Abstract:
A flat or a flared tubular end portion devoid of dimples is provided at the end of a tube  11  which is to be inserted into a header with the length, of the flat tubular portion being 1.5 mm or less along the direction of the length of the tube to prevent rapid reduction and enlargement of the cross-sectional area of the refrigerant path in the vicinity of the joint of the tube and the header, so as to reduce the pressure loss of the refrigerant which flows in and out from the header to the tube. A tube insertion stop is also provided consisting either, of a cut formed in the longitudinal edge of the flat end portion or a guard member which is formed aft of the flared, end portion so as to abut the header and seal off the tube insertion aperture of the header.

Description:
This application is based on Japanese Patent Application No. Hei 11-60230. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a heat exchanger arranged in an air conditioner for a vehicle or the like. 
     2. Description of the Related Arts 
     In a conventional heat exchanger in an air conditioner for a vehicle, a tube for a heat exchanger as shown in FIG. 10 has been used. This tube is manufactured by an extrusion process, then, a plurality of thin tubes are located inside the tube by forming a plurality of partitions  2  in a flat tube  1  when extruding. 
     Since a tube like the above is molded by extrusion, it is difficult to form the flat tube  1  and the partitions  2  so that they are thin, therefore, some problems have been observed, for example, a large amount of materials for the tube is required, therefore, production costs increase and the heat exchanging property cannot be improved because of the flat tube  1  and the partitions  2  have thick walls. 
     Recently, a tube for a heat exchanger to take the place of the above extruded tube, a tube such as shown in FIG. 11 has been proposed. A tubular portion  3  as this type of tube is formed by the steps of bending a flat plate in two, forming the upper and lower walls  4   a  and  4   b  roughly in parallel, overlapping the side edges of the upper and lower walls  4   a  and  4   b,  and brazing the overlapped side edges. The tubular portion  3  is characterized in that, since dimples (cavities)  5  are formed on the outer surfaces of the upper and lower walls  4   a  and  4   b,  the dimples  5  protrude inward when the dimples  5  are observed from the inside of the tubular portion  3  and a plurality of columns  6  are formed between the walls  4   a  and  4   b  by closely contacting the inner top of the dimple  5  formed on the either side wall to the inner top of the dimple  5  formed on the other side wall. By arranging the columns  6  in the tubular portion  3 , turbulent flow occurs in the refrigerant which runs through the tubular portion  3 . Therefore, its heat exchanging property is improved. 
     According to the dimple tube mentioned above, since the tubular portion is formed by bending a flat plate in two, the walls of the dimple tube can be thin. This provides several advantages, e.g., less material is used in the dimple tube, production costs decrease, and the heat exchanging property is improved. Furthermore, the columns  6  consisting of the dimples  5  are regularly arranged in the dimple tube along the length direction, so that a sufficient amount of pressure is obtained even if the thickness of the walls of the dimple tube are thin. This type of dimple tube will be introduced in air conditioners for vehicles in the future. 
     FIG. 12 shows a cross section of a part of the heat exchanger using the dimple tube. The ends of dimple tube  7  are inserted into a header  8  having a hollow cylindrical shape through a tube inserting hole  8   a  where they are joined by brazing. 
     One of the factors determining the heat exchanging property is pressure loss depending on rapid reduction and enlargement of the cross-sectional area of the refrigerant path when, for example, in the joint of the dimple tube  7  and the header  8  shown in FIG. 12, the refrigerant flows into the dimple tube  7  from the header  8  and the refrigerant flows into the header  8  from the dimple tube  7 . This is because a plurality of dimples  5  are formed from one end to the other end of the dimple tube in a conventional dimple tube  7  and the columns  6  consisting of the dimples  5  reduce the opening area of the end of the dimple tube  7 , so that the cross-sectional area of the refrigerant path is rapidly reduced or enlarged when the refrigerant flows through a joint of the dimple tube  7  and the header  8 , therefore, pressure loss is increased. 
     BRIEF SUMMARY OF THE INVENTION 
     In the light of the above, an object of the present invention is to provide a heat exchanger wherein rapid reduction and enlargement of the refrigerant path are prevented when the refrigerant flows at the joint of the dimple tube and the header and pressure loss of the refrigerant which flows into and out of the header to the tube is reduced. 
