Abstract:
A heat exchanger for a refrigeration cycle that in terms of functionality and quality is within the allowable range of and comparable to a conventional heat exchanger for a refrigeration cycle, has substantially the same structure as a conventional heat exchanger for a refrigeration cycle, and enables reduced costs, as well as method for manufacturing the heat exchanger are provided. A heat exchanger for a refrigeration cycle is configured so that a refrigerant discharged from a compressor is circulated to a condenser, a capillary tube, an evaporator, a suction pipe, and the compressor, and so that the external surfaces of the capillary tube and the suction pipe are thermally in contact with each other. The material of the capillary tube and the suction pipe is aluminum. The locations at which the external surfaces of the capillary tube and the suction pipe are joined where fillets of a brazing material being an Al—Si alloy and a Zn—Al alloy are formed.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a National Stage application of International Application No. PCT/JP2011/073331, filed on Oct. 11, 2011, which claims priority of Japanese application Serial Number 2010-231617 filed on Oct. 14, 2010, Japanese application Serial Number 2010-268579 filed on Dec. 1, 2010 and Japanese application Serial Number 2011-007757 filed on Jan. 18, 2011, all of which are incorporated herein by reference in their entireties. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to a heat exchanger for a refrigeration cycle used in, for instance, refrigerators, and a manufacturing method for the same. 
         [0004]    2. Background Art 
         [0005]    In general, a refrigerator has a refrigeration cycle that refrigerant discharged from a compressor passes through a condenser, capillary tube, an evaporator, and a suction pipe in order and returns to the compressor. 
         [0006]    The refrigerant compressed in the compressor is converted into gas of high temperature and pressure and sent to the condenser, and radiates heat in the condenser so as to be liquefied. The liquefied refrigerant is sent to the evaporator after passing through the capillary tube. The liquefied refrigerant sent from the capillary tube to the evaporator is evaporated by the evaporator and takes heat around the refrigerant so as to generate cold air. The evaporated refrigerant passes through the suction pipe, and then, returns to the compressor so as to be compressed again. 
         [0007]    In the above refrigeration cycle, the refrigerant passing through the capillary tube has relatively high temperature. In order to improve cooling efficiency, it is effective to reduce temperature of the refrigerant introduced into the evaporator from the capillary tube. For this, well-known is a method of abutting the suction pipe in which refrigerant of relatively lower temperature flows on the capillary tube. That is, heat exchange is carried out between the refrigerant of the suction pipe and the refrigerant of the capillary tube so as to reduce the temperature of the refrigerant flowing in the capillary tube. In order to connect the capillary tube and the suction pipe with each other in the heat exchanger for the refrigeration cycle, a method of soldering the capillary tube and the suction pipe in a state where they abut on each other in parallel has been frequently used. 
         [0008]    The capillary tube is generally a thin tube which is about Φ0.6 mm to Φ0.8 mm in inner diameter and is about Φ2.0 mm to Φ3.0 mm in outer diameter, and the suction pipe is a round pipe which is about Φ4.5 mm to Φ6.5 mm in inner diameter and is about Φ6.0 mm to Φ8.0 mm in outer diameter. Moreover, the capillary tube and the suction pipe are respectively about 2,000 mm to 5,000 mm in length, but their lengths may be changed according to sizes of refrigerators. 
         [0009]    In the case of heat exchangers for the refrigeration cycle equipped in refrigerators on the market all over the world including Japan, the suction pipe made of copper and the capillary tube made of copper are joined integrally with each other in a state where their external surfaces are in thermal contact with each other. The copper-made suction pipe and the copper-made capillary tube have been practically applied up to now because they have high heat-exchanging efficiency and excellent corrosion resistance and are easy to be connected integrally by soldering. 
         [0010]    Various patent documents, for instance, the patent documents 1, 2 and 5 respectively disclose improved heat exchangers, in which a copper-made suction pipe and a copper-made capillary tube are in thermal contact with each other by soldering. Moreover, the patent document 7 discloses a heat exchanger in which a copper-made suction pipe and a copper-made capillary tube are in thermal contact with each other by seam welding. 
         [0011]    In the patent document 3, materials for the suction pipe and the capillary tube are not described, but judging by the description, “the capillary tube is soldered with the suction pipe to form a counter current flow heat exchanger”, it seems that the suction pipe and the capillary tube are respectively made of copper. In the patent document 5, the material for the capillary tube is not described, but judging by the description, “the suction pipe and the capillary tube are in thermal contact with each other to a predetermined distance by soldering so as to heat-exchange each other and the portion of the suction pipe, which gets in thermal contact with the capillary tube, is made of metal such as copper”, it seems that the capillary tube is also made of copper. Such a view that the suction pipe and the capillary tube of the heat exchanger described in the patent documents 3 and 5 are all made of copper can be sufficiently accepted through the description of paragraph [0011] to [0012] in the patent document 6, “In order to connect the suction pipe and the capillary tube, soldering is generally carried out using tin(Sn). Moreover, in order to improve heat-exchanging efficiency and corrosion resistance between the suction pipe and the capillary tube, the suction pipe and the capillary tube are generally made of copper.” 
         [0012]    The patent document 1 relates to a refrigerator which carries out heat-exchanging between the suction pipe and the capillary tube. The capillary tube and the suction pipe are all made with copper pipes, and are in thermal contact with each other by soldering in a state where they are attached to each other in parallel. 
         [0013]    The patent document 2 relates to an improved multiplex heat exchanger used in refrigerators. The multiplex heat exchanger includes a fluid flow pipe (outer pipe) and another fluid flow pipe (inner pipe) arranged inside the outer pipe, and carries out heat-exchange of a fluid. In the patent document 2, it is described that preferably, the fluid flow pipe (outer pipe), which corresponds to the suction pipe, and the fluid flow pipe (inner pipe), which corresponds to the capillary tube, are made of copper or copper alloy which has excellent plastic working, thermal conductivity, brazing performance, soldering performance, and corrosion resistance, and so on. 
         [0014]    The patent document 3 relates to a refrigerator which carries out heat-exchanging between the suction pipe and the capillary tube. The capillary tube and the suction pipe are attached to each other in parallel and soldered to form the counter current flow heat exchanger. 
         [0015]    The patent document 4 relates to a heat exchanger applicable to a refrigeration circuit of a refrigerator. The heat exchanger uses a capillary tube made of copper alloy and a suction pipe made of aluminum alloy. Because the capillary tube and the suction pipe are made of metal of different kinds, if moisture is attached to the heat exchanger, a local cell is formed between the different metals, and hence, the heat exchanger may be corroded. Therefore, in a state where the copper alloy-made capillary tube and the aluminum alloy-made suction pipe are attached to each other in parallel, melted aluminum-silicon series brazing filler metal is poured onto the capillary tube and the suction pipe and is coagulated. Accordingly, the copper alloy-made capillary tube and the aluminum alloy-made suction pipe are joined together thermally, and at the same time, the outer circumferences of the capillary tube and the suction pipe are continuously covered with the brazing material. 
         [0016]    The patent document 5 relates to a refrigeration system for preventing dew condensation by the refrigeration cycle. Because the suction pipe is made of metal such as copper which has excellent thermal conductivity, dew condensation is likely to occur. In order to solve the above problem, a part of the suction pipe is made of resin with thermal conductivity lower than metal such as copper. The suction pipe and the capillary tube are in thermal contact with each other to a predetermined distance by soldering so as to carry out heat-exchange. The thermal contact portion of the suction pipe is made of metal such as copper, but the remaining portion except the thermal contact portion is made of resin with high gas barrier efficiency. 
