JPH04126998A - Boiling heat transfer tube - Google Patents

Abstract

PURPOSE:To improve heat transfer performance by continuously providing a plurality of oblique grooves in a direction at a predetermined slope to a tube axial direction and a plurality of parallel grooves in a direction parallel to the axial direction in a crossing state on the inner periphery of a tube. CONSTITUTION:Oblique grooves 10 are continuously formed in a direction at a predetermined slope to a direction of a tube axis (n) and parallel grooves 11 are formed in a direction parallel with the direction of the axis (n) on the inner periphery 8a of a boiling heat transfer tube 8. In refrigerant flowing in a passage 9 in the tube, liquid refrigerant flowing to the bottom of the tube is pulled up by a capillary tube phenomenon in an area having a relatively small flowing speed to increase its effective heat transfer area. Since the grooves 10, 11 are provided, liquid refrigerant holding amount is much, the liquid refrigerant flow is obtained along the grooves 10, 11 not only in a high dryness area but in much liquid refrigerant area with relatively low dryness area to sufficiently obtain heat transfer acceleration effect. In the area having large refrigerant flowing speed, the liquid refrigerant flow along the grooves 11 is more than that flowing along the oblique groove 10, the thickness of the liquid refrigerant is made uniformly thin by the capillary tube mainly with the grooves 11 to accelerate its heat transfer.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to boiling heat transfer tubes used in heat exchangers for transferring heat between fluids such as refrigerant and air, such as air conditioners, refrigeration equipment, and automobile equipment. It is something.

2. Description of the Related Art In recent years, heat exchangers have been required to be made more compact in terms of equipment design, and heat exchanger tubes that form the refrigerant side flow path of heat exchangers have also been disclosed in Japanese Utility Model Publication No. 14956/1983 and Utility Model Publication No. 55-1982.
As disclosed in Japanese Patent No. 26706, high efficiency has been achieved by providing a spiral groove on the inner circumferential surface of the pipe.

Hereinafter, the above-mentioned conventional boiling heat exchanger tube will be explained with reference to the drawings.

Figure 5 shows the cross-sectional shape of a conventional boiling heat exchanger tube, Figures 6 and 7 show the shape of the heat transfer surface of the boiling heat exchanger tube before tube manufacturing, and Figure 8 shows the shape of the heat transfer surface of the boiling heat exchanger tube before tube manufacturing. FIG. 2 is an external view showing an example of a heat exchanger. In FIGS. 5 to 7, reference numeral 1 denotes a boiling heat transfer tube having a substantially cylindrical cross section, with a flow path 2 formed inside. Reference numeral 8 denotes a 7-shaped groove provided on the tube inner circumferential surface 1a of the boiling heat exchanger tube 1, and a large number of grooves are provided continuously in a spiral shape with respect to the axis m direction of the boiling heat exchanger tube 1. In addition, this boiling heat transfer tube 1 is formed through pipe making and welding processing, and after processing the groove 3 at the stage of forming the flat heat transfer surface 4 before the pipe forming process, the pipe is made from a flat plate shape to a tubular shape, Furthermore, the end surfaces 5a at both ends of the heat transfer surface 4
and 5b are welded together.

The boiling heat exchanger tube 1 configured as described above is generally used as a part of a heat exchanger. In FIG. 8, 6 is an example of a heat exchanger using the boiling heat exchanger tube 1, which is composed of fins 7 arranged in parallel at regular intervals and the boiling heat exchanger tube 1 inserted at right angles to the fins 7. Heat exchange is performed between the airflow flowing between the fins 7 and the refrigerant in the boiling process flowing through the flow path 2 in the boiling heat transfer tube 1. At this time, by providing the 7-shaped groove 3 in a spiral shape on the inner circumferential surface 1a of the boiling heat transfer tube 1, the liquid refrigerant flowing in the bottom of the flow path 2 of the horizontal boiling heat transfer tube 1 is caused by capillary action. As the inside of the groove 3 was pulled down, the entire inner circumferential surface 1a of the tube was wetted with a refrigerant liquid film, and although the effective heat transfer area was increased, the heat transfer performance was improved.

