpose of increasing the heat exchange rate by increasing the surface area. In terms of the purpose, a plurality of prominences and recession is formed on the surfaces of the first ribs  21   a  and the second ribs  22   a , thereby further increasing the surface area. 
     As shown in  FIG.  13 A , the first half shell  21  and the second half shell  22  are each formed in a semi-cylinder shape obtained by longitudinally cutting a cylinder. First ends in the circumferential direction of the first half shell  21  and the second half shell  22  are connected to each other. That is, the first half shell  21  and the second half shell  22  are integrally connected through a bridge  23 . 
     Accordingly, as shown in  FIG.  13 B , when the first half shell  21  and the second half shell  22  are pivoted toward each other on the bridge  23 , a cylindrical shape is formed by the first half shell  21  and the second half shell  22 . Fluid such as high-temperature combustion gas flows through the cylindrical first half shell  21  and second half shell  22 . 
     A first rib  21   a  extends toward the inner space from the inner circumferential surface of the first half shell  21  and a second rib  22   a  extends toward the inner space from the inner circumferential surface of the second half shell  22 . In this case, pluralities of first ribs  21   a  and second ribs  22   a  that have fin shapes are provided to increase the heat exchange rate by increasing the surface area. 
     In particular, according to the present invention, a folding groove  32   a  is formed at the bridge  23  where the first half shell  21  and the second half shell  22  are integrally connected to each other. Accordingly, the first half shell  21  and the second half shell  22  can be easily closed, as shown in  FIG.  13 B , even in the state in which the first half shell  21  and the second half shell  22  are open away from each other. 
     The folding groove  23   a , as shown in the figures, is formed in a V-shaped cross-section on the inner side of the bridge  23 , so it guides the first half shell  21  and the second half shell  22  such that they can be easily closed when they are coupled to each other, and grooves having other various shapes can be used as long as the half shell can be easily closed. 
     It is exemplified in  FIGS.  13 A and  13 B  that second ends  21   b  and  22   b  (i.e., the ends opposite to the bridge) of the first half shell  21  and the second half shell  22  are flat. However, first prominences and recessions may be formed on the second end  21   b  of the first half shell  21  and second prominences and recessions may be formed on the second end  22   b  of the second half shell  22 . 
     When the first prominences and recessions and the second prominences and recessions are provided, the second ends  21   b  and  22   b  of the first half shell  21  and the second half shell  22  are engaged in close contact with each other, thereby considerably reducing leakage of condensate water, etc. produced by condensation of combustion gas. The first ends of the first half shell  21  and the second half shell  22  are integrally connected to each other already in the forming process, leakage of condensate water, etc. is completely prevented. 
     Further, according to the present invention, the lengths of the first ribs  21   a  and the second ribs  22   a  are adjusted such that when ends of the first ribs  21   a  and ends of the second ribs  22   a  are respectively sequentially connected by virtual lines, they respectively form an S-shape. Ends, which face each other, of the first ribs  21   a  and the second ribs  22   a  are spaced part from each other not to be in contact with each other Accordingly, flow of fluid is monotonous because ribs of a heat exchanger pipe are arranged in comb shape in the related art, but the present invention further has an S-shaped passage, so fluctuation of fluid increases. 
     Further, the thermal contact amount of fluid such as high-temperature combustion gas with the first ribs  21   a  or the second ribs  22   a  increases, so the heat transfer amount to the outer pipe P increases. Accordingly, the heat exchange efficiency with raw water, etc. outside the outer pipe P increases. 
     As described above, according to the present invention, since the first half shell  21  and the second half shell  22  are connected through the bridge  23  like a single part, it is easy to form the heat exchanger pin  20  itself. This is because it is possible to manufacture the first half shell  21  and the second half shell  22  simultaneously in extrusion. 
     In the related art, a first half shell ( 1003  in  FIG.  1   ) and a second half shell ( 1004  in  FIG.  1   ) are completely separated from each other, so there is a problem that it is required to cut each of the first half shell  1003  and the second half shell  1004  one time, that is, a total of cutting twice is required. However, according to the present invention, when the heat exchanger fin  20  is manufactured with an appropriate length, it is possible to cut the first half shell  21  and the second half shell  22  simultaneously. 
