JPS6361896A - Heat transfer pipe with small diameter - Google Patents

Abstract

PURPOSE:To provide a pipe with more excellent heat transfer performance in comparison with a pipe with smooth grooves by a method wherein on the internal surface of a pipe with specified small outer diameter, grooves which are spiral or continuous in the pipe axial direction and of which depth, width, and number are fixed in a specified range are formed and the internal surface of the pipe is brought in a coarse condition or/and corrugation is made on the side wall of the grooves in the pipe axial direction. CONSTITUTION:On the internal surface of a pipe with a small outer diameter of 3-6mm, a large number of fine grooves which are spiral or continuous in the pipe axial direction and have a groove depth of 0.1-0.3mm, a groove width of 0.05-0.2mm, and a number of 30-60 are formed and an overall pipe internal surface including the inside of the grooves is brought in a coarse surface condition like rough skin or corrugations are made on the side wall of the grooves in the pipe axial direction and both of the coarse surface condition and corrugation making are carried out under certain circumstances. As the corrugation making is carried out on the side walls of the grooves in the pipe axial direction, the internal surface area of the pipe is increased to improve heat transfer performance and moreover pulsation is generated in refrigerant liquid flow to promote turbulent flow effect.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention is a heat transfer tube for a small heat exchanger that exchanges heat by evaporating or condensing a refrigerant such as Freon, which enables thinner walls and lighter weight, and a heat transfer tube. This paper relates to the improvement of small-diameter heat exchanger tubes with the aim of improving thermal performance.

(Prior art) Heat exchangers for small air conditioners such as room air conditioners and car air conditioners that use refrigerants such as Freon generally have a large number of spiral grooves on the inner surface of the tube that are continuous in the axial direction of the tube in order to promote energy conservation. A heat exchanger tube formed with a However, in recent years, there has been a strong demand for smaller diameter and thinner heat exchanger tubes in order to reduce the cost of heat exchangers. In response to this, the present inventors have previously developed a small-diameter heat exchanger tube with an outer diameter of 3 to 6 wR, with a groove depth of 01 to 0.3 ran and a groove width α of 05 to 0.2 that are spiral or continuous in the tube axial direction on the inner surface of the tube. developed a small diameter heat exchanger tube as shown in FIG. 1 (Japanese Patent Application No. 237136/1982) having 30 to 60 grooves.

However, although the above-mentioned small-diameter heat exchanger tubes have achieved smaller diameters and thinner walls, the performance of the heat exchanger tubes is still insufficient depending on the intended use.

(Means and effects for solving the problems) The present invention has been made to solve the above problems.
mm small-diameter heat exchanger tube, the inner surface of the tube has a spiral groove or a continuous groove in the tube axis direction with a depth of 01-03 fins and a groove width of 0.05-0.
This is a small-diameter heat exchanger tube characterized by forming 50 to 60 grooves, and having a rough inner surface and/or a groove side wall corrugated in the tube axis direction.

That is, the present invention forms a large number of fine grooves in a spiral shape or continuous in the tube axis direction on the inner surface of a small-diameter heat exchanger tube with an outer diameter of 3 to 6, and roughens the entire inner surface of the tube including the inside of the groove. The groove side wall is either roughened or corrugated along the entire tube axis direction, and in some cases both the roughened surface and corrugation are applied in combination. However, in the present invention, the outer diameter of the heat exchanger tube is set to 3 to 6. If the outer diameter is less than 3 times, it will not only be difficult to form the prescribed grooves, but also the wall will become thick, making it impossible to achieve the purpose of thinning. This is because if the thickness exceeds 61, the thickness cannot be made thinner in terms of pressure resistance. Also, set the groove depth to 0.
．． 1 to 0.3 throat, groove width between 0.05 and 0.2, number of grooves to 5
The reason why the range was limited to 0 to 6o was to improve the heat transfer characteristics as a heat transfer tube, because even if the groove depth is less than 01, and the groove width is less than 0.05 rra, the groove effect as a refrigerant flow path will not be exhibited. The same thing can be said when the number of grooves exceeds 60, but it is important to note that machining the grooves and peaks will be extremely difficult, and if the groove depth exceeds 0.5 ran f, As the groove depth increases, the pressure drop of the refrigerant flowing inside the pipe increases, and even if the groove width exceeds 0.2 mm f or the number of grooves is less than 30, the groove width ratio increases and the groove effect weakens, resulting in poor heat transfer performance. This is because no improvement can be obtained.

Further, the reason why the entire inner surface of the tube is made rough is to increase the surface area inside the tube, enhance the heat transfer effect, and cause turbulent flow of the refrigerant liquid film. Therefore, if the roughness is too fine or too large, it will not be effective, and a roughness of about 1/10 to 1/2 of the groove width is appropriate.

Corrugating the entire groove side wall in the pipe axial direction increases the surface area and improves heat transfer performance, as well as creating pulsations in the refrigerant liquid flow and promoting a turbulent flow effect. If the width is too large, the groove width will be narrow and the effect will be low, and if the width of the corrugation is too small, it will be the same as without corrugation, so the width of the corrugation should be selected appropriately depending on the groove width. .

