Abstract:
A heat exchanger tube, which has a high pressure resistance, includes a tube body, wherein the interior of the tube body defines a fluid flow passage. The inner and outer surfaces of the tube body of the heat exchanger tube defines heat entrance and exit surfaces for the fluid. The tube body of the heat exchange tube has first and second wall portions which are opposed to each other. Either the first wall porition has a plurality of bowl-shaped bulging wall portions which bulge toward the direction of the second wall portion to fixedly meet the second wall portion or else both the first and second wall portion both have a plurality of bowl-shaped bulging wall portions which are correspondingly located so that a bulging leading end of a bowl-shaped bulging wall portion in a first wall portion bulges toward and fixedly meets a bulging leading end of a bowl-shaped bulging wall portion in the second wall portion which bulges toward the first wall portion.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is related to and claims priority, under 35 U.S.C. §119, from Japanese Patent Application No. 2000-013400, filed on Jan. 21, 2000, the entire contents of which are hereby incorporated by reference herein. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a heat exchanger tube preferably used for a heat exchanger tube for a cooling medium or the like which constitutes a condenser of an air conditioner or a refrigerator. 
     This application is based on Japanese Patent Application No. 2000-13400, the contents of which are incorporated herein by reference. 
     2. Discussion of Background 
     In a cooling device such as an air conditioner or a refrigerator or the like, a cooling medium (fluid) of Freon or the like is first compressed to form a high temperature and high pressure gas and is then liquefied by cooling the gas with a condenser. In the condenser is incorporated a heat exchanger tube through which a cooling medium flows, and a high temperature and high pressure gaseous cooling medium is gradually cooled by heat dissipation while passing through the tube so that it is condensed into a liquid. As this kind of heat exchanger tubes, a heat exchanger tube shown in FIG. 10 or the like has been known. A tube body  7  is constituted by a solder material-cladded band-shaped metallic plate member  1  being folded or bent with a fold  2  in a direction of its extension, connecting end portions  5 ,  5 , which are mutually brought into contact with end portions of one wall portion  3  and the other wall portion  4  folded and extended in the same direction, are formed and are welded thereto, and a cooling medium passage  6  is formed between these wall portions. 
     Further, the curvature radius of the fold  2  is smaller than the width of the wall portion  3  or  4 , and the distance between the wall portions  3  and  4  is smaller than the width of the wall portion  3  or  4 . This shape is defined to reduce the time required for heat dissipation by decreasing the distance from the center of the tube body  7  to the wall portion. 
     The thus formed interior defines a cooling medium passage  6 . A plurality of bulging wall portions  8 ,  8  . . . bulging in a bowl shape toward a direction of the opposite wall portions are formed on both opposite wall portions  3  and  4  of the tube body  7  in which the inner surface and the outer surface are defined as the heat entrance and exit surfaces for the cooling medium, and bulging leading ends of the bulging wall portions  8 ,  8  . . . are defined as connecting portions  9 ,  9  . . . The connecting portions  9 ,  9  . . . are brought into contact with opposite bulging wall portions in a plane and are welded by soldering. A cooling medium that flows in the interior of the tube is caused to generate a turbulent flow by these bulging wall portions  8 ,  8  . . . and is uniformly agitated within the tube body so that the temperature distribution of a fluid in a plane vertical to the flow is made uniform. Further, the opposite wall portions  3  and  4  are connected to each other by the plurality of welded bulging wall portions  8 ,  8  . . . and are supported against a pressure applied to the wall portions  3  and  4  of the flat tube body  7  when a high pressure cooling medium flows in the tube, thereby enhancing the pressure resistance of the tube body  7 . 
     However, the above-mentioned conventional heat exchanger tube has the following problems. 
     Since the tube body is formed by folding a band-shaped metallic plate member with a fold, it tends to be deformed by an effect of the spring back at the fold, that is, the restoration of the bent portions, in such a manner that the opposite wall portions are separated from each other. 