         [0017]    The patent document 6 relates to a suction pipe assembly with an improved thermal conductivity. The suction pipe assembly includes a capillary tube disposed therein and a heat transfer pipe having a contact portion disposed on the outside of the suction pipe assembly for widening a contact area with a suction pipe, and the contact portion of the heat transfer pipe is connected to the outer circumference of the suction pipe by thermally conductive adhesives. Because the contact area between the heat transfer pipe and the suction pipe is increased, heat-exchange is effectively carried out between refrigerant moving in the suction pipe and refrigerant moving in the capillary tube inserted into the heat transfer pipe. The capillary tube is made of copper, but may be made of aluminum or steel, and the heat transfer pipe may be made of aluminum or one of various materials. The suction pipe may be made of copper or aluminum, but it is preferable that the suction pipe is made of steel which has excellent machinability and bending property and is relatively inexpensive. If the suction pipe is made of steel and is plated with a corrosion-resistant material, an industrially applicable suction pipe with corrosion resistance can be made. In the embodiment of the patent document 6, the steel-made suction pipe, the copper-made capillary tube, and the aluminum-made heat transfer pipe are used. 
         [0018]    The patent document 7 relates with a method for connecting a suction pipe and a capillary tube in a thermal contact with each other by welding. In detail, a part of the suction pipe protrudes from the outer circumferential surface of a copper pipe of the suction pipe by plastic deformation, so that a pair of protrusions extending in the pipe axis direction are formed at a spaced interval, which is almost equal to the outer diameter of the capillary tube, in a circumferential direction. After that, the copper pipe of the capillary tube is arranged between the protrusions, and the protrusions are joined to the capillary tube by seam welding. 
       CITED REFERENCE 
       [0019]    Japanese Patent Laid-open No. 2002-130912 
         [0020]    Japanese Patent Laid-open No. 2006-292182 
         [0021]    Japanese Patent Laid-open No. 2008-121980 
         [0022]    Japanese Patent Laid-open No. 2008-267757 
         [0023]    Japanese Patent Laid-open No. 2009-41810 
         [0024]    Japanese Patent Publication No. 2010-525297 
         [0025]    Japanese Patent Laid-open No. 2001-248979 
       SUMMARY OF THE INVENTION 
       [0026]    Cost reduction of products is a permanent task in the manufacturing industry. If cost reduction of the heat exchangers for the refrigeration cycle is realized, cost reduction of refrigerators as products can be also realized. In order to realize the cost reduction of the refrigerators as the products, it is demanded that functions and quality of the heat exchanger suffer nothing by comparison with a conventional heat exchanger within a permissible range. Moreover, people should avoid improving the heat exchanger so as to change the structure into a refrigeration cycle system or changing the entire structure of the refrigerator. For this, the improved heat exchanger must has substantially the same structure as a conventional heat exchanger, namely, the shapes of the suction pipe and the capillary tube, for instance, the inner diameter, the outer diameter, the length of the pipe or the tube) of the heat exchanger must be kept in the permissible range. 
         [0027]    The inventors of the present invention have judged that it was possible to provide a cost-reducible heat exchanger for a refrigeration cycle, which suffers nothing by comparison with a conventional heat exchanger with the refrigeration cycle, has the same structure as a conventional heat exchanger for the refrigeration cycle in fact, if the suction pipe and the capillary tube may be made of aluminum instead of copper, the heat exchanger for the refrigeration cycle. 
         [0028]    In the case that the base materials, which have extremely different diameters, like the suction pipe and the capillary tube are soldered or brazed, it is preferable to use a soldering material or a brazing material having a large difference in melting point between the base materials and the soldering material or the brazing material. In the case of soldering, because there is a large difference in melting point between an aluminum material which is the base material and the soldering material, the external surface of the suction pipe and the external surface of the capillary tube can be connected with each other without any influence on the base material. However, the heat exchanger for the refrigeration cycle in which the aluminum-made suction pipe and the aluminum-made capillary tube are joined with each other by aluminum soldering (for instance, Sn—Zn alloy) has a problem in corrosion resistance, and hence, cannot avoid deterioration of the connected portion under usage environment, and needs a anticorrosion treatment in order to prevent the deterioration. 
         [0029]    In the case that aluminum materials are bonded by a brazing material selected from Al—Si alloy or Zn—Al alloy, it has no problem in corrosion resistance, and hence, does not need the anticorrosion treatment for protecting the bonded portion. However, in the case that a thin aluminum-made capillary tube with length of 2,000 mm to 3,000 mm and an extremely thick aluminum-made suction pipe are attached with each other in parallel and heated, it is difficult to raise heat of the suction pipe and the capillary tube to the same temperature due to a thermal capacity difference between the suction pipe and the capillary tube, and if the brazing temperature is raised to a proper temperature, the thin capillary tube may be overheated to thereby be melted and damaged. 
         [0030]    In the patent document 7, the copper-made suction pipe and the copper-made capillary tube are joined with each other by seam welding. In order to connect the copper-made suction pipe and the copper-made capillary tube with each other, welding such as seam welding or arc welding may be applied. However, if an aluminum-made suction pipe and an aluminum-made capillary tube are used instead of the copper-made suction pipe and the copper-made capillary tube, it is impossible to connect them by seam welding or arc welding. 
         [0031]    The reason is as follows. Because the specific heat (0° C.) of copper is 0.880 J/g·K, the specific heat (0° C.) of aluminum is 0.379 J/g·K, the specific gravity (20° C.) of copper is 8.96, and the specific gravity (20° C.) of aluminum is 2.71, the copper-made suction pipe is 7.7 times more in thermal capacity than the aluminum-made suction pipe, and likewise, the copper-made capillary tube is 7.7 times more in thermal capacity than the aluminum-made capillary tube. Accordingly, even though the same thermal capacity is applied, the copper material is less in temperature change than the aluminum material. Furthermore, because the melting point of copper is about 1083° C. and the melting point of the aluminum is about 660° C., it is possible to connect the copper-made suction pipe and the copper-made capillary tube with each other by seam welding or arc welding, but if the aluminum-made suction pipe and the aluminum-made capillary tube are joined with each other by seam welding or arc welding, the thin capillary tube may be overheated to thereby be melted and damaged. 
         [0032]    For reasons mentioned above, till now, in my opinion, there has been no proposal of the heat exchanger for the refrigeration cycle using the aluminum-made capillary tube and the aluminum-made suction pipe. 
         [0033]    Accordingly, the present invention has been made to solve the above-mentioned problems occurring in the prior arts, and it is an object of the present invention to provide a heat exchanger for a refrigeration cycle and a manufacturing method of the heat exchanger, which includes a suction pipe and a capillary tube respectively made of aluminum, instead of the copper-made suction pipe and the copper-made capillary tube of a conventional heat exchanger for the refrigeration cycle, thereby suffering nothing in functions and quality within the permissible range by comparison with a conventional heat exchanger for the refrigeration cycle, having substantially the same structure as a conventional heat exchanger, providing excellent productivity, and reducing manufacturing costs. 
         [0034]    The inventors have judged that if a brazing temperature can be raised to a proper temperature uniformly in a state where a brazing material selected from Al—Si alloy or Zn—Al alloy is supplied to the connected portion and the aluminum-made suction pipe and the aluminum-made capillary tube which are coated with flux are attached to jigs in parallel, it could solve the problem that the capillary tube is overheated to thereby be melted and damaged, and hence, invented the present invention. 
         [0035]    To achieve the above objects, the present invention provides a heat exchanger for a refrigeration cycle, which is configured so that a refrigerant discharged from a compressor is circulated, in order, to a condenser, a capillary tube, an evaporator, a suction pipe, and the compressor, and so that the external surface of the capillary tube and the external surface of the suction pipe are thermally in contact with each other, wherein the capillary tube and the suction pipe are all made of aluminum material, and the locations at which the external surface of the capillary tube and the external surface of the suction pipe are joined are in a state where fillets of a brazing material selected from an Al—Si alloy and a Zn—Al alloy are formed. 
         [0036]    In another aspect of the present invention, the present invention provides a manufacturing method of a heat exchanger for a refrigeration cycle, which is configured so that a refrigerant discharged from a compressor is circulated, in order, to a condenser, a capillary tube, an evaporator, a suction pipe, and the compressor, and so that the external surface of the capillary tube and the external surface of the suction pipe are thermally in contact with each other, including: 1) a process of preparing a work piece on a jig: (a) the work piece is arranged on the jig in a state where the aluminum-made suction pipe and the aluminum-made capillary tube are attached in parallel; and (b) the work piece is coated with flux to which a brazing material selected from an Al—Si alloy or a Zn—Al alloy is supplied; 2) a process of inserting the work piece prepared on the jig into a brazing furnace preheated; 3) a process of heating the work piece and melting the brazing material so as to form fillets at the portion where the suction pipe and the capillary tube are joined with each other; and 4) a process of cooling the work piece so as to coagulate the fillets. 
