Patent Publication Number: US-6340050-B1

Title: Internally grooved heat exchanger pipe and metal bar working roll for internally grooved heat exchanger pipes

Description:
TECHNICAL FIELD 
     This invention relates to an internally-grooved heat exchanger tube for use in a heat exchanger of a refrigerating machine and an air conditioning machine or the like, and a metal strip machining roll for machining a metal strip for such an internally-grooved heat exchanger tube by means of rolling. 
     More specifically, the present invention relates to an internally-grooved heat exchanger tube structured such that the internal surface of a metal tube is divided into a plurality of continuous areas parallel to the axial direction of the tube, and fine parallel fins different in fin pattern (i.e., a fin lead angle to the axial direction of the tube, a fin vertical angle and a fin pitch or the like) are respectively formed in the adjacent areas, and a metal strip machining roll suitably used for machining a metal strip for such a heat exchanger tube by means of rolling. 
     BACKGROUND ART 
     In Japanese Patent Laid-open Nos. 3-13796 and 4-158193, for instance, there is provided an internally-grooved heat exchanger tube structured such that the internal surface of a metal tube is divided into a plurality of continuous areas parallel to the axial direction of the tube, and a large number of fins different in fin pattern are respectively formed in the adjacent areas. 
     A description will now be given of the internally-grooved heat exchanger tube disclosed in the above Japanese Patent Laid-open No. 3-13796 with reference to FIG.  19 . 
     The internal surface of a metal tube  1  is divided into a plurality of continuous areas W 1 , W 2 , W 1 , W 2  parallel to the axial direction L of the tube, and a large number of fine parallel fins  10 ,  11  respectively having the reversed lead angles θ, θ′ to the axial direction L of the tube are formed in the adjacent areas W 1 , W 2 . 
     In manufacture of the internally-grooved heat exchanger tube shown in FIG. 19, a belt-like metal strip  1   a  of a certain width made of copper or copper alloy, for instance, needs to be rolled in the manner of passing such a metal strip through a gap between a machining roll  3  shown in FIG. 20 and a support roll (not shown) having a flat surface pressed against the machining roll  3 . 
     The machining roll  3  is equivalent to a roll of a predetermined length formed by combining a plurality of discshaped roll pieces  3   a ,  3   b ,  3   a ,  3   b  of a predetermined thickness together in layers parallel to the axial direction, and a large number of fine parallel grooves  30 ,  31  respectively having the reversed lead angles θ1, θ1′ to the axial direction are formed densely on the outer surfaces of the adjacent roll pieces  3   a ,  3   b.    
     Thus, the large number of fins  10 ,  11  described above are respectively formed on one surface of the rolled metal strip  1   a  shown in FIG. 19 in the manner of transferring the large number of grooves  30 ,  31  of the machining rolls  3   a ,  3   b  to one surface of the rolled metal strip. 
     Subsequently, the metal strip  1   a  is formed in a tubular shape by the steps of setting the metal strip in an electro-uniting device (not shown) with the fin-formed surface turned to the inside, then rounding the metal strip in the cross direction in the manner of passing the metal strip through a gap between each pair of forming rolls (not shown) installed in the electro-uniting device in multiple stages, and welding the butted ends in the cross direction together. 
     Further, the tubular molding is formed into the metal tube  1  as shown in FIG. 19 by the steps of removing a weld bead portion from the tubular molding, and subjecting the tubular molding to sinking by a predetermined drawing device to reduce the diameter of the tubular molding to a predetermined size. 
     According to the heat exchanger tube shown in FIG. 19, in the case of letting the refrigerant flow toward an upper portion in the tube in FIG. 19, for instance, the refrigerant flows toward each boundary portion a′ between the adjacent areas W 1 , W 2  while being guided by the fins  10 ,  11 , and the collision between the flows of refrigerant occurs in each boundary portion a′ to form a turbulent flow, so that this turbulent flow makes it possible to prevent the temperature gradient from being caused in the refrigerant, resulting in the improvement in tube heat transfer performance. 
     In the case of incorporating the heat exchanger tube of the prior art described above into a heat exchanger, this heat exchanger tube accelerates the formation of the turbulent flow of refrigerant in the boundary portions a′ to permit the improvement in heat transfer performance. 
     However, since the boundary portions a′ run parallel to the axial direction L of the tube, and the interference between the turbulent flows respectively formed in the boundary portions a′ before and behind the flowing direction of refrigerant occurs to thereby cancel the effects of turbulent flow each other, the sufficient heat transfer performance could not be improved. 
     Further, while the heat exchanger tube of the prior art may eliminate the temperature gradient parallel to the axial direction L of the tube, the temperature gradient is easily caused parallel to the peripheral direction by this heat exchanger tube, and as a result, there is a problem in that it is not possible to sufficiently improve the heat transfer performance. 
     An object of the present invention is to provide an internally-grooved heat exchanger tube, which makes it possible to greatly improve the tube heat transfer performance by restraining the turbulent flows of refrigerant flowing in the axial direction of the tube from interfering with each other in a boundary portion between the adjacent areas W 1 , W 2 , while sequentially guiding a turbulent-flow formed portion of the refrigerant toward the inner peripheral side of the tube. 
     Another object of the present invention is to provide a metal strip machining roll, which may smoothly machine a metal strip for the internally-grooved heat exchanger tube capable of achieving the above object. 
     DISCLOSURE OF THE INVENTION 
     For solving the above problems, an internally-grooved heat exchanger tube according to the present invention has the following structure. 
     That is, an internally-grooved heat exchanger tube in the first mode according to the present invention is characterized in that the internal surface of a metal tube  1  is divided into a plurality of continuous areas W 1 , W 2  parallel to the axial direction L of the tube, a large number of fine parallel fins  10 ,  11  are respectively formed in the adjacent areas W 1 , W 2 , the fins  10  in one area W 1  out of the adjacent areas and the fins  11  in the other area W 2  are different in at least one selected among lead angle θ, θ′ to the axial direction L of the tube, fin vertical angle α, α′ and fin pitch p, p′, and a boundary portion a between at least one area W 1  and the other area W 2  adjacent to the one area W 1  is formed in the state of meandering to the axial direction L of the metal tube  1 . 
     An internally-grooved heat exchanger tube in the second mode according to the present invention is characterized in that, in the internally-grooved heat exchanger tube in the first mode, the fins  10  formed in one area W 1  out of the adjacent areas and the fins  11  formed in the other area W 2  have the reversed lead angles θ, θ′ to the axial direction L of the tube. 
     An internally-grooved heat exchanger tube in the third mode according to the present invention is characterized in that, in the internally-grooved heat exchanger tube in the second mode, the lead angle θ of each fin  10  in one area W 1  out of the adjacent areas ranges from 15° to 50°, while the lead angle θ′ of each fin  11  in the other area W 2  ranges from −15° to −50°. 
     An internally-grooved heat exchanger tube in the fourth mode according to the present invention is characterized in that, in the internally-grooved heat exchanger tube in the first or second mode, the boundary portion a between the adjacent areas W 1 , W 2  is formed in the state of meandering to the axial direction L of the tube at a certain meandering pitch P, and the meandering pitch P is 8 to 60 times as large as a cross-sectional peripheral length W of the metal tube  1 . 
     An internally-grooved heat exchanger tube in the fifth mode according to the present invention is characterized in that, in the internally-grooved heat exchanger tube in the first or second mode, each of the fins  10 ,  11  in the adjacent areas W 1 , W 2  is substantially acute triangular in cross section, and a vertical angle α of each of the fins  10 ,  11  ranges from 10° to 30°. 
     An internally-grooved heat exchanger tube in the sixth mode according to the present invention is characterized in that, in the internally-grooved heat exchanger tube in the first or second mode, a height h of each of the fins  10 ,  11  in the adjacent areas W 1 , W 2  is {fraction (1/15)} to {fraction (1/70)} as small as an outside diameter R of the metal tube  1 . 
     For solving the above problems, a metal strip machining roll for an internally-grooved heat exchanger tube in the first mode according to the present invention comprises a roll of a predetermined length formed by combining a plurality of roll pieces  2   a ,  2   b  together in layers parallel to the axial direction, wherein a large number of fine parallel grooves  20 ,  21  are respectively formed on the outer surfaces of the adjacent roll pieces  2   a ,  2   b , the grooves  20  on one roll piece  2   a  out of the adjacent roll pieces and the grooves  21  on the other roll piece  2   b  are different in at least one selected among lead angle θ1, θ1′ to the axial direction, bottom angle α1, α1′ and groove pitch p 1 , p 1 ′, and a contact surface c of at least one roll piece  2   a  with the other roll piece  2   b  adjacent to the roll piece  2   a  forms a surface inclined at a predetermined inclination angle to the axial direction of each of the roll pieces  2   a ,  2   b.    
     For solving the above problems, a metal strip machining roll for an internally-grooved heat exchanger tube in the second mode according to the present invention comprises a roll of a predetermined length formed by combining a plurality of roll pieces  2   a ,  2   b  together in layers parallel to the axial direction, wherein a large number of fine parallel grooves  20 ,  21  are respectively formed on the outer surfaces of the adjacent roll pieces  2   a ,  2   b , the grooves  20  on one roll piece  2   a  out of the adjacent roll pieces and the grooves  21  on the other roll piece  2   b  are different in at least one selected among lead angle θ1, θ1′ to the axial direction, bottom angle α1, α1′ and groove pitch p 1 , p 1 ′, and a contact surface c of at least one roll piece  2   a  with the other roll piece  2   b  adjacent to the roll piece  2   a  is composed of a plurality of continuous surfaces respectively inclined at different inclination angles to the axial direction of each of the roll pieces  2   a ,  2   b.   
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a partially development plan view showing an internally-grooved heat exchanger tube in the first embodiment according to the present invention; 
     FIG. 2 is a schematic front view showing a metal strip machining roll for manufacturing the internally-grooved heat exchanger tube in the first embodiment according to the present invention; 
     FIG. 3 is a partially enlarged sectional view showing a rolled metal strip before the internally-grooved heat exchanger tube in the first embodiment of FIG. 1 is manufactured; 
     FIG. 4 is a schematic front view showing a metal strip machining roll for manufacturing an internally-grooved heat exchanger tube in the second embodiment according to the present invention; 
     FIG. 5 is a partially development plan view schematically showing the internally-grooved heat exchanger tube in the second embodiment manufactured by using the metal strip machining roll of FIG. 4; 
     FIG. 6 is a schematic front view showing a metal strip machining roll for manufacturing an internally-grooved heat exchanger tube in the third embodiment according to the present invention; 
     FIG. 7 is a partially development plan view schematically showing the internally-grooved heat exchanger tube in the third embodiment manufactured by using the metal strip machining roll of FIG. 6; 
     FIG. 8 is a schematic front view showing a metal strip machining roll for manufacturing an internally-grooved heat exchanger tube in the fourth embodiment according to the present invention; 
     FIG. 9 is a partially development plan view schematically showing the internally-grooved heat exchanger tube in the fourth embodiment manufactured by using the metal strip machining roll of FIG. 8; 
     FIG. 10 is a schematic front view showing a metal strip machining roll for manufacturing an internally-grooved heat exchanger tube in the fifth embodiment according to the present invention; 
     FIG. 11 is a partially development plan view schematically showing the internally-grooved heat exchanger tube in the fifth embodiment manufactured by using the metal strip machining roll of FIG. 10; 
     FIG. 12 is a schematic front view showing a metal strip machining roll for manufacturing an internally-grooved heat exchanger tube in the sixth embodiment according to the present invention; 
     FIG. 13 is a partially development plan view schematically showing the internally-grooved heat exchanger tube in the sixth embodiment manufactured by using the metal strip machining roll of FIG. 12; 
     FIG. 14 (A) is a schematic front view showing a metal strip machining roll for manufacturing an internally-grooved heat exchanger tube in the seventh embodiment according to the present invention; 
     FIG.  14 (B) is an enlarged sectional view showing a groove on the surface of one of roll pieces of the metal strip machining roll of FIG.  14 (A); 
     FIG.  14 (C) is an enlarged sectional view showing a groove on the surface of the other roll piece of the metal strip machining roll of FIG.  14 (A); 
     FIG.  15 (D) is a partially development plan view schematically showing the internally-grooved heat exchanger tube in the seventh embodiment manufactured by using the machining roll of FIG. 14; 
     FIG.  15 (E) is an enlarged sectional view showing a fin in one of areas of the internally-grooved heat exchanger tube of FIG.  15 (D); 
     FIG.  15 (F) is an enlarged sectional view showing a fin in the other area of the internally-grooved heat exchanger tube of FIG.  15 (D); 
     FIG. 16 is a schematic front view showing a metal strip machining roll for manufacturing an internally-grooved heat exchanger tube in the eighth embodiment according to the present invention; 
     FIG. 17 is a partially development plan view schematically showing the internally-grooved heat exchanger tube in the eighth embodiment manufactured by using the machining roll of FIG. 16; 
     FIG. 18 is a schematic plan view showing a metal strip machining roll for manufacturing an internally-grooved heat exchanger tube in the yet further embodiment; 
     FIG. 19 is a partially development view showing an internally-grooved heat exchanger tube in the prior art as described in Japanese Patent Laid-open No. 3-13796; and 
     FIG. 20 is a schematic front view showing a metal strip machining roll for manufacturing the internally-grooved heat exchanger tube of FIG.  19 . 
    
