JPH0631327Y2 - Heat transfer tube - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to a heat transfer tube used for a heat exchanger or the like of an air conditioner.

[Prior Art] Conventionally, a heat transfer tube with a groove is used in a heat pump air conditioner or the like for high efficiency and compactness. FIG. 5 is a perspective view of a grooved heat transfer tube for a conventional air conditioner, and FIG. 6 is an enlarged view of the grooved grooved heat transfer tube. This is formed by forming a triangular or corrugated concavo-convex strip on the inner surface of the pipe in a spiral shape by rolling. By forming the spiral ridges and grooves on the inner surface of the tube, the evaporation heat transfer coefficient inside the tube is improved by the effect of increasing the inner surface area of the tube and stirring the fluid. Typical dimensions of such a grooved heat transfer tube are shown below.

Pipe outer diameter d 9.52 to 6.35 mm Lead angle 15 to 20 degrees Vertical angle θ 30 to 60 degrees Bottom wall thickness t 0.25 to 0.35 mm Fin height h 0.15 to 0.25 mm Pitch p 0.4 ~ 1mm In order to improve the heat transfer performance with air, plate fins are attached to the outer surface of the heat transfer tube.

[Problems to be Solved by the Invention] The conventional grooved heat transfer tube is as described above, and the spiral groove (irregular stripe) of the grooved heat transfer tube is formed by the rolling process. For technical reasons of rolling and rolling, the number of spiral grooves and the twist angle are limited, and the boiling heat transfer performance of this grooved heat transfer tube is at most 1.2 to 1.5 times that of the smooth tube. Recently, there is a strong demand for downsizing of heat exchangers, and development of heat transfer tubes having excellent boiling heat transfer performance is desired.

The present invention has been made to meet such a problem, and an object thereof is to obtain a heat transfer tube having excellent boiling heat transfer performance.

[Means for Solving the Problems] A heat transfer tube according to the present invention is provided with an outer tube and a double tubular shape fitted in the outer tube, and is formed into a cylindrical shape from the outer surface and narrows in a conical shape near the inner surface. The inner surface is composed of an inner tube having a large number of small holes formed so as to have an opening having a smaller diameter than the outer surface.

[Operation] The heat transfer tube according to the present invention comprises an outer tube and an inner tube that are fitted to each other, and the inner tube is formed into a cylindrical shape from the outer surface and is conically narrowed near the inner surface, so that the inner surface has an opening having a smaller diameter than the outer surface. Since it has a large number of small holes formed in this way, the outer surface side of the large number of small holes opened in this inner tube contacts the inner surface of the outer tube to form a cavity, It serves as a core and maintains stable boiling, improving heat transfer performance. Especially, in the case of a fluid having a small surface tension such as a chlorofluorocarbon refrigerant, the inner surface side of the small hole is conically narrowed and opened, so that the gas-liquid interface in this small hole becomes concave, and the dynamics of bubbles are It becomes a stable and continuous bubble generation nucleus that satisfies the stability conditions.

[Embodiment] An embodiment of the present invention will be described below with reference to the drawings. First
1 is a partially cutaway perspective view of a heat transfer tube according to an embodiment of the present invention, FIG. 2 is an enlarged sectional view of an essential part according to the first embodiment, and FIG. 3 is an enlarged sectional view of an essential part according to the second embodiment. In the figure, 1 is an outer tube, 2 is an inner tube, 3 is a small hole, and 4 is a communication hole.

This heat transfer tube is composed of an outer tube 1 and an inner tube 2 that are fitted to each other, and a fluid such as a refrigerant flows inside the tube and air flows outside the tube for heat exchange. Fins (not shown) are attached to the outside of the outer tube 1. The inner pipe 2 has a large number of small holes 3 penetrating from the outer surface to the inner surface. It is preferable to provide as many small holes 3 as possible. As shown in FIG. 2, the small hole 3 is formed in a cylindrical shape from the outer surface of the inner tube 2, is narrowed conically near the inner surface side, and is opened on the inner surface with a diameter smaller than the opening diameter of the outer surface.

An example of the geometrical dimensions of the small holes 3 is as follows: inner surface hole diameter d ₁ = 0.1-0.2 mm main hole diameter d ₀ = 0.25-0.4 mm hole height h = 0.3-0.5 mm cone The angle of the surface is> (180 ° −2θ). Here, θ is the solid-liquid interface contact angle of the liquid (refrigerant) flowing in this tube.

In the second embodiment shown in FIG. 3, a groove is dug in the outer surface of the inner pipe 2 to form a communication hole 4 for communicating between the small holes 3.

Next, the function and action will be described. The heat transfer tube comprises an outer tube 1 and an inner tube 2, the inner tube 2 is fitted in the outer tube 1, and the inner tube 2 is provided with a large number of small holes 3 penetrating from the outer surface to the inner surface. 3 is formed in a cylindrical shape from the outer surface of the inner tube 2, becomes conical in the vicinity of the inner surface side, and has an opening smaller than the opening diameter of the outer surface on the inner surface, so that the small hole 3 becomes a cavity, It becomes the core of evaporation bubbles. In particular, in a fluid having a small surface tension such as a futon-based refrigerant, the inner surface side of the small hole is narrowed and opened in a conical shape, and the angle of the conical surface is formed to be larger than (180 ° -2θ). Therefore, due to the contact angle of the liquid-refrigerant solid-liquid interface, the gas-liquid interface in this small hole is concave, which satisfies the mechanical stability condition of the bubble and becomes a stable and continuous bubble generation nucleus. .

Further, when the communication hole 4 shown in FIG. 3 is provided, when there are small holes 3 that actively generate bubbles and small holes 3 that are not active,
When the liquid moves from the inert cavity to the active cavity or the bubbles move from the active cavity to the inert cavity through the communication hole 4, the inert cavity is activated due to the decrease in pressure, and the active cavity becomes liquid. To maintain a stable active state.

FIG. 4 shows the heat transfer coefficient of the heat transfer tube according to the present invention in comparison with that of the conventional grooved heat transfer tube. The heat transfer tube according to the present invention has a heat transfer coefficient about three times that of the conventional heat transfer tube. can get.

[Effects of the Invention] As described above, according to the present invention, the heat transfer tube has a double structure including an outer tube and an inner tube having a large number of small holes, and the small holes of the inner tube have a narrow opening on the inner surface side. Since it is formed in a hollow shape, the large number of small holes become stable nuclei for evaporation bubbles, and bubbles are continuously generated, so that a heat transfer tube having remarkably excellent heat transfer performance can be obtained.

[Brief description of drawings]

FIG. 1 is a partially cutaway perspective view of a heat transfer tube according to an embodiment of the present invention, FIG. 2 is a sectional view of an essential part of the first embodiment, and FIG. 3 is a sectional view of an essential part of the second embodiment. FIG. 4 is a view showing a comparison of heat transfer rates, FIG. 5 is a perspective view of a grooved heat transfer tube according to a conventional example, and FIG. 6 is a partially enlarged view of a grooved heat transfer tube according to a conventional example. In the figure, 1 is an outer tube, 2 is an inner tube, 3 is a small hole, and 4 is a communication hole.

Claims (1)

[Scope of utility model registration request] 1. An outer tube and a double tube fitted into the outer tube to be formed into a cylindrical shape from the outer surface, conically narrowing near the inner surface, and having an opening smaller in diameter than the outer surface on the inner surface. Heat transfer tube comprising an inner tube having a large number of small holes formed therein.