     On the other hand, the opposite cooling medium agitating bulging portions bulging in bowl shapes are soldered in a plane at the connecting portions brought into contact with each other. However, when an oxide film formed on the surface of a solder material has been separated for soldering with flux, the bulging portion has a structure making discharge of the separated oxide film from the outer periphery of the surface-shaped connecting portion difficult. Thus, it is actually difficult to solder at the center of the connecting portion. 
     Therefore, in addition to the circumstances of difficult soldering, when a force which separates the opposite wall portions by the spring back is applied to the tube body, firm welding is not performed at the connecting portion between the bulging wall portion leading ends. As a result, the tube body has no support against the pressure of the cooling medium, whereby the pressure resistance of the tube body deteriorates. 
     SUMMARY OF THE INVENTION 
     The present invention was made in consideration of the above-mentioned circumstances. The object of the present invention is to provide a heat exchanger tube having an improved soldering process and high pressure resistance by forming a structure which easily discharges an oxide film separated with flux, and prevents the deformation of the tube body due to the spring back effect. 
     A first aspect of the invention relates to a heat exchanger tube having the tube body whose interior is defined as a passage of a fluid and whose inner and outer surfaces are defined as heat entrance and exit surfaces of the fluid and is characterized in that a bulging wall portion bulging toward a direction of opposite wall portions is formed on one or both of the opposite wall portions of said tube body, the bulging leading ends of said bulging wall portions are defined as connecting portions linearly protruding and said connecting portions are linearly brought into contact with the opposite wall portions and are fixed thereto. 
     By providing such a configuration, a soldering material oxide separated with flux at the connecting portion of the leading end of the bulging wall portion flows out of a linear connecting portion whereby soldering is improved and the opposite wall portions are firmly soldered without occurrence of a weld failure. 
     A second aspect of the invention relates to a heat exchanger tube, and is characterized in that it provides a first bulging wall portion bulging in a bowl shape in a direction of wall portions opposite to said bulging wall portion, with a plurality of said first bulging wall portions being formed on said tube body. 
     By providing such a configuration, the opposite wall portions are connected to each other at a plurality of positions by a plurality of first bulging wall portions. Further, a fluid flowing in the interior of the tube generates a turbulence flow with the plurality of first bulging wall portions and is uniformly agitated in the tube body. 
     A third aspect of the invention relates to a heat exchanger tube, and is characterized in that a plurality of protrusions with triangular sections protruding linearly in the direction of the extension of the tube body are formed on the inner surface of said tube body in such a manner that they are adjacent to each other, said protrusions being defined as said connecting portions. 
     By providing such a configuration, positions which are linearly soldered are increased at the connecting portions of the leading ends of the first bulging wall portions where opposite wall portions are connected to each other. Thus, the opposite wall portions are firmly connected to each other. 
     Further, since the surface area of the inner surface of the tube body defined as the heat entrance or exit surface is increased, a contact area with the fluid is increased. 
     A fourth aspect of the invention relates to a heat exchanger tube, and is characterized in that it provides a second bulging wall portion including a first extending portion extending toward the direction of wall portions opposite from one reference position of the wall portion to serve as said bulging wall portion, a return portion which is folded back from said first extending portion to the direction of said reference position and a second extending portion which is folded back from the return portion to said one reference position of the wall portion. 
     By providing such a configuration the folded portion of the second bulging wall portion and the opposite wall portions are linearly brought into contact with each other in a direction of the extension of the tube body, a soldering length is increased and the soldering material oxide separated from flux speedily flows out of the linear connecting portion whereby soldering can be improved. Thus, the opposite wall portions are firmly connected to each other. 
     A fifth aspect of the invention relates to a heat exchanger tube, and is characterized in that said tube body is formed by a band-shaped plate member extending in one direction, said plate member is defined as said one wall portion in the intermediate portion of the plate member in the width direction and is folded with two folds in a direction of the extension of the tube body in both end portions of said one wall portion, said folded portions are extended to each other in an adjacent direction to form the other wall portion, said folded portion is further folded in a direction of said one wall portion at a contact position and is extended toward the same direction of said one wall portion to form a third extending portion, the end portion of said third extending portion being brought into contact with said other wall portion and being fixed thereto. 