Problems to be Solved by the Invention However, in the above configuration, a thin refrigerant liquid film is formed on the entire inner circumferential surface 1a of the boiling heat transfer tube, and the heat transfer promotion effect can only be obtained at a low refrigerant flow rate. And only in the region where the dryness of the refrigerant is large, that is, in the latter half of the boiling process. On the other hand, at the beginning of the boiling process, the dryness of the refrigerant is small and there is a large amount of liquid refrigerant in the tube, so the liquid refrigerant quickly fills the 7-shaped groove 3 and the liquid refrigerant passes across the V-shaped groove 3. Therefore, the effect of promoting heat transfer due to the increase in the effective heat transfer area as described above cannot be expected. Furthermore, even in areas where the dryness of the refrigerant is high, when the refrigerant flow rate is high, the liquid refrigerant will overcome the grooves 3 due to the high flow rate, making it impossible to obtain a flow of liquid refrigerant along the grooves 3. Another problem was that the heat transfer performance deteriorated due to peeling of the inner circumferential surface 1a of the tube and a significant increase in flow resistance.

In view of the above two problems, the present invention significantly improves heat transfer performance under any refrigerant condition, regardless of the flow rate or degree of dryness of the refrigerant, by devising the shape of the inner circumferential surface of the boiling heat transfer tube. The aim is to improve the performance of heat exchangers using heat transfer tubes.

Means for Solving the Problems In order to solve the second problem, the boiling heat exchanger tube of the present invention has a plurality of inclined grooves continuous in a direction having a constant inclination with respect to the tube axis direction and A plurality of parallel grooves that are continuous in parallel directions are provided in the inner circumferential surface of the pipe in an intersecting manner.

Effect of the present invention With the above-described configuration, first, in a region where the refrigerant flow velocity is relatively low, the liquid refrigerant flowing at the bottom of the tube is lifted up along the inclined groove by capillary action, as in the past, to increase the effective heat transfer area and heat transfer. However, since not only slanted grooves but also parallel grooves are provided, the amount of liquid refrigerant held in the groove is larger than before, and the liquid refrigerant is absorbed not only in high dryness areas but also in relatively low dryness areas. Even in a large area, the flow of liquid refrigerant along the inclined grooves or parallel grooves can be obtained, and the effect of promoting heat transfer in the first stage can be sufficiently obtained. In addition, in areas where the refrigerant flow velocity is high, the liquid refrigerant flows more along the parallel grooves than along the inclined grooves due to the high refrigerant flow velocity. The thickness of the liquid refrigerant is uniformly thinned by the capillary phenomenon mainly in the parallel grooves, without peeling off from the surface or significantly increasing the flow resistance. / can promote heat transfer.

EXAMPLES Hereinafter, boiling heat exchanger tubes according to examples of the present invention will be described with reference to the drawings.

Figures 1, 3, and 4 show the shape of the heat transfer surface of the boiling heat exchanger tube in the embodiment of the present invention before the tube manufacturing process, and Figure 2 shows the shape of the boiling heat exchanger tube in the embodiment of the present invention after the tube manufacturing process. The circumferential cross-sectional shape of is shown. In FIGS. 1 to 4, 8 is a boiling heat transfer tube having a substantially cylindrical cross section, forming a flow vr9 inside. 10
and 11 are an inclined groove and a parallel groove formed on the tube inner circumferential surface 8a of the boiling heat exchanger tube 8, respectively.The inclined groove 10 is oriented in a direction with a constant inclination to the tube axis n direction, and the parallel groove 11 is oriented in a direction with a constant inclination to the tube axis n direction. The inclined grooves 10 and the parallel grooves 11 are provided continuously in a direction parallel to the direction, and are arranged in an intersecting manner over the entire inner circumferential surface 8a of the tube. The boiling heat transfer tube 8 is formed through pipe making and welding, and after the inclined grooves 10 and the parallel grooves 11 are formed at the stage of forming the flat heat transfer surface 12 before the tube forming process, the boiling heat transfer tube 8 is formed from a flat plate shape. It is made into a tubular shape and further has a heat transfer surface 12.
It is formed by welding the end faces 1.3a and 13b at both ends.

The boiling heat transfer tube 8 configured as described above is used as a part of a heat exchanger as in the conventional example, and is used by flowing a refrigerant in the boiling process through the tube. In this usage state, the refrigerant flowing through the flow path 9 in the tube first pulls up the liquid refrigerant flowing at the bottom of the tube by capillary action in the region where the refrigerant flow rate is relatively low, increasing the effective heat transfer area and promoting heat transfer. However, since not only the inclined grooves 10 but also the parallel grooves 11 are provided, the amount of liquid refrigerant held in the grooves is larger than before, and the refrigerant is not only in high dryness areas but also in relatively low dryness areas. Even in a region where there is a large amount of heat transfer, the liquid refrigerant can flow along the inclined grooves 10 and the parallel grooves 11, and the first heat transfer promoting effect can be sufficiently obtained. In addition, in a region where the refrigerant flow velocity is high, the liquid refrigerant flows more along the parallel grooves 11 than the liquid refrigerant flows along the inclined grooves, and unlike the conventional example, the liquid refrigerant overcomes the inclined grooves 10 and enters the pipe. The thickness of the liquid refrigerant can be uniformly reduced by the capillary phenomenon mainly caused by the parallel grooves 11 to promote heat transfer without peeling off from the peripheral surface 8a or significantly increasing flow resistance.