         [0037]    In the case that the aluminum-made suction pipe and the aluminum-made capillary tube are brazed by the high frequency induction heating method, when high frequency induction heating is carried out, if the external surface of the suction pipe and the external surface of the capillary tube which are attached in parallel are in contact with each other, because temperature of the suction pipe becomes almost equal to temperature of the capillary tube, even though the brazing temperature is raised to a proper temperature, the thin capillary tube is not melted and damaged due to overheat. 
         [0038]    According to the second manufacturing method of the heat exchanger for the refrigeration cycle, the present invention provides a manufacturing method of a heat exchanger for a refrigeration cycle, which is configured so that a refrigerant discharged from a compressor is circulated, in order, to a condenser, a capillary tube, an evaporator, a suction pipe, and the compressor, and so that the external surface of the capillary tube and the external surface of the suction pipe are thermally in contact with each other, wherein a brazing material selected from Al—Si alloy or Zn—Al alloy is supplied, and while a work piece, which is in a state where an aluminum-made suction pipe and an aluminum-made capillary tube coated with flux are attached in parallel, moves relatively into a high frequency induction heating coil in a state where the external surfaces of the suction pipe and the capillary tube are welded together with pressure, the external surface of the suction pipe and the external surface of the capillary tube are heated by the high frequency induction heating coil so that the brazing material is melted and fillets are formed at the connected portion of the suction pipe and the capillary tube, and then, the work piece is cooled so as to coagulate the fillets. 
         [0039]    The second manufacturing method will be described in more detail. The manufacturing method of a heat exchanger for a refrigeration cycle, which is configured so that a refrigerant discharged from a compressor is circulated, in order, to a condenser, a capillary tube, an evaporator, a suction pipe, and the compressor, and so that the external surface of the capillary tube and the external surface of the suction pipe are thermally in contact with each other, including: 1) a process of preparing a work piece on a jig: (a) the work piece is arranged on the jig in a state where the aluminum-made suction pipe and the aluminum-made capillary tube are attached in parallel; and (b) the work piece is coated with flux to which a brazing material selected from an Al—Si alloy or a Zn—Al alloy is supplied; 2) a process of transferring the work piece prepared on the jig to a work piece maintaining device in which a member abutting on the work piece is arranged inside a high frequency induction heating coil: (a) the work piece maintaining device comprises: a suction pipe pressing member pressing the side of the suction pipe, which is one side of the work piece, toward the capillary tube, which is the other side of the work piece; and a capillary tube pressing member pressing the side of the capillary tube toward the suction pipe; 3) a process of transferring the work piece to the high frequency induction heating coil by the work piece maintaining device in the state where the external surfaces of the aluminum-made suction pipe and the aluminum-made capillary tube are welded together with pressure, heating the external surfaces of the suction and the capillary tube by the high frequency induction heating coil so as to melt the brazing material and form fillets at the connected portion of the suction pipe and the capillary tube; and 4) a process of cooling the work piece so as to coagulate the fillets. 
         [0040]    In the state where the external surface of the aluminum-made suction pipe and the external surface of the aluminum-made capillary tube are welded together with pressure, the welded portion is heated by a small spot heat source within a short period of time without having any thermal influence on the suction pipe and the capillary tube, and so, the heat exchanger for the refrigeration cycle with excellent heat-exchanging performance can be manufactured. 
         [0041]    In other words, in the case that the external surface of the aluminum-made suction pipe and the external surface of the aluminum-made capillary tube are melted and connected together, when laser welding is carried out using laser beams as a heat source in the state where the external surfaces of the suction pipe and the capillary tube are welded together with pressure, the thin capillary tube is not deformed or melted and damaged due to overheat by minimizing a thermal influence on the suction pipe and the capillary tube. 
         [0042]    The present invention provides a heat exchanger for a refrigeration cycle which is configured so that a refrigerant discharged from a compressor is circulated, in order, to a condenser, a capillary tube, an evaporator, a suction pipe, and the compressor, and so that the external surface of the capillary tube and the external surface of the suction pipe are thermally in contact with each other, wherein the capillary tube and the suction pipe are all made of aluminum material, and the external surface of the capillary tube and the external surface of the suction pipe are joined are in a state where the external surfaces are melted. 
         [0043]    According to the second manufacturing method of the heat exchanger for the refrigeration cycle, the present invention provides a manufacturing method of a heat exchanger for a refrigeration cycle, which is configured so that a refrigerant discharged from a compressor is circulated, in order, to a condenser, a capillary tube, an evaporator, a suction pipe, and the compressor, and so that the external surface of the capillary tube and the external surface of the suction pipe are thermally in contact with each other, including the steps of: i) pressing an aluminum-made suction pipe and an aluminum-made capillary tube by a pressure jig in a state where they are attached in parallel, so as to weld the external surfaces of the suction pipe and the capillary tube together with pressure; and ii) radiating laser beams to the portion where the external surface of the suction pipe and the external surface of the capillary tube are joined while relatively moving along the laser beams in the state where the external surfaces of the suction pipe and the capillary tube are welded together with pressure, so that the external surfaces are melted and connected together. 
         [0044]    In the present invention, “the state where the aluminum-made suction pipe and the aluminum-made capillary tube are attached to each other in parallel” means that the external surface of the aluminum-made suction pipe  105  and the external surface of the aluminum-made capillary tube  103  are arranged side by side in such a way as to abut on each other as shown in  FIGS. 4 ,  7 ,  13  and  16 . Meanwhile, like the first manufacturing method and the second manufacturing method, in the case that the brazing fillet is formed, when a brazing sheet is used as the brazing material, the external surface of the aluminum-made suction pipe  105  and the external surface of the aluminum-made capillary tube  103  are arranged side by side in such a way as to abut on each other through the brazing sheet. 
         [0045]    The heat exchanger for the refrigeration cycle according to the present invention suffers nothing in functions and quality within the permissible range by comparison with a conventional heat exchanger for the refrigeration cycle, has substantially the same structure as a conventional heat exchanger, namely, the shapes (inner diameter, outer diameter, and length) of the suction pipe and the capillary tube constituting the heat exchanger are within the permissible range, and enables reduced manufacturing costs because aluminum is nearly ⅓ less in weight cost than copper and nearly ⅓ less in specific gravity than copper. Moreover, in the third manufacturing method, because the external surface of the suction pipe and the external surface of the capillary tube are joined with each other by laser welding, the heat exchanger for the refrigeration cycle can be manufactured on the basis of mass production and remarkably reduce the manufacturing costs because the brazing material is not used. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0046]    The above and other objects, features and advantages of the present invention will be apparent from the following detailed description of the preferred embodiments of the invention in conjunction with the accompanying drawings, in which: 
           [0047]      FIG. 1  is a view showing a structure of a refrigeration cycle using a heat exchanger according to the present invention; 
           [0048]      FIG. 2  is a perspective view of the heat exchanger according to the present invention in which fillets are formed and bonded at connected portions; 
           [0049]      FIG. 3  is a sectional view of  FIG. 2 ; 
           [0050]      FIG. 4  is a perspective view showing a state where a work piece according to the present invention is prepared on a jig used in the first manufacturing method; 
           [0051]      FIG. 5  is a sectional view of  FIG. 4 ; 
           [0052]      FIG. 6  is a schematic diagram of a brazing furnace used for the first manufacturing method; 
           [0053]      FIG. 7  is a perspective view showing a state where the heat exchanger shown in  FIG. 2  is manufactured by a high frequency induction heating method which is the second manufacturing method; 
           [0054]      FIG. 8  is a front view of  FIG. 7 ; 
           [0055]      FIG. 9  is a mimetic diagram showing a state where a work piece maintaining device used in the second manufacturing method presses the work piece; 
           [0056]      FIG. 10  is a mimetic diagram showing a state where a suction pipe pressing member and a capillary tube pressing member of the work piece maintaining device respectively press the side of the suction pipe and the side of the capillary tube diagonally downward; 
           [0057]      FIG. 11  is a perspective view of the heat exchanger in which the connected portions are melted and connected together; 
           [0058]      FIG. 12  is a conceptual diagram of a fiber laser welding machine; 
           [0059]      FIG. 13  is a view showing a state where the external surface of the suction pipe and the external surface of the capillary tube are welded with pressure when pressure rollers press the word piece; 
           [0060]      FIG. 14  is a mimetic diagram showing the third manufacturing method; 
           [0061]      FIG. 15  is an enlarged view showing a state where laser beams (LB) are radiated to the work piece on which the external surface of the suction pipe and the external surface of the capillary tube are welded with pressure; 
           [0062]      FIG. 16  is a conceptual diagram showing a method of automatically manufacturing the heat exchanger shown in  FIGS. 11 ; and 
           [0063]      FIG. 17  is a photograph of the heat exchanger shown in  FIG. 11 . 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0064]    In the present invention, a capillary tube  103  which is made of aluminum is simply named a capillary tube  103 , and a suction pipe  105  which is made of aluminum is simply named a suction pipe  105 . Moreover, heat exchangers obtained by the first manufacturing method and the second manufacturing method are named as heat exchangers  106 A, and a heat exchanger obtained by the third manufacturing method is named as a heat exchanger  106 B. The heat exchangers  106 A and  106 B are generally called a heat exchanger  106 . 
