JPH0445753B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a heat exchanger used in air conditioners, refrigerators, etc.

Conventional Structure and Problems There has conventionally been used a finned heat exchanger as shown in FIG. 1 as a heat exchanger in which a working fluid such as a refrigerant flows through heat transfer tubes while undergoing a phase change. This consists of a large number of fins 1 arranged in parallel at regular intervals and a plurality of heat transfer tubes 2 arranged through the fins 1, and heat exchange between the refrigerant inside the heat transfer tubes 2 and the air outside the tubes. will be held. Arrow 3 in the figure indicates the flow direction of the refrigerant. As the heat exchanger tube 2, as shown in FIG. 2, an internal spiral grooved tube is used, in which a spiral groove 4 having a constant groove depth h is provided on the inner wall of the tube.

By providing the groove 4 in this internal spiral grooved tube, in the case of evaporative heat transfer, the liquid refrigerant at the bottom of the tube rises in the groove due to capillary action, and a refrigerant liquid film is formed on the heat transfer surface inside the tube. In the case of condensation heat transfer, the condensate gathers at the bottom of the groove due to surface tension, and the average thickness of the condensate film formed on the heat transfer surface inside the tube becomes thinner, which both improves heat transfer performance. was said to improve.

However, according to our experience, for example, in the case of evaporative heat transfer, a thin refrigerant liquid film is formed on the entire heat transfer surface in the tube, and a significant heat transfer promotion effect can be obtained if the refrigerant is highly dry. That is, only in the latter stages of the evaporation process. On the other hand, at the beginning of the evaporation process, the dryness of the refrigerant is low and the flow rate of the liquid refrigerant in the pipes is large. Therefore, the liquid refrigerant easily fills the groove and flows over the groove. Therefore, a significant heat transfer promoting effect due to the evaporation mechanism as described above cannot be expected. From the above, in order to dramatically improve the heat transfer performance of the evaporator, there is a problem that the remarkable heat transfer promoting effect in the region where the degree of dryness of the refrigerant is large must be utilized more effectively.

On the other hand, the heat transfer performance of the spiral grooved tube in the pipe when the working fluid in the pipe is a single-phase flow is much lower than the heat transfer performance in the case where the working fluid in the pipe is a two-phase flow.
It is almost equivalent to the single-phase flow heat transfer performance of a smooth tube with a smooth inner wall. That is, when the working fluid in the pipe is a single-phase flow, the effect of the grooves is small. From the above, it is not very effective to use internal spiral grooved pipes in single-phase flow areas.

Purpose of the Invention The present invention solves the above-mentioned conventional drawbacks, and aims to provide a high-performance heat exchanger that significantly improves the heat transfer performance of a spirally grooved tube in a region where the dryness of the refrigerant is large. purpose.

Structure of the Invention The heat exchanger of the present invention includes a heat exchanger tube in which the inside of the heat exchanger tube is a flow path for a phase-changing fluid, an inner wall of the heat exchanger tube is provided with at least two types of helical grooves having different groove depths, and the helical groove is The groove depth is smaller on the inlet side of the fluid in the pipe and larger on the outlet side.

DESCRIPTION OF EMBODIMENTS Hereinafter, one embodiment of the present invention will be described in FIGS. 3 to 5.
This will be explained with reference to the figures.

FIG. 3 is a sectional view of an evaporator according to an embodiment of the present invention. In FIG. 3, a large number of fins 5 arranged in parallel at regular intervals, a plurality of heat transfer tubes 6, 7, 8, 9 arranged through the fins 5, and each of the heat transfer tubes 6 to 9 are connected to each other. The U-shaped bend 10 constitutes an evaporator. Refrigerant flows inside the tube in the direction of arrow 11, and air flows between the fins 5 outside the tube to perform heat exchange. The heat transfer tubes 6 and 9 through which single-phase liquid refrigerant and refrigerant vapor flow are smooth tubes with smooth inner wall surfaces. Further, on the inner walls of the heat exchanger tubes 7 and 8 where evaporative heat transfer is performed, fourth tubes are respectively installed.
As shown in the figure, a spiral groove 12 having a triangular cross section,
13 is provided, and the groove depth h ₁ of the helical groove 12 of the heat transfer tube 7 in the region of low refrigerant dryness near the evaporator inlet is small (for example, h ₁ = 0.15 mm) and is close to the evaporator outlet. The groove depth h ₂ of the helical groove 13 of the heat exchanger tube 8 in the region of high dryness is considerably larger than the groove depth h ₁ (for example, h ₂ =0.25 mm). Note that 14 is a side plate.

This configuration produces the following functions and effects.

Since the heat transfer tubes 6 and 9 through which single-phase liquid refrigerant and refrigerant vapor flow are smooth tubes with smooth inner wall surfaces, the heat transfer performance of the smooth tubes 6 and 9 and the spiral grooved tube in the tube in the above-mentioned single-phase region is as follows. Because they are almost equal, the processing cost of the heat exchanger tubes is low, without reducing the heat transfer performance of the heat exchanger tubes, that is, an inexpensive evaporator can be obtained.