As described above, according to this embodiment, a plurality of inclined grooves 10 are continuous in a direction having a constant inclination with respect to the tube axis n direction, and a plurality of parallel grooves 10 are continuous in a direction parallel to the tube axis n direction. Groove 1
1 in a continuous manner in a crosswise manner on the inner circumferential surface 8a of the pipe, the amount of liquid refrigerant held in the groove is increased in the region where the refrigerant flow rate is low, and the amount of liquid refrigerant held in the groove is increased not only in the high refrigerant dryness region but also in the low dryness region. Even in areas where there is a large amount of refrigerant, the liquid refrigerant flowing at the bottom of the tube is pulled up by capillary action to increase the effective heat transfer area where the inner circumferential surface 8a and the liquid refrigerant are in contact. By obtaining such a flow of liquid refrigerant, separation of the liquid refrigerant from the tube inner peripheral surface 8a and a significant increase in flow resistance can be suppressed, and the thickness of the liquid refrigerant can be uniformly thinned by capillary action to promote heat transfer. Therefore, the heat transfer performance can be significantly improved under any refrigerant conditions regardless of the flow rate or dryness of the refrigerant, and the performance of the heat exchanger using the boiling heat exchanger tube 8 can be significantly improved.

Effects of the Invention As described above, the present invention has a plurality of inclined grooves continuous in a direction having a constant inclination with respect to the tube axis direction and a plurality of parallel grooves continuous in a direction parallel to the tube axis direction. By providing a continuous intersecting pattern on the inner circumferential surface of the pipe, the amount of liquid refrigerant held in the groove section is increased in areas where the refrigerant flow rate is low, and it is possible to increase the amount of liquid refrigerant held in the grooves not only in areas with high refrigerant dryness but also in areas with a large amount of liquid refrigerant in low dryness areas. However, the capillary phenomenon pulls up the liquid refrigerant flowing at the bottom of the tube to increase the effective heat transfer area where the inner peripheral surface of the tube and the liquid refrigerant are in contact, and in addition, in areas where the refrigerant flow velocity is high, the flow of the liquid refrigerant mainly through parallel grooves is improved. As a result, separation of the liquid refrigerant from the inner circumferential surface of the pipe and a significant increase in flow resistance can be suppressed, and the thickness of the liquid refrigerant can be uniformly reduced by capillary action to promote heat transfer. Therefore,
Heat transfer performance can be significantly improved under any refrigerant conditions, regardless of the flow rate or dryness of the refrigerant, and the performance of a heat exchanger using this boiling heat transfer tube can be significantly improved.

[Brief explanation of the drawing]

FIG. 1 is a plan view showing the shape of the heat transfer surface of the boiling heat transfer tube before tube forming in an embodiment of the present invention, and FIG. 2 is a circle showing the shape of the boiling heat transfer tube of FIG. 1 after the tube forming process. Circumferential sectional view, 3rd
The figure is a sectional view taken along the line A-A in FIG. 1, FIG. 4 is a sectional view taken along the line BB in FIG. Figure 5 is a plan view showing the shape of the heat transfer surface of the boiling heat exchanger tube before tube manufacturing, Figure 7 is a cross-sectional view taken along line C-C in Figure 6, and Figure 8 is a heat exchanger using the boiling heat exchanger tube. FIG. 8... Boiling heat exchanger tube, 8a... Tube inner peripheral surface, 10...
Inclined groove, 11...Parallel groove. Name of agent: Patent attorney Yoshiaki Ogawa and 2 other people 1 Hejojo

Claims (1)

[Claims] A plurality of inclined grooves continuous in a direction having a certain inclination with respect to the pipe axis direction and a plurality of parallel grooves continuous in a direction parallel to the pipe axis direction are provided in a continuous cross-like manner on the inner peripheral surface of the pipe. A boiling heat transfer tube characterized by: