JPS6218865Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention is a heat exchanger tube used in a heat exchanger in which a refrigerant evaporates or condenses within the tube, and relates to the structure of an internally grooved heat exchanger tube in which a spiral groove is provided on the inner surface.

Conventionally, inner finch tubes, corrugated tubes, internally grooved tubes, and the like have been used as heat transfer tubes for the above-mentioned heat exchangers. Among these, inner finches have a star-shaped cross-section inserted into the inner surface of the tube, and although they have excellent heat transfer characteristics, they are expensive, have a large weight per unit volume, and have very large pressure losses. There are drawbacks. Further, although corrugated tubes have no problem in terms of price, they have problems with heat transfer characteristics (particularly condensation characteristics) and have large pressure losses, making them impractical.

On the other hand, internally grooved tubes have spiral fins carved into the inner surface of the tube with an inclination of In addition to being excellent, the pressure loss is extremely small, making it an excellent heat exchanger tube.

Heat pump systems have become mainstream in recent refrigerators, and the heat exchangers used in these systems operate as evaporators or condensers, so the heat transfer tubes also require a balance of performance during evaporation and condensation. It is becoming more and more like that. In this regard, in the case of internally grooved pipes, in terms of condensation performance, the height of the fins should be increased, and
Although it can be greatly improved by increasing the cross-sectional area of the fin valley and setting the lead angle to an appropriate value, the effect of these on evaporation performance is small, and such structural changes only increase pressure loss. Generally, the evaporation performance is lower than the condensation performance, resulting in an imbalance.

Therefore, when an internally grooved tube is applied to a heat exchanger tube, such as a heat exchanger for a heat pump, in which the fluid exchanges heat while undergoing a phase change (evaporation or condensation) within the tube, the capacity during evaporation will be lower than the capacity during condensation. There was a problem of lack of capacity.

The purpose of this invention is to improve the performance of the above-mentioned internally grooved tube during evaporation without impairing the performance during condensation. The ratio H/Di is 0.01~
It has many fins with a torsion angle X of 0.05 to the tube axis of 15 to 35 degrees, and one slope of the fins has a fine crack structure from the bottom of the fins to the top of the fins that promotes nucleate boiling. The present invention aims to provide a heat exchanger tube with internal grooves.

The cross-sectional shape of the fin portion of the internally grooved heat exchanger tube according to the present invention is as shown in Fig. 2, and the inner diameter of the tube is Di,
The height from the trough 1 to the top 2 of the fin is H, and the cross-sectional shape of each fin is roughly triangular or trapezoidal as shown in Figure 2, with a fine crack structure 3 on one side. have.

First, as a result of conducting various experiments on the characteristics of an internally grooved tube that does not have such a crack structure, the characteristics shown in FIGS. 4 to 6 were obtained. Figure 4 shows the changes in the tube inner heat transfer coefficient Hi when the ratio of the tube inner diameter Di to the fin height H is varied, and Figure 5 also shows the pressure loss △ versus H/Di. This shows the relationship between P and all test results obtained during both evaporation and condensation.

4 and 5, in the case of evaporation, the tube inner heat transfer coefficient Hi is the ratio H/Di of the tube inner diameter Di and the fin height H.
It can be seen that the pressure loss ΔP increases slightly as H/Di becomes larger, and the pressure loss ΔP rapidly increases from the vicinity where H/Di exceeds 0.05. In the case of condensation, the heat transfer coefficient inside the tube
It can be seen that Hi reaches a maximum near H/Di slightly exceeding 0.05, and pressure loss ΔP is almost proportional to the increase in H/Di.

Also, Figure 6 shows the tube inner heat transfer coefficient with respect to the twist angle
This summarizes the relationship between Hi and shows that in the case of evaporation, the tube inside heat transfer coefficient Hi peaks when the twist angle I understand. Also, in the case of condensation,
It can be seen that the tube inside heat transfer coefficient Hi reaches a maximum when X is around 25°.

From the above results, when using an internally grooved tube for a heat exchanger, when H/Di is in the range of 0.01 to 0.05 and It can be seen that it has satisfactory characteristics.

However, even within this range, the tube inside heat transfer coefficient Hi is higher during condensation than during evaporation, so it is necessary to improve the evaporation performance. As a method for improving such evaporation performance, it is desirable to make the surface of the fin a porous sintered metal structure or a so-called nucleate boiling promoting structure, such as a mechanically uneven structure. In such a nucleate boiling promoting structure, bubbles held in minute spaces formed by porous or uneven shapes grow by heating, fly out of these spaces, and some of them remain in the spaces, and then continue to grow. The liquid flows into different places, and the bubbles left behind in these spaces serve as starting points for subsequent growth and continue boiling, significantly improving evaporation performance.