     By providing such a configuration the end portion of the third bulging wall portion and the other wall portion are linearly brought into contact with each other in a direction of the extension of the tube body, the soldering length is increased, and the soldering material oxide separated from flux speedily flows out of the linear connecting portion whereby soldering can be improved. Thus, the opposite wall portions are firmly connected to each other. 
     Further, since the weld surface in the third extending portion composed of a mutual contact portion is pressed from both sides by the pressure of a fluid flowing in the passage to be press bonded, the pressure resistance is enhanced. 
     A sixth aspect of the invention relates to a heat exchanger tube, and is characterized in that an opening portion for allowing the fluid passages partitioned with said third extending portion to communicate with each other is formed in said third extending portion. 
     By providing such a configuration a fluid flowing through the tube body is passed between the passages of a fluid divided with the third extending portion, whereby it flows through the entire interior of the tube body. 
     A seventh aspect of the invention relates to a heat exchanger tube, and is characterized in that said tube body comprises a pair of plate members extending in the direction of the extension of said tube body, the plate members are formed so that the passage for said fluid is formed between the plate members, and the plate members have connected end portions overhanging on each side, on both respective end portions, the respective connected end portions of these plate members being brought into contact with each other and being fixed thereto. 
     By providing such a configuration, both the wall portions of the tube body are formed with a pair of band-shaped plate members. Thus, to form both wall portions it is not necessary to fold a band-shaped plate member by 180 degrees with a fold in a direction of the extension of the plate member. The spring back is increased with the magnitude of the bending angle. Accordingly, a bending angle required for forming the tube body is decreased and a force which acts on the wall portion by the spring back is decreased. 
     A eighth aspect of the invention relates to a heat exchanger tube, and is characterized in that said connecting end portion is fastened with a U-shaped folded fastening plate member. 
     By providing such a configuration the connecting portions which are brought into contact with each other in a plane and are soldered therewith are externally reinforced with a fastening plate member, and a force due to the spring back applied to the weld surface or a force due to the fluid pressure is reduced. 
     A ninth aspect of the invention relates to a heat exchanger tube having the tube body whose interior is defined as a passage for a fluid and whose inner and outer surfaces are defined as heat entrance and exit surfaces for the fluid and is characterized in that in said tube body a band-shaped plate member is folded with a fold in the direction of the extension of the plate member, a passage of said fluid is formed between one wall portion and the other wall portion extending in the same direction by the folding, a plurality of spring back preventing portions where said one and the other wall portions are brought into contact with each other and are fixed in said folded portion is formed, connecting end portions brought into contact with each other are formed on the end portions of said one and the other wall portions, and said connecting end portions are fixed. 
     By providing such a configuration a force which causes the tube body to deform by the spring back is locally acted on the spring back preventing portion and the magnitude of the force of separating opposite wall portions is reduced. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING FIGURES 
     FIG. 1 is a view showing a first embodiment of the present invention that is a perspective view showing one example of a heat exchanger tube; 
     FIG. 2 is a view showing a first embodiment of the present invention that is a perspective view showing another example (first example) of a heat exchanger tube; 
     FIG. 3 is a view showing a second embodiment of the present invention that is a perspective view showing one example of a heat exchanger tube; 
     FIG. 4 is a view showing a second embodiment of the present invention that is a perspective view showing another example (first example) of a heat exchanger tube; 
     FIG. 5 is a view showing a second embodiment of the present invention that is a perspective view showing another example (second example) of a heat exchanger tube; 
     FIG. 6 is a view showing a second embodiment of the present invention that is a perspective view showing another example (third example) of a heat exchanger tube; 
     FIG. 7 is a view showing a third embodiment of the present invention that is a perspective view showing one example of a heat exchanger tube; 
     FIG. 8 is a view showing a third embodiment of the present invention that is a perspective view showing another example (first example) of a heat exchanger tube; 
     FIG. 9 is a view showing a fourth embodiment o f the present invention that is a perspective view showing another example of a heat exchanger tube; and 
     FIG. 10 is a perspective view showing one example of a conventional heat exchanger tube. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     First to fourth embodiments of a heat exchanger tube according to the present invention will now be described with reference to drawings. 
     First Embodiment 
     A first embodiment of a heat exchanger tube according to the present invention is shown in FIG.  1 . In a heat exchanger tube A shown in FIG. 1, a tube body  70  is configured in such a manner that a soldering material-cladded band-shaped metallic plate member  10  is folded with a fold  20  in a direction of the extension of the plate member, connecting portions  50 ,  50 , which are brought into contact with each other, are formed at end portions of one wall portion  30  and the other wall portion  40  extending in the same direction by the folding and then are welded (fixed) by soldering to form a cooling medium passage  60  between these wall portions. Further, the connecting portions  50 ,  50  welded by soldering are fastened and fixed with a U-shaped folded fastening plate member  51  formed by the extension of the one connecting end portion  50 . 
     Such an interior of the tube body  70  defines the cooling medium passage  60 . A plurality of bowl-shaped bulging wall portions (first bulging wall portions)  80 ,  80  . . . bulging toward the direction of the opposite wall portions in bowl-shapes are formed on both opposite wall portions  30  and  40  of the tube body  70 , the inner surface and the outer surface of the wall portion being defined as the heat entrance and exit surfaces for the fluid. 
     On the inner surface of the tube body  70  are formed adjacently to each other with triangle-shaped cross-sections with a sharp vertical angle a plurality of protrusion members  100 ,  100  . . . linearly extending in a direction of the extension of the tube body  70 , which is smaller than the bowl-shaped bulging wall portions  80 ,  80  . . . , and the protrusion members  100 ,  100  . . . are defined as connecting portions  90 ,  90  . . . at the bulging leading ends of the bowl-shaped bulging wall portions  80 ,  80  . . . Opposite bowl-shaped bulging portions  80 ,  80  are linearly brought into contact with each other by the protrusion members  100 ,  100  at these connecting portions  90 ,  90  to be soldered to each other. 
     In the heat exchanger tube A having this configuration, oxides of the soldering material separated by flux speedily flow out of the linear contact portions of the plurality of protrusion members  100 ,  100  . . . at the leading end connecting portions  90 ,  90  of the bowl-shaped bulging wall portions  80 ,  80  so as to allow improved soldering. Accordingly, the opposite wall portions  30  and  40  can be connected to each other without occurrence of weld failures. Further, the opposite wall portions  30  and  40  are further firmly connected to each other at positions by the plurality of the bowl-shaped bulging wall portions  80 ,  80  . . . 
     Furthermore, a fluid flowing in the passage  60  generates turbulence flows at the plurality of the bowl-shaped bulging wall portions  80 ,  80  . . . Thus, the fluid is uniformly agitated in the tube body  70 . 
     According to the heat exchanger tube A shown in FIG. 1, superior soldering is carried out at the leading end connecting portions  90  and  90  of the bowl-shaped bulging wall portions  80 ,  80  . . . , which connects opposite wall portions  30  and  40  to each other, so that strong weld is obtained. Further, by providing these bowl-shaped bulging wall portions  80 ,  80  . . . at a plurality of positions, the opposite wall portions  30  and  40  are further firmly connected to each other by a high pressure resistance that is imparted to the tube body. 
     Further, the connecting end portion is externally fixed with the fastening plate member  51 , and a deformation of the tube body due to the spring back is prevented so that the welding is easily carried out, and after the formation of the tube body, a force due to the flow pressure applied to the connecting end portion is decreased so that a high pressure resistance is imparted to the tube body. 
     Further, since the fluid is agitated, a temperature of the fluid in a plane vertical to the flow can be made uniform. Additionally, since the surface area of the inner surface is increased by the plurality of protrusion members  100 ,  100  . . . , the contact surface area between the fluid and the tube body is increased and the thermal conductivity from the fluid to the tube body can be improved. 
