JPS6352310B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a heat exchanger tube that evaporates or condenses a refrigerant such as freon inside the tube to exchange heat with a fluid flowing outside the tube.In particular, the present invention relates to a heat exchanger tube that evaporates or condenses a refrigerant such as Freon inside the tube and exchanges heat with a fluid flowing outside the tube. , and the condensation effect is enhanced to improve heat transfer characteristics. Generally, heat exchangers such as air conditioners and refrigerators use heat transfer tubes that evaporate or condense a refrigerant such as Freon inside the tubes and exchange heat with a fluid flowing outside the tubes. Conventionally, smooth tubes were used as such heat exchanger tubes, but recently, heat exchanger tubes with many spiral grooves in one direction formed on the inner surface of the tube, and many spiral grooves formed intersecting on the inner surface of the tube have recently been introduced. heat exchanger tubes are used. These heat exchanger tubes with internal grooves are designed to improve the heat transfer performance within the tube and suppress the increase in pressure loss, and exhibit superior heat transfer performance compared to heat exchanger tubes with smooth inner surfaces. However, recently, from the viewpoint of energy saving, heat transfer tubes with even better heat transfer performance are required. In view of this, the present invention aims to further improve the heat transfer characteristics of conventional internally grooved heat transfer tubes, and to improve the flow behavior, heat transfer performance, and pressure loss during the evaporation and condensation phenomena of refrigerants such as Freon flowing inside the tubes. Various experiments were conducted to investigate the relationship between the shape of the protrusions formed on the surface.
As a result of our studies, we found that compared to heat transfer tubes with multiple spiral grooves in one direction or multiple intersecting spiral grooves on the inner surface of the tube, this product has much better heat transfer performance with the same pressure loss. This is a developed heat transfer tube that evaporates or condenses the refrigerant inside the tube and exchanges heat with the fluid flowing outside the tube. A large number of spiral grooves having α ₁ and α ₂ and protrusions of the same shape are formed between the grooves, undulations are provided in the spiral direction of the groove with a lead angle α ₁ , and the groove with a lead angle α ₂ is formed into a spiral shape. The groove side slope of the protrusion with a lead angle α ₁ is a concave surface, the groove side slope with a lead angle α ₂ is a convex surface, and the shape of the protrusion is a diamond shape with a distorted base and a saddle-shaped or rounded top. The lead angles α _{1 and} α ₂ of the diamond-shaped and spiral shapes are 5 to 45 degrees, the pitch P ₁ of the groove with lead angle α ₁ and the pitch P ₂ of the groove with lead angle α ₂ are 0.2 to 1.0 mm, and the height of the protrusion is Sah
It is characterized by having a diameter of 0.05 to 0.75 mm. That is, the present invention provides a heat exchanger tube 1 as shown in FIG.
As shown in FIG. 2, spiral grooves 2 and 3 having lead angles α ₁ and α ₂ in opposite directions with respect to the tube axis A are formed on the inner surface of the tube, and grooves 2 and 3 having the same shape are formed between the grooves 2 and 3, respectively. A groove 2 with a lead angle α ₁ is formed as shown in the figure.
is undulated in the helical direction, the groove 3 with the lead angle α ₂ is made to run straight in the helical direction, and the groove 2 with the lead angle α ₁ of the protrusion 4 is formed.
The surface 5 facing the _protrusion 4 is a concave slope as shown in FIG. 4 is a diamond shape with a distorted base and a saddle-shaped or rounded top (the figure shows a saddle shape), and the lead angles α ₁ and α ₂ are opposite to each other with respect to the tube axis A. Pitch P ₁ of groove 2 with lead angle α ₁ and pitch P 2 of groove 3 with lead angle α ₂ , respectively _.
are respectively 0.2 to 1.0 mm, and the height h of the protrusion 5 is
is set to 0.05 to 0.75 mm. Various materials can be used for the heat exchanger tubes, such as steel, nonferrous metals, and resins, but copper, copper alloys, aluminum, aluminum alloys, and the like, which have excellent thermal conductivity, are particularly suitable. The heat exchanger tube of the present invention has the above-mentioned configuration and is used as a heat exchanger tube for a heat exchanger such as an air conditioner or a refrigerator, by evaporating or condensing a refrigerant such as Freon within the tube, and exchanging heat with a fluid flowing outside the tube. By doing so, the heat transfer performance will be improved as follows. (1) The numerous protrusions formed inside the tube expand the inner surface area of the tube, which acts as an effective heat transfer area and improves heat transfer performance. (2) When the refrigerant condenses in the pipe, a thin film is formed on the saddle-shaped or rounded diamond-shaped tops of the many protrusions and the curved slopes, promoting the condensation action. Furthermore, when the refrigerant evaporates in the pipe, the refrigerant mainly flows in a straight spiral groove, and from the groove flows into a groove with undulations in the spiral direction, and the undulation groove space acts as a nucleus for nucleate boiling, causing evaporation. Increases effect. (3) Lead angles α ₁ and α ₂ in opposite directions with respect to the tube axis
The spiral grooves stir the flow of refrigerant, resulting in a significant turbulence effect, which improves the heat transfer performance within the tube. (4) Lead angle α ₁ , α ₂ and appropriate groove pitch P ₁ , P ₂
As a result, the capillary phenomenon in the groove portion is significant, and the refrigerant and its wet vapor completely cover and adsorb the inner surface of the tube, effectively acting as a heat transfer surface. Therefore, in the heat exchanger tube of the present invention, the lead angles α ₁ , α ₂ ,
The pitches of the grooves P ₁ and P ₂ and the height h of the protrusions are limited as described above for the following reasons. The lead angles α ₁ and α ₂ are the lead angles α 1 and α ₂ shown in FIG.
As is clear from the experimental results of α ₂ , heat transfer performance, and pressure drop, excellent characteristics are exhibited when the lead angles α ₁ and α ₂ are in the range of 5 to 45°, but when the lead angles α ₁ and α ₂ are 5°, This is because if the angle is less than 45°, the performance will clearly deteriorate, and if it exceeds 45°, the pressure loss will increase. This is also because when manufacturing the heat exchanger tube of the present invention, the larger the lead angles α ₁ and α ₂ are, the lower the workability is. Also, the height h of the protrusion is 0.05 to 0.75 mm, and the groove pitch P ₁ and P ₂ are 0.2 to 1.0 mm.
The reason for this is that even if the protrusion height is less than 0.05 mm, the groove pitch will not occur.
Even if P ₁ and P ₂ are less than 0.2 mm, the inner surface of the heat exchanger tube will be close to that of a smooth tube, and the performance described above will not be obtained, and the height h of the protrusion will exceed 0.75 mm, and the groove pitch P ₁ ,
When P ₂ exceeds 1 mm, heat transfer performance improves, but
This is because the pressure loss of the fluid flowing inside the tube increases, so that the effect of the heat transfer tube of the present invention, which only aims to increase heat transfer performance, cannot be obtained. This means that
This is also clear from the experimental results shown in FIGS. 9 and 10. In addition, the shape of the top of the protrusion is saddle-shaped or rounded rhombus, one of the grooves with lead angles α ₁ and α ₂ is undulated in the spiral direction, and the other is made to run straight in the helical direction. This allows the condensate to flow down more smoothly, forming a thin film in the liquid to promote condensation, and in the evaporation of the refrigerant, the straight grooves are used as the main flow of wet steam, and the flow is diverted to the undulating spaces in the grooves. This is to make the space act as a boiling nucleus that generates nucleate boiling, and further, the lead angles α ₁ and α ₂ are set to α ₁ ≒ α ₂ , and the groove pitches P ₁ and P ₂ are set to P ₁
When ≒P ₂ , the flow of the refrigerant becomes uniform, and the above-mentioned effect works more effectively. In addition, the top of the protrusion is saddle-shaped or rounded diamond-shaped, the lead angles α ₁ and α ₂ are α ₁ ≒ α ₂ , and the groove pitches P ₁ and P ₂
By setting P ₁ ≒ P ₂ , in the production of the heat exchanger tube of the present invention, processing force is uniformly applied to the tube, and a product of good quality can be obtained. Furthermore, when used as a heat transfer tube in a plate fin type heat exchanger such as an air conditioner, the tip of the protrusion is less likely to be crushed during the tube expansion work to fix the plate fin, and because of the uniform processing, there are fewer assembly errors and no distortion. Since the heat exchanger can be manufactured, it is easy to apply it to mass production and automatic assembly lines. Hereinafter, the present invention will be described in detail with reference to examples. A heat transfer tube of the present invention having the dimensions shown in Table 1 and the shape shown in FIG. Losses were measured. The result is the fifth
This is shown in Figures 1 to 10.