         [0065]    Hereinafter,  FIG. 1  is a view showing a structure of a refrigeration cycle using a heat exchanger according to the present invention,  FIG. 2  is a perspective view of the heat exchanger according to the present invention in which fillets are formed and bonded at connected portions,  FIG. 3  is a sectional view of  FIG. 2 ,  FIG. 4  is a perspective view showing a state where a work piece according to the present invention is prepared on a jig used in the first manufacturing method,  FIG. 5  is a sectional view of  FIG. 4 , and  FIG. 6  is a schematic diagram of a brazing furnace used for the first manufacturing method. 
         [0066]    A refrigeration cycle illustrated in  FIG. 1  includes a compressor  101  for sucking and discharging refrigerant; a condenser  102  having an end connected to a refrigerant discharge side of the compressor  101 ; an aluminum-made capillary tube  103  having an end connected to the other end of the condenser  102 ; an evaporator  104  having an end connected to the other end of the capillary tube  103 ; and an aluminum-made suction pipe  105  having an end connected to the other end of the evaporator  104  and the other end connected to a refrigerant suction side of the compressor  101 . In the refrigeration cycle, the heat exchanger  106  according to the present invention when the external surface of the aluminum-made suction pipe  105  and the external surface of the aluminum-made capillary tube  103  get in thermal contact with each other. 
         [0067]    The refrigeration cycle according to the present invention may further include an accumulator, which is disposed between the evaporator  104  and the suction pipe  105  for separating evaporated gas refrigerant from liquid refrigerant so as to face the gas refrigerant toward the compressor  101 , and a drier, which is disposed between the condenser  102  and the capillary tube  103  for removing moisture. 
         [0068]    In the heat exchanger  106 A, the connected portions of the external surface of the aluminum-made suction pipe  105  and the external surface of the aluminum-made capillary tube  103  are joined in a state where fillets of a brazing material selected from Al—Si alloy or Zn—Al alloy are formed. 
         [0069]    The refrigerant compressed in the compressor  101  becomes gas of high temperature and pressure and is sent to the condenser  102 , and then, radiates heat in the condenser  102  to be liquefied. The liquefied refrigerant is decompressed while passing through the capillary tube  103  and sent to the evaporator  104 , and here, the liquefied refrigerant takes heat around the refrigerant while being evaporated, and hence, the surrounding air is cooled. The evaporated refrigerant of low temperature passes through the suction pipe  105  and returns to the compressor  101  so as to be compressed. It is preferable that the used refrigerant is hydrocarbon-based refrigerant, such as cyclopentane, isobutene, and so on, which is low in coefficient of global warming. 
         [0070]    In the refrigeration cycle, because the aluminum-made capillary tube  103  and the aluminum-made suction pipe  105  are in thermal contact with each other, the liquid-phase refrigerant flowing in the capillary tube  103  is cooled by refrigerant of low temperature flowing in the suction pipe  105  so as to improve cooling efficiency. 
         [0071]      FIG. 2  is a perspective view of the heat exchanger according to the present invention in which fillets are formed and bonded at the connected portions, and  FIG. 3  is a sectional view of  FIG. 2 . The capillary tube  103  and the suction pipe  105  of the heat exchanger  106 A are all made of aluminum. Furthermore, because the connected portions of the external surface of the capillary tube  103  and the external surface of the suction pipe  105  are bonded in a state where fillets  201  of a brazing material selected from Al—Si alloy or Zn—Al alloy are formed, the capillary tube  103  and the suction pipe  105  are in thermal contact with each other. 
         [0072]    Except that the capillary tube  103  and the suction pipe  105  of the heat exchanger  106  are made of aluminum, they are almost identical in shape, length, outer diameter and inner diameter with the capillary tube and the suction pipe of the existing freezers, refrigerators, and refrigeration devices. Additionally, the aluminum material for the suction pipe  105  and the capillary tube  103  may be aluminum or aluminum alloy. 
         [0073]    In consideration of melting point, thermal conductivity, corrosion resistance of the connected portions, intensity, and workability, Al—Si alloy or Zn—Al alloy is selected as the brazing material. The heat exchanger  106  according to the present invention is mainly applicable to a freezer or a refrigerator, and a recommended period for a replacement cycle of the heat exchanger is somewhat different according to manufacturers, but is about ten years to twelve years. Moreover, according to a survey, 70 percent of those surveyed said that the replacement cycle is more than ten years. Considering the survey, corrosion resistance of the connected portions is an important factor, and hence, it is preferable that the brazing material used in the heat exchanger  106 A is Al—Si alloy. 
         [0074]    In order to remove an oxidized film on the surface of the aluminum material and improve wettability and liquidity of the melted brazing material, flux is used. CeF flux, chloride flux, and noncorrosive fluoride flux may be used. It is preferable to use the noncorrosive fluoride flux because it does not need washing after the heat exchanger  106 A is brazed. 
         [0075]      FIG. 4  is a perspective view showing a state where a work piece according to the present invention is prepared on a jig used in the first manufacturing method,  FIG. 5  is a sectional view of  FIG. 4 . The aluminum-made suction pipe  105  and the aluminum-made capillary tube  103  are attached in parallel and arranged on a jig  400  in a state where the external surfaces of the suction pipe  105  and the capillary tube  103  are in contact with each other. The reference numeral  502  designates the brazing material of a thin linear type. The brazing material may be a sheet type brazing material such as a brazing sheet, and in this instance, the suction pipe  105  and the capillary tube  103  are attached together in parallel by the brazing sheet inserted, and then, are arranged on the jig  400 . Here, the brazing material is supplied as the third material, but the brazing material may be supplied to the aluminum-made suction pipe or the aluminum-made capillary tube in a clad type. 
         [0076]    The work piece  501  according to the present invention is coated with flux. As the flux coating method, there are a coating method using a brush, a spray coating, an impregnation method of impregnating the work piece  501  in a flux liquid, and so on, and hence, one of the methods may be adopted. Furthermore, mixture of the flux and the brazing material, for instance, a paste brazing material in which a powder brazing material is mixed with flux in the form of paste or a flux-containing brazing material in which flux is contained in the brazing material, may be used. 
         [0077]    The jig  400  includes an L-shaped jig  401  and a pressure cover  402 . The L-shaped jig  401  and the pressure cover  402  may be made of stainless steel. The L-shaped jig  401  is manufactured by a bottom plate  401   a  and a side plate  401   b  bonded by laser welding. The jig  400  is about 500 mm to 1,000 mm in length, and a plurality of the jigs may be used according to the length of the work piece  501  in order to prevent deformation due to thermal expansion of the aluminum-made capillary tube  103 . 