     Alternatively, as shown in FIG. 2, the heat exchanger tube A may be configured so that it is composed of a pair of band-shaped plate members  11  and  12  extending in the direction of the extension of the tube body  70 , a passage  60  of the fluid is formed between these plate members  11  and  12 , the heat exchanger tube A is formed so as to have connecting portions  50 ,  50  and  52 ,  52  extending to the sides at the respective both end portions, the respective connecting portions of these plate members are welded and fastened to each other by U-shaped folded fastening plate members  51  and  53  respectively. 
     In the heat exchanger tube A having said configuration, one wall portion  30  and the other wall portion  40  of the tube body are formed by a pair of band-shaped plate members  11  and  12 . Therefore, to form the both wall portions  30  and  40  it is not necessary to fold one band-shaped plate member by 180 degrees with a fold in a direction of the extension of the plate member. The spring back is increased with the increase of the bending angle. Thus, by reducing the bending angle required for the formation of the tube body the force which acts on the wall portion by the spring back is also reduced. 
     Further, connections at the connecting end portions are reinforced with the fastening plate members  51  and  53  and the force applied to the soldered or welded surface of the connecting end portion due to the fluid pressure is reduced. 
     As described above, according to the heat exchanger tube A shown in FIG. 2, effects due to the spring back are reduced. Accordingly, reliable soldering can be performed while maintaining the shape of the tube body, and a higher pressure resistance can be imparted to the tube body. 
     Second Embodiment 
     FIG. 3 shows a second embodiment of a heat exchanger tube according to the present invention. A heat exchanger tube B shown in FIG. 3 includes a wedge-shaped bulging wall portion  200  (second bulging wall portion) composed of an extending portion  201  (first extending portion) extending from the wall portion reference position  30   a  (one wall portion reference position) of the wall portion  30  to the direction of the opposite wall portion  40 , a folded portion  202  folded from the extending portion  201  to the reference position and an extending portion  203  (second extending portion) which is folded back from the folded portion  202  to the wall portion reference position  30   a.    
     Further, the folded portion  202  of the wedge-shaped bulging wall portion  200  and the opposite wall portion  40  are linearly brought into contact with each other in the direction of the extension of the tube body  70 , and the leading end (bulging end) of the folded portion  202  of the wedge-shaped bulging wall portion  200  defines a connecting portion  90  and is welded to each other by soldering. 
     In the heat exchanger tube B shown in FIG. 3 portions corresponding to the portions shown in FIGS. 1 and 2 respectively are denoted by the same reference numerals and the details thereof are omitted. 
     Thus, in the heat exchanger tube B having the above-mentioned configuration, the length of the soldered portion in a direction of the extension of the tube body  70  is increased and soldering material oxides separated by flux speedily flow out of the linear connecting portion to obtain better soldering. Accordingly, the weld is strengthened so that the opposite wall portions are firmly connected to each other. 
     According to the heat exchanger tube B shown in FIG. 3, the opposite wall portions  30  and  40  are firmly connected to each other and a high pressure resistance can be imparted to the tube body. 
     Alternatively, as shown in FIG. 4, the heat exchanger tube B may be configured so that it is composed of a pair of band-shaped plate members  11  and  12  extending in the direction of the extension of the tube body  70 , a passage  60  for the fluid is formed between these plate members  11  and  12 , the exchanger tube B is formed so as to have connecting portions  50 ,  50  and  52 ,  52  extending to the sides at the both respective end portions, the both respective connecting portions of these plate members are welded to each other and fastened to each other with U-shaped folded fastening plate members  51  and  53  respectively. 
     In the heat exchanger tube B having said configuration, one wall portion  30  of the tube body and the other wall portion  40  thereof are formed by a pair of band-shaped plate members  11  and  12 . Therefore, to form both wall portions  30  and  40 , it is not necessary to fold one band-shaped plate member by  180  degrees with a fold in a direction of the extension of the plate member. The spring back is increased with the increase of the bending angle. Thus, by reducing the bending angle required for the formation of the tube body, the force which acts on the wall portion by the spring back is also reduced. 
