JPS6361895A - Heat transfer pipe - Google Patents

Abstract

PURPOSE:To improve condensing heat transfer coefficient with the help of smooth flowing of refrigerant liquid by a method wherein a number of fine ridges and grooves formed in a straight or spiral shape to the pipe axis are installed in the inside of a heat transfer pipe and a number of locally broken parts used as liquid flow passages between adjoining grooves are installed. CONSTITUTION:A number of ridges 2 and grooves 3 formed in a straight or spiral shape to the pipe axis are installed in the inside of a heat transfer pipe 1 and a number of locally broken parts 4 are installed in the longitudinal direction of the furrows 2. These broken parts are used as the refrigerant liquid flow passages between adjoining grooves 3 in the circumferential direction of the pipe and force the liquid to flow in branched state to improve heat transfer characteristic. When the broken parts are excessively provided, the branched flow of liquid is increased to reduce the flow in the axial direction and therefore, the number of the broken parts should be selected properly. When the broken parts are installed in adjoining ridges to lie in alignment in the circumferential direction, the flowing quantity is increased in the circumferential direction, and therefore duplication should be avoided if possible.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an improved heat exchanger tube for a heat exchanger that exchanges heat by evaporating or condensing a refrigerant such as Freon.

(Prior art) Small heat exchangers such as car air conditioners and room air conditioners that exchange heat using a refrigerant such as Freon have a spiral shape on the inner surface of the tube (1) or a large number of tubes in the axial direction as shown in Fig. 7. A heat exchanger tube provided with minute ridges (2) and grooves (3) is used. In this heat transfer tube, the ridges and grooves are formed independently and continuously in the tube axis direction, so the refrigerant liquid flows well in the longitudinal direction of the tube, but the refrigerant flow in the circumferential direction of the tube is divided. difficult,
For this reason, it had the disadvantage of poor heat transfer performance. In order to improve this, as shown in Figure 8, the ridges (2) are removed by cutting, etc., and grooves (3) are connected in the circumferential direction of the pipe by creating grooves (3) in the missing parts of the ridges. A heat exchanger tube has been developed that facilitates the flow of refrigerant liquid to.

However, in this heat transfer tube, since the defective parts of the ridges are provided across multiple grooves, the flow of the refrigerant liquid in the longitudinal direction is poor, and there is a problem that the heat transfer performance is deteriorated due to the stagnation of the liquid. Furthermore, since it is manufactured by machining, it has drawbacks such as poor productivity.

(Means and effects for solving the problems) The present invention has been made to solve the above problems, and includes a heat exchanger tube with a large number of fine ridges arranged linearly or spirally with respect to the tube axis. This heat transfer tube is characterized by having grooves and providing a large number of localized defects in the longitudinal direction of the ridges to form liquid flow paths between adjacent grooves.

In other words, the heat exchanger tube of the present invention has a heat exchanger tube (1) in which a large number of ridges (2) and grooves (3) are formed inside the tube (in this case, the tubes are directly aligned with the tube axis), as shown in FIG. ) This ridge (2) has a large number of local defects (A) in its longitudinal direction. These defective portions allow adjacent grooves (3) to have no flow path for refrigerant liquid in the circumferential direction of the pipe, thereby causing liquid to flow in the circumferential direction, thereby promoting heat transfer characteristics. Therefore, by providing a large number of these defective parts in the longitudinal direction of the ridge, the effect will be improved.
If the number is too large, the liquid flow will increase in the circumferential direction and the flow in the tube axis direction will decrease, so the number should be selected appropriately, but it is approximately 2 to 10 times the ridge width. It is better to provide them at a density of about one per ridge length.

If the defective part of the cut is placed so that it overlaps the adjacent ridges in the circumferential direction, there will be more flow paths in the pipe circumferential direction.
It is better to avoid duplication as much as possible.

However, in order to manufacture the heat transfer tube of the present invention, first, a large number of fine ridges and grooves are formed on the inner surface of the tube by rolling or drawing using a grooved plug to form a large number of fine ridges and grooves that are linear or spiral with respect to the tube axis. establish. This heat transfer tube is then produced by air drawing which provides strong diameter reduction without a grooved plug. In other words, by applying strong tensile stress to the pipe and continuously stretching it, strain occurs due to material elongation inside the pipe and in the ridges, causing ductile fracture locally only in the ridges. A defective part of the spring is formed.