However, in order to manufacture the small diameter heat exchanger tube of the present invention, first the outer diameter is 6.
Grooving on the inner surface of the tube above the body is done by rolling or drawing using a plug, creating a spiral groove or a continuous groove in the tube axis direction with a depth of 0.
11~0.6 mm, groove width o, 15~0.6 range, number of grooves 3
0-60, side wall i 15-30' (7) grooves with sloped angles are formed at equal intervals in the circumferential direction, and the outer diameter is thicker than 6 gates with fine grooves inside the tube as shown in Figure 1. Fabricate a heat exchanger tube. Next, the heat transfer tube is compressed to a desired outer diameter by air drawing without any plugs at the mouth of the heat transfer tube, and at the same time, the entire inner surface of the tube is roughened. This diameter reduction machining rate gives a machining rate of 5 to 20% at one time,
By performing this processing, intermediate annealing if necessary, and performing diameter reduction processing two to four times, diameter reduction and surface roughening can be performed simultaneously. In addition, in order to corrugate the groove side wall in the tube axis direction, one time of diameter reduction machining failure is 60 to 50% without plugs in all of the heat exchanger tubes having the above-mentioned fine grooves and having an outer diameter larger than 6wn. By performing intermediate annealing if necessary and processing 2 to 5 times, diameter reduction, roughening and corrugation processing can be performed simultaneously.

It is thought that in the above processing, surface roughening is achieved at a relatively low processing rate, and corrugation is performed at a relatively high processing rate. By inserting intermediate annealing if necessary, the degree of processing is relaxed, and diameter reduction, surface roughening, corrugation, etc. can be performed simultaneously and easily.

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

A phosphorus-deoxidized copper tube was used as the raw tube, a grooved plug was inserted into the tube, and an inner grooved tube with an outer diameter of 6.8.10° and 12-φ was produced by rolling. Next, the processing rate of this tube is 40
% processing rate and once at a processing rate of 10 to 20% to form a fine groove (2) with an outer diameter of 5.6ff II + Iφ as shown in Figure 2. In addition, a small diameter heat exchanger tube (1) having a rough surface (3) on the surface of the ridges and corrugations (4) on the side walls of the grooves was obtained. For comparison, a tube with a rough surface and an internal groove without corrugations was also fabricated. The surface condition is shown in FIG.

The above-mentioned pipes of the present invention and comparison were assembled into a double-pipe heat exchanger, Freon R-22Q was flowed inside the pipes, and water to be cooled was flowed in a completely cross flow outside the pipes under the conditions shown in Table 1 to determine the heat transfer coefficient inside the pipes. Measurements were made. The results are shown in FIG.

As is clear from Table 1 and Figure 5, the small diameter heat exchanger tube (Nα1) which has fine grooves of the present invention, a rough surface on its surface, and waves on the side walls of the groove is different from the conventional smooth groove. .

Next, the inner grooved tube with an outer diameter of 6.8. A small-diameter heat exchanger tube having a groove on the inner surface with a diameter of 6 mm and a rough surface on the entire surface of the groove was fabricated. A microscopic photograph of the surface condition is shown in FIG. As is clear from the figure, as a result of measuring the peak, the evaporative heat transfer coefficient was approximately L2 times higher than that of the one with a smooth i-groove.

For comparison, FIG. 5 shows a microscopic photograph of the surface condition of a conventional small-diameter heat exchanger tube having all smooth fine grooves.

(Effects) As explained above, the small diameter heat transfer tube of the present invention has superior heat transfer performance compared to conventional tubes with smooth grooves, and is extremely useful as a heat transfer tube for small heat exchangers. It is.

[Brief explanation of drawings]

Fig. 1 is a cross-sectional view of an intermediately processed pipe of the present invention, Fig. 2 is a longitudinal cross-sectional view of a small-diameter heat exchanger tube having fine grooves, a rough surface, and waves on the groove side wall in the pipe of the present invention, and Fig. 5 is a cross-sectional view of a small-diameter heat transfer tube of the present invention. A diagram showing the characteristics of a small-diameter heat exchanger tube. Figure 4 is a micrograph of the surface of a small-diameter heat exchanger tube with fine grooves and ridges on the entire surface of the tube according to the present invention. Figure 5 is a microscope photo of the inner surface of a conventional small-diameter heat exchanger tube. It's a photo. 1...Small diameter heat exchanger tube, 2...Groove, 5...Rough surface,
・Waves on groove side walls

Claims (1)

[Claims] In a small-diameter heat exchanger tube with an outer diameter of 3 to 6 mm, grooves on the inner surface of the tube are spiral or continuous in the tube axis direction, with a depth of 0.1 to 0.3 mm, a groove width of 0.05 to 0.2 mm, and a groove number of 30 to 60. What is claimed is: 1. A small-diameter heat exchanger tube having a rough inner surface and/or a groove side wall corrugated in the tube axis direction.