     Further, the fastening plate members  51  and  53  strengthen the connection at the connecting end portions, thereby reducing a force applied by the fluid pressure onto the welded surface of the connecting end portions. 
     According to the heat exchanger tube B shown in FIG. 4, the effects due to the spring back are reduced. Accordingly, reliable soldering can be performed while maintaining the shape of the tube body, and a higher pressure resistance can be imparted to the tube body. 
     Alternatively, as shown in FIGS. 5 and 6, a heat exchanger tube B may be formed by a band-shaped plate member  10  or a pair of band-shaped plate members  11  and  12 , wedge-shaped bulging wall portions  200 ,  200  are provided on both sides of opposite wall portions  30  and  40 , and the leading ends (bulging leading ends) of these wedge-shaped bulging wall portions  200 ,  200  are linearly brought into contact with each other in a direction of the extension of the tube body  70  at the respective folded portions  202 ,  202  to form a connecting portion  90  and are welded by soldering. 
     Alternatively, although each of the heat exchanger tubes shown in FIGS. 3 to  6  has a configurations provided with a single wedge-shaped bulging wall portion, they may have a plurality of bulging wall portions. 
     Third Embodiment 
     FIG. 7 shows a third embodiment of a heat exchanger tube according to the present invention. A heat exchanger tube C shown in FIG. 7 is formed with a band-shaped plate member  10  extending in one direction. The plate member  10  is defined as a wall portion  40  in the intermediate portion in the width direction of the plate member  10  and is folded with two folds  21  and  22  in the direction of the extension of the tube body  70  at both the ends of the wall portion  40 . The folded portions  31  and  32  are extended in their closing directions to form the other wall portion  30 . Further, the portions  31  and  32  are bent in the direction of the wall portion  40  at the contact position  30   b  and are extended in the direction of the wall portion  40  to form extending portions  300 ,  300  (third extending portions). The end portions  301 ,  301  of the extending portions  300 ,  300  are brought into linear contact with the wall portion  40  in a direction of the extension of the body tube  70  to be welded to each other by soldering, and serves as a connecting portion  90 . 
     In the heat exchanger tube C shown in FIG. 7, portions corresponding to the portions shown in FIGS. 1 to  6  respectively are denoted by the same reference numerals and the details thereof are omitted. 
     Thus, in the heat exchanger tube C having the above-mentioned configuration, the length of the soldered portion in a direction of the extension of the tube body  70  is increased and soldering material oxides separated by flux speedily flow out of the linear connecting portion to obtain better soldering. Accordingly, the weld is strengthened so that the opposite wall portions are firmly connected to each other. 
     Further, the weld surfaces in the extending portions  300 ,  300  brought into contact with each other are pressed from both sides by the pressure of fluid flowing in the passage  60 ,  60 , and a pressure resistance is enhanced. 
     According to the heat exchanger tube C shown in FIG. 7, both end portions of the band-shaped plate member are directly used as bulging wall portions. Therefore, a simple configuration can be obtained without the need to provide a new bulging wall portion, and since the seam of the plate member at the connecting portion is welded to the tube body, the pressure resistance can be enhanced. 
     Thus, by the welding of the extending portions  300 ,  300  at the connecting portion  90  separation of the opposite wall portions  30  and  40  is prevented and a high pressure resistance can be imparted to the tube body. 
     Alternatively, in the heat exchanger tube C, openings  400 ,  400  . . . which are allowed to lead to fluid passages  60 ,  60  divided with the extending portions  300 ,  300  may be formed in the extending portions  300 ,  300 , as shown in FIG.  8 . 
     According to the heat exchanger tube C shown in FIG. 8, a fluid flows through the entire interior of the tube body  70 . Thus, the difference between temperatures of the fluid do not occur between the passages  60 ,  60  divided with the extending portions  300 ,  300 . 
