JPS6066097A - Heat transfer pipe - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] Industrial Application Field The present invention relates to a heat exchanger tube, such as a heat exchanger for an air conditioner or refrigerator, which allows a phase-changing refrigerant to flow inside the tube to exchange heat with a fluid outside the tube. .

Structure of conventional example and its problems Conventionally, as shown in FIG. 1, as a heat transfer tube of this type, an internal spiral grooved tube 2 having a plurality of helical narrow grooves 1 formed at an angle of β with respect to the tube axis on the inner wall of the tube has been used. ing.

This internal spiral grooved pipe 2 has an angle β of 4 to 1 with respect to the pipe axis.
By providing a 5° narrow groove, in the case of condensation heat transfer, the condensate gathers at the bottom of the groove due to the effect of surface tension, and the average thickness of the condensate film formed on the tube wall becomes thinner, which improves the boiling heat transfer. In this case, the liquid refrigerant at the bottom of the tube rises in the narrow groove due to capillary action, and the average thickness of the refrigerant liquid film formed on the tube wall is thinner, which is said to improve heat transfer performance.

However, according to our experience, for example, in the case of condensation heat transfer, the condensate collects at the bottom of the narrow groove and flows inside the groove, creating a thin condensate film at the top of the groove because the refrigerant is very dry. That is, only at the beginning of the condensation process. 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 beyond the narrow grooves, so that the heat transfer performance does not improve much. In addition, in the case of boiling heat transfer, as the boiling process progresses and reaches a high dryness region, the liquid refrigerant flowing along the pipe wall collides with the narrow grooves and becomes droplets, which separate from the pipe wall and float in the steam. Therefore, the heat transfer performance is not improved at all.

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 and capable of capturing suspended liquid refrigerant, and in addition, a thin temperature boundary layer is provided on the heat transfer surface. The purpose is to significantly improve heat transfer performance by forming .

Structure of the Invention The heat transfer tube of the present invention is an annular outer tube having a plurality of spiral thin grooves on the inner wall, a plurality of cut-out portions having openings at both ends in the tube axis direction, and a plurality of small holes. A thin-walled member is inserted and brought into thermal contact with the outer tube.

With this configuration, in the case of condensation heat transfer,
The plurality of cut and raised portions of the annular thin-walled member function as fins, or heat transfer surfaces, and even if the spiral groove is filled with condensate, the cut and raised portions remain in the steam and form a thin temperature boundary layer before the boundary layer. Condenses steam by edge effect. Furthermore, even if the cut-out portion is buried in condensate, the condensate film has a laminar flow, so it is highly effective in forming a thin temperature boundary layer. Next, in the case of boiling heat transfer, the multiple cut-outs of the annular thin-walled member are in the liquid refrigerant at the beginning of the boiling process, and function as fins to form a thin temperature boundary layer, resulting in the boundary layer leading edge effect. evaporate the liquid refrigerant. In extremely dry regions, the cut and raised portions collide with the narrow grooves, capture droplets that have separated from the pipe wall, and evaporate them.

・Furthermore, the multiple small holes in the annular thin-walled member allow the inflow of refrigerant vapor into the narrow spiral groove in condensation heat transfer, and the inflow of liquid refrigerant into the narrow spiral groove and the outflow of evaporated refrigerant vapor in boiling heat transfer. Be active.

In addition, since both ends of the cut and raised portion of the annular thin-walled member are open in the tube axis direction, shape resistance is small and pressure loss hardly increases.

From the above, the present invention can achieve a significant improvement in heat transfer performance.

Description of examples 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.

As shown in the figure, an outer tube 4 having a plurality of spiral grooves 3 on its inner wall.
A thin annular member 7 having a plurality of cut-out portions 5 and a plurality of small holes 6 is inserted into the heat exchanger tube, and is brought into close contact with the top of the spiral groove 3 in order to obtain thermal contact with the outer tube 4, thereby forming a heat transfer tube. ing. The plurality of cut-out portions 5 provided on the annular thin-walled member 7 are arranged in the tube axis direction.
That is, an opening sa that is open at both ends in the flow direction of the refrigerant;
sb, and a plurality of small holes 6 are provided in the annular thin member 7 substrate other than the cut and raised portion 5. The annular thin member 7 is
As shown in FIG. 3, a plurality of cut and raised holes 5 and a plurality of small holes 6 are provided in a thin plate 8, and as shown in FIG. The tube is formed into an annular shape with a certain curvature, and both ends in the tube axis direction are joined.

In addition, in order to make good line contact with the top of the narrow groove 3 when the annular thin-walled member 7 is inserted into the outer tube 4, the annular thin-walled member 7 is coated with brazing material in advance and heated after being inserted into the outer tube 4. It may be made of wax.