    
     BEST MODE FOR EMBODYING THE INVENTION 
     Hereinafter will be described the embodiments of an internally-grooved heat exchanger tube according to the present invention with reference to FIGS. 1 to  18 . 
     First Embodiment 
     As shown in FIG. 1, the internal surface of a metal tube  1  made of deoxidized copper and having a thickness of 0.25 mm and a peripheral length W (i.e., a width of a rolled metal strip  1   a ) of 21 mm (an outside diameter of about 6.7 mm) is divided into four continuous areas W 1 , W 2 , W 1 , W 2  parallel to the axial direction L of the tube such that the width of each of the areas varies parallel to the peripheral direction. 
     While a developed portion of the metal tube  1  shows a rolled metal strip  1   a , boundary portions a between the adjacent areas W 1 , W 2  on the opposite sides of the rolled metal strip  1   a  are formed in the state of regular meandering to the axial direction L of the tube at a certain meandering pitch P of about 377 mm while maintaining a certain meandering width (6 mm), and a boundary portion b between the adjacent areas W 2 , W 1  in the center is formed parallel to the axial direction L of the tube, as a matter of fact. 
     A large number of parallel fins  10  each having a lead angle θ of 20° to the axial direction L of the tube, a height (i.e., a height from the bottom) h of 0.2 mm and a vertical angle α of 30° as shown in FIG. 3 are formed in each odd-numbered area W 1 , while a large number of parallel fins  11  each having a reversed lead angle θ′ of −20° to the axial direction L of the tube, a height h′ of 0.2 mm and a vertical angle aα of 30° are formed in each even-numbered area W 2  respectively adjacent to the odd-numbered areas W 1 . A narrow flat portion  12  is formed on the opposite edges of the rolled metal strip  1   a  in the cross direction. 
     The pitches p, p′ (i.e., the mean interval between the centers of the fin tops in the ringed cross-sectional circumference of the metal tube  1 ) of the fins  10 ,  11  are set to be equal to about 0.31 mm on an average. . 
     A metal strip machining roll  2  shown in FIG. 2 is used for manufacturing the internally-grooved heat exchanger tube in the first embodiment. 
     The machining roll  2  is structured such that a plurality of roll pieces  2   a ,  2   b ,  2   a ,  2   b  made of hard metal is fixed to a shaft  22  in layers parallel to the axial direction, and a contact surface c of one roll piece  2   a  out of a set of adjacent roll pieces with the other roll piece  2   b  forms a surface inclined at a predetermined inclination angle θ2 to the axial direction of the roll pieces  2   a ,  2   b . A contact surface d of the second roll piece  2   b  from the left with the third roll piece  2   a  crosses at a right angle to the axial direction. 
     A large number of parallel grooves  20 ,  21  respectively having the reversed lead angles θ1, θ1′ to the axial direction are formed on the outer surfaces of the roll pieces  2   a ,  2   b  at the same pitch (i.e., an interval between the groove tops in the longitudinal direction of the roll  2 ) so as to correspond to the fins  10 ,  11  of the metal tube  1 . 
     In the machining roll  2  in this mode, the outside diameter (i.e., an outside diameter of the groove bottom) of each of the roll pieces  2   a ,  2   b  is 120 mm, the inclination angle θ2 of the contact surface c of the roll piece  2   a  with its adjacent roll piece  2   b  to the axial direction is about 3°, and each of the lead angles θ1, θ1′ of the grooves 20, 21 to the axial direction is ±20°. 
     When the metal strip is rolled by the machining roll  2  as described in the above embodiment together with a support roll (not shown) having a flat surface, four areas W 1 , W 2 , W 1 , W 2  are formed on one surface of the rolled metal strip  1 a, while the large number of fine parallel fins  10 ,  11  are formed in the areas W 1 , W 2  correspondingly to the roll pieces  2   a ,  2   b  and also the large number of grooves  20 ,  21  formed on these roll pieces, as shown in FIG.  1 . 
     In the rolled metal strip  1   a , each boundary portion a between the odd-numbered area W 1  from the left and the even-numbered area W 2  is formed in the state of meandering to the axial direction of the tube at a pitch P (of about 377 mm) corresponding to the cross-sectional peripheral length of each of the roll pieces  2   a ,  2   b , while maintaining a meandering width corresponding to the inclination angle of each contact surface c of the odd-numbered roll piece  2   a  with the even-numbered roll piece  2   b  adjacent to the roll piece  2   a  in the machining roll  2 . 
     After the large number of fins  10 ,  11  have been formed in the areas W 1 , W 2  of one surface of the rolled metal strip  1   a  as shown in FIG. 1, this rolled metal strip  1   a  is formed into the shape of the metal tube  1  as shown in FIG. 1 according to the similar procedure to the conventional method described above. 
     According to the metal tube  1  serving as the internally-grooved heat exchanger tube in the first embodiment, when this metal tube is incorporated into a heat exchanger (not shown) to let the refrigerant flow within the tube in parallel to the axial direction L of the tube (toward an upper portion in FIG.  1 ), the refrigerant flows along the fins  10 ,  11  formed in the adjacent areas W 1 , W 2 , and the collision between the flows of refrigerant occurs in each boundary portion a between the areas W 1 , W 2  to form a turbulent flow, so that this turbulent flow makes it possible to accelerate the exchange of heat between the refrigerant and the internal surface of the tube, resulting in the improvement in heat transfer efficiency. 
     At this time, since each boundary portion a between the areas W 1 , W 2  to cause the collision between the flows of refrigerant for the formation of a turbulent flow is formed in the state of meandering to the axial direction L of the tube so that positions of a refrigerant collision/turbulent-flow formed portion (i.e., the boundary portion a) in the inner peripheral direction of the tube are different little by little before and behind the flowing direction of refrigerant, the interference between the turbulent flows formed before and behind the flowing direction of refrigerant is restrained to thereby make it possible to prevent the heat transfer efficiency from being reduced. 
     Further, since the refrigerant collision/turbulent-flow formed portion is shifted in a zigzag shape along each meandering boundary portion a toward the inner peripheral side of the tube, the temperature gradient parallel to the peripheral direction is also restrained to thereby make it possible to sufficiently improve the heat transfer performance. 
     EXAMPLE 1 
     A metal strip made of deoxidized copper was used to manufacture a heat exchanger tube as the example 1 according to the present invention based on the mode as shown in FIG. 1, that is, a heat exchanger tube structured such that the internal surface of the tube is divided into four continuous areas W 1 , W 2 , W 1 , W 2  parallel to the axial direction of the tube, the cross-sectional peripheral length W (i.e., the width of the metal strip) is 21 mm, the thickness (i.e., the thickness of the groove bottom) t is 0.25 mm, the meandering pitch P of the boundary portion a between the adjacent areas W 1 , W 2  is 30W (630 mm), the meandering width of the boundary portion a is 6 mm, each of the heights h, h′ of the fins  10 ,  11  is 0.2 mm, each of the pitches p, p′ of the fins  10 ,  11  is 0.31 mm, each of the fin vertical angles α, α′ is 30°, the lead angle θ of each fin  10  to the axial direction L of the tube is 20°, and the lead angle θ°′ of each fin  11  to the axial direction L of the tube is −20°. 
     COMPARATIVE EXAMPLE 1 
     A metal strip made of deoxidized copper was used to manufacture a heat exchanger tube as the comparative example based on the prior art mode as shown in FIG. 19, that is, a heat exchanger tube structured such that the internal surface of the tube is divided into four uniform areas W 1 , W 2 , W 1 , W 2  parallel to the peripheral direction, the cross-sectional peripheral length W is 21 mm, the thickness (i.e., the thickness of the groove bottom) t is 0.25 mm, the height h of each of the fins  10 ,  11  is 0.2 mm, the pitch of the fins  10 ,  11  is 0.31 mm, the vertical angle of each fin is 30°, the lead angle θ of each fin  10  to the axial direction L of the tube is 20° and the lead angle θ′ of each fin  11  to the axial direction L of the tube is −20°. 
     The measurement of the coefficient of heat transfer with condensation and that of the coefficient of heat transfer with vaporization were made on the heat exchanger tube as the example 1 and the heat exchanger tube as the comparative example 1 every flow rate of refrigerant by making it condition that the flow rate of refrigerant was varied. The percentage of the coefficient of heat transfer with condensation and that of the coefficient of heat transfer with vaporization are shown in Tables 1,2. Each percentage of the coefficient of heat transfer was given by making the measurement ten times on both the heat exchanger tubes in the state of a single tube by using a measuring device, and then finding the average of the measured values to make a comparison by assuming each measured value of the heat exchanger tube as the comparative example on the basis of each flow rate of refrigerant to be 100. 
     As shown in Tables 1, 2, it was ascertained that the heat transfer performance of the heat exchanger tube as the example 1 according to the present invention was improved greater than that of the heat exchanger tube as the comparative example, that is, the heat exchanger tube as the example 1 produced an increase 48 to 62% in coefficient of heat transfer with condensation and an increase of 28 to 38% in coefficient of heat transfer with vaporization. 
     