     Further, according to the present invention, since the first half shell  21  and the second half shell  22  are connected to each other, the heat exchanger fin  20  is conveniently inserted into the outer pipe P and productivity is improved. In the related art, as shown in  FIG.  1   , since the first half shell  21  and the second half shell  22  are separated, it is difficult to insert the half shells into the outer pipe P while holding the half shells. Further, there is problem that the first half shell  21  and the second half shell  22  fall into disorder when they are inserted. Further, according to the present invention, since the first half shell  21  and the second half shell  22  are integrally connected through the bridge  23 , condensate water does not leak to the outside at least through the bridge  23 . Since condensate water is acidic, it causes environment contamination, etc. when leaking, so it is very important to prevent leakage of condensate water. 
     Hereafter, a method of a heat exchanger pipe according to an embodiment is described. 
       FIGS.  14 A to  14 E  are views showing a method of manufacturing the heat exchanger pipe according to the seventh embodiment of the present invention. 
     First, as shown in  FIG.  14 A , a bed T, T′ is prepared to manufacture a heat exchanger pipe according to the present invention. The bed T, T′ is composed of a lower bed T and an upper bed T′ fixed on the lower bed T. 
     The upper bed T′ has the same size as the diameter of the heat exchanger fin  20  obtained by combining the first half shell  21  and the second half shell  22 , so the heat exchanger fin  20  is placed on the upper bed T′, and the outer pipe P is placed on the lower bed T because the lower bed T is larger in diameter than the upper bed T′. 
     Next, as shown in  FIG.  14 B , the heat exchanger fin  20  is placed on the upper bed T′. 
     Next, as shown in  FIG.  14 C , a prototypal outer pipe P′ is placed on end on the lower bed, whereby the heat exchanger fin  20  is disposed in the prototypal outer pipe P′. The prototypal outer pipe P′ not machined yet is larger in diameter than the heat exchanger fin  20 , so the prototypal outer pipe P′ can be fitted over the heat exchanger fin  20  from above. 
     Next, as shown in  FIG.  14 D , a dice mold D having a tapered portion, which gradually decreases in width upward, at a lower portion therein, and having a pressing portion over the tapered portion is disposed over the outer pipe P. 
     Next, as shown in  FIG.  14 E , the dice mold D is moved down such that the prototypal outer pipe P′ is fitted in the dice mold D, and then the dice mold D is further moved down, thereby pressing the prototypal outer pipe P′ with the pressing portion. 
     Accordingly, the inner circumferential surface of the outer pipe P formed by contraction of the prototypal outer pipe P′ comes in close contact with the outer surface of the heat exchanger fin  20 , so the heat exchanger fin  120 , P is simply manufactured. 
     Hereafter, an elliptical heat exchanger pipe according to an eighth embodiment of the present invention and a hot water storage type heat exchanger having the elliptical heat exchanger pipe are described with reference to the accompanying drawings. 
       FIG.  15    is a perspective view showing an elliptical heat exchanger pipe according to an eighth embodiment of the present invention. 
     First, an elliptical heat exchanger pipe  240  according to the present invention shown in  FIG.  15    is used as a component of various heating/cooling system such as a boiler, a heat pump, and an air conditioner, and has an elliptical cross-section and a predetermined length. 
     The elliptical heat exchanger pipe  240  enables heat exchange between fluid flowing therethrough and fluid exiting outside, thereby being able to supply not only hot water or heating water, but also hot air or cold air. 
     For example, the fluid flowing through the elliptical heat exchanger pipe  240  is high-temperature combustion gas produced by the burner of a boiler and the fluid existing outside the elliptical heat exchanger pipe  240  is low-temperature liquid such as raw water. 
     Accordingly, high-temperature combustion gas exchanges heat with raw water while flowing through the elliptical heat exchanger pipe  240 , where by hot water or heating water is supplied to heating loads such as a house, a factory, an office, or the like. 
     To this end, the elliptical heat exchanger pipe  240  according to the present invention includes an elliptical heat exchanger tube  241  and a plurality of heat exchanger fins  242  increasing a heat transfer area and a heat exchange rate by protruding toward the empty space inside the heat exchanger tube  241 . 