In addition, although the cut-and-raised portions 5 are arranged in a base arrangement, they may be arranged in a staggered manner.Furthermore, the top of the cut-and-raised portions 5 is made parallel to the tube axis because it is easy to form into an annular shape, but the velocity component perpendicular to the tube axis is In order to promote the inflow of refrigerant into the spiral narrow groove 3, the opening 5 is tilted or oriented with respect to the tube axis.
The heights of a and 5b may be changed and cut up.

Next, the action and effects will be explained.

First, in the case of condensation heat transfer, the plurality of cut-out portions 5 of the annular thin-walled member 7 function as fins, that is, heat transfer surfaces, and because they exist intermittently at certain intervals in the flowing refrigerant, the temperature boundary layer is thin and the heat transfer surface is The so-called boundary layer leading edge effect with high transmission rate can be utilized. Even if the spiral narrow groove 3 is filled with condensate, the cut-and-raised portion 5 remains in the steam, forming a thin temperature boundary layer and condensing the steam. Furthermore, even when the cut-out portion 6 is buried in condensate, the condensate film is a laminar flow, so the effect of forming a thin temperature boundary layer is significant.

Next, in the case of boiling heat transfer, the plurality of cut-out parts 5 of the annular thin-walled member 7 are in the liquid refrigerant at the beginning of the boiling process, and function as fins, forming a thin temperature boundary layer and causing the liquid to cool. Evaporate the refrigerant. In addition, in a high dryness region, the cut-and-raised portion 5 traps liquid refrigerant, which is attracted by the evaporated vapor flow and increases in speed, collides with the narrow grooves, separates from the pipe wall, and tries to float in the vapor flow. evaporate.

Furthermore, the plurality of small holes 6 in the annular thin-walled member 7 are in close contact with the inner wall of the outer tube 4, and the refrigerant vapor flows into the spiral pores 3 during condensation heat transfer, and into the spiral narrow grooves 3 during boiling heat transfer. The inflow of liquid refrigerant and the outflow of the refrigerant vapor evaporated in the spiral grooves 3 are activated, respectively, and the heat transfer coefficient in the spiral grooves 3 is promoted.

On the other hand, since the cut-out portion 5 of the thin annular member has openings 5a and 5b at both ends in the tube axis direction, the shape resistance is small and the pressure loss hardly increases.

From the above, the heat transfer performance for condensation and boiling can be significantly improved.

Moreover, since the inner wall of the outer tube 4 has the spiral narrow groove 3,
The annular thin-walled member 7 is in line contact with the top of the spiral thin groove 3 and can be easily inserted along the spiral by rotating it, so manufacturing is simple, and since the frictional resistance during insertion is small, less power is required for insertion.

Effects of the Invention As described above, the present invention has a plurality of cut-out portions having a plurality of helical narrow grooves on the inner wall thereof, and a plurality of cut-out portions having a plurality of cut-out portions and a plurality of cut-out portions at both ends in the axial direction of the tube. Since it is a heat exchanger tube in which a thin annular member with a small hole is inserted and is in thermal contact with the outside X^, the following effects are achieved.

(1) The cut-and-raised portion has a boundary layer leading edge effect/functions as a capture plate for unevaporated droplets separated from the hyphen and the tube wall, thereby significantly improving both condensation and boiling heat transfer performance.

(2) Since the flow of refrigerant from the small holes to the narrow grooves is activated, the heat transfer performance for both condensation and boiling is significantly improved.

[Brief explanation of the drawing]

Figures 1a and 1b are a front view and a side sectional view of a conventional heat exchanger tube,
Fig. 2a is a front 1Ifr side view of the heat exchanger tube of the present invention, Fig. 2 is a cross-sectional view taken along line A-A in Fig. 2a, and Fig. 3a is a developed view of an annular thin-walled member used in the heat exchanger tube. , Figure 3 is the third
FIG. 4 is a cross-sectional view taken along the line A--A in Figure a, and a perspective view of the open annular thin member. 3... Spiral thin groove, 4... Outer tube, 5.
... Cut-out portion, 5a, 5b... Opening, 6
・Small hole, A... Annular thin wall member, 8... Thin plate. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Figure (O-) (b) Figure 2 (α) (b) Figure 3 Figure 4

Claims (1)

[Claims] An annular thin-walled member having a plurality of cut and raised portions having openings at both ends in the tube axis direction and a plurality of small holes is inserted into an outer tube having a plurality of spiral thin grooves on the inner wall, and the outer tube A heat exchanger tube in thermal contact with.