       
         
           
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                 (Percentage of coefficient of heat transfer with condensation) 
               
            
           
           
               
               
               
            
               
                 Flow rate of 
                   
                   
               
               
                 refrigerant 
                 Heat exchanger tube as 
                 Heat exchanger tube 
               
               
                 (kg/m 2  s) 
                 comparative example 
                 as example 
               
               
                   
               
               
                 150 
                 100 
                 148 
               
               
                 200 
                 100 
                 152 
               
               
                 250 
                 100 
                 156 
               
               
                 300 
                 100 
                 162 
               
               
                 350 
                 100 
                 154 
               
               
                 400 
                 100 
                 150 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 2 
               
             
            
               
                   
               
               
                 (Percentage of coefficient of heat transfer with vaporization) 
               
            
           
           
               
               
               
            
               
                 Flow rate of 
                   
                   
               
               
                 refrigerant 
                 Heat exchanger tube as 
                 Heat exchanger tube 
               
               
                 (kg/m 2  s) 
                 comparative example 
                 as example 
               
               
                   
               
               
                 150 
                 100 
                 128 
               
               
                 200 
                 100 
                 131 
               
               
                 250 
                 100 
                 134 
               
               
                 300 
                 100 
                 138 
               
               
                 350 
                 100 
                 133 
               
               
                 400 
                 100 
                 130 
               
               
                   
               
            
           
         
       
     
     EXAMPLE 2 
     8 kinds of heat exchanger tubes as the example 2 were manufactured by making it condition that the constituent elements were set to be equal to those of the heat exchanger tube as the example 1, except that each of the vertical angles α, α′ of the fins  10 ,  11  was varied within the range of 5 to 40°, and the meandering pitch P of the boundary portion a between the adjacent areas W 1 , W 2  was set to 30W (wherein W represents the cross-sectional peripheral length of the tube). 
     Subsequently, the measurement of the coefficient of heat transfer with condensation in the case of setting the flow rate of refrigerant to 200 Kg/m 2 s was made on each of the above heat exchanger tubes. The percentage of the coefficient of heat transfer with condensation in each of the heat exchanger tubes as the example 2 is shown in Table 3. 
     Each percentage of the coefficient of heat transfer was given by making the measurement ten times on each of the heat exchanger tubes in the state of a single tube by using a measuring device and then finding the average of the measured values to make a comparison by assuming the percentage of the coefficient of heat transfer with condensation in the heat exchanger tube having the fin vertical angles α, α′ of 30° as the example 2 to be 100. 
     As shown in Table 3, it was ascertained that the preferable range of each of the fin vertical angles α, α′ was 10 to 30, on the tube diameter or the fin density. 
     