         [0078]    Next, the first manufacturing method which is a brazing method inside a furnace will be described. The suction pipe  105  and the capillary tube  103  are attached to the L-shaped jig  401  in parallel, and then, the Al—Si alloy  502  of the thin linear type is supplied. The noncorrosive fluoride flux (NOCOLOK flux) is coated by a brush, and then, the work piece  501  is fixed by the pressure cover  402 . Here, because the aluminum-made suction pipe of 3,000 mm and the aluminum-made capillary tube of 3,000 mm are used, three jigs  400  of 1,000 mm are arranged in series side by side. 
         [0079]      FIG. 6  is a schematic diagram of a brazing furnace used for the first manufacturing method. The work piece  501  fixed by the jig  400  is inserted into the brazing furnace  600 . In  FIG. 6 , the brazing furnace  600  is a continuous furnace having a preheating room  601 , a brazing room  602 , and a cooling room  603 . The jig  400  on which the work piece  501  is fixed is set on a returning belt (not shown), and then, the work piece  501  is inserted into the preheating room  601 . The preheating room  601  is controlled in such a way as to be always maintained at 320° C. and be heated to 480° C. when the work piece  501  is inserted. The returning speed is varied according to the quantity of the work pieces  501  brazed at once, but is 1 m/minute when there is one set of work pieces. 
         [0080]    Next, the work piece  501  preheated in the preheating room  601  is transferred to the brazing room  602  heated at 620° C. to 630° C. Brazing is carried out by heating the work piece  501  to brazing temperature (melting point of the brazing material) by a heat disposed in the brazing room  602 . Because Al—Si alloy is used as the brazing material, the brazing temperature is 602° C.±5° C. Because nitrogen gas is introduced from a liquid nitrogen tank  605  through a supply pipe  604  having an opening and closing valve  604   a  inside the brazing room  602 , the inside of the brazing room  602  is kept at a nitrogen gas atmosphere. Oxygen concentration in the nitrogen gas atmosphere is less than 100 ppm, the dew point of the nitrogen gas atmosphere is less than −40° C., and pressure of the nitrogen gas atmosphere is atmospheric pressure. Because the inside of the brazing room  602  is kept at the nitrogen gas atmosphere, it prevents an oxide film from being formed on the surfaces of the aluminum-made suction pipe  105  and the aluminum-made capillary tube  103 . By the brazing method using the Al—Si alloy and the noncorrosive fluoride flux, the Ai—Si alloy is melted on the portion where the suction pipe  105  and the capillary tube  103  are joined so as to form the fillets  201 , so that the work piece  501  can be connected well. The brazing room  602  is communicated with the preheating room  601  and the brazing room  602  is communicated with the cooling room  603  without any door, and hence, the rooms can be kept in the nitrogen gas atmosphere. 
         [0081]    When brazing in the brazing room  602  is finished, the work piece  501  is returned to the cooling room  603  having a water cooling jacket (not shown) and is gradually cooled, so that the fillets  201  formed in the brazing room  602  are coagulated. 
         [0082]    When the work piece  501  cooled in the cooling room  603  is returned to the outside of the brazing furnace  600 , manufacturing of the heat exchanger  106 A is finished. Because there is no pin hole at the connected portion of the aluminum-made suction pipe  105  and the aluminum-made capillary tube  103 , brazing is carried out continuously. Furthermore, because the work piece  501  is gradually cooled, a bending process can be easily carried out due to an annealing effect. 
         [0083]    The heat exchanger  106 A can be manufactured by the high frequency induction heating method because the aluminum-made suction pipe and the aluminum-made capillary tube are heated in the state where the external surfaces of them forcedly abut on each other, namely, in the state where the external surfaces are welded with pressure. 
         [0084]    Hereinafter, referring to the drawings, the manufacturing method of the heat exchanger according to the present invention will be described. 
         [0085]      FIG. 7  is a perspective view showing a state where the heat exchanger shown in  FIG. 2  is manufactured by a high frequency induction heating method which is the second manufacturing method,  FIG. 8  is a front view of  FIG. 7 ,  FIG. 9  is a mimetic diagram showing a state where a work piece maintaining device used in the second manufacturing method presses the work piece, and  FIG. 10  is a mimetic diagram showing a state where a suction pipe pressing member and a capillary tube pressing member of the work piece maintaining device respectively press the side of the suction pipe and the side of the capillary tube diagonally downward. 
         [0086]    In  FIG. 7 , the work piece  501  prepared on the jig is transferred to a work piece maintaining device, in which a member getting in contact with the work piece  501  is arranged inside a high frequency induction heating coil  700 , in an arrow direction (←) (from right to left in the drawing) so as to manufacture the heat exchanger  106 A. Like the first manufacturing method, the Al—Si alloy is supplied and the work piece  501  is coated with the noncorrosive fluoride flux. In the meantime, the components of the heat exchanger  106 A have the same reference numerals as the heat exchanger according to the first manufacturing method. That is, the reference numeral  103  designates an aluminum-made capillary tube,  105  designates an aluminum-made suction pipe,  501  designates work piece,  201  designates fillets, and  502  designates a brazing material. 
         [0087]    Referring to  FIG. 8 , the work piece maintaining device will be described. The work piece maintaining device includes: a suction pipe pressing member  810 , which has a suction pipe contact portion  811 , a spring portion  812 , and a post  813 ; and a capillary tube pressing member  820 , which has a capillary tube contact portion  821 , a spring portion  822 , and a post  823 . The suction pipe pressing member  810  presses one side of the work piece  501 , which is the side of the suction pipe  105 , toward the other side of the work piece  501 , which is the side of the capillary tube  103 . The capillary tube pressing member  820  presses the side of the capillary tube  103  toward the suction pipe  105 . 
         [0088]    It is preferable that the work piece maintain device has at least one suction pipe pressing member  810  and at least one capillary tube pressing member  820 , and may further include a support member  830  for supporting a lower surface of the suction pipe  105  and a lower surface of the capillary tube  103 , and in the drawing, the support member  830  includes a suction pipe bottom face supporting portion  831 , a suction pipe bottom face post  832 , a capillary tube bottom face supporting portion  833  and a capillary tube bottom face post  834 , so that the work piece maintain device can maintain the work piece  501  in more safety. The reference numeral  840  designates a floor part for supporting the posts  813 ,  823 ,  832  and  834 . 
         [0089]    In the drawing, the posts  813  and  823  are arranged outside the high frequency induction heating coil  700 , but may be arranged inside the high frequency induction heating coil  700 . In the present invention, it is essential that during the high frequency induction heating, the external surface of the aluminum-made suction pipe  105  and the external surface of the aluminum-made capillary tube  103  are forcedly in contact with each other, namely, welded with pressure in the parallel attached state. For this, the entire length of the work piece maintaining device is nearly equal to the coil length of the high frequency induction heating coil  700 . 
         [0090]    Because the work piece maintaining device plays an important role in manufacturing the heat exchanger  106 A by the high frequency induction heating method which is the second manufacturing method, referring to  FIGS. 9 and 10 , the present invention will be described in more detail. In  FIGS. 9 and 10 , in order to simplify the drawings, the suction pipe pressing member  810  is indicated as a suction pipe contact portion  811  and the capillary tube pressing member  820  is indicated as a capillary tube contact portion  821 . Additionally, the support member  830  is indicated as the suction pipe bottom face supporting portion  831  and the capillary tube bottom face supporting member  833 . In addition, a pressing direction of the suction pipe pressing member  810  is indicated as an arrow (→) directed from the left to the right in the drawing, and a pressing direction of the capillary tube pressing member  820  is indicated as an arrow (←) directed from the right to the left in the drawing. Moreover, in  FIGS. 9 and 10 , the brazing material  502  is not illustrated. 