     However, a contact shell SH may be further disposed between the heat exchanger tube  241  and the heat exchanger fins  242 , and in this case, the heat exchanger fins  242  protrude from the inner surface of the contact shell SH and the outer surface of the contact shell SH is in surface contact with the inner side of the heat exchanger tube  241 , whereby heat transfer occurs. 
     The heat exchanger fins  242  are formed by drawing a metallic material (e.g., stainless steel), etc. which have high thermal conductivity, as an embodiment, and the contact shell SH may be included in drawing. The heat exchanger fins  242  manufactured in this way are inserted in the heat exchanger tube  241 . 
     The heat exchanger tube  241  is formed in a tube shape having an elliptical cross-section and having a hollow portion so that a heat source (i.e., fluid) flows through it. A plurality of heat exchanger fins  242  protrude from the inner circumferential surface of the heat exchanger tube  241  and are provided to increase the heat exchange rate. 
     The reason of making the heat exchanger tube  241  in an elliptical shape in the present invention is for increasing the amount of flow of heat exchange fluid (e.g., combustion gas) by making the apsidal line of the heat exchanger tube  241  long, in which the length of the apsidal line is appropriately adjusted in accordance with heat exchange capacity. 
     Further, by providing a heat exchanger pipe having an elliptical cross-section, it is possible to increase the heat transfer area in comparison to other-shaped heat exchanger pipe having the same size of outer pipe (i.e., tube) and it is possible to prevent coming-off when inserting and pressing heat exchanger fins in the outer pipe. 
     In detail, the case of an elliptical heat exchanger pipe, as in the present invention, and the case of other-shaped heat exchanger pipe, that is, a circular or oblong heat exchanger pipe, etc. are compared hereafter. 
       FIGS.  16 A to  16 C  are plan views showing the elliptical heat exchanger pipe according to the eighth embodiment of the present invention and an another-shaped heat exchanger pipe. 
       FIG.  16 A  is a plan view showing a common circular heat exchanger pipe having a circular cross-section,  FIG.  16 B  is an elliptical heat exchanger pipe  240  of the present invention, and  FIG.  16 C  is an oblong heat exchanger pipe having an oblong cross-section. 
     First, the circular heat exchanger pipe shown in  FIG.  16 A  has a very small radius of curvature, so even if the diameter is physically increased, a large number of heat exchanger fins cannot be efficiently disposed and the number of heat exchanger fins that can be received in one circular heat exchanger pipe is very small. 
     Further, if the lengths D 2  and D 3  of the apsidal lines of the elliptical heat exchanger pipe shown in  FIG.  16 B  and the oblong heat exchanger pipe shown in  FIG.  16 C  are the same (D 2 =D 3 ), it is possible to increase the heat transfer area of the elliptical heat exchanger pipe. 
     That is, for example, when the width of heat exchanger fins of the elliptical heat exchanger pipe is increased, sixteen heat exchanger fins provide the same heat transfer effect as seventeen heat exchanger fins of the oblong heat exchanger pipe. 
     Accordingly, it can be seen that the elliptical heat exchanger pipe  240  of the present invention needs a relatively small number of heat exchanger fins to provide the same heat transfer area rather than increasing the width of the heat exchanger fins in comparison to the oblong heat exchanger pipe. 
     The oblong heat exchanger pipe has straight portions spaced in parallel and curved portions connecting the ends of the straight portions, and in this case, it is difficult to manufacture the oblong heat exchanger pipe because coming-off occurs between the heat exchanger fins and the straight portions when the heat exchanger fins are inserted into the oblong heat exchanger pipe and heat transfer does not normally occur if a defect is generated. 
     However, the elliptical heat exchanger pipe  240  of the present invention has only a round portion without a straight portion in the entire shape, coming-off described above is prevented in the manufacturing process, thereby considerably increasing the heat transfer rate (i.e., heat exchange rate). 
     Further, several heat exchanger fins  242  are provided in the present invention, are disposed on a line extending from a side to the other side of the inner circumferential surface of the heat exchanger tube  241 , and are spaced in the direction of the apsidal line of the heat exchanger tube  241 . 
       FIGS.  17 A and  17 B  are plan views showing other examples of the heat exchanger pipe according to the eighth embodiment of the present invention. 