       
         
           
               
             
               
                 TABLE 3 
               
             
            
               
                   
               
               
                 (Relation between change in fin vertical angle α and 
               
               
                 percentage of coefficient of heat transfer with condensation, 
               
               
                 wherein flow rate of refrigerant is set to 200 Kg/m 2  s) 
               
            
           
           
               
               
               
            
               
                   
                   
                 Percentage of coefficient of heat 
               
               
                   
                   
                 transfer with condensation (Heat 
               
               
                   
                 Fin vertical angle α 
                 exchanger tube having α of 30° is 
               
               
                   
                 (°) 
                 assumed to be 100) 
               
               
                   
                   
               
            
           
           
               
               
               
            
               
                   
                 5 
                 90 
               
               
                   
                 10 
                 117 
               
               
                   
                 15 
                 119 
               
               
                   
                 20 
                 114 
               
               
                   
                 25 
                 110 
               
               
                   
                 30 
                 100 
               
               
                   
                 35 
                 85 
               
               
                   
                 40 
                 78 
               
               
                   
                   
               
            
           
         
       
     
     Second Embodiment 
     A metal strip machining roll  2  shown in FIG. 4 is formed by combining three sets of roll pieces  2   a ,  2   b , i.e., six roll pieces in total structured such that each of contact surfaces c facing each other forms a surface uniformly inclined to the axial direction of the roll, while each of other contact surfaces d forms a surface perpendicular to the axial direction of the roll. 
     The odd-numbered roll pieces  2   a  and the even-numbered roll pieces  2   b  are respectively placed in alternately inverse positions. 
     In the internally-grooved heat exchanger tube in the second embodiment manufactured by using the metal strip machining roll  2  shown in FIG. 4, a rolled metal strip  1   a  is machined as shown in the tube in FIG.  5 . 
     The internally-grooved heat exchanger tube in the second embodiment has more boundary portions a meandering to the axial direction of the tube than the internally-grooved heat exchanger tube in the first embodiment, and therefore, shows the greater improvement in coefficient of heat transfer as long as both the heat exchanger tubes are equal in outside diameter to each other in the case of letting the refrigerant flow from an upper portion to a lower portion in the tube in FIG.  5 . 
     Further, using a heat exchanger tube having a larger outside diameter does much to improve the coefficient of heat transfer with the increase in number of the continuous areas W 1 , W 2  parallel to the axial direction L of the tube, together with the increase in number of the meandering boundary portions a between the areas, like the heat exchanger tube in the second embodiment. 
     Other constitution, operation and effects of the internally-grooved heat exchanger tube in the second embodiment are similar to those of the heat exchanger tube in the first embodiment, and hence, the description thereof will be omitted. 
     Third Embodiment 
     A metal strip machining roll  2  shown in FIG. 6 is formed by combining two sets of roll pieces  2   a ,  2   b  structured such that each of contact surfaces c forms a surface inclined uniformly to the axial direction of the roll, while the other contact surface forms a surface perpendicular to the axial direction of the roll. The odd-numbered roll pieces  2   a  and the even-numbered roll pieces  2   b  are respectively placed in similar positions. 
     In an internally-grooved heat exchanger tube in the third embodiment manufactured by using the metal strip machining roll  2  shown in FIG. 6, a rolled metal strip  1   a  is machined as shown in FIG.  7 . 
     Two lines of boundary portions a meandering to the axial direction L of the tube are formed on the internal surface of the internally-grooved heat exchanger tube in the third embodiment so as to be similar in position in the axial direction L of the tube, meandering direction and meandering amount to each other. 
     Other constitution, operation and effects of the internally-grooved heat exchanger tube in the third embodiment are similar to those of the internally-grooved heat exchanger tube in the first embodiment, and hence, the description thereof will be omitted. 
     Fourth Embodiment 
     A metal strip machining roll  2  shown in FIG. 8 is formed by combining two sets of roll pieces  2   a ,  2   b  structured such that each of contact surfaces c forms a surface uniformly inclined to a surface perpendicular to the axial direction of the roll. Each of the outside end surfaces of the opposite-end roll pieces  2   a ,  2   b  is formed perpendicularly to the axial direction of the roll, while a contact surface c of the roll piece  2   b  with its adjacent roll piece  2   a  in the center is uniformly inclined to a surface perpendicular to the axial direction of the roll. 
     In an internally-grooved heat exchanger tube in the fourth embodiment manufactured by using the metal strip machining roll  2  shown in FIG. 8, a rolled metal strip  1   a  is machined as shown in FIG.  9 . 
     A boundary portion a meandering to the axial direction L of the tube is formed between the adjacent areas W 1 , W 2 , between those W 2 , W 1  and between those W 1 , W 2  in order from the left in FIG. 9 on the internal surface of the internally-grooved heat exchanger tube in the fourth embodiment. 
     In the case of letting the refrigerant flow from a lower portion to an upper portion in the heat exchanger tube in FIG. 9, the turbulent flow of refrigerant is formed mainly at portions of the opposite boundary portions a, a. On the other hand, in the case of letting the refrigerant flow from the upper portion to the lower portion in FIG. 9, the turbulent flow of refrigerant is formed mainly at a portion of the center boundary portion a. 
     Thus, as long as one surface of the rolled metal strip  1   a  is divided into five continuous areas parallel to the axial direction L of the heat exchanger tube, and each boundary portion a meandering to the axial direction L of the tube is formed between the adjacent areas, the boundary portions a of the same number may be available for the formation of the turbulent flow of refrigerant even when the refrigerant flows in any direction, so that the substantially uniform heat transfer efficiency may be achieved even in the case of letting the refrigerant flow within the heat exchanger tube in any direction. 
     Other constitution, operation and effects of the internally-grooved heat exchanger tube in the fourth embodiment are similar to those of the heat exchanger tube in the first embodiment, and hence, the description thereof will be omitted. 
     Fifth Embodiment 
     A metal strip machining roll  2  shown in FIG. 10 is formed by combining three roll pieces  2   a ,  2   b ,  2   a  together, contact surfaces c of the opposite roll pieces  2   a  with the center roll piece  2   b  are uniformly inclined to the axial direction of the roll, and the opposite roll pieces  2   a ,  2   a  are in contact with the center roll piece  2   b  in alternately inverse positions. 
     In an internally-grooved heat exchanger tube in the fifth embodiment manufactured by using the metal strip machining roll  2  shown in FIG. 10, a rolled metal strip  1   a  is machined as shown in FIG.  11 . 
     A boundary portion a meandering to the axial direction L of the tube is formed between the areas W 1 , W 2  and between those W 2 , W 1  on the internal surface of the internally-grooved heat exchanger tube in the fifth embodiment. These boundary portions a are parallel to each other. 
     According to the internally-grooved heat exchanger tube in the fifth embodiment, the substantially uniform heat transfer efficiency may be achieved even in the case of letting the refrigerant flow in any direction. 
     Other constitution, operation and effects of the internally-grooved heat exchanger tube in the fifth embodiment are similar to those of the heat exchanger tube in the first embodiment, and hence, the description thereof will be omitted. 
     Sixth Embodiment 
     A metal strip machining roll  2  shown in FIG. 12 is formed by combining four roll pieces  2   a ,  2   b ,  2   a ,  2   b  together in layers parallel to the axial direction, and a large number of fine parallel grooves  20 ,  21  respectively having the reversed lead angles θ1, θ1′ to the axial direction are formed on the surfaces of the adjacent roll pieces  2   a ,  2   b.    
     A contact surface c of the roll piece  2   a  with its adjacent roll piece  2   b  is composed of a surface inclined at a predetermined inclination angle θ2 to a surface perpendicular to the axial direction of the roll  2  and a surface continuous to the above inclined surface and also inclined at the reversed inclination angle θ2′ to the surface perpendicular to the axial direction of the roll  2 . 
     A contact surface d of the roll piece  2   b  with its adjacent roll piece  2   a  in the center forms a surface perpendicular to the axial direction of the roll  2 . 
     In an internally-grooved heat exchanger tube in the sixth embodiment manufactured by using the metal strip machining roll  2  shown in FIG. 12, a rolled metal strip la is machined as shown in FIG.  13 . 
     The internal surface of the internally-grooved heat exchanger tube in the sixth embodiment is divided into four areas W 1 , W 2 , W 1 , W 2  correspondingly to the roll pieces  2   a ,  2   b , and each boundary portion a meandering to the axial direction L of the tube at a certain pitch P is formed between the adjacent areas W 1 , W 2  correspondingly to each contact surface c. The boundary portions a, a are formed symmetrically in the state of meandering without being parallel to each other. A center boundary portion b between the adjacent areas W 2 , W 1  is formed parallel to the axial direction L of the tube. 
     A large number of fine parallel fins  10  each having a predetermined lead angle θ to the axial direction L of the tube are formed in one area W 1  out of the adjacent areas correspondingly to the grooves  20 , while a large number of fine parallel fins  11  each having the reversed lead angle θ′ of the lead angle θ to the axial direction L of the tube are formed in the area W 2  adjacent to the area W 1  correspondingly to the grooves  21 . The pitches p, p′ of the fins  10 ,  11  are equal to each other. 
     According to the metal strip machining roll  2  in the sixth embodiment, since each contact surface c of the roll piece  2   a  with its adjacent roll piece  2   b  is composed of a plurality of continuous surfaces respectively inclined at different inclination angles to the surface perpendicular to the axial direction of the roll  2 , each boundary portion a between the adjacent areas W 1 , W 2  formed on the metal strip  1   a  is formed at a smaller pitch P of meandering to the axial direction L of the tube, in comparison with the case of the metal strip machining roll  2  in the first embodiment, even though the roll  2  of a relatively larger diameter is in use. 
     The boundary portions a are formed at the smaller meandering pitch P as described above, and as a result, the internally-grooved heat exchanger tube in the sixth embodiment may improve the heat transfer performance greater than that of the internally-grooved heat exchanger tube in the first embodiment. 
     The metal strip machining roll and the internally-grooved heat exchanger tube in the sixth embodiment are substantially similar in other constitution, operation and effects to those in the first embodiment. 
     EXAMPLE 3 
     A metal strip made of deoxidized copper was used to manufacture a heat exchanger tube as the example  3  according to the present invention based on the mode as shown in FIG. 13 (the sixth embodiment), that is, a heat exchanger tube structured such that the internal surface of the tube is divided into four continuous areas W 1 , W 2 , W 1 , W 2  parallel to the axial direction of the tube, the cross-sectional peripheral length W (i.e., the width of the metal strip) is 20 mm, the thickness (i.e., the thickness of the groove bottom) t is 0.25 mm, the meandering pitch P of the boundary portion a between the adjacent areas W 1 , W 2  is 15W (300 mm), the meandering width of the boundary portion a is 6 mm, each of the heights h, h′ of the fins  10 ,  11  is 0.2 mm, each of the pitches p, p′ of the fins  10 ,  11  is 0.22 mm, each of the fin vertical angles α, α′ is 25° the lead angle θ of each fin  10  to the axial direction L of the tube is 20°, and the lead angle θ of each fin  11  to the axial direction L of the tube is −20°. 
     COMPARATIVE EXAMPLE 3 
     A metal strip made of deoxidized copper was used to manufacture a heat exchanger tube as the comparative example  3  based on the prior art mode as shown in FIG. 19, that is, a heat exchanger tube structured such that the internal surface of the tube is divided into four uniform areas W 1 , W 2 , W 1 , W 2  parallel to the peripheral direction, the cross-sectional peripheral length W is 20 mm, the thickness (i.e., the thickness of the groove bottom) t is 0.25 mm, the height h of each of the fins  10 ,  11  is 0.2 mm, the pitch of the fins  10 ,  11  is 0.22 mm, each fin vertical angle is 25°, the lead angle θ of each fin  10  to the axial direction L of the tube is 20°, and the lead angle θ of each fin  11  to the axial direction L of the tube is −20°. 
     The measurement of the coefficient of heat transfer with condensation and that of the coefficient of heat transfer with vaporization were made on the heat exchanger tube as the example 3 and the heat exchanger tube as the comparative example 3 every flow rate of refrigerant by making it condition that the flow rate of refrigerant was varied. The percentage of the coefficient of heat transfer with condensation and that of the coefficient of heat transfer with vaporization are shown in Tables 4, 5. Each percentage of the coefficient of heat transfer was given by making the measurement ten times on both the heat exchanger tubes in the state of a single tube by using a measuring device, and then finding the average of the measured values to make a comparison by assuming each measured value of the heat exchanger tube as the comparative example 3 on the basis of each flow rate of refrigerant to be 100. 
     As shown in Tables 4, 5, it was ascertained that the heat transfer performance of the heat exchanger tube as the example 3 according to the present invention was improved greater than that of the heat exchanger tube as the comparative example 3, that is, the heat exchanger tube as the example 3 produced an increase of 58 to 71 % in coefficient of heat transfer with condensation and also an increase of 38 to 48% in coefficient of heat transfer with vaporization. 
     
