JPH0113038B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a heat exchanger tube, such as a condenser or evaporator of a refrigerator, in which a phase-changing refrigerant flows within the tube to exchange heat with a fluid outside the tube.

Conventional Structure and Problems Conventionally, as shown in FIG. 1, this type of heat exchanger tube uses an internal helical grooved tube 2 having a plurality of helical grooves 1 on the inner wall of the tube at an angle of β to the tube axis. ing.

This internal spiral grooved tube 2 has an angle β with respect to the tube axis.
By providing narrow grooves with an angle of 4 to 15 degrees, in the case of condensation heat transfer, the condensate gathers at the bottom of the grooves due to surface tension, and the average thickness of the condensate film formed on the tube wall becomes thinner. It was said that the heat transfer performance was significantly improved compared to smooth heat transfer tubes.

However, according to our experience, the condensate collects at the bottom of the narrow groove, flows through the groove, and forms a thin condensate film at the top of the groove only when the refrigerant is very dry, that is, at the beginning of the condensation process. It is. As the condensation process progresses and the degree of dryness decreases, a large amount of condensate that is generated easily fills the narrow grooves and flows over the narrow grooves, so that the heat transfer performance does not improve much. Note that the flow of the condensate film is considered to be a laminar flow based on the experimental result that the heat transfer coefficient α (heat flux) is ^-0.33 .

Purpose of the Invention The present invention eliminates the above-mentioned drawbacks of the conventional technology by adding a heat transfer surface that is difficult to be buried in condensate in a completely dry temperature range, and forming a thin temperature boundary layer on the heat transfer surface. The purpose is to significantly improve heat transfer performance.

Structure of the Invention The heat exchanger tube of the present invention includes an annular thin-walled member provided with a plurality of cut-out portions having openings at both ends in the tube axis direction, inserted into an outer tube having a plurality of spiral grooves on the inner wall, It is brought into thermal contact with the outer tube, and the height of the cut-and-raised portion is increased as the dryness of the fluid inside the tube decreases.

With this configuration, the cut-out portions of the annular thin-walled member function as fins, and because they exist intermittently at certain intervals in the flowing refrigerant, the temperature boundary layer is thin and the heat transfer coefficient is high, so-called boundary layers. You can take advantage of the layer leading edge effect. Therefore, even if the spiral groove is filled with condensate, the cut and raised part increases in height as the degree of dryness decreases, so it is in the steam flow and forms a thin temperature boundary layer, which prevents the steam from flowing. to condense. Furthermore, even if the cut-and-raised portion is buried in condensate in a considerably low dryness region, the condensate film is laminar, so it is highly effective in forming a thin temperature boundary layer. Therefore, the heat transfer coefficient is significantly improved over the entire dryness range.

On the other hand, since both ends of the cut and raised portion are open in the tube axis direction, the shape resistance is small and pressure loss hardly increases.

From the above, a remarkable improvement in heat transfer performance can be achieved.

DESCRIPTION OF EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

FIG. 2 is an overall view of the heat exchanger tube, FIG. 3 is a developed view of the annular thin-walled member, and FIG. 4 is a perspective view of the annular thin-walled member. White arrows indicate the flow direction of the refrigerant.

As shown in the figure, a thin annular member 6 having a plurality of cut-out portions 5 is inserted into an outer tube 4 having a plurality of spiral thin grooves 3 on the inner wall, and brought into thermal contact with the outer tube 4 to form a heat transfer tube. are doing. The plurality of cut-out portions 5 provided in the annular thin-walled member 6 have openings 5a and 5b that are open at both ends in the tube axis direction, that is, in the flow direction of the refrigerant.
Moreover, the height of the cut-and-raised portion is increased in each of the blocks a, b, c, and d consisting of a plurality of rows as the flow direction of the refrigerant, that is, the degree of dryness decreases. As shown in FIG. 3, the annular thin member 6 has a plurality of cut-out portions 5 of different heights on a thin plate 7.
4, and this thin plate 7, as shown in FIG.
It is formed into an annular shape with a curvature commensurate with the inner diameter of the outer tube, and both ends in the tube axis direction are joined.

Note that the annular thin-walled member 6 is inserted into the outer diameter 4, and in order to make good line contact with the top of the spiral thin groove 3, the annular thin-walled member 6 is coated with brazing material in advance, and then heated after being inserted into the outer tube 4. You can also braze it.

Further, although the cut-out portions 5 are arranged in a base arrangement in this embodiment, they may be arranged in a staggered manner.
In this example, the top part is made parallel to the tube axis because it is easy to form into an annular shape, but in order to promote the flow of steam into the spiral narrow groove by giving it a velocity component perpendicular to the tube axis. In other words, the opening 5a may be cut and raised so that the height of the opening 5a is higher than that of the opening 5b.

Next, the action and effects will be explained.

First, at the beginning of the condensation process, that is, in the high dryness region,
The thin spiral grooves 3 of the outer tube 4 make it possible to thin the condensate film formed on the tube wall, and also to thin the temperature boundary layer of steam generated in the cut-and-raised portions 5 that function as fins, resulting in a significant heat transfer coefficient. improves.

As the condensation process progresses, the dryness becomes medium to low, and even if the spiral grooves 3 are filled with condensate, the cut and raised portions 5 remain in the steam or condensate.

If it is in steam, the cut-and-raised portion 5 acts as an effective transfer surface to condense the steam, and even if it is in condensate, the cut-and-raised portion 5 promotes convective heat transfer with the condensate, so that the heat transfer coefficient is low. is significantly improved.

On the other hand, since both ends of the cut-and-raised portion 5 in the tube axis direction are open, the shape resistance is small and there is almost no increase in pressure loss due to insertion of the annular thin-walled member 6.

From the above, a remarkable improvement in heat transfer performance can be achieved.

In addition, since the inner wall of the outer tube 4 has a narrow spiral groove 3, the thin annular member 6 is in line contact with the top of the narrow spiral groove 3, and can be easily inserted along the spiral by rotating it, making it easy to manufacture. It is easy to insert, and since the frictional resistance during insertion is small, the insertion power is also low.

Effects of the Invention As described above, the present invention provides an annular thin-walled member in which an outer tube having a plurality of spiral thin grooves on the inner wall is provided with a plurality of cut-out portions having openings at both ends in the tube axis direction. Since this is a heat transfer tube that is inserted into the tube and brought into thermal contact with the outer tube, and the height of the multiple cut-out portions is increased as the dryness of the fluid inside the tube decreases, the cut-out portions are As a result, heat transfer performance can be significantly improved over the entire range from high dryness to low dryness.

[Brief explanation of drawings]

Figures 1a and b are front sectional views and side sectional views of a conventional heat exchanger tube, Figure 2a is a front sectional view of the heat exchanger tube of the present invention, and Figure 2b is taken along the line AA in Figure 2a. 3A is a developed view of the annular thin-walled member used in the heat exchanger tube, FIG. 3B is a sectional view taken along line AA in FIG. 3A, and FIG. 4 is a perspective view of the annular thin-walled member. be. 3... Spiral thin groove, 4... Outer tube, 5... Cut-and-raised portion, 5a, 5b... Opening, 6... Annular thin member, 7... Thin plate.

Claims (1)

[Claims] 1. An annular thin-walled member provided with a plurality of cut-out portions having openings at both ends in the tube axis direction is inserted into an outer tube having a plurality of spiral thin grooves on the inner wall, and is brought into thermal contact with the outer tube. and the height of the plurality of raised portions is increased as the dryness of the fluid within the tube decreases.