JPS5938597A - Heat transmitting tube for boiling medium - Google Patents

Abstract

PURPOSE:To stabilize the nucleus for foam which is effective to transfer boiling heat, and to obtain a good heat transmitting performance even in case that a fluid such as a refrigerant of Freon system, of which surface tension is small, is used, by forming a plurality of fine grooves in the shape of a V or a U on the inside wall of a heat transmitting tube, and by forming a number of recesses in the shape of a reverse V, of which radius of opening is 0.1-100mum, on the side and the bottom surfaces of the grooves. CONSTITUTION:V-shaped spiral grooves 5 are formed on the inside surface of a smooth tube 4, and a number of recesses 6 in the shape of a reverse V, of which radius of opening is 0.1-100mum, are formed on the side surface of the groove 5. The numerical 7 is fluid which flows along the wall of the tube receiving turning force, while the numerical 8 are foams which grow and get off the recesses 6 in the shape of a reverse V which serve as the nucleus for foam. Because the spiral grooves 5 are formed, the fluid flows along the inside wall of a tube, receiving the turning force, forming a thin liquid film so as to cover the inside wall of the tube completely by the capillarity of fine grooves. Accordingly, the neighborhood of the recesses 6 formed on the side surface of the grooves 5 can also be utilized effectively as the wetted nucleus of foam.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention is applicable to boiling of fluids, such as evaporators of air conditioners.
This invention relates to heat exchanger tubes used in heat exchangers that involve evaporation.

Conventional configuration and its problems Conventionally, in the evaporators of air conditioners and refrigerators, the heat transfer on the refrigerant side is boiling heat transfer, which has good heat transfer, so there was no need to take this thermal resistance into account too much. . However, recently, for example, with the development of high-performance fins, heat transfer on the air side has been significantly improved, and it has become necessary to consider the thermal resistance of the refrigerant in the evaporative heat transfer tube. In order to achieve this, it has become necessary to promote heat transfer outside the tube as well as heat transfer on the refrigerant side inside the tube.

A conventional heat exchanger tube will be explained below with reference to the drawings.

FIG. 1 shows a cross section of a conventional heat transfer tube, in which a plurality of V-shaped spiral grooves 2 are provided on the inner wall surface of a smooth tube 1. As a result, the fluid 3 flows along the pipe wall while being subjected to a swirling force, so that a certain degree of heat transfer promotion effect can be obtained, but even if the interval between adjacent grooves is very small,
Since it is approximately 0.1M, when using a fluid with low surface tension such as a fluorocarbon-based refrigerant, the liquid will enter the grooves, so these grooves are bubble nuclei that are effective for boiling heat transfer. It had the disadvantage that it could not be.

Purpose of the Invention The present invention solves the above-mentioned drawbacks, and even when using a fluid with low surface tension such as a fluorocarbon-based refrigerant, it stabilizes the bubble nuclei that are effective in boiling heat transfer, and provides excellent heat transfer performance. The purpose of this invention is to provide a heat exchanger tube for boiling.

Structure of the Invention The present invention forms a plurality of thin grooves in the shape of a 7 or U shape on the inner wall surface of a heat exchanger tube, and on the side and bottom surfaces of the grooves,
A large number of concavities with an opening radius of 0.1 to 100 μm are formed.

DESCRIPTION OF THE EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. 2 to 6 of the drawings.

Generally, when the temperature of the heat transfer surface is higher than the saturation temperature of the fluid, the liquid fluid in contact with the heat transfer surface is overheated near the heat transfer surface, giving rise to the possibility of generating bubbles there. (1) The radius r of a bubble that can exist in a liquid fluid near the heat transfer surface while maintaining thermodynamic equilibrium. is given by the following equation.

Here, ρ7 is the density of vapor, ρL is the density of the liquid fluid and the latent heat of vaporization, σ is the surface tension, Ts is the saturation temperature, and ■ is the work equivalent of heat. Using the above formula, R-2 whose saturation temperature is O'C
The results of determining the equilibrium bubble radius in case 2 are shown in FIG.

The size of the bubble nucleus that is effective for boiling heat transfer is set to the minimum radius of this equilibrium bubble, and is large enough to prevent liquid fluid from penetrating due to surface tension. That is, in a normal heat exchanger, if the maximum degree of superheating of the heat transfer surface is about 10°C, then from Fig. 2, the minimum radius of the effective bubble nucleus is R-2.
In the case of 2, it is about 0.1 μm, and the maximum radius is experimentally about 100 μm.

However, even if the wall temperature decreases, the concavity that widens toward the end always retains a bubble nucleus and is never filled with liquid fluid, so that a stable heat transfer promoting effect can be obtained.