     To achieve the above object, the present invention provides a heat exchanger comprising a tube containing an upper wall and a lower wall arranged roughly in parallel, an overlap width, a path for a refrigerant, a plurality of protrusions protruding toward the path arranged on at least one of the inner surfaces of the upper and lower walls, and a plurality of columns formed by contacting the tops of the protrusions to the inner surface of the other wall and a header having a hollow cylindrical shape so that both ends of the tube are put into the header through a tube inserting hole and joined by brazing; wherein a flat tubular portion without the protrusions is provided at the end of the tube to be inserted into the header and the length of the flat tubular portion is 15 mm or less along the direction of the length of the tube. 
     Furthermore, the length of the flat tubular portion may be from 5 to 15 mm. 
     Moreover, the overlap width may have a cut portion. 
     In this heat exchanger, since the flat tubular portion without columns is provided at the end of the tube, the opening area of the end of the tube is not reduced thereby. Therefore, rapid reduction and enlargement of the refrigerant path are presented when the refrigerant flows through the vicinity of the joint of the tube and the header and pressure loss of the refrigerant which flows into and out of the header to the tube is reduced. 
     Furthermore, as to another aspect, the present invention provides a heat exchanger comprising: a tube containing an upper wall and a lower wall arranged roughly in parallel and consisting of a part of a path for a refrigerant, a plurality of protrusions protruding toward the path arranged on at least one of inner surfaces of the upper and lower walls, and a plurality of columns formed by contacting the tops of the protrusions to the inner surface of the other wall and a header having a hollow cylindrical shape in which both ends of the tubes are put into the header through a tube inserting hole and joined by brazing; wherein the tube includes a flared outer end portion and a guard or stop located intermediate the protrusions and the end portion and closing the tube inserting hole by contacting the side of the header when the tube is inserted in the tube inserting hole. 
     In this heat exchanger, since an expanded tubular portion is provided, the area of the open end of the tube is larger than the cross-sectional area of the refrigerant path in the tube without the expanded tubular portion. Therefore, rapid reduction and enlargement of the cross-sectional area of the refrigerant path are prevented in the vicinity of the joint of the tube and the header and pressure loss of the refrigerant which flows in and out from the header to the tube is reduced. Since the tube inserting hole is required to be larger than the expanded tubular portion, the guard is located at the end of the tube and seals off the tube inserting hole, so that the refrigerant is prevented from leaking. 
     According to the present invention, since a portion of the tube without columns is provided at the end of the tube, the opening area of the end of the tube is not reduced by the columns. Therefore, rapid reduction and enlargement of the cross-sectional area of the refrigerant path are further prevented at the vicinity of the joint of the tube and the header, and pressure loss of the refrigerant which flows in and out from the header to the tube is reduced. 
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
     FIG. 1 is a front view of a heat exchanger in accordance with the first embodiment of the present invention. 
     FIG. 2 is a perspective view of a tube for the heat exchanger shown in FIG.  1 . 
     FIG. 3 is a cross-sectional view taken on line III—III in FIG.  2 . 
     FIG. 4 is a traverse sectional view of a joint of a header and a tube. 
     FIGS. 5A-5D are illustrative of the manufacturing process for producing the heat exchanger shown in FIG.  1 . 
     FIG. 6 is a longitudinal cross-sectional view of a joint of the header and the tube shown in FIG.  5 D. 
     FIG. 7 is a perspective view of a tube for the heat exchanger in accordance with a second embodiment of the present invention. 
     FIG. 8 is a perspective view of a joinder of a header and a tube for the heat exchanger shown in FIG.  7 . 
     FIG. 9 is a longitudinal cross-sectional view of the joinder of the header and the tube for the heat exchanger shown in FIG.  8 . 
     FIG. 10 is a perspective view of an example of a conventional extrusion molding tube for a heat exchanger. 
     FIG. 11 is a perspective view of an example of a conventional dimpled tube. 
     FIG. 12 is a longitudinal cross-sectional view of a joint of a header and a dimple tube shown in FIG.  11 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The first embodiment of the heat exchanger of the present invention is described in detail with reference to FIGS. 1 to  6 . 
     As shown in FIG. 1, a heat exchanger  10  of the present invention is a parallel flow type heat exchanger and comprises a plurality of flat tubes  11  which are arranged apart from each other roughly in parallel, a pair of headers  12  and  13  which are inserted at both ends of corresponding tube  11  and connect with the refrigerant path in the tube, and fins  14  for cooling which have a corrugated shape and are arranged between the tubes  11 . 