In order to create the above-mentioned appropriate defects, the outside diameter of the pipe, the wall thickness,
The diameter reduction rate may vary slightly depending on the size of the ridges, etc. For relatively large ridges, a reduction rate of 50 to 70% is preferable, and for thin ridges, a reduction rate of about 40 to 60% is preferable. If the processing rate is lower than this, no defects will be formed, and if the processing rate is higher than this, there is a risk that the pipe will be destroyed. This processing may be performed at one time, or may be performed several times, and annealing may be performed as needed.

Further, although the heat exchanger tube of the present invention is mainly applied to a small outer diameter of 3 to 10 mm, it can also be applied to a tube with a larger diameter or a smaller diameter.

(Example) An embodiment of the present invention will be described below.

Insert a grooved plug into a phosphorus deoxidized steel pipe with an outer diameter of 20ffIffIφ and roll it to a groove depth of 0.2ff1ff+,
A heat exchanger tube having 50 grooves and a ridge width of 0.4 mm and having ridges and grooves perpendicular to the tube axis was manufactured. This heat transfer tube was subjected to diameter reduction processing at a processing rate of 60%,
Defects (4) in the longitudinal direction of the ridge (2) as shown in Figure 2
), and this portion serves as the liquid flow path of the grooves (3), (3).A heat transfer tube of the present invention having an outer diameter of 7.9 nm+n was manufactured. FIG. 6 shows a photograph of the inner surface of this heat exchanger tube cut vertically.

In this photo, the white parts show the ridges, but it can be seen that these ridges are divided in places in the longitudinal direction, creating black defects. Note that the other black parts are grooves. Figures 4 to 6 show the results of measuring the heat transfer coefficient under the test conditions shown in Table 1 for the above-mentioned heat exchanger tube of the present invention and a heat exchanger tube of the same size with ordinary grooves manufactured for comparison. Shown in the figure.

As can be seen from Table 1, Figures 4 and 5, the present invention is significantly effective in both evaporation and condensation performance. Fig. 6 shows a conventional heat exchanger tube and a heat exchanger tube of the present invention of the same length, brazed together, placed on the inlet side and outlet side, respectively, and tested for evaporation performance. As a result, it can be seen that the heat exchanger tube of the present invention has a higher transfer coefficient when placed on the refrigerant outlet side than when placed on the inlet side. This is because the refrigerant is a two-phase flow consisting mainly of a liquid layer on the inlet side, but as it moves from the center of the pipe to the outlet side, it changes to a two-phase flow consisting mainly of a gas phase, so the inlet side usually evaporates. The fact that the effect is exhibited on the outlet side can be interpreted to be due to the improved performance of the heat exchanger tube itself.

(Effects) As explained above, in the heat transfer tube of the present invention, the flow of the refrigerant liquid is carried out smoothly in the circumferential direction and the axial direction of the tube, thereby significantly improving the heat transfer performance, particularly the condensing heat transfer coefficient. Therefore, it can contribute to the miniaturization of the heat exchanger, and it is also easy to manufacture, which provides excellent effects.

[Brief explanation of the drawing]

Fig. 1 is a developed longitudinal cross-sectional view of the heat exchanger tube of the present invention, Fig. 2 is an enlarged developed longitudinal cross-sectional view of the heat exchanger tube of the present invention, Fig. 5 is a surface photograph of the longitudinal cross-section of the heat exchanger tube of the present invention, Figs. FIG. 6 is a diagram showing the heat transfer coefficient of the heat exchanger tube of the present invention, and FIGS. 7 and 8 are developed vertical cross-sectional views of conventional heat exchanger tubes.

Claims (1)

[Claims] A large number of fine ridges and grooves are provided in the tube of the heat exchanger tube in a straight or spiral manner with respect to the tube axis, and the ridges are provided with a large number of local defects in the longitudinal direction, and adjacent grooves are provided. A heat transfer tube characterized by having a liquid flow path between the tubes.