     According to another embodiment of the present invention, as shown in  FIGS.  17 A and  17 B , some of heat exchanger fins  242  are ‘discontinuous type heat exchanger fins  242   a ’ that are disconnected at the middle portions in the longitudinal direction and the others are ‘continuous type heat exchanger fins  242   b ’ that are entirely continuous in the longitudinal direction. 
     Accordingly, the discontinuous type heat exchanger fins  242   a  increase the amount of flow of fluid such as combustion gas and fluctuates flowing fluid, thereby increasing the heat exchange rate. 
     On the contrary, the continuous type heat exchanger fins  242   b  prevent deformation of the heat exchanger tube  241 , increase productivity, and provide divided exhaust loads that divide and discharge fluid. This is because the continuous type heat exchanger fins  242   b  provide a strong supporting force (or reinforcing force) and divide the inside of the heat exchanger tube  241 . 
     In detail, the continuous type heat exchanger fins  242   b  are integrally formed (or two tub ends are bonded to each other) across the inside of the heat exchanger tube  241 , they are used as reinforcing members inserted between the straight portions of the heat exchanger tube  241 . Therefore, they prevent deformation of the heat exchanger tube  241 . 
     Further, when the heat exchanger tube  241  deforms, gaps is generated between the heat exchanger fins  242  and the heat exchanger tube  241  and thermal contact is removed, this problem is solved by one design change rather than improving repeated processes or adding processes, so productivity is improved. 
     Further, since the inside of the heat exchanger tube  241  is divided into a plurality of sections by the continuous type heat exchanger fins  242   b , one heat exchanger pipe actually provides a plurality of heat exchanger pipes and fluid such as combustion gas is separately discharged. 
     In particular, the heat exchanger tube  2241  may include a ‘continuous fin group G 1 ’ in which one or more continuous heat exchanger fins  242   b  are continuously disposed. 
     For example, as shown in  FIGS.  17 A and  17 B , a continuous fin group G 1  composed of three continuous type heat exchanger fins  242   b  are continuously disposed in the heat exchanger tube  241  is provided. 
     Obviously, the number of the continuous type heat exchanger fins  242   b  included in one continuous fin group G 1  may be variously adjusted, for example, as two, four, or five. 
     However, the larger the number of the continuous type heat exchanger fins  242   b  included in the continuous fin group G 1 , the larger the reinforcing force and the more the deformation of the heat exchanger tube  241  is prevented, but the number of the discontinuous type heat exchanger fins  242   a  decreases, so it is required to appropriately adjust the number of the continuous type heat exchanger fins. 
     Further, at least one (i.e., one or more) continuous fin group G 1  is provided and may be disposed between the sections composed of discontinuous type heat exchanger fins  242   a.    
     That is, since the inside of the heat exchanger tube  241  is divided by the continuous fin group G 1 , a ‘discontinuous fin group G 2 ’ composed of discontinuous type heat exchanger fins  242   a  and another ‘continuous fin group G 1 ’ may be alternately disposed. 
     For example, as shown in  FIG.  17 A , one continuous fin group G 1  is disposed at the entry in the apsidal line of the heat exchanger tube  241 , discontinuous type heat exchanger fins  242   a  are disposed in each of the left and right sections divided by the continuous fin group. 
     When two continuous fin groups G 1  are provided, a discontinuous type heat exchanger fin  242   a  is disposed in each of the section between the two spaced continuous fin groups G 1  and the sections outside the continuous fin groups G 1 , so more continuous fin groups G 1  can be provided in this way. 
     However, the number and lengths of discontinuous type heat exchanger fins  242   a  sequentially disposed in the section divided by the continuous fin group G 1  may be adjusted such that the ends of the discontinuous type heat exchanger fins  242   a  make an S-shape when they are sequentially connected by a virtual line. 
     The S-shape may be formed by one discontinuous fin group G 2  or adjacent or spaced several discontinuous fin groups G 2 . 
     Accordingly, fluid fluctuates in an S-shape in the sections in which the separate type heat exchanger fins  242   a  are disposed, so he heat exchange rate further increases. 
     A hot water storage type heat exchanger having an elliptical heat exchanger pipe having the above configuration according to an embodiment of the present invention is described hereafter. 
       FIG.  18    is a perspective view showing a hot water storage type heat exchanger having the elliptical heat exchanger pipe according to the eighth embodiment of the present invention. 