       
         
           
               
             
               
                 TABLE 4 
               
             
            
               
                   
               
               
                 (Percentage of coefficient of heat transfer with condensation) 
               
            
           
           
               
               
               
            
               
                 Flow rate of 
                   
                   
               
               
                 refrigerant 
                 Heat exchanger tube as 
                 Heat exchanger tube 
               
               
                 (kg/m 2  s) 
                 comparative example 
                 as example 
               
               
                   
               
               
                 150 
                 100 
                 158 
               
               
                 200 
                 100 
                 163 
               
               
                 250 
                 100 
                 166 
               
               
                 300 
                 100 
                 171 
               
               
                 350 
                 100 
                 167 
               
               
                 400 
                 100 
                 165 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 5 
               
             
            
               
                   
               
               
                 (Percentage of coefficient of heat transfer with vaporization) 
               
            
           
           
               
               
               
            
               
                 Flow rate of 
                   
                   
               
               
                 refrigerant 
                 Heat exchanger tube as 
                 Heat exchanger tube 
               
               
                 (kg/m 2  s) 
                 comparative example 
                 as example 
               
               
                   
               
               
                 150 
                 100 
                 138 
               
               
                 200 
                 100 
                 141 
               
               
                 250 
                 100 
                 144 
               
               
                 300 
                 100 
                 148 
               
               
                 350 
                 100 
                 143 
               
               
                 400 
                 100 
                 140 
               
               
                   
               
            
           
         
       
     
     EXAMPLE 4 
     20 kinds of heat exchanger tubes as the example 4 were manufactured by making it condition that the constituent elements were set to be equal to those of the heat exchanger tube as the example 3 except that the meandering pitch P of each boundary portion a between the adjacent areas W 1 , W 2  was varied within the range of 4 to 80 W times as large as the cross-sectional peripheral length W of the tube (i.e., the width of the metal strip  1   a ) 
     Subsequently, the measurement of the coefficient of heat transfer with condensation in the case of setting the flow rate of refrigerant to 200 Kg/m 2  s was made on each of the above heat exchanger tubes. The percentage of the coefficient of heat transfer with condensation of each of the above heat exchanger tubes as the example 4 is shown in Table 6, together with the presence or absence of roll chipping (broken grooves  20 ,  21  of the machining roll  2 ) in the case of rolling the metal strip. 
     The percentage of the coefficient of heat transfer in each heat exchanger tube was given by making the measurement ten times on each heat exchanger tube in the state of a single tube by using a measuring device and then finding the average of the measured values to substitute the average value with a value as of the time of assuming the coefficient of heat transfer with condensation (the flow rate of refrigerant is set to 200 Kg/m 2  s) in the heat exchanger tube as the comparative example 3 to be 100. 
     As to the occurrence of roll chipping, the presence of roll chipping at the time of rolling the metal strip is expressed by x, while the absence of roll chipping is expressed by ◯. 
     As shown in Table 6, when the meandering pitch P of each boundary portion a was four times as large as the cross-sectional peripheral length W of the tube, high coefficient of heat transfer was ensured, while the roll chipping occurred at the time of rolling the metal strip. 
     On the other hand, when the meandering pitch P of each boundary portion a exceeded 60 times as large as the cross-sectional peripheral length W of the tube, it was ascertained that a difference in coefficient of heat transfer with condensation between the heat exchanger tube as the example 4 and that as the comparative example was reduced. It is supposed that the above fact results from the interference between the turbulent flows formed at butted portions of the fins on the boundary line portions a for the reason that the meandering pitch P exceeds 60W to extremely reduce the number of meandering portions per unit length of each boundary portion a. 
     Judging from the above result, the meandering pitch P of each boundary portion a to the axial direction L of the tube is preferably 8 to 60 times as large as the cross-sectional peripheral length W of the tube, depending on the outside diameter of the metal tube  1 , the number of areas W 1 , W 2 , the fin height or the like. 
     
