Patent Publication Number: US-2002011332-A1

Title: Refrigerant tube for heat exchangers

Description:
BACKGROUND OF THE INVENTION  
       [0001] 1. Field of the Invention  
       [0002] The present invention relates to a refrigerant tube for heat exchangers and, more particularly, to a refrigerant tube for heat exchangers of air conditioning systems, provided with a plurality of internal spiral fins on its inner surface for improving its heat exchange effect.  
       [0003] 2. Description of the Prior Art  
       [0004]FIG. 1 is a perspective view of a conventional heat exchanger for air conditioning systems. As shown in the drawing, the conventional heat exchanger comprises a refrigerant tube  11  and a plurality of air guide fins  3 . The refrigerant tube  11  is regularly bent to form a zigzag-shaped tube assembly. This tube  11  forms a refrigerant passage of the heat exchanger. The air guide fins  3  are vertically arranged at regular intervals, with the linear parts of the zigzagged refrigerant tube  11  passing through the fins  3 . During an operation of the heat exchanger, refrigerant flowing in the refrigerant tube  11  absorbs or dissipates heat from or to air currents flowing around the tube  11 .  
       [0005] As shown in FIGS. 2 and 3, the conventional refrigerant tube  11  for such heat exchangers has an outer diameter of 7 mm or 9 mm, with a plurality of internal spiral fins  13  regularly formed on the inner surface of the tube  11  while defining a plurality of grooves  15  between them. The internal fins  13  and grooves  15  enlarge the heat transferring surface area of the tube  11 , in addition to agitating the thermal boundary layer inside the refrigerant flowing in the tube  11 . Therefore, the fins  13  and grooves  15  promote heat transfer between the refrigerant inside the tube  11  and air currents outside the tube  11 , thus improving the heat exchange effect of the heat exchanger.  
       [0006] In a detailed description, the fins  13  and grooves  15  enlarge the internal surface area of the tube  11 , at which the tube  11  comes into contact with liquid or gas refrigerant. The fins  13  and grooves  15  also produce capillary effect and shear flow in refrigerant flowing in the tube  11  at a low flow rate, thus increasing the turbulent intensity of the liquid layer in the tube  11 . In such a case, the internal surface area of the tube  11 , and the turbulent intensity and thickness of the liquid layer in the tube  11  vary in accordance with the number and shape of the fins  13 .  
       [0007] While designing such refrigerant tubes  11  for heat exchangers, it is necessary to predetermine the optimal design factors of the internal fins  13 , such as the number, height, projecting angle and spiral angle of the fins  13 .  
       [0008] In the prior art, a standard method of predetermining the design factors of such internal fins of refrigerant tubes has not been proposed, but the internal fins have been designed in accordance with an optimal combination of design factors obtained from repeated tests.  
       [0009] That is, the tests are performed while changing the design factors of the internal fins under a variety of expected conditions, such as the quantity and kind of refrigerant and environmental conditions, so as to produce an optimal combination of the design factors.  
       [0010] The conventional refrigerant tube  11  for heat exchangers designed through the above-mentioned process has an outer diameter of 7 mm or 9 mm and a thickness (t 1 ) of 0.27 mm, with sixty internal fins  13  each having a height (H 1 ) of 0.15 mm, a projection angle (β 1 ) of 56°, and a spiral angle (α 1 ) of 18°.  
       [0011] In recent years, it is desired to reduce the outer diameter of the refrigerant tube  11  in an effort to reduce the production cost and air-side pressure loss of the tube  11 .  
       [0012] When the above-mentioned design factors of the fins  13  are applied to a refrigerant tube  11 , having such a reduced outer diameter, without changing the design factors of the fins  13 , the refrigerant-side pressure loss of the tube  11  is undesirably increased, thus reducing the heat exchange efficiency of the tube  11 . In addition, the above-mentioned design factors of the internal fins  13  exceed design limits of fins that can be practically formed on the tube  11  having such a reduced outer diameter, and so it is almost impossible to produce a desired refrigerant tube, having such a reduced outer diameter and provided with fins  13  having such design factors.  
       [0013] The conventional refrigerant tube  11  is designed without considering the use of newly proposed alternative refrigerant in place of typical refrigerant, and so the tube  11  used with such alternative refrigerant cannot perform its designed operational function due to pressure loss and heat transfer coefficient of the alternative refrigerant which are different from those of the typical refrigerant.  
       [0014] Therefore, it is necessary to propose a refrigerant tube, which has a reduced outer diameter and internal fins having optimally designed number and shape, thus reducing the pressure loss of refrigerant and improving the heat transfer characteristics of the refrigerant, such as heat transfer coefficient.  
       SUMMARY OF THE INVENTION  
       [0015] Accordingly, the present invention has been made keeping in mind the above problems occurring in the prior art, and an object of the present invention is to provide a refrigerant tube for heat exchangers, which has a desirably reduced outer diameter, in addition to internal fins having optimal design factors preferably compatible with the reduced outer diameter of the tube, and which thus reduces the production cost of the heat exchangers and accomplishes the recent trend of compactness of the heat exchangers, and which has several advantages expected from small-diameter refrigerant tubes, such as a reduction in air-side pressure loss, and which improves heat transfer efficiency of the heat exchangers, and enhances the heat exchange operational performance of the heat exchangers.  