     As shown in  FIG.  18   , a hot water storage type heat exchanger  200  having an elliptical heat exchanger pipe according to the present invention includes a heat exchanger body  210  having a water storage space therein. 
     The heat exchanger body  210  has an inlet IN at a lower portion through which low-temperature raw water (or pre-heated water) flows inside and an outlet OUT at an upper portion through which hot water or heating water heated through heat exchange is discharged. 
     A downward type burner (see  2151  in  FIG.  2   ) is disposed on the heat exchanger body  210  and a predetermined space defined inside the upper portion of the heat exchanger body  210  is used as a combustion chamber  211  into which a flame and combustion gas are spouted. 
     A top end plate  220 -T, a bottom end plate  220 -B, a circular heat exchanger pipe  230 , and an elliptical heat exchanger pipe  240  are disposed in the heat exchanger body  210 . 
     The top end plate  220 -T and the end plate  220 -B are spaced up and down a predetermined distance apart from each other in the heat exchanger body  210 , and the circular exchanger pipe  230  and the elliptical heat exchanger pipe  240  are vertically fitted between the plates. 
     The hot water storage type heat exchanger having this configuration according to the present invention enables heat exchange between combustion gas in the heat exchanger body  210  and raw water outside the body, and the raw water heated by heat exchange is supplied as hot water or heating water. 
     To this end, the combustion chamber  211  over the top end plate  220 -T is exposed to a burner  2151  in  FIG.  3    and the bottom end plate  220 -B is connected to the exhaust port  2140  in  FIG.  3   , so high-temperature combustion gas produced in the burner is discharged outside through the heat exchanger pipes  230  and  240 . 
       FIG.  19    is a plan view showing the hot water storage type heat exchanger having the elliptical heat exchanger pipe according to the eighth embodiment of the present invention. 
     As shown in  FIGS.  18  and  19   , the top end plate  220 -T has a disc shape and has a first top stage  220   a -T at the center and a second top stage  220   b -T around (i.e., outside) the first top stage  220   a -T. 
     A plurality of circular fitting-holes is formed through the first top stage  220   a -T to fit the heat exchanger pipes  230  and elliptical fitting-holes are formed through the second top stage  220   b -T to fit the elliptical heat exchanger pipe  240 . 
     Similarly, the bottom end plate  220 -B also has disc shape and has a first bottom stage at the center and a second bottom stage around (i.e., outside) the first bottom stage. 
     The bottom end plate  220 -B is disposed at the lower end of the heat exchanger body  210  and is spaced in parallel downward from the top end plate  220 -T. Accordingly, a water chamber is defined in the space surrounded by the top end plate  220 -T, the bottom end plate  220 -B, and the heat exchanger body  210  and the heat exchanger pipes  230  and  240  are disposed in the water chamber. 
     In the bottom end plate  220 -B, similar to the top end plate  220 -T, circular fitting-holes in which a plurality of circular heat exchanger pipes  230  is fitted are formed through the first bottom stage and elliptical fitting-holes in which a plurality of elliptical heat exchanger pipes  240  is fitted are formed through the second bottom stage. 
     The upper and lower open ends of the circular heat exchanger pipe  230  are connected to the top end plate  220 -T and the bottom end plate  220 -B, respectively. Since the circular heat exchanger pipes  230  are circular pipes having a circular cross-section, so they are fitted in the circular fitting-holes of the top end plate  220 -T and the bottom end plate  220 -B. 
     In particular, the circular heat exchanger pipes  230  are disposed at the center portions of the top and bottom end plates  220 -T and  220 -B. That is, the upper ends of the circular heat exchanger pipes  230  pass through the first top stage  220   a -T of the top end plate  220 -T and the lower ends pass through the first bottom stage of the bottom end plate  220 -B. 
     Heat exchanger fins are disposed in the circular heat exchanger pipe  230 , similar to the elliptical heat exchanger pipe  240  described above. The heat exchanger fins increase a heat transfer amount by increasing the contact surface area with combustion gas. 
     The upper and lower open ends of the elliptical heat exchanger pipe  240  are connected to the top end plate  220 -T and the bottom end plate  220 -B, respectively. Since the elliptical heat exchanger pipes  240  are elliptical pipes having an elliptical cross-section, so they are fitted in the elliptical fitting-holes of the top end plate  220 -T and the bottom end plate  220 -B. 