       
         
           
               
             
               
                 TABLE 6 
               
             
            
               
                   
               
               
                 (Relation of meandering pitch P of boundary portion a between 
               
               
                 areas W1, W2 to coefficient of heat transfer with condensation, 
               
               
                 and also to occurrence of roll chipping, wherein flow rate of 
               
               
                 refrigerant is set to 200 kg/m 2  s) 
               
            
           
           
               
               
               
            
               
                   
                 Percentage of 
                   
               
               
                   
                 coefficient of heat 
               
               
                   
                 transfer with 
               
               
                   
                 condensation (Heat 
               
               
                   
                 exchanger tube as 
               
               
                 Meandering pitch P 
                 comparative 
               
               
                 of boundary portion 
                 example is assumed 
                 Occurrence of roll 
               
               
                 a (W to P ratio) 
                 to be 100) 
                 chipping 
               
               
                   
               
               
                  4W 
                 163 
                 X 
               
               
                  8W 
                 163 
                 ∘ 
               
               
                 12W 
                 163 
                 ∘ 
               
               
                 16W 
                 155 
                 ∘ 
               
               
                 20W 
                 154 
                 ∘ 
               
               
                 24W 
                 153 
                 ∘ 
               
               
                 28W 
                 153 
                 ∘ 
               
               
                 32W 
                 150 
                 ∘ 
               
               
                 36W 
                 148 
                 ∘ 
               
               
                 40W 
                 146 
                 ∘ 
               
               
                 44W 
                 145 
                 ∘ 
               
               
                 48W 
                 143 
                 ∘ 
               
               
                 52W 
                 142 
                 ∘ 
               
               
                 56W 
                 138 
                 ∘ 
               
               
                 60W 
                 134 
                 ∘ 
               
               
                 64W 
                 119 
                 ∘ 
               
               
                 68W 
                 108 
                 ∘ 
               
               
                 72W 
                 104 
                 ∘ 
               
               
                 76W 
                 103 
                 ∘ 
               
               
                 80W 
                 101 
                 ∘ 
               
               
                   
               
            
           
         
       
     
     EXAMPLE 5 
     12 kinds of heat exchanger tubes were manufactured by making it condition that the constituent elements were set to be equal to those of the heat exchanger tube as the example 3 except that the lead angles θ, θ′ of the fins  10 ,  11  to the axial direction L of the tube were varied within the range of ±50° to ±60°, and the meandering pitch P of each boundary portion a between the adjacent areas W 1 , W 2  was set to 15W (W represents the cross-sectional peripheral length of the heat exchanger tube). 
     Subsequently, the measurement of the coefficient of heat transfer with condensation in the case of setting the flow rate of refrigerant to 200Kg/m 2  s was made on each of the above heat exchanger tubes as the example 5. The percentage of the coefficient of heat transfer with condensation in each heat exchanger tube as the example 5 is shown in Table 7. 
     The percentage of the coefficient of heat transfer in each heat exchanger tube was given by making the measurement ten times on each heat exchanger tube in the state of a single tube by using a measuring device and then finding the average of the measured values to make a comparison by assuming the percentage of the coefficient of heat transfer with condensation in the heat exchanger tube having the fin lead angles θ, θ′ of ±20° to the axial direction L of the tube to be 100. 
     As shown in table 7, it was ascertained that the preferable range of the lead angle 0 of each fin  10  was 15 to 50°, while that of the lead angle 0′ of each fin  11  was −15 to −50°, depending on the outside diameter of the tube or other elements. 
     
       
         
           
               
             
               
                 TABLE 7 
               
             
            
               
                   
               
               
                 (Relation between change in lead angles θ, θ′ of fins and 
               
               
                 coefficient of heat transfer with condensation, wherein flow rate 
               
               
                 of refrigerant is set to 200 kg/m 2  s) 
               
            
           
           
               
               
               
            
               
                   
                   
                 Percentage of coefficient of heat 
               
               
                   
                   
                 transfer with condensation (Heat 
               
               
                   
                 Lead angle θ, θ′ of fin 
                 exchanger tube having θ, θ′ of 
               
               
                   
                 (±°) 
                 ±20° is assumed to be 100) 
               
               
                   
                   
               
            
           
           
               
               
               
            
               
                   
                 5 
                 60 
               
               
                   
                 10 
                 76 
               
               
                   
                 15 
                 96 
               
               
                   
                 20 
                 100 
               
               
                   
                 25 
                 105 
               
               
                   
                 30 
                 110 
               
               
                   
                 35 
                 113 
               
               
                   
                 40 
                 114 
               
               
                   
                 45 
                 115 
               
               
                   
                 50 
                 110 
               
               
                   
                 55 
                 80 
               
               
                   
                 60 
                 75 
               
               
                   
                   
               
            
           
         
       
     
     EXAMPLE 6 
     15 kinds of heat exchanger tubes as the example 6 were manufactured by making it condition that the constituent elements were set to be equal to those of the heat exchanger tube as the example 3 except that the fin height h was varied within the range of R/80 to R/10 as small as the outside diameter R of the metal tube  1 , and the meandering pitch P of each boundary portion a between the adjacent areas W 1 , W 2  was set to 15W (W represents the cross-sectional peripheral length of the tube). 
     Subsequently, the measurement of the coefficient of heat transfer with condensation and that of the condensing pressure loss in the case of setting the flow rate of refrigerant to 200 kg/m 2 s were made on each of the heat exchanger tubes as the example 6. The percentage of the coefficient of heat transfer with condensation in each of the above heat exchanger tubes as the example 6 is shown in Table 8, together with the percentage of the condensing pressure loss. 
     The percentage of the coefficient of heat transfer and that of the condensing pressure loss in each heat exchanger tube were given by making the measurement ten times on each heat exchanger tube in the state of a single tube by using a measuring device and then finding the average of the measured values to make a comparison by assuming the percentage of the coefficient of heat transfer with condensation and that of the condensing pressure loss in the heat exchanger tube having the fin height h of R/40 as the example 6 to be respectively 100. 
     As shown in Table 8, with the increasing fin height h, high coefficient of heat transfer with condensation was ensured, while the condensing pressure loss was increased. Judging from the above fact, it was ascertained that the preferable range of the fin height h was R/70 to R/15. 
     
       
         
           
               
             
               
                 TABLE 8 
               
             
            
               
                   
               
               
                 (Fin height h, percentage of coefficient of heat transfer with 
               
               
                 condensation and percentage of condensing pressure loss, 
               
               
                 wherein flow rate of refrigerant is set to 200 kg/m 2  s and R 
               
               
                 represents the outside diameter of the tube) 
               
            
           
           
               
               
               
            
               
                   
                 Percentage of coefficient 
                 Percentage of condensing 
               
               
                   
                 of heat transfer (Heat 
                 pressure loss (Heat 
               
               
                 Fin height h 
                 exchanger tube having h of 
                 exchanger tube having h of 
               
               
                 (R to h ratio) 
                 R/40 is assumed to be 100) 
                 R/40 is assumed to be 100) 
               
               
                   
               
            
           
           
               
               
               
            
               
                 R/10 
                 142 
                 165 
               
               
                 R/15 
                 136 
                 130 
               
               
                 R/20 
                 128 
                 121 
               
               
                 R/25 
                 121 
                 116 
               
               
                 R/30 
                 112 
                 107 
               
               
                 R/35 
                 107 
                 104 
               
               
                 R/40 
                 100 
                 100 
               
               
                 R/45 
                 97 
                 96 
               
               
                 R/50 
                 95 
                 93 
               
               
                 R/55 
                 94 
                 91 
               
               
                 R/60 
                 92 
                 89 
               
               
                 R/65 
                 91 
                 87 
               
               
                 R/70 
                 89 
                 84 
               
               
                 R/75 
                 79 
                 70 
               
               
                 R/80 
                 72 
                 65 
               
               
                   
               
            
           
         
       
     