[Table] Each heat exchanger tube was installed in a double tube heat exchanger using Freon R-22 as the refrigerant, and the evaporation characteristics were measured at an evaporation pressure of 3.5 to 4.2 Kgf/cm ² G, and the condensation characteristics were measured. The condensation pressure was set at 17.0 to 18.2 Kgf/cm ² G. Moreover, the length of all heat exchanger tubes was 5 m. Figure 5 shows the refrigerant flow rate on the horizontal axis and the evaporative heat transfer performance in the tubes on the vertical axis.
Both are approximately 3 times larger than conventional smooth tube No. 8, and approximately 1.3 to 1.3 times larger than conventional internally grooved tubes No. 5 to No. 7.
It can be seen that the evaporation performance inside the tube is 1.5 times higher.
In addition, Fig. 6 shows the refrigerant flow rate on the horizontal axis and the condensation heat transfer performance in the tube on the vertical axis.
No. 4 is approximately 2.8 times larger than the conventional smooth tube No. 8.
Approximately 1.2 compared to conventional internally grooved tubes No. 5 to No. 7
It can be seen that the pipe condensation heat transfer performance is ~1.5 times higher. Fig. 7 shows the refrigerant flow rate on the horizontal axis and the pressure loss on the vertical axis. Heat exchanger tubes No. 1 to No. 4 of the present invention are compared with conventional smooth inner surface tube No. 8 at the same refrigerant flow rate. Although the pressure loss is somewhat larger, it is almost the same as the conventional internally grooved tubes No. 5 to 7. FIG. 8 also shows the lead angles α ₁ and α ₂ in the opposite direction to the tube axis for heat exchanger tube No. 1 of the present invention in Table 1.
Change the refrigerant flow rate in the range of 0° to 60° at 50 kg/h.
The figure shows the results of measuring the heat transfer performance and pressure loss in the tube by fixing the lead angles α ₁ and α ₂ on the horizontal axis, and the heat transfer coefficient and pressure loss in the tube on the vertical axis (A in the figure shows the evaporation performance,
B represents condensation performance and ΔP represents pressure loss). As can be seen from the figure, when the lead angles α ₁ and α ₂ are 5° or more, there is not much difference in heat transfer performance, and when the lead angles are less than 5°, the heat transfer performance decreases. On the other hand, when the lead angles α ₁ and α ₂ exceed 45°, the pressure loss increases rapidly. Similarly, FIG. 9 shows heat exchanger tube No. 4 of the present invention in Table 1.