     Fourth Embodiment 
     FIG. 9 shows a fourth embodiment of a heat exchanger tube according to the present invention. In a heat exchanger tube D shown in FIG. 9, a band-shaped plate member  10  is folded with a fold  20  in a direction of its extension, and the folded portions  500 ,  500  of the wall portions  30  and  40  include a plurality of spring back prevention portions  503 ,  503  . . . welded to each other in contact surfaces  501  and  502 . 
     In the heat exchanger tube D shown in FIG. 9, portions corresponding to the portions shown in FIGS. 1 to  8  respectively are denoted by the same reference numerals and the details thereof are omitted here. 
     In the heat exchanger tube D having the above-mentioned configuration, the spring back force that deforms the tube body  70  is locally added to the spring back prevention portions  503 ,  503  and the magnitude of the force due to the spring back which separates the opposite portions  30  and  40  are decreased. 
     According to the heat exchanger tube D shown in FIG. 9, the spring back effect is reduced by a simple reinforcement to deform the shape of a fold. Thus, reliable soldering can be performed while keeping the shape of the tube body and a higher pressure resistance can be imparted to the tube body. 
     Alternatively, the heat exchanger tubes A, B, and C shown in FIGS. 1,  3 ,  5 ,  7  and  8  may have a configuration in which the spring back prevention portions as shown in FIG. 9 can be provided on the folded portions of the band-shaped plate members. 
     By providing such spring back prevention portions, reliable soldering can be performed while maintaining the shape of the tube body and a higher pressure resistance can be imparted to the tube body. 
     The present invention exhibits the following effects. 
     As described above, according to the heat exchanger tube according to a first aspect, opposite wall portions are firmly connected to each other and a high pressure resistance can be imparted to the tube body. 
     According to the heat exchanger tube according to a second aspect, opposite wall portions are firmly connected to each other at a plurality of positions by the first bulging wall portions and a higher pressure resistance can be imparted to the tube body. 
     Further, since the plurality of first bulging wall portions agitate a fluid flowing through the interior of the tube body, a distribution of a fluid temperature in the plane vertical to the direction of the flow can be made uniform. 
     According to the heat exchanger tube according to a third aspect, the connection between the leading ends of the first bulging wall portions which connects opposite wall portions can be reinforced by a plurality of protrusion members and a high pressure resistance can be imparted to the tube body. Further, since the surface area of the inner surface of the tube body is increased, the thermal conductivities from a fluid to the tube body can be enhanced. 
     According to the heat exchanger tube according to a fourth aspect, the opposite wall portions can be linearly connected to each other by better soldering with the second extending portions and a high pressure resistance can be imparted to the tube body. 
     According to the heat exchanger tube according to a fifth aspect, the opposite wall portions can be linearly connected to each other by better soldering with the third extending portions and a high pressure resistance can be imparted to the tube body. 
     Further, since the both end portions of band-shaped plate members can be used as bulging wall portions as they are, the configuration of the tube body can be simplified without the need to provide bulging wall portions by bending and a seam of the plate member can be welded to the tube body and the pressure resistance can be further enhanced. 
     According to the heat exchanger tube according to a sixth aspect, a fluid flowing in the interior of the tube body can freely flow through the interior of the tube body. Therefore, a difference between fluid temperatures between passages divided by extending portions is prevented. 
     According to the heat exchanger tube according to a seventh aspect, since the spring back force for deforming the tube body is reduced, reliable soldering can be performed while keeping the shape of the tube body, and a higher pressure resistance can be imparted to the tube body. 
     According to the heat exchanger tube according to an eighth aspect, the connections at the connecting end portions are reinforced with a fastening plate member, and a higher pressure resistance can be imparted to the tube body. 
     According to the heat exchanger tube according to a ninth aspect, by a simple reinforcement to deform the shape of a fold, reliable soldering can be performed while maintaining the shape of the tube body, and a higher pressure resistance can be imparted to the tube body.