Next, FIG. 5 shows experimental results regarding the evaporative heat transfer performance of various heat transfer tubes under the following experimental conditions when the flow state of the refrigerant is a two-phase flow state in which liquid refrigerant and refrigerant vapor flow simultaneously.

Refrigerant used...R ₂₂ evaporation temperature...5℃ Refrigerant weight flow rate...250Kg/ ^m2・S Heat flux...6000kcal/ ^m2・h The vertical axis is the heat transfer coefficient of each heat transfer tube, and the horizontal axis is the heat transfer coefficient of each heat transfer tube. It is the dryness of the refrigerant. As the dryness of the refrigerant increases, the difference in heat transfer coefficient between the smooth tube and the spirally grooved tube increases. In other words, the greater the degree of dryness, the more significant the effect of promoting heat transfer by the internal spiral grooves becomes. In addition, in areas where the degree of dryness of the refrigerant is small, the groove depth of the spiral grooved tube has little effect, but as the degree of dryness increases and the amount of refrigerant vapor increases, the heat transfer performance increases significantly as the groove depth increases. do.
On the other hand, the pressure loss due to the refrigerant increases as the groove depth increases. However, the rate of increase in pressure loss due to the increase in groove depth in a region where the dryness of the refrigerant is large is a small value compared to the rate of increase in the heat transfer coefficient described above.

Based on the above experimental results, in this embodiment, a spiral groove 12 with a small groove depth is provided in the heat transfer tube 7 in a region where the degree of dryness of the refrigerant is small. When the degree of dryness of the refrigerant is low and the flow rate of the liquid refrigerant in the pipe is large, the liquid refrigerant does not flow along the grooves, but flows over the grooves. Therefore, by using a spiral grooved tube with a small groove depth, pressure loss due to the refrigerant can be reduced without deteriorating heat transfer performance.

Further, in this embodiment, the helical grooves 13 having a large groove depth are provided in the heat exchanger tubes 8 in regions where the degree of dryness of the refrigerant is large. As the dryness of the refrigerant increases and the flow rate of the liquid refrigerant in the tube decreases, the flow state of the refrigerant in the tube tends to transition to an annular flow or an annular jet flow due to the capillary phenomenon caused by the spiral groove, and the flow state of the refrigerant in the tube tends to change to an annular flow or an annular jet flow. A very thin refrigerant liquid film is formed, which significantly improves heat transfer performance. Therefore, the larger the groove depth in the spirally grooved tube, the thinner the refrigerant liquid film is formed on the wider inner surface of the groove, and the heat transfer performance can be significantly improved.

Note that although the internal spiral grooved tubes 7 and 8 of the above embodiments were provided with a groove having a triangular cross section as the spiral groove, the same effect could be obtained by providing a groove having a polygonal cross section other than a triangle. It goes without saying that you can get it. In addition, although the groove depths of the spiral grooves are set to two types, h ₁ and h ₂ , it is clear that the depths may be greater than that.

Further, the present invention exhibits the same effect in condensation heat transfer as in evaporative heat transfer. In other words, by providing spiral grooves with a large groove depth in the heat exchanger tubes in areas where the dryness of the refrigerant is large, the average thickness of the condensate film formed on the inner surface of all grooves in the tubes can be made extremely thin.
Heat transfer performance can be significantly improved.

Effects of the Invention As described above, the heat exchanger of the present invention has the heat exchanger tube as a flow path for a phase-changing fluid, and the inner wall of the heat exchanger tube is provided with at least two types of helical grooves having different groove depths. The groove depth of the spiral groove is small in the low dryness region on the inlet side of the fluid in the pipe and large in the high dryness region on the outlet side. It is possible to form a thin refrigerant liquid film, and it is possible to significantly improve the heat transfer performance of a heat exchanger, which has great industrial effects.

[Brief explanation of the drawing]

FIG. 1 is a perspective view of a conventional finned heat exchanger, and FIGS. 2a and 2b are a partially cutaway front view and a half-cutted side sectional view of a spiral grooved tube in the pipe of the same finned heat exchanger.
FIG. 3 is a partially cutaway front view of an evaporator showing an embodiment of the present invention, and FIGS. 4a and 4b are a partially cutaway front view and a half-cut side cross-section of the internal spiral grooved tube 7 of the same evaporator. Figures 4c and 4d are a partially cut-away front view and a half-cut side sectional view of the internal spiral grooved tube 8 of the same evaporator, and Figure 5 is a characteristic diagram showing the results of an evaporation performance experiment of the heat transfer tube. . 5...fin, 6,7,8,9...heat exchanger tube, 12,
13...Spiral groove.

Claims (1)

[Claims] 1. The inside of the heat transfer tube is used as a phase-changing fluid flow path,
At least two types of helical grooves having different groove depths are provided on the inner wall of the heat exchanger tube, and the groove depth of the helical grooves is small on the inlet side of the fluid in the tube and large on the outlet side.