However, due to manufacturing issues, it is difficult to form a porous sintered metal structure on the inner surface of the tube, which can cause deterioration over time due to clogging due to oil contained in the refrigerant, and peeling due to tube expansion during heat exchanger assembly. It is even more difficult to mechanically form a fine uneven structure inside the tube, and there are other disadvantages such as the structure being destroyed due to tube expansion during heat exchanger assembly.

The present invention is an attempt to solve this problem, and the fins of the internally grooved heat exchanger tube have only one side slope of the fins having a hexagonal structure as shown in Figs. 2 and 3. 4 is intended to serve as a space for holding air bubbles.

Therefore, such a crack structure is composed of a laminated structure of thin pieces made of the same material as the pipe base material, and since it hardly damages the shape of the internally grooved pipe, it maintains its performance during condensation and causes microscopic damage. The aim is to improve evaporation performance with a nucleate boiling promoting structure consisting of a crack structure.

By forming the above-mentioned crack structure only on the slope of one side of the fin, it is possible to suppress the performance degradation during condensation as much as possible, and by giving a slight deviation to the groove index during processing, the crack structure can be manufactured easily. .
Further, the fine cracks 4 are formed at a slight angle with respect to the fins, as shown in FIG.

Due to the presence of such fine crack gaps, the bubbles held in these gaps grow by heating, and by repeating nucleate boiling, nucleate boiling is promoted even at a small heating degree, greatly improving evaporation performance. .

The heat exchanger tube of the present invention (15.88 x 0.8) and an internally grooved tube (15.88 x 0.8
Figure 7 shows the relationship between the overall heat transfer coefficient K and the water flow velocity when 0.8) is applied.

From FIG. 7, it can be seen that the performance of the heat exchanger tube of the present invention during evaporation is greatly improved and approaches the performance during condensation, and it is also understood that the performance during condensation is hardly degraded.

In this test, the refrigerant during evaporation was flowed from the side with the crack structure and the side without it, and there was almost no difference in performance between the two. However, the pressure loss was smaller when the refrigerant was flowed from the side with no crack structure, and was almost the same as the pressure loss in an internally grooved tube without a crack structure.

When applying this invention, if the shape of the internally grooved tube is made to have as good a condensing performance as possible, both condensation and evaporation performance can be improved, and as mentioned above, H/
The optimum value is obtained within the range of Di from 0.01 to 0.05 and X from 15 to 35 degrees.

As described above, this invention is a heat transfer tube in which the fluid undergoes a phase change (evaporation or condensation) while exchanging heat. The ratio H/H of the inner diameter Di and the fin height H on the inner surface of the tube is
Di is 0.01 to 0.05, and the twist angle X of the fin relative to the tube axis is
The inner grooved heat transfer tube has many fins with an angle of 15 to 35 degrees, and one side of the fin has a fine crack structure that promotes nucleate boiling from the bottom to the top of the fin. Therefore, it can be easily processed with just a little modification during the inner groove processing, and the balance of performance during evaporation and condensation is improved, making it suitable for use in heat transfer tubes where heat exchange occurs while the fluid changes phase inside the tube, such as in heat pumps.

[Brief explanation of the drawing]

Fig. 1 is a perspective view showing the internal structure of a general internally grooved tube, Fig. 2 is a detailed sectional view of the fin portion of an internally grooved heat exchanger tube which is an embodiment of the present invention, and Fig. 3 is a perspective view showing the internal structure of a general internally grooved tube. The A-A cross-sectional view in the figure, Figures 4 and 5 are for H/Di of an internally grooved pipe that does not have a crack structure.
A graph showing the relationship between Hi and △P, Figure 6 shows the torsion angle
Figure 7 is a graph showing the effect of the present invention, showing the relationship between water flow velocity and overall heat transfer coefficient with and without a crack structure. Figure 8 a and b are graphs showing the relationship between Hi. 3 is a metal structure photograph showing the cross section of the metal shown in FIGS. 2 and 3. FIG. 1...Fin bottom, 2...Fin top, 3...
Crack structure, 4...Crack gap.

Claims (1)

[Claims for Utility Model Registration] 1. A heat transfer tube that exchanges heat while a fluid undergoes a phase change (evaporation or condensation) inside the tube.
It has many fins with a ratio H/Di of 0.01 to 0.05 and a torsion angle X of the fins with respect to the tube axis of 15 to 35 degrees. A heat exchanger tube with internal grooves characterized by having a micro-crack structure that promotes fine cracks. 2. The internally grooved heat exchanger tube according to claim 1, wherein the cross-sectional shape of the fins is generally triangular or trapezoidal as a whole, with symmetrical surfaces having and not having a crack structure.