         [0091]    In order to weld the external surface of the aluminum-made suction pipe  105  and the external surface of the aluminum-made capillary tube  103  with pressure, brazing is carried out as shown in  FIG. 9 . That is, the suction pipe pressing member  810  (suction pipe contact portion  811  in the drawing) presses the side of the suction pipe  105  in a horizontal direction (the arrow (→) directed from the left to the right in the drawing) toward the center (OS) of the suction pipe, and the capillary tube pressing member  820  (capillary tube contact portion  821  in the drawing) presses the side of the capillary tube  103  in a horizontal direction (the arrow (←) directed from the right to the left in the drawing) toward the center (OC) of the capillary tube  103 . 
         [0092]    As described above, in the case that the pressing member presses horizontally toward the center, according to the principle, the support member  830  (the suction pipe bottom face supporting portion  831  and the capillary tube bottom face supporting portion  833  in the drawing) is not needed, but is stable if it is used. The degree of safety depends on the area that the suction pipe contact portion  811  and the capillary tube contact portion  821  are respectively in contact with the side of the suction pipe  105  and the side of the capillary tube  103 , but in the view point of thermal efficiency, it is preferable that the contact area is small if possible. When the contact area is small, one or both sides of the work piece  501  may drop in an upward direction. 
         [0093]    Accordingly, as shown in  FIG. 10 , the suction pipe pressing member  810  (the suction pipe contact portion  811  in the drawing) presses the side of the suction pipe  105  diagonally downward (in the diagonal arrow direction from the upper side of the left to the lower side of the right in the drawing) toward the center (OS) of the suction pipe. Furthermore, the capillary tube pressing member  820  (the capillary tube contact portion  821  in the drawing) presses the side of the capillary tube  103  diagonally downward (in the diagonal arrow direction from the upper side of the right to the lower side of the left in the drawing) toward the center (OC) of the capillary tube. After that, it is preferable that the support member  830  (the suction pipe bottom face supporting portion  831  and the capillary tube bottom face supporting portion  833  in the drawing) is disposed. Through the above structure, while the suction pipe  105  and the capillary tube  103  are moved in safety in the state where their external surfaces are welded with pressure, the external surfaces of the aluminum-made suction pipe  105  and the aluminum-made capillary tube  103  to which the brazing material is supplied are heated by the high frequency induction heating coil  700 , so that the brazing material is melted and the fillets (not shown) are formed at the connected portions. 
         [0094]    As shown in  FIGS. 9 and 10 , the contact portions of the suction pipe contact portion  811  and the capillary tube contact portion  821  are in an R-shaped form which is the same as the side of the suction pipe  105  and the side of the capillary tube  103 . Moreover, upper portions of the suction pipe contact portion  811  and the capillary tube contact portion  821  are bent toward the outside, so that the work piece  501  can be moved smoothly. 
         [0095]    The material for the work piece maintaining device is not specially restricted, but preferably, a material which does not generate heat or is difficult to generate heat by the high frequency induction heating is used. Particularly, it is preferable that the members (the suction pipe contact portion  811 , the capillary tube contact portion  821 , the suction pipe bottom face supporting portion  831 , and the capillary tube bottom face supporting portion  833 ) which are in contact with the work piece  501  of the work piece maintaining device are made of a material which does not generate heat by the high frequency induction heating, for instance, non-magnetic ceramic. 
         [0096]    Returning to  FIG. 7 , a process of preparing the work piece on the jig is not illustrated in the drawing. If the jig can keep the state where the suction pipe  105  and the capillary tube  103  are attached in parallel, the jig which arranges the work pieces  501 , namely, the suction pipe  105  and the capillary tube  103 , in the parallel attached state may adopt any structure. Here, the jig has the same structure as the work piece maintaining device. 
         [0097]    The aluminum-made suction pipe  105  of 3,000 mm and the aluminum-made capillary tube  103  of 3,000 mm which are attached in parallel are called the work piece  501 , and the work piece  501  is maintained on the jig which has the same structure as the work piece maintaining device. Here, because the high frequency induction heating coil  700  is 20 cm in length, the entire length of the jig which is the work piece maintain device is about 20 cm. In the meantime, the brazing material is supplied to the work piece  501  and flux is coated thereon, but because it is identical with the description of the first manufacturing method, its detail description will be omitted. 
         [0098]    Lids made of heat-resistant resin (not shown), each of which has a thin steel wire mounted at one end, are respectively inserted into opening portions of the suction pipe  105  and the capillary tube  103 , and the front end of the wire passes through the work piece maintaining device illustrated in  FIG. 7 , and then, is connected to a driving device (not shown) arranged on the outside of the high frequency induction heating coil  700  in the arrow direction (from the right to the left in  FIG. 7 ). The heat-resistant resin lids, the thin steel wire, and the driving device function as means for returning the work piece  501  prepared on the jig to the work piece maintaining device illustrated in  FIG. 7  (hereinafter, called ‘returning means’). 
         [0099]    Not shown in the drawing, but the jig on which the work piece  501  is prepared and the work piece maintaining device of  FIG. 7  are arranged in series. The work piece  501  prepared on the jig is in the state where the external surface of the suction pipe  105  and the external surface of the capillary tube  103  are welded with pressure. In this state, the work piece  501  is returned to the work piece maintaining device of  FIG. 7  by the returning means. 
         [0100]    It is preferable that frequency used for brazing by the high frequency induction heating method, which is the second manufacturing method, is 20 kHz to 200 kHz and the heating output is 20 kW to 40 kW. Furthermore, the returning speed by the work piece returning means is varied according to kinds of the brazing material and the heating output, but is about 0.5 m/minute to 15 m/minute. 
         [0101]    After the work piece  501  is returned to the work piece maintaining device, one side of the work piece  501 , namely, the side of the suction pipe  105 , is pressed toward the other side of the work piece  501 , namely, the side of the capillary tube  103  by the suction pipe pressing member  810 . Additionally, the side of the capillary tube  103  is pressed toward the side of the suction pipe  105  by the capillary tube pressing member  820 . As described above, because the sides of the suction pipe  105  and the capillary tube  103  are pressed, the external surface of the suction pipe  105  and the external surface of the capillary tube  103  are heated in the state where they are welded with pressure, namely, in the contact state. The brazing material  502  starts to be gradually melted from the vicinity of an inlet of the high frequency induction heating coil  700  (right side in  FIG. 7 ), and then, is completely melted in the vicinity of an outlet of the high frequency induction heating coil  700  so as to form the fillets  201 . Here, for the brazing material, the Al—Si alloy of the thin linear type was used, and noncorrosive fluoride flux was used. Moreover, in order to raise the brazing temperature to 602° C.±5° C., the heating output was 20 kW, and the returning speed of the work piece was 0.5 m/minute. 
         [0102]    The work piece  501  discharged from the high frequency heating coil  700  is gradually cooled at room temperature so as to be coagulated into the fillets  201 . Because there is no pin hole at the connected portion of the aluminum-made suction pipe  105  and the aluminum-made capillary tube  103 , brazing is carried out continuously. Furthermore, because the work piece  501  is gradually cooled, a bending process can be easily carried out due to an annealing effect. 
         [0103]    The heat exchanger  106 A can be manufactured by the laser brazing method. That is, the brazing material selected from the Ai—Si alloy or the Zn—Al alloy is supplied to the connected portions, and the aluminum-made suction pipe and the aluminum-made capillary tube are coated with flux. After that, in the state where the aluminum-made suction pipe and the aluminum-made capillary tube are attached in parallel, the brazing material is melted by laser beams, which is a heat source for heating the brazing material so as to form the fillets at the portion where the suction pipe and the capillary tube are joined, and then, is cooled so as to coagulate the fillets. In the manufacturing method of the heat exchanger for the refrigeration cycle according to the present invention by the laser brazing method, a refrigerant discharged from a compressor is circulated, in order, to a condenser, a capillary tube, an evaporator, a suction pipe, and the compressor, and the external surface of the capillary tube and the external surface of the suction pipe are thermally in contact with each other. The manufacturing method of the heat exchanger for the refrigeration cycle according to the present invention includes: 
         [0104]    1) a process of preparing a work piece on a jig: 
         [0105]    (a) the work piece is arranged on the jig in a state where the aluminum-made suction pipe and the aluminum-made capillary tube are attached in parallel; and 
         [0106]    (b) the work piece is coated with flux to which a brazing material selected from an Al—Si alloy or a Zn—Al alloy is supplied; 
         [0107]    2) a process of radiating laser beams to the brazing material while the work piece prepared on the jig moves relatively to the laser beams, so that the brazing material is melted so as to form fillets on the portion where the suction pipe and the capillary tube are joined; and 
         [0108]    3) a process of cooling the work piece so as to coagulate the fillets. 
         [0109]    Therefore, the heat exchanger for the refrigeration cycle is manufactured by the laser brazing method including the 1) to 3) processes. 
         [0110]    When the heat exchanger  106 A is manufactured by the laser brazing method, the work piece prepared on the jig is identical with the work piece  501  of the first manufacturing method. Like the first manufacturing method, the work piece prepared on the jig is prepared in the state where the aluminum-made suction pipe and the aluminum-made capillary tube are attached in parallel. In the above state, laser beams are radiated to the brazing material, so that the brazing material is melted so as to form the fillets at the portion where the suction pipe and the capillary tube are joined. 
         [0111]    Like the second manufacturing method, for brazing, laser beams may be radiated to the brazing material in the state where the external surfaces of the aluminum-made suction pipe and the aluminum-made capillary tube forcedly abut on each other, namely, in the state where the external surfaces are welded with pressure. In this instance, as the jig, the work piece maintaining device used in the second manufacturing method may be used, or the pressure jig may be used. 
         [0112]    In order to radiate laser beams, the laser welding machine used in the third manufacturing method may be used. In the case that the Al-Si alloy is used for the brazing material, the laser beam radiation condition is the same as the third manufacturing method. 
         [0113]    Next, referring to the drawings, the heat exchanger  106 B, in which the external surface of the aluminum-made capillary tube  103  and the external surface of the aluminum-made suction pipe  105  are joined in the state where the external surfaces of the capillary tube  103  and the suction pipe  105  are melted, and a representative manufacturing method of the heat exchanger  106 B will be described. 
         [0114]    The configuration of the refrigeration cycle using the heat exchanger  106 B according to the present invention is the same as the refrigeration cycle illustrated in  FIG. 1 , and hence, its detailed description will be omitted. In the refrigeration cycle, the heat exchanger  106 B (see  FIG. 11 ) is configured with the aluminum-made suction pipe  105  and the aluminum-made capillary tube  103 . In the heat exchanger  106 B, the external surface of the aluminum-made capillary tube  103  and the external surface of the aluminum-made suction pipe  105  are joined with each other in the state where the external surfaces of the capillary tube  103  and the suction pipe  105  are melted. 
         [0115]      FIG. 11  is a perspective view of the heat exchanger in which the connected portions are melted and connected together. The capillary tube  103  and the suction pipe  105  of the heat exchanger  106 B according to the present invention are respectively made of aluminum. Because the external surface of the aluminum-made capillary tube  103  and the external surface of the aluminum-made suction pipe  105  are joined with each other in the state where the external surfaces of the capillary tube  103  and the suction pipe  105  are melted by radiation of laser beams, the capillary tube  103  and the suction pipe  105  are in thermal contact with each other. 
         [0116]    Except that the capillary tube  103  and the suction pipe  105  of the heat exchanger  106  are made of aluminum, they are almost identical in shape, length, outer diameter and inner diameter with the capillary tube and the suction pipe of the existing freezers, refrigerators, and refrigeration devices. Additionally, the aluminum material for the suction pipe  105  and the capillary tube  103  may be aluminum or aluminum alloy. 
         [0117]      FIG. 12  is a conceptual diagram of a laser welding machine used when the heat exchanger  106 B according to the present invention is manufactured. Here, a fiber laser welding machine is illustrated as the laser welding machine. The reference numeral  1301  designates a fiber laser main body,  1302  designates optical fiber (fiber diameter is Φ), and  1303  designates a laser beam radiation unit. Laser beams (LB), which are indicated by broken lines in the drawing, induced to the laser beam radiation unit  1303  are configured to become parallel beams by a lens L 1  (focal distance is f 1 ), and to be collected by another lens L 2  (focal distance is f 2 ), so that the laser beams (LB) of a predetermined spot diameter are radiated to a work piece  1405  (See  FIG. 13 ) moving in one direction relative to the laser beams (LB). 
         [0118]    In the meantime, while the work piece  1405  is pressed by pressure rollers  1401  and  1402 , the external surfaces of the aluminum-made suction pipe  105  and the aluminum-made capillary tube  103  are welded with pressure (See  FIG. 13 ), but in the drawings, it is illustrated with simplicity. In the drawing, the work piece  1405  is moved in an arrow (→) direction (from the left to the right in the drawing). The reference numeral  1308  designates a nitrogen bombe, and  1307  designates a nitrogen gas injection nozzle. In laser welding, inert gas, such as argon gas, may be used in order to prevent oxidation of the work piece  1405 . 
         [0119]      FIG. 13  is a view showing a state where the pressure rollers  401  and  402  which are pressing jigs press the work piece  405  (which means a state where the aluminum-made suction pipe  105  and the aluminum-made capillary tube  103  are attached to each other in parallel) so that the external surfaces of the suction pipe and the capillary tube are welded with pressure by the pressure rollers, wherein  FIG. 13(   a ) is a side elevation view and  FIG. 13(   b ) is a plan view. 
         [0120]    The pressure roller  1401  presses the side of the suction pipe  105  toward the capillary tube  103 . The pressure roller  1401  is a roller which has an arc-shaped recess formed in correspondence with the outer diameter of the suction pipe  105 . The pressure roller  1402  presses the side of the capillary tube  103  toward the suction pipe  105 . The pressure roller  1402  is a roller which has an arc-shaped recess formed in correspondence with the outer diameter of the capillary tube  103 . The reference numeral  1403  designates a shaft of the pressure roller  1401 , and  1404  designates a shaft of the pressure roller  1402 . At least one side of the shaft  1403  and the shaft  1404  is fixed in such a way as to be adjustable in position in a vertical direction (a direction of a line passing central points of the suction pipe  105  and the capillary tube  103 ) to an axial direction of a housing (not shown). 
         [0121]    In  FIG. 13 , two pairs of the pressure rollers  1401  and  1402  disposed at a proper spaced interval from each other press the work piece  1405  so as to weld the external surfaces of the suction pipe  105  and the capillary tube  103  with pressure, but the present invention is not restricted to the above. For instance, a pair of the pressure rollers  1401  and  1402  may press the work piece  1405  so as to weld the external surfaces of the suction pipe  105  and the capillary tube  103  with pressure. Moreover, according to the method of automatically manufacturing the heat exchanger  106 B as shown in  FIG. 16 , a pair of the pressure rollers  1401  and  1402  and a pair of guide rollers  1701  and  1702  form the pressure jig, and the pressure jig presses the work piece  1405  so that the external surfaces of the suction pipe  105  and the capillary tube  103  are welded with pressure. The pressure rollers  1401  and  1402  may be made of copper, brass or aluminum which provides excellent thermal conductivity, or may be made of polymer, such as urethane. 
         [0122]      FIG. 14  is a mimetic diagram for showing the manufacturing method of the heat exchanger according to the present invention, wherein  FIG. 14(   a ) is a side elevation view and  FIG. 14(   b ) is a plan view. In  FIG. 14 , a pair of pressure rollers  1401  and  1402  press the work piece  1405  so that the external surfaces of the suction pipe  105  and the capillary tube  103  are welded together with pressure, and then, laser welding is carried out while nitrogen gas is injected. The work piece  1405  is moved in an arrow (←) direction relative to the laser beams (LB) (from the right to the left in the drawing). The movement speed of the work piece  1405  becomes faster when output of the fiber laser becomes larger, but the standard of the movement speed of the work piece  1405  is about 3 m/minute to 5 m/minute when the peak output of the fiber laser is about 1000 W. 