     The header  12  is internally separated into two parts with a partition plate  15  which is arranged below the center of the header  12 . In the upper part of the header  12 , a refrigerant inlet pipe  16  is connected to the header  12 . In the lower part of the header  12 , a refrigerant outlet pipe  17  is connected to the header  12 . Therefore, as shown by the arrows in FIG. 1, the refrigerant passing through the tube  11  flows from the header  12  to the header  13  in the area a above the partition plate  15  and flows from the header  13  to the header  12  in the area b below the partition plate  15 . 
     As shown in FIG. 2, the tube  11  is formed by bending a flat plate  20  in two, forming the upper and lower walls  21  and  22  roughly in parallel, and brazing the overlapping side edges of the upper and lower walls to each other so as to form a tubular shape. In the tube  11 , the upper wall  21  and the lower wall  22  are separated from each other roughly in parallel and a refrigerant path  23  is formed between the upper and lower walls  21  and  22 . 
     Furthermore, in the tube  11 , dimples  24  are formed by pressing the upper and the lower walls  21  and  22  inwardly from the outside. When these dimples  24  are formed, a plurality of inward protrusions  25  are formed at the walls  21  and  22 , that is, in the refrigerant path  23 . 
     These protrusions  25  are elliptical in shape, having their larger diameter along the length direction when the walls  21  and  22  of the tube  11  are observed in a plane view. Furthermore, as shown in FIG. 3, since opposing surfaces  25   a  are in mutual contact, a column  26  whose transverse cross-section is also elliptical in shape is provided between the upper and lower walls  21  and  22 . The shape of the column  26  may be not only an ellipse, but also a circle or a race track shape. 
     As shown in FIG. 4, the protrusions  25  are arranged so that two protrusions obliquely arrayed adjacent to each other along the length direction of the tube  11  are partly overlapped along the length direction of the tube  11 , so that the protrusions  25  on the tube  11  form a zigzag-like pattern. Similarly, protrusions  25  are also provided in the other tubes and columns  26  are formed by this arrangement. Furthermore, the end of the tube  11  to be inserted into the header  12  is flat without any columns  26  so as to provide a flat tubular portion  27  whose inner walls do not have an irregular shape. 
     As shown in FIGS. 2 and 4, the tube  11  includes an overlap width  30  which is brazed at the side edges of the tube  11 . A part of the end of the overlap width  30  is cut off so as to provide a cut portion  34  so that both ends of the tube  11  can be inserted into the headers  12  and  13  respectively. On the other hand, a plurality of tube inserting holes  36  whose shapes are the same as the shape of the end of the tube  11  are formed at the header  12  for receiving other tubes therein. Furthermore, a groove  37  is formed at one side of these tube inserting holes  36  so as to receive the cut portion  34  of the overlap width  30  in the header  12 . 
     The width w 1  of the tube inserting hole  36  is approximately the same as the width w 2  of the tube  11  comprising the cut portion  34  and the width w 3  of the tube  11  comprising the overlap width  30  is wider than the width w 1  or w 2 . Accordingly, when the end of the tube  11  is inserted into the tube inserting hole  36 , the step between the overlap width  30  and the cut portion  34  touches the surface of the header  12 , therefore, the overlap width  30  cannot be further inserted and thus acts as a stop. 
     Next, a manufacturing process of the heat exchanger  10  having the above structure is described in detail with reference to FIG.  5 . 
     As shown in FIG. 5A, a flat plate  20  is prepared to form the tube  11 , a brazing filler metal is clad on both surfaces of the flat plate  20 , and the cut portion  34  is formed at the edges of the flat plate  20 . The cut portion  34  is formed after bending the flat plate  20  in two. 
     As shown in FIG. 5B, protrusions  25  are formed in the flat plate  20  by press molding or roll molding so that the protrusions  25  are formed at the inside of the tube  11 . A width for bending  40  is formed at a bending portion, and the overlap widths  30  are formed at both edges of the tube  11 . The protrusions  25  are not formed at the outer end portion  27 . 
     As shown in FIG. 5C, the flat plate  20  is bent in two along the width  40  for bending. The flat plate  20  bent in two now becomes the tube  11  having a flat shape by putting together the overlap widths  30  and the tops  25   a  of the protrusions  25  so they face each other. 