     Seventh Embodiment 
     A metal strip machining roll  2  shown in FIG. 14 is formed by combining two roll pieces  2   a ,  2   b  together in layers parallel to the axial direction, and a large number of fine parallel grooves  20 ,  21  respectively having the reversed lead angles θ1, θ1′ to the axial direction are formed on the surfaces of the adjacent roll pieces  2   a ,  2   b . The bottom angle α 1  of each groove  20  is set to be smaller than that α1′ of each groove  21 . 
     A contact surface c of the roll piece  2   a  with the roll piece  2   b  adjacent thereto is inclined at a predetermined inclination angle θ2 to a surface perpendicular to the axial direction of the roll  2 . 
     In an internally-grooved beat exchanger tube in the seventh embodiment manufactured by using the metal strip machining roll  2  shown in FIG. 14, a rolled metal strip  1   a  is machined as shown in FIG.  15 . 
     The internal surface of the internally-grooved heat exchanger tube in the seventh embodiment is divided into two areas W 1 , W 2  correspondingly to the roll pieces  2   a ,  2   b , and a boundary portion a meandering to the axial direction L of the tube at a certain pitch P is formed between the adjacent areas W 1 , W 2  correspondingly to the contact surface c. 
     A large number of fine parallel fins  10  each having a predetermined lead angle θ to the axial direction L of the tube are formed in one area W 1  out of the adjacent areas correspondingly to the grooves  20 , while a large number of fine parallel fins  11  each having a lead angle θ′ equal in direction and amount to the lead angle θ to the axial direction L of the tube are formed in the area W 2  adjacent to the area W 1  correspondingly to the grooves  21 . The pitches of the fins  10 ,  11  are equal to each other. 
     The vertical angle α of each fin  10  in the area W 1  is formed to be smaller than the vertical angle α′ of each fin  11  in the area W 2  according to the difference between the bottom angles α1, α1′ of the grooves  20 ,  21 . 
     According to the heat exchanger tube in the seventh embodiment, since the fins  10 ,  11  in the adjacent areas W 1 , W 2  are different in vertical angle α, α′, and besides, the boundary portion a between both the areas W 1 , W 2  is formed in the state of meandering to the axial direction of the tube, the interference between the turbulent flows of refrigerant may be prevented by the butted portions of the fins in the boundary portion a before and behind the flow direction, and as a result, it is possible to provide an internally-grooved heat exchanger tube of higher heat transfer performance. 
     The heat exchanger tube in the seventh embodiment is substantially similar in other constitution, operation and effects to the heat exchanger tube in the first embodiment. 
     EXAMPLE 7 
     A metal strip made of deoxidized copper was used to manufacture  22  samples of heat exchanger tubes as the example 7 as shown in FIG. 15, that is, a heat exchanger tube structured such that the internal surface of the tube is divided into two continuous areas W 1 , W 2  parallel to the axial direction of the tube, the cross-sectional peripheral length W (i.e., the width of the metal strip) is 20 mm, the thickness (i.e., the thickness of the groove bottom) t is 0.25 mm, the meandering pitch P of the boundary portion a between the adjacent areas W 1 , W 2  is 15W (300 mm), the meandering width of the boundary portion a is 10 mm, each of the heights h, h′ of the fins  10 ,  11  is 0.2 mm, each of the pitches p, p′ of the fins  10 ,  11  is 0.30 mm, each of the lead angles θ, θ′ of the fins  10 ,  11  to the axial direction L of the tube is 20°, and the fin vertical angles α, α′ (except for one of the heat exchanger tubes) are not equal to each other by varying the vertical angle a of each fin  10  within the range of 5 to 30°, while varying the vertical angle α′ of each fin  11  within the range of 10 to 35°. 
     Subsequently, the measurement of the percentage of the coefficient of heat transfer with condensation and that of the percentage of the condensing pressure loss in the case of setting the flow rate of refrigerant to 200 Kg/m 2  s were made on each of the heat exchanger tubes in the example 7. The percentage of the coefficient of heat transfer with condensation in each of the above heat exchanger tubes as the example 7 is shown in Table 9, together with the percentage of the condensing pressure loss. At the same time, the expansion of each heat exchanger tube was carried out (by pressing an expanding bar into the tube to expand the tube by a certain amount). The presence or absence of the fall of the fins at the time of expanding the tube is also shown in Table 9. 
     Incidentally, the percentage of the coefficient of heat transfer with condensation and that of the condensing pressure loss in each of the above heat exchanger tubes as the example 7 were given by making the measurement ten times on each of the heat exchanger tubes in the state of a single tube by using a measuring device and then finding the average of the measured values to make a comparison by assuming the percentage of the coefficient of heat transfer with condensation and that of the condensing pressure loss in the heat exchanger tube having the vertical angles α, α′ of 25° for the fins  10 ,  11  to be respectively 100. As to the occurrence of the fall of the fins at the time of expanding the tube, the presence of the fall of the fins is expressed by X, while the absence of the fall of the fins is expressed by ◯. 
     As shown in Table 9, when either of the fin vertical angles α, α′ was less than 10°, the fall of the fins occurred at the time of expanding the tube. On the other hand, when either of the fin vertical angles α, α′ exceeded 30°, it was ascertained that there was a tendency to increase the condensing pressure loss in excess of the improvement in the coefficient of heat transfer with condensation. Thus, the fin vertical angles α, α′ are preferably selected from values within the range of 10 to 30°. 
     Further, it was also ascertained that the heat transfer performance could be improved by differentiating the fin vertical angles α, α′ such as to set one of the fin vertical angles to be not more than 20° while setting the other fin vertical angle to be not more than 30°. 
     
       
         
           
               
             
               
                 TABLE 9 
               
             
            
               
                   
               
               
                 (Percentage of coefficient of heat transfer with condensation, 
               
               
                 percentage of condensing pressure loss and presence or absence 
               
               
                 of fall of fins in expansion of tube in case of independently 
               
               
                 varying fin vertical angles α, α′) 
               
            
           
           
               
               
               
               
               
            
               
                 Fin 
                 Fin 
                 Percentage of 
                   
                 Presence of 
               
               
                 vertical 
                 vertical 
                 coefficient of 
                 percentage of 
                 absence of 
               
               
                 angle 
                 angle 
                 heat transfer 
                 condensing 
                 fall of fins in 
               
               
                 α (°) 
                 α′ (°) 
                 with condensation 
                 pressure loss 
                 expansion 
               
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 5 
                 10 
                 — 
                 — 
                 X 
               
               
                 5 
                 15 
                 — 
                 — 
                 X 
               
               
                 5 
                 20 
                 — 
                 — 
                 X 
               
               
                 5 
                 25 
                 — 
                 — 
                 X 
               
               
                 5 
                 30 
                 — 
                 — 
                 X 
               
               
                 5 
                 35 
                 — 
                 — 
                 X 
               
               
                 10 
                 15 
                 130 
                 121 
                 ∘ 
               
               
                 10 
                 20 
                 125 
                 117 
                 ∘ 
               
               
                 10 
                 25 
                 120 
                 115 
                 ∘ 
               
               
                 10 
                 30 
                 115 
                 112 
                 ∘ 
               
               
                 10 
                 35 
                 109 
                 111 
                 ∘ 
               
               
                 15 
                 20 
                 120 
                 110 
                 ∘ 
               
               
                 15 
                 25 
                 114 
                 108 
                 ∘ 
               
               
                 15 
                 30 
                 110 
                 107 
                 ∘ 
               
               
                 15 
                 35 
                 104 
                 105 
                 ∘ 
               
               
                 20 
                 25 
                 108 
                 103 
                 ∘ 
               
               
                 20 
                 30 
                 104 
                 101 
                 ∘ 
               
               
                 20 
                 35 
                 99 
                 100 
                 ∘ 
               
               
                 25 
                 25 
                 100 
                 100 
                 ∘ 
               
               
                 25 
                 30 
                 100 
                 97 
                 ∘ 
               
               
                 25 
                 35 
                 88 
                 91 
                 ∘ 
               
               
                 30 
                 35 
                 76 
                 89 
                 ∘ 
               
               
                   
               
            
           
         
       
     