Figure 10 shows the results of measuring the heat transfer characteristics and pressure loss in the tube by varying only the protrusion height h between 0.02 and 0.8 mm. This figure shows the results of measuring the in-pipe heat transfer performance and pressure loss while varying the pitches P ₁ and P ₂ in the range of 0.1 to 1.2 mm, with the refrigerant flow rate fixed at 50 kg/h. As can be seen from the figure, the protrusion height h is
Even if the groove pitches P ₁ and P ₂ are less than 0.05 mm, the evaporation performance A and condensation performance B will decrease significantly, and even if the protrusion height h exceeds 0.75 mm, the groove pitches P ₁ and P ₂ will decrease significantly.
Pressure loss △P increases rapidly even when it exceeds 1.0 mm. In this way, the heat exchanger tube of the present invention can be used as a heat exchanger tube in a type of heat exchanger that evaporates or condenses a refrigerant such as Freon inside the tube and exchanges heat with a fluid flowing outside the tube, without increasing pressure loss. It can significantly improve evaporation and condensation heat transfer performance, making it possible to reduce the size, weight, and cost of heat exchangers.
Furthermore, it can be used in heat pipes and has remarkable effects such as improving heat transfer performance.

[Brief explanation of the drawing]

Fig. 1 is a partially cutaway side view of an example of the heat transfer tube of the present invention, Fig. 2 is an enlarged perspective view of the inner surface of Fig. 1, and Fig. 3 is a cross section taken along line Y-Y in Fig. 2. Figure 4 is a cross-sectional view taken along line X-X in Figure 2,
Figures 5 to 7 show the heat transfer characteristics of the heat exchanger tube of the present invention and the conventional heat exchanger tube. Figure 5 is a relationship between the refrigerant flow rate and the evaporation performance in the tube, and Figure 6 is the relationship between the refrigerant flow rate and the condensation performance in the tube. Figure 7 is a diagram of the relationship between refrigerant flow rate and pressure loss, Figure 8 is a diagram of the relationship between lead angle, internal heat transfer coefficient and pressure loss in the heat exchanger tube of the present invention, and Figure 9 is a diagram of the relationship between the refrigerant flow rate and pressure loss. Fig. 10 is a diagram showing the relationship between the groove pitch, the heat transfer coefficient in the pipe, and pressure loss. 1... Heat exchanger tube, 2, 3... Spiral groove having lead angles α ₁ and α ₂ in mutually opposite directions with respect to the tube axis, 4...
Protrusion, A...evaporation property, B...condensation property, △P...
...Pressure loss.

Claims (1)

[Claims] 1. In a heat transfer tube that evaporates or condenses a refrigerant inside the tube and exchanges heat with a fluid flowing outside the tube, a lead angle α in mutually opposite directions with respect to the tube axis is formed on the inner surface of the tube. A large number of spiral grooves having lead angles _{α 1} and α ₂ and protrusions of the same shape are formed between the grooves, and the lead angle α ₁
The groove has undulations in the helical direction, the groove with a lead angle α ₂ runs straight in the helical direction, the slope on the groove side of the protrusion with a lead angle α ₁ is made concave, the slope on the groove side with a lead angle α ₂ is made a convex surface, and the protrusion The shape is a rhombus with a distorted base and a saddle or rounded top, the lead angles α ₁ and α ₂ of the spiral groove are 5 to 45°, and the pitch of the groove with the lead angle α ₁ is P ₁ And the pitch P ₂ of the groove with lead angle α ₂ is 0.2 to 1.0.
mm, and the height h of the protrusions is 0.05 to 0.75 mm. 2 Lead angles α ₁ and α ₂ in opposite directions with respect to the tube axis
The heat exchanger tube according to claim 1, wherein α ₁ ≒ α ₂ . 3. The heat exchanger tube according to claim ₁ or 2, wherein the pitch P ₁ of the groove with a lead angle α 1 and the pitch P ₂ of the groove with a lead angle α ₂ satisfy P ₁ ≈P ₂ . 4. The outer diameter of the pipe should be 6 to 20 mm, and the minimum wall thickness should be 0.2 to 1.2 mm.
A heat exchanger tube according to claim 1, 2, or 3.