FIG. 3 is a sectional view of the boiling heat exchanger tube according to the first embodiment of the present invention, and FIG. 4 is a sectional view taken along line A--A in FIG. 3. As shown in FIGS. 3 and 4, a seven-shaped helical groove 5 is formed on the inner wall of the smooth tube 4.
A large number of recesses 6 with an opening radius of 0.1 to 100 μm are formed on the side surface of the recess. Note that 7 is a fluid that flows along the tube wall while being subjected to rotational force, and 8 is a bubble that has grown and separated from the concave 6 that expanded toward the end and became a bubble nucleus.

Figure 6 shows the conventional smooth pipe and the groove shown in Figure 1.
Regarding the heat exchanger tube and the boiling heat exchanger tube of the present invention, the saturation temperature o
R-22 of 'c, weight flow rate + 701<,/lm2s
Wall surface superheat degree ΔTs ('C) when circulating with EC
These are the experimental results for determining the relationship between the temperature and the heat flux q (1 cal/m2h). As is clear from this figure, the boiling heat exchanger tube of the present invention has a heat flux approximately 2 to 6 times that of a smooth tube, and approximately 1.5 to 3 times that of the grooved heat exchanger tube shown in FIG. (The amount of heat transferred per unit time and unit area) increases. In particular, when the degree of wall superheating ΔTs is small, the increase in heat flux q is large, and a large amount of heat can be transmitted with a small temperature difference.
It can be seen that it is extremely superior in terms of effective energy use.

This is because, as shown in FIGS. 3 and 4, the concavity 6 that widens toward the end and has an opening radius of 0.1 to 100 μm formed on the side surface of the groove 6 effectively acts as a bubble nucleus, even at a small degree of superheating. This is because a sufficient boiling phenomenon is caused.

Since the trenches form spiral grooves 6, the fluid flows along the tube wall while receiving swirling force, and due to the capillary action caused by the narrow grooves, a thin liquid film is formed to completely cover the inner wall of the heat transfer tube. Since it flows while being formed, the vicinity of the depression 6 formed on the side surface of the groove 6 is also wetted and can effectively act as a bubble nucleus.

FIG. 6 is a partial sectional view of a boiling heat exchanger tube according to a second embodiment of the present invention, in which a U-shaped spiral groove 10 is formed on the inner wall surface of a smooth tube 9.
is formed, and the opening radius is 0 on the side and bottom surfaces of this groove 10.
．． A large number of depressions 11 with a diameter of 1 to 100 μm are formed.

It is clear that such a U-shaped groove also has the same effect as the aforementioned 7-shaped groove.

In addition, in the present invention, after forming a spiral groove by plastic working, a concavity that widens toward the end is processed by etching, resulting in an irregular concavity. Even if the aperture radius is 0.1 to 10
It is clear that the same effect as the present invention can be obtained if the thickness is 0 μm.

Effects of the Invention As described above, according to the present invention, a plurality of thin grooves in the shape of 7 or U are formed on the inner wall surface of the heat exchanger tube, and the opening radius is o, 1 to 1 on the side and bottom surfaces of the grooves. By forming a large number of 100 μm widening concavities, it can be used even when using fluids with low surface agitation such as fluorocarbon-based refrigerants.
It stabilizes bubble nuclei, which are effective in boiling heat transfer, and provides excellent heat transfer performance. In particular, when the degree of wall superheating is low, it exhibits extremely good heat transfer performance, so a large amount of heat can be transferred with a small temperature difference, and it is also excellent in terms of effective energy use.

[Brief explanation of drawings]

Figure 1 is a cross-sectional view of a conventional boiling heat exchanger tube, Figure 2 is a characteristic diagram showing the relationship between the degree of superheating and the equilibrium bubble radius, and Figure 3 is a cross-section of a boiling heat exchanger tube according to the first embodiment of the present invention. Figure 4 is a cross-sectional view taken along the line A-A in Figure 3, Figure 6 is a characteristic diagram showing the results of a performance experiment of the boiling heat exchanger tube of the present invention, Figure 6 is a cross-sectional view taken along line A-A in Figure 3, Figure 6 is a characteristic diagram showing the results of a performance experiment of the boiling heat exchanger tube of the present invention, It is a partial sectional view of the heat exchanger tube for boiling of 2nd Example. 1.4.9...Smooth pipe, 2,6...
・・7-shaped spiral groove, 6, 11 ・・・・・ concavity that widens at the end, 3° 7 ・・・fluid. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Figure 2 Tonzenya Otsu T ('cn Figure 3 Ha Figure 4

Claims (1)

[Claims] A boiling heat exchanger tube in which a plurality of 7-shaped or U-shaped thin grooves are formed on the inner wall surface of the heat exchanger tube, and a large number of recesses with an opening radius of 0.1 to 100 μm that widen toward the end are formed on the side and bottom surfaces of the grooves. .