JPS6218864Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to an extratube boiling heat exchanger tube used as a heat exchanger tube in a flooded evaporator or the like.

Conventionally, loaf inch tubes and the like have been used as this type of heat transfer tube, but the boiling heat transfer coefficient has not been sufficiently improved.

In general, as a heat transfer surface shape that is effective for boiling liquid refrigerant by immersing it in it, it is desirable to have concavities that widen toward the end or porous (both of which have boiling nuclei). It is desirable that the recesses have a shape that allows the superheated refrigerant liquid to be smoothly supplied into the recesses, that is, a shape in which the recesses are continuous like a tunnel.

The purpose of this invention is to improve the boiling heat transfer coefficient by two to three times compared to conventional loaf inch tubes by providing a heat transfer tube with the heat transfer surface shape as described above. A band-shaped fin having a large number of opposing fin pieces is wound and fixed in a spiral around the outer periphery of the heat exchanger tube body, and each of these opposing fin pieces is deformed in the same direction, thereby deforming the band-shaped fin. A continuous tunnel-like space is formed inside and outside along the band-like fins, and the space is connected to the outside through minute gaps formed between the opposing fin pieces and between the adjacent fin pieces. A liquid refrigerant that undergoes a gas-liquid phase change is caused to flow outside the tube, and the liquid refrigerant is heated by the fluid flowing inside the tube.

DESCRIPTION OF THE PREFERRED EMBODIMENTS A heat exchanger tube for extra-tube boiling according to an embodiment of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 shows the manufacturing sequence of an extra-tube boiling heat exchanger tube according to an embodiment of the present invention.

That is, a metal strip 1' made of a thermally conductive material
After forming a large number of fin pieces 3, 3... and 4, 4... divided by a large number of equally spaced cut lines 2, 2... on both sides of the (shown in Fig. 1 A), The fin pieces 3 and 4 are raised to face each other to form a band-shaped fin 1 (as shown in FIG. 1C). After the band-shaped fins 1 are wound and fixed around the outer periphery of the heat exchanger tube body 5 (as shown in FIG. 1, D), the belt-shaped fins 1 are wound so that the outer diameter d 1 of the heat exchanger tube body ₅ is larger than the outer diameter d ₂ of the tip of the band-shaped fins 1. The fin pieces _{3 and} 4 are passed through a cutting die 6 having an inner diameter of d 3 and pushed in the axial direction (that is, in the same direction) to deform them so that they are continuous inside and outside the band-like fin 1 along the band-like fin 1. Tunnel-shaped cavities 7, 7 are formed (as shown in FIG. 1, E).

When this heat transfer tube is used as a heat transfer tube of a flooded evaporator, and a liquid refrigerant that undergoes a gas-liquid phase change such as fluorocarbon is passed outside the heat transfer tube, and a fluid such as water is passed inside the heat transfer tube, the void 7 are for promoting the formation of boiling bubble nuclei, and are formed between opposing fin pieces 3, 4 and between adjacent fin pieces 3, 3 and 4, 4. It is communicated with the outside via 9... (see Figure 2). The minute gaps 8 and 9 have the function of allowing the refrigerant bubbles grown within the space 7 to escape to the outside.

In addition to the method of pressing the fin pieces in this embodiment, in addition to the method of forming the pressing part y uniformly as shown in FIG. A push-down portion y may be formed, or a push-down portion y divided in the axial direction may be formed.

In the above embodiment, assuming that the width of the fin pieces 3 and 4 is S, the height of the fin pieces 3 and 4 is _Fh1 , the width of the strip-shaped fin 1 is Fr, the winding pitch is P, and the size of the minute gaps 8 and 9 is w, the effective dimensions for achieving the object of this invention are as follows:

S...0.4~2.0mm Fh ₁ ...0.5~1.0mm Fr...0.5~2.0mm P...1.0~4.0mm w...0.05~0.2mm Figure 8 shows the heat transfer performance (a line)
and the heat transfer performance (b) of the heat transfer tube according to the embodiment of the present invention.
line) and the temperature difference △ between the temperature of the tube wall and the temperature of the refrigerant.
A comparison is shown using a graph in which t is plotted on the horizontal axis and heat flux q is plotted on the vertical axis.

According to this, it can be seen that the heat exchanger tube according to the example of the present invention has a significantly improved extra-tube heat transfer coefficient compared to a smooth tube.

Next, the effects of the extra-tube boiling heat exchanger tube of the present invention will be described. According to the present invention, on the outer periphery of the heat exchanger tube main body 5, a large number of opposing fin pieces 3, 3... and 4, 4...
By winding and fixing the band-like fin 1 in a spiral manner, and deforming the opposing fin pieces 3 and 4 in the same direction, the band-like fin 1 is attached to the inside and outside of the band-like fin 1. Since a continuous tunnel-like cavity 7 is formed along the tunnel so that boiling bubble nuclei can be formed within the cavity 7, liquid refrigerant is always supplied into the cavity 7. This has the practical effect of being able to continuously form bubbles and promoting boiling of the liquid refrigerant on the outside of the tube.

Further, the space 7 is formed between the upper ends of each fin piece 3, 4 and between each adjacent fin piece 3, 3 and 4, 4 through minute gaps 8, 8... and 9, 9... Since we made it possible to communicate with the outside, empty space 7
The air bubbles formed inside the tube can easily escape to the outside, and there is also the effect that inhibition of heat transfer on the outside of the tube due to accumulation of air bubbles can be prevented.

Further, since the band-like fins 1 are thin, there is an advantage that the cost is lower than that of conventional loaf inch tubes.

[Brief explanation of the drawing]

Figures 1A to 1E are manufacturing sequence diagrams of the heat exchanger tube for boiling outside the tube according to the first embodiment of the present invention, and Figure 2 is an enlarged view of the main parts of the heat exchanger tube for boiling outside the tube according to the first embodiment of the present invention. Perspective views, Figures 3A to 3C are explanatory diagrams showing various methods of pushing down the fin pieces of the heat exchanger tube for boiling outside the tube in Figure 1, and Figure 4 shows the conventional smooth tube (A line) and the implementation of the present invention. It is a characteristic diagram comparing heat transfer performance with an example of an extra-tube boiling heat transfer tube (b line). 1... band-like fin, 3, 4... fin piece, 5...
... Heat exchanger tube body, 7... Vacancy, 8, 9... Minute gap.

Claims (1)

[Scope of utility model registration request] A band-shaped fin 1 having a large number of opposing fin pieces 3, 3..., 4, 4... is spirally wound and fixed on the outer periphery of the heat exchanger tube body 5, and each of the opposing fin pieces 3 . can be communicated with the outside through minute gaps 8, 8..., 9, 9... formed between the upper ends of each of the fin pieces 3, 4 and between the adjacent fin pieces 3, 3, 4, 4. A heat transfer tube for boiling outside the tube, characterized in that a liquid refrigerant that undergoes a gas-liquid phase change is passed outside the tube, and the liquid refrigerant is heated by the fluid flowing inside the tube.