         [0123]    It is preferable that the laser beams (LB) to the work piece  1405  are radiated in an inclined direction to the work piece  1405  in order to avoid light returning from the work piece  1405 . The laser beam radiation unit  1303  is inclined toward the upstream side of the movement direction of the work piece (in this instance, the laser beams (LB) are radiated toward the front side of the heading direction of the work piece  1405 ), or inclined toward the downstream side of the movement direction of the work piece (in this instance, the laser beams (LB) are radiated toward the rear side of the heading direction of the work piece  1405 ). 
         [0124]    It is preferable that a radiation location of the laser beams (LB) to the work piece  1405  is within a range from the position where a pair of the pressure rollers  1401  and  1402  press the work piece  1405  to a position directly next to the downstream side of the work piece movement direction, and more preferably, the radiation location of the laser beams (LB) to the work piece  1405  is the position where a pair of the pressure rollers  1401  and  1402  press the work piece  1405 . Moreover, in the case that two pairs of the pressure rollers  1401  and  1402  press the work piece  1405  so that the external surfaces of the suction pipe  105  and the capillary tube  103  are welded together with pressure, it is preferable that the radiation location of the laser beams (LB) is within a range from the position where the pressure rollers  1401  and  1402  located at the downstream side of the work piece movement direction press the work piece  1405  to the position directly next to the downstream side of the work piece movement direction. More preferably, the radiation location of the laser beams (LB) is the position where the pressure rollers  1401  and  1402  located at the downstream side of the work piece movement direction press the work piece  1405 . 
         [0125]    In the meantime, in  FIG. 14(   b ), it is illustrated that the radiation location of the laser beams (LB) is more downward than the position directly next to the downstream side of the work piece movement direction, which is the position where a pair of the pressure rollers  1401  and  1402  press the work piece  1405 . The reason is to draw the laser beam radiation unit  1303  and the nitrogen gas injection nozzle  1307  on the same plane for convenience sake. 
         [0126]    Not shown in the drawing, in a device in which the work piece is pressed and fixed by the pressure jig and moves together with the pressure jig in one direction relative to the laser beams, the radiation location of laser beams to the work piece in the work piece movement direction may be set to a certain location. 
         [0127]    It is preferable that an injection location of the nitrogen gas injected from the nitrogen gas injection nozzle  1307  toward the work piece  1405  is nearly the same as the radiation location of the laser beams (LB). Furthermore, it is preferable that the injection direction of nitrogen gas is the same as the movement direction of the work piece  1405 . When nitrogen gas is injected in the above direction, the connected portions directly after welding are covered with a nitrogen gas atmosphere so as to securely block it from oxygen. A flow rate of nitrogen gas is about 101/minute (10 liter per minute). Meanwhile, in  FIG. 14(   b ), the signal of xxxxx at the contact portions of the suction pipe  105  and the capillary tube  103  indicates the state where the external surfaces of the suction pipe  105  and the capillary tube  103  are melted and connected by laser beam welding. 
         [0128]      FIG. 15  is an enlarged view showing a state where laser beams (LB) are radiated to the work piece  1405  on which the external surface of the suction pipe  105  and the external surface of the capillary tube  103  are welded with pressure, wherein  FIG. 15(   a ) is a side view and  FIG. 15(   b ) is a plan view. In order to connect the external surfaces of the suction pipe  105  and the capillary tube  103  by laser beam welding, laser beams are radiated to the portion where the external surfaces of the suction pipe  105  and the capillary tube  103  are in contact with each other. In other words, laser beams (LB) are radiated in such a manner that a contact line (LC) formed when the external surfaces of the suction pipe  105  and the capillary tube  103  are welded with pressure is interposed therebetween. The spot diameter of the laser beam spot (LBS) is about Φ0.05 mm to 0.6 mm. 
         [0129]    It is preferable that the radiation location of the laser beams (LB) to the work piece  1405  is leaned to the suction pipe  105  as shown in  FIG. 15(   b ). In other words, it is preferable that the spot center (S 0 ) of the laser beams (LB) is more leaned to the suction pipe  105  than the contact line (LC). Numerically, the spot center (S 0 ) of the laser beams (LB) is leaned to the suction pipe within a range of the spot diameter (Φ)×⅙ to the spot diameter (Φ)×⅓ on the basis of the contact line (LC). 
         [0130]      FIG. 16  is a conceptual diagram showing a method of automatically manufacturing the heat exchanger. The reference numerals  1703  and  1704  designate driving rollers,  1401  and  1402  designate pressure rollers, and  1701  and  1702  designates guide rollers. An uncoiler  1705  includes an aluminum tube (CA) for the capillary tube and an aluminum tube (SA) for the suction pipe, which are wound in a coil type. The driving roller  1703  and  1704  driven by a motor (not shown) transfer the work piece  1405  in a → direction (from the left to the right in the drawing). The aluminum tube (SA) for the suction pipe and the aluminum tube (CA) for the capillary tube which are drawn out from the uncoiler  1705  are wound and corrected while passing through correction devices  1706  and  1707  arranged at the downstream side, and then are induced to the guide rollers  1701  and  1702 . In the state where the aluminum tube (SA) for the suction pipe and the aluminum tube (CA) for the capillary tube are attached in parallel by the guide rollers  1701  and  1702 , they are transferred in the direction of the pressure rollers  1401  and  1402  arranged at the downstream side. 
         [0131]    The guide rollers  1701  and  1702  and the pressure rollers  1401  and  1402  arranged at the downstream side form the pressure jig, and the pressure jig presses the work piece  1405 , so that the external surface of the aluminum tube (SA) for the suction pipe and the external surface of the aluminum tube (CA) for the capillary tube are welded together with pressure. The laser beam radiation unit  1303  is arranged in such a way as to radiate the laser beams (LB) to the position where a pair of the pressure rollers  1401  and  1402  press the work piece  1405 . 
         [0132]    The nitrogen gas injection nozzle  1307  is arranged in such a manner that the injection direction is the same as the movement direction of the work piece  1405  and the injection position of nitrogen gas to the work piece  1405  is nearly the same as the radiation position of the laser beams (LB). The welded work piece is cut to a predetermined length by a cutter  1708  arranged at the downstream side of the driving rollers  1703  and  1704 . The heat exchanger  106 B manufactured as described above is loaded on a stocker  1709 . 
         [0133]      FIG. 17  is a photograph of the heat exchanger  106 B manufactured by connecting the aluminum-made suction pipe and the aluminum-made capillary tube using the fiber laser welding machine. 
         [0134]    Aluminum-made suction pipe: Φ6.4 mm in outer diameter, 0.7 mm in thickness, Φ5 mm in inner diameter 
         [0135]    Aluminum-made capillary tube: Φ2 mm in outer diameter, 0.7 mm in thickness, Φ0.6 mm in inner diameter 
         [0136]    Fiber laser welding machine: 1070 nm to 1100 nm in oscillation wavelength, Φ0.1 mm in fiber diameter of an optical fiber  302 , 100 mm in focal distance(f 1 ) of lens(L 1 ), 200 mm in focal distance(f 2 ) of lens(L 2 ), Φ0.2 mm in laser beam spot diameter, and 800 W in peak output 
         [0137]    The laser beam spot diameter was Φ0.2 mm, the focal location was the surface of the work piece  1405 . On the basis of the contact line (LC) (See  FIG. 15 ), the spot center of the laser beams (LB) was adjusted in such a way as to be biased toward the suction pipe by 0.05 mm, and the radiation location of the laser beams (LB) in the work piece movement direction relative to the work piece  1405  was adjusted to the position where the pressure rollers  1401  and  1402  press the work piece  1405 . The pressure rollers  1401  and  1402  were made of copper. The movement speed of the work piece  1405  was 30 mm/second and 50 mm/second. Furthermore, nitrogen gas whose flow rate was 101/minute (10 liter per minute) was used as shielding gas, and was injected in the same direction as the movement direction of the work piece  405 . 
         [0138]    The heat exchanger obtained by connecting the aluminum-made suction pipe and the aluminum-made capillary tube with each other suffers nothing by comparison with a conventional heat exchanger obtained by soldering the copper-made suction pipe and the copper-made capillary tube. cl INDUSTRIAL APPLICABILITY 
         [0139]    The heat exchanger according to the present invention is applicable to freezers, refrigerators, and so on.