     Eighth Embodiment 
     A metal strip machining roll  2  shown in FIG. 16 is formed by combining three roll pieces  2   a ,  2   b ,  2   a  together in layers parallel to the axial direction. 
     A contact surface c of the left roll piece  2   a  with the center roll piece  2   b  and a contact surface c of the center roll piece  2   b  with the right roll piece  2   a  as shown in FIG. 16 are respectively composed of two continuous surfaces respectively inclined at the reverse inclination angles to a surface perpendicular to the axial direction of the roll  2 , and the opposite contact surfaces c, c are formed in a symmetrical shape. 
     A large number of fine parallel grooves  20  each having a certain lead angle θ1 to the axial direction of the roll  2  are formed on the peripheral surfaces of the roll pieces  2   a ,  2   a.    
     A large number of fine parallel grooves  21  each having the reversed lead angle θ1′ of the lead angle θ1 to the axial direction of the roll  2  are formed on the peripheral surface of the center roll piece  2   b.    
     The grooves  20  on the peripheral surfaces of the roll pieces  2   a ,  2   a  are formed at a pitch (i.e., an interval between the centers of the bottom in the cross direction of the roll) p 1  smaller than the pitch p 1 ′ of the grooves  21  on the center roll piece 
     In an internally-grooves heat exchanger tube in the eighth embodiment manufactured by using the metal strip machining roll  2  shown in FIG. 16, a rolled metal strip  1   a  is machined as shown in FIG.  17 . 
     A boundary portion a meandering to the axial direction L of the tube at a certain pitch P is formed between the adjacent areas W 1 , W 2  and between those W 2 , W 1  in order from the left of FIG. 17 correspondingly to the contact surfaces of the roll pieces  2   a ,  2   b ,  2   a  on the internal surface of the internally-grooved heat exchanger tube in the eighth embodiment. The boundary portions a, a are formed in the state of meandering in a symmetrical shape. 
     A large number of fine parallel fins  10  each having a predetermined lead angle θ to the axial direction L of the tube are formed in the opposite areas W 1 , W 1 , while a large number of fine parallel fins  11  each having the reversed lead angle θ′ of the lead angle θ to the axial direction L of the tube are formed in the center area W 2 . 
     Since the pitch p 1  of the grooves  20  of the roll  2  is smaller than the pitch p 1 ′ of the grooves  21 , the fins  10  in the areas W 1 , W 1  are also formed at a pitch p smaller than the pitch p′ of the fins  11  in the center area W 2 . 
     According to the internally-grooved heat exchanger tube in the eighth embodiment, since not only the boundary portion a between the adjacent areas W 1 , W 2  is formed in the state of meandering to the axial direction L of the tube, but also the lead angles θ, θ′ of the fins  10 ,  11  in the adjacent areas W 1 , W 2  are reversed, while the pitches p, p′ of the fins  10 ,  11  are also different from each other, the interference between the flows of refrigerant in the joined portion of the fins  10 ,  11  in the boundary portion a less occurs, resulting in the greater improvement of heat transfer performance. 
     The internally-grooved heat exchanger tube in the eighth embodiment is substantially similar in other constitution, operation and effects to the internally-grooved heat exchanger tube in the sixth embodiment. 
     Other Embodiments 
     When a metal strip machining roll for an internally-grooved heat exchanger tube according to the present invention is formed by combining a set of roll pieces  2   a ,  2   b  adjacent to each other through a contact surface c composed of a plurality of F continuous inclined surfaces, and the other set of roll pieces  2   a ,  2   b  adjacent to each other through a contact surface c composed of a plurality of continuous inclined surfaces as shown in FIG. 18, each of the contact surfaces c, c need not be composed of the inclined surfaces of the same number. 
     Further, in the roll shown in FIG. 16 or  18 , one contact surface c composed of a plurality of continuous inclined surfaces and the other contact surface c composed of one inclined surface are also useful. 
     Further, when the contact surface c is composed of the plurality of continuous inclined surfaces, the inclined surfaces need not be equal in length to each other. 
     In the internally-grooved heat exchanger tube according to the present invention, while the fins  10 ,  11  in the adjacent areas W 1 , W 2  (or W 2 , W 1 ) have preferably the reversed lead angles θ, θ′ to the axial directions L of the tube similarly to the case of the above embodiments, it is to be understood that the lead angles θ, θ′ may be different from each other without being reversed. 
     As long as the boundary portion a between the adjacent areas W 1 , W 2  is formed in the state of meandering to the axial direction of the tube as a whole, a boundary portion having a portion formed parallel to the axis of the tube is also useful. 
     The reason is that even if the boundary portion a may have the portion parallel to the axial direction of the tube, the similar operation and effects to those described above may be also displayed in other meandering portions of the boundary portion. 
     The number of the areas W 1 , W 2  formed in the tube may be varied according to the outside diameter of the tube. 
     POSSIBILITY OF INDUSTRIAL UTILIZATION 
     According to the internally-grooved heat exchanger tube in the present invention, in the case of letting the refrigerant flow within the tube parallel to the axial direction L of the tube, the refrigerant flows along the fins  10 ,  11  formed in the adjacent areas W 1 , W 2  to form the turbulent flow in the boundary portion a between the areas W 1 , W 2 , so that this turbulent flow makes it possible to accelerate the exchange of heat between the refrigerant and the internal surface of the tube, resulting in the improvement in heat transfer efficiency. 
     At this time, since the boundary portion a between the areas W 1 , W 2  for the formation of the turbulent flow of refrigerant is formed in the state of meandering to the axial direction L of the tube so that the positions of the turbulent-flow formed portion (the boundary portion a) of the refrigerant in the inner peripheral direction of the tube are different little by little before and behind the flow direction of refrigerant, the interference between the turbulent flows formed before and behind the flow direction of refrigerant is restrained to thereby make it possible to prevent the heat transfer efficiency from being reduced. 
     Further, since the turbulent-flow formed portion of refrigerant is shifted in a zigzag shape toward the inner side of the tube along the meandering boundary portion a, the temperature gradient parallel to the peripheral direction is restrained to thereby make it possible to more sufficiently improve the heat transfer performance. 
     According to the internally-grooved heat exchanger tube in the present invention as defined in claim  2 , since the fins  10  formed in one area W 1  out of the adjacent areas and the fins  11  formed in the other area W 2  respectively have the reversed lead angles θ, θ′ to the axial direction L of the tube, the collision between the flows of refrigerant occurs in the boundary portion a between the adjacent areas W 1 , W 2  to form a more active turbulent flow, and as a result, the heat transfer performance is improved. 
     According to the internally-grooved heat exchanger tube in the present invention as defined in claim  3 , since the boundary portion a between the adjacent areas W 1 , W 2  is formed in the state of meandering to the axial direction L of the tube at a certain meandering pitch P, and the meandering pitch P is 8 to 60 times as large as the cross-sectional peripheral length W of the metal tube  1 , the roll chipping may be prevented from occurring in the case of forming the fins on the metal strip for the heat exchanger tube, while higher heat transfer performance may be displayed. 
     According to the internally-grooved heat exchanger tube in the present invention as defined in claim  4 , since the fins  10 ,  11  in the adjacent areas W 1 , W 2  are substantially acute triangular in cross section, and the vertical angle a of each of the fins  10 ,  11  ranges from 10 to 30°, the heat transfer efficiency may be further improved. 
     According to the internally-grooved heat exchanger tube in the present invention as defined in claim  5 , since each of the lead angles θ, θ′ of the fins  10 ,  11  in the adjacent areas W 1 , W 2  ranges from ±15 to ±50°, the heat transfer efficiency is further improved. 
     According to the internally-grooved heat exchanger tube in the present invention as defined in claim  6 , since the height h of each of the fins  10 ,  11  in the adjacent areas W 1 , W 2  is {fraction (1/15)} to {fraction (1/70)} as small as the outside diameter R of the metal tube  1 , the heat transfer performance may be further improved while the increase of the pressure loss is restrained. 
     According to the metal strip machining roll for the internally-grooved heat exchanger tube in the present invention as defined in claim  7 , since the plurality of roll pieces  2   a ,  2   b  are combined together in layers parallel to the axial direction, the large number of parallel grooves  20 ,  21  different in at least one selected among lead angle θ1, θ1′ to the axial direction of the roll, bottom angle α1,α1′ and groove pitch p 1 , p 1 ′ are formed on the outer surfaces of the adjacent roll pieces  2   a ,  2   b , and the contact surface c of the roll piece  2   a  with the roll piece  2   b  adjacent to the roll piece  2   a  forms a surface inclined to the surface perpendicular to the axial direction of the roll, the rolled metal strip for manufacturing the internally-grooved heat exchanger tube according to the present invention may be machined industrially and smoothly. 
     According to the metal strip machining roll for the internally-grooved heat exchanger tube in the present invention as defined in claim  8 , since the plurality of roll pieces  2   a ,  2   b  are combined together in layers parallel to the axial direction, the large number of parallel grooves  20 ,  21  different in at least one selected among lead angle θ1,θ1′ to the axial direction of the roll, bottom angle α1,α1′ and groove pitch p 1 , p 1 ′ are formed on the outer surfaces of the adjacent roll pieces  2   a ,  2   b , and the contact surface c of the roll piece  2   a  with the roll piece  2   b  adjacent to the roll piece  2   a  is composed of the plurality of continuous surfaces respectively inclined to the surface perpendicular to the axial direction of the roll, the meandering pitch P of the boundary portion a between the adjacent areas W 1 , W 2  may be made smaller in the case of machining the rolled metal strip for manufacturing the internally-grooved heat exchanger tube according to the present invention.