     As shown in FIG. 5D, the header  12 ( 13 ) including the tube inserting hole  36  is prepared and the end of the tube  11 , namely, the flat tubular portion  27 , is inserted into the header  12 ( 13 ). During assembly of the heat exchanger  10 , corrugated fins  14  are fitted between tubes  11 . The assembled heat exchanger  10  is next put into a furnace (not shown) and heated to a predetermined temperature for a predetermined time, so that the brazing filler metal clad onto the flat plate  20  fuses and brazes each portion of the heat exchanger  10 , that is, both overlap widths  30 , the tops  25  of the protrusions  25  facing each other, both ends of the tube  11  and the tube inserting holes  36  of the header  12  ( 13 ), and the portions where the tube  11  and the corrugated fins  14  touch each other are brazed. The fabrication of the heat exchanger  10  is now complete. 
     In the heat exchanger  10  prepared by the above process, as shown in FIG. 6, since the flat tubular portion  27  without columns  26  is located at the end of the tube  11  so as to be inserted into the header  12  ( 13 ), the area of the opening at the end of the dimple tube  7  inserted in the header is not narrow but relatively wide as shown. On the other hand, the area of the opening at the end of the conventional dimple tube is relatively narrow. Accordingly, rapid reduction and enlargement of the cross-sectional area of the refrigerant path  23  is prevented and pressure loss is reduced. 
     The length X of the flat tubular end portion  27  is preferably 15 mm or less, more preferably, 5 mm≦X≦15 mm. If the length X is more than 15 mm, the deterioration of the heat exchanging property due to the decreased number of dimples  24  (protrusions  25 ) is bigger than the effect of reduction of the pressure loss, and if the length X is less than 5 mm, the opening area of the tube  11  is narrowed because the columns  26  approach the end of the tube  11 . 
     The second embodiment of the heat exchanger of the present invention will be described in detail with reference to FIGS. 7 to  9 . The elements in the second embodiment already described in the above first embodiment are given the same reference numbers and the explanations of these elements are omitted. 
     In the heat exchanger  10  of the second embodiment, an end portion having no columns  26  is located at the end of the tube  11  where it is to be inserted into the header  12  ( 13 ). An expanded tubular portion  28  which is flared so as to have a funnel-shape and which gradually expands toward the end of the tube  11  is formed thereat, and a guard  29  which also acts as a tube insertion stop is fitted onto the end portion having no columns  26  between the expanded tubular portion  28  and the tube  11  having columns  26 . The guard  29  seals off the tube inserting hole  36  by closely contacting the side of the header  12  ( 13 ). The expanded tubular portion  28  and the guard  29  are formed by molding the flat plate.  20  using press molding or roll molding similar to the protrusions  25  or the like. Furthermore, the guard  29  may be formed by welding the other member at the end of the tube  11  using bead molding. 
     The tube inserting hole  36  is formed so as to have the same size as the circumference of the expanded tubular portion  28  to be inserted into the header  12 . Furthermore, the guard  29  is formed to be larger than the expanded tubular portion  28  and has the same shape as the curved shape of the header  12  ( 13 ) so as to completely seal the tube inserting hole  36  by the guard  29 . 
     The tube  11  comprising the expanded tubular portion  28  mentioned above is arranged so that the guard  29  contacts the surface of the header  12  as shown in FIG. 8 when the heat exchanger  10  is assembled. Heating the tube  11  in the furnace, the brazing filler metal fuses and brazes the guard  29  and the header  12  as well as the other portions for brazing so that the tube inserting hole  36  is sealed. 
     In the heat exchanger  10  formed according to the above and as shown in FIG. 9, by providing an expanded tubular portion  28  at the end of the tube  11  which is to be inserted into the header  12  ( 13 ), the area of the opening of the tube  11  is formed larger than the cross-sectional area of the remaining refrigerant path  23 . Moreover; since the expanded tubular portion  28  is formed in a funnel-shape, rapid reduction and enlargement of the refrigerant path  23  is prevented and pressure loss is reduced. 
     Furthermore, the guard  29  forms an integral portion of the tube  11  in the second embodiment and is adapted to close the tube inserting hole  36  when the heat exchanger  10  assembled and brazed so as to seal the tube inserting hole  36 .