     In particular, the circular heat exchanger pipes  240  are disposed at the outer portion between the top and bottom end plates  220 -T and  220 -B. That is, the upper ends of the elliptical heat exchanger pipes  240  pass through the second top stage  220   b -T of the top end plate  220 -T and the lower ends pass through the second bottom stage of the bottom end plate  220 -B. 
     Further, as described with reference to  FIGS.  15 ,  16   , etc., the heat exchanger fins  242  are inserted in the elliptical heat exchanger pipe  240 , thereby increasing the contact surface are with combustion gas and the heat transfer amount. 
     Since the long radius of the elliptical heat exchanger pipe  240  is two times larger or more than the radius of the circular heat exchanger pipe  230 , the heat transfer area is considerably wide, and short radius of the elliptical heat exchanger pipe  240  is also larger than the radius of the elliptical heat exchanger  240 . 
     Accordingly, the elliptical heat exchangers  240  are disposed outside (i.e., in the second state of) the end plate having a large circumference and the circular heat exchanger pipes  230  are disposed at the center (i.e., in the first stage) of the end plate having a small circumference. 
     Accordingly, the heat transfer area by the entire heat exchanger pipes  220  and  230  to the outer diameter of the entire hot water storage type heat exchanger is considerably increased by the elliptical heat exchangers  240 , and a relatively small number of heat exchanger pipes are used to provide the same thermal efficiency, whereby it is possible to reduce the size of the hot water storage type heat exchanger. 
     Further, a plurality of elliptical heat exchanger pipes  240  is circumferentially arranged along the second top stage  220   b -T and the second bottom stage. 
     Accordingly, the ratio of the entire cross-sectional area of the elliptical heat exchanger pipes  240  to the entire area of the second top stage  220   b -T (or the second bottom stage) is very large. 
     That is, density of the elliptical heat exchanger pipes  240  increases, so the heat transfer area further increases and the heat exchange rate further increases. 
     Further, the top end plate  220 -T of the present invention may be a multi-stage top end plate  220 -T of which the second top stage  220   b -T is higher than the first top stage  220   a -T. 
     Accordingly, when a heat source (e.g., flame and combustion gas) produced by the burner is circumferentially spouted, the distances to the first top stage  220   a -T and the second top stage  220   b -T are uniform. 
     Therefore, concentration of heat transfer at a specific portion in the water chamber in the heat exchanger body  210  is prevented, so low-temperature raw water is uniformly heated. 
     The interface  220   c -T between the first top stage  220   a -T and the second top stage  220   b -T of the multi-stage top end plate  220 -T is sloped (indicated by a dotted line). 
     The sloped interface  220   c -T enables smooth flow of fluid such as combustion gas, so combustion gas increases thermal efficiency while they are guided to the circular heat exchanger pipes  230  and the elliptical heat exchanger pipes  240 . 
     The bottom end plate  220 -B of the present invention is also a multi-stage bottom end plate  220 -B of which the second bottom stage is higher than the first bottom stage and the multi-stage bottom end plate  220 -B has the same steps as the multi-stage top end plate  220 -T. 
       FIG.  20    is a front view showing the hot water storage type heat exchanger having the elliptical heat exchanger pipe according to the eighth embodiment of the present invention. 
     Since the first bottom stage at the center of the bottom end plate  220 -B is lower than the second bottom stage disposed around the first bottom stage, only the first bottom stage is shown when seen from the front, as shown in  FIG.  20   . 
     Accordingly, since the circular heat exchanger pipes  230  and the elliptical heat exchanger pipes  240  are the same in length, the distances that the combustion gas flows through the circular heat exchanger pipes  230  and the elliptical heat exchanger pipes  240  are the same, so it uniformly transmits heat to the entire inside of the water tank  1120 . 
     Specific embodiments of the present invention were described above. However, it would be understood by those skilled in the art that the spirit and scope of the present invention are not limited to the specific embodiments and the present invention may be modified in various ways without departing from the spirit of the present invention. Therefore, the embodiments described above are provided to completely let those skilled in the art of the scope of the present invention, so the embodiments should be understood as only example not limiting the present invention and the present invention is defined only by the range of claims.