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 (t₁) of 0.27 mm, with sixty internal fins 13 each having a height (H₁) of 0.15 mm, a projection angle (β₁) of 56°, and a spiral angle (α₁) 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°.