       [0016] In order to accomplish the above object, the present invention provides a refrigerant tube assembled with a plurality of air guide fins in a heat exchanger, wherein the refrigerant tube has an outer diameter of not larger than 5.3 mm, with a plurality of internal spiral fins formed on the inner surface of the refrigerant tube.  
       [0017] The refrigerant tube has a thickness of 0.16 mm˜0.2 mm.  
       [0018] In addition, the internal spiral fins are set in their number to 40˜50, and each have a height of 0.15 mm˜0.18 mm, a projection angle of 38°˜42°, and a spiral angle of 6°˜20°. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0019] The above and other objects, features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which:  
     [0020]FIG. 1 is a perspective view of a conventional heat exchanger;  
     [0021]FIG. 2 is a broken view of a conventional refrigerant tube for heat exchangers, showing the interior of the tube;  
     [0022]FIG. 3 is a sectional view of a part of the conventional refrigerant tube for heat exchangers;  
     [0023]FIG. 4 is a broken view of a refrigerant tube for heat exchangers in accordance with the preferred embodiment of the present invention, showing the interior of the tube; and  
     [0024]FIG. 5 is a sectional view of a part of the refrigerant tube of this invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
     [0025] Reference now should be made to the drawings, in which the same reference numerals are used throughout the different drawings to designate the same or similar components.  
     [0026]FIG. 4 is a broken view of a refrigerant tube for heat exchangers in accordance with the preferred embodiment of the present invention, showing the interior of the tube. FIG. 5 is a sectional view of a part of the refrigerant tube.  
     [0027] As shown in the drawings, the refrigerant tube  51  according to the present invention is used in a heat exchanger for air conditioning systems, which consists of a plurality of air guide fins (not shown) vertically arranged at regular intervals, with the linear parts of the refrigerant tube  51  passing through the air guide fins. The refrigerant tube  51  of this invention has an outer diameter of not larger than 5.3 mm, with a plurality of internal spiral fins  53  formed on the inner surface of the tube  51  while defining a plurality of grooves  55  between them.  
     [0028] The tube  51  has a thickness (t) of 0.16 mm˜0.2 mm, while the number of the internal fins  53  is set to 40˜50. In addition, the internal fins  53  each have a spiral angle (α) of 6°˜20°, a height (H) of 0.15 mm˜0.18 mm, and a projection angle (β) of 38°42°.  
     [0029] In the present invention, the spiral angle (α) of the internal fins  53  is preferably set to 6°˜10° or 16°˜20°.  
     [0030] In comparison with a heat exchanger using a conventional refrigerant tube  11  having an outer diameter of 7 mm or 9 mm, a heat exchanger using the refrigerant tube  51  of this invention having a reduced outer diameter of 5.3 mm is increased in its refrigerant-side pressure loss at the same flow rate of refrigerant, but is reduced in the thickness (t) of its refrigerant tube  51 . The internal fins  53  of the tube  51  according to this invention are designed such that they are optimally compatible with the reduced outer diameter of the tube  51 , while considering both the increased refrigerant-side pressure loss and the reduced tube thickness (t). It is noted that the refrigerant-side pressure loss of the refrigerant tube  51  according to this invention is preferably reduced to improve the heat exchange operational performance of the heat exchanger. In addition, it is possible for manufacturers of such heat exchangers to easily manage the allowance of the internal fins  53  during a process of producing the refrigerant tubes  51 .  
     [0031] In addition, the refrigerant tube  51  having the internal fins  53  of this invention can easily use alternative refrigerant in place of typical refrigerant without changing the dimension of the tube  51  or the internal fins  53  since the fins  53  are designed in consideration of a change in the pressure loss and heat transfer coefficient in the case of replacing typical refrigerant with alternative refrigerant.  
     [0032] As described above, the present invention provides a refrigerant tube for heat exchangers. The tube of this invention has a desirably reduced outer diameter, in addition to internal fins having optimal design factors preferably compatible with the reduced outer diameter of the tube. This tube thus reduces the production cost of heat exchangers and accomplishes the recent trend of compactness of the heat exchangers, in addition to having several advantages expected from small-diameter refrigerant tubes, such as a reduction in air-side pressure loss. The refrigerant tube of this invention also improves heat transfer efficiency of the heat exchangers, and enhances the heat exchange operational performance of the heat exchangers.  
     [0033] In addition, since the internal fins of this invention are designed such that they are compatible with a small-diameter refrigerant tube, the tube optimally reduces refrigerant-side pressure loss. It is also possible for manufacturers of the heat exchangers for air conditioning systems to easily manage the allowance of the internal fins during a process of producing the refrigerant tubes.  
     [0034] Although a preferred embodiment of the present invention has been described for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.