JPH10318691A - Heat transfer tube for falling liquid film evaporator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a heat transfer tube for a falling liquid film evaporator having excellent wet spreadability of refrigerant by increasing an outer surface area. SOLUTION: The heat transfer tube for a falling liquid film evaporator comprises a tube body 1, fins 2 provided on an outer surface of the body to extend in a direction perpendicularly or obliquely to a tube axis direction, and a cutout part 4 for cutting out the fins extended in a direction of crossing the fins 2. A depth of the part 4 is substantially the same as a height of the fins 2. And, the fins 2 have a pitch in a tube axis direction of 0.62 to 1.27 mm, and a pitch of the part 4 in a tube circumferential direction is 0.50 to 0.9 mm, and a height of the fin 2 is 0.2 to 0.4 mm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat transfer tube for a falling liquid film evaporator suitable for being incorporated in a falling liquid film evaporator such as an absorption refrigerator.

[0002]

2. Description of the Related Art In a falling liquid film type evaporator such as an absorption chiller / heater, a refrigerant is caused to flow down on the outer peripheral surface of a heat transfer tube, and heat is exchanged between, for example, water flowing through the tube and the refrigerant. Cooling the water in the pipe. The refrigerant in contact with the heat transfer tube spreads on the surface of the heat transfer tube, evaporates at a low pressure, and removes heat from the heat transfer surface of the heat transfer tube, thereby cooling the water inside the heat transfer tube. Also,
When the refrigerant spread and wet on the surface of the heat transfer tube evaporates, heat of vaporization is taken from the heat transfer tube, so that water and the like in the tube can be efficiently cooled. Therefore, in order to obtain a high-performance heat transfer tube having good heat transfer performance, it is necessary to increase the contact area between the refrigerant and the heat transfer tube (that is, the area of the heat transfer surface) as much as possible.

[0003] In order to increase the contact area between the refrigerant and the heat transfer tube, it is necessary to increase the outer surface area of the heat transfer tube and to improve the wetting and spreading of the refrigerant on the surface of the heat transfer tube.

Therefore, a fin extending in the circumferential direction is provided on the outer surface of the tube, cracks are provided at a predetermined pitch in the circumferential direction of the tip of the fin, and a heat transfer tube for dispersing a dripping liquid is proposed in which the tip is divided at minute intervals. (JP-A-62-206356). The pitch of the fins is 0.5 to 1.5 mm,
The fin height is 0.5 to 2 mm, the fin crack pitch is 2 mm or less, and the fin crack depth is 2 mm or less.

Further, a heat transfer tube for a falling liquid film type evaporator having a groove formed at the top of the fin along the fin has been proposed (Japanese Patent Laid-Open No. 7-71889). The fins are provided in 905 to 1102 rows per 1 m in the tube axis direction, the height of the fins is 0.2 to 0.8 mm, and the notch is 0.5 to 1.0 mm in the circumferential direction of the tube. They are provided at a pitch.

[0006]

However, in the heat transfer tube disclosed in Japanese Patent Application Laid-Open No. 62-206356, the height of the fin is high, so that the refrigerant sprayed on the fin has a predetermined pitch in the circumferential direction of the fin. Before being drawn into the crack provided in the above, it is drawn into the groove between the fins, and the refrigerant does not fall into a predetermined crack, so that the wet spread is small, and the refrigerant does not wet the tube wall and easily falls. In addition, since the tip of the fin is sharp, there is a problem that the refrigerant is hardly wet and spread over the entire wall surface of the fin, and the wet spread property is particularly deteriorated in the upper part of the heat transfer tube.

Further, in the heat transfer tube disclosed in Japanese Patent Application Laid-Open No. 7-71889, the groove is formed at the top of the fin and the tip of the fin is divided into two, so that the refrigerant does not easily spread to the groove between the fins. There is a disadvantage that the wet spreading property is low.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a heat transfer tube for a falling liquid film type evaporator, which has a large outer surface area and excellent refrigerant wetting and spreading properties.

[0009]

A heat transfer tube for a falling film evaporator according to the present invention comprises: a tube main body; and a fin provided on an outer surface of the tube main body and extending in a direction orthogonal or inclined to a tube axis direction. A heat transfer tube for a falling film evaporator having a notch extending in a direction intersecting the fin and notching the fin, wherein the depth of the notch is substantially the same as the height of the fin. .

In this heat transfer tube for a falling film evaporator,
The fins have a pitch in the tube axis direction of 0.62 to 1.27.
mm, and the pitch of the notch in the circumferential direction of the pipe is 0.50 mm.
To 0.9 mm, and the height of the fin is preferably 0.2 to 0.4 mm.

In the present invention, since the depth of the notch is substantially the same as the height of the fin, the bottom of the notch and the bottom of the groove between the fins are on the same plane. Is extremely excellent in spreading property in the axial direction of the tube.

Preferably, the height of the fin is 0.2 to 0.4 mm. Fin height 0.2-0.4m
m, the refrigerant sprayed from above toward the heat transfer tube is drawn into the fin groove, but the fin height is 0.4 mm.
If it exceeds mm, the dripping liquid tends to flow in the circumferential direction of the tube, and the wet-spreading property in the axial direction of the tube deteriorates. On the other hand, when the fin height is less than 0.2 mm, wet spreading in the circumferential direction of the tube is deteriorated. Therefore, the fin height is preferably set to 0.2 to 0.4 mm.

The pitch of the fins in the tube axis direction is preferably 0.62 to 1.27 mm. If the fin pitch is less than 0.62 mm, the refrigerant is likely to flow without the refrigerant being drawn into the fin grooves, resulting in poor wettability. Conversely, when the fin pitch exceeds 1.27 mm,
Although the refrigerant is drawn into the groove between the fins, the refrigerant tends to flow quickly in the circumferential direction of the tube, and often flows down without wetting the bottom surface of the fin. For this reason, the fin pitch is preferably from 0.62 to 1.27 mm.

The pitch of the notch in the pipe circumferential direction is 0.9 mm.
Above, the refrigerant in the groove between the fins at the upper part of the tube tends to flow down the tube along the groove between the fins before being drawn into the notch. The wet-spreading property is reduced. That is, the effect of the notch can be obtained only in the lower part of the heat transfer tube. Further, when the pitch of the notch in the pipe circumferential direction is less than 0.50 mm, the pitch is too small, so that the refrigerant is less likely to enter the pipe axis direction,
For this reason, the refrigerant in the groove between the fins easily flows down in the pipe circumferential direction along the groove between the fins, and the wet-spreading property in the pipe axis direction decreases.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be specifically described below with reference to the accompanying drawings. FIG. 1 is a perspective view showing a part of the outer surface of the heat transfer tube according to the present embodiment. Fins 2 are formed on the outer surface of the pipe main body 1 at predetermined pitches in the pipe axis direction, extending vertically or inclining in the pipe axis direction. The height of the fins 2 is H, and the pitch of the fins 2 in the tube axis direction is P. A notch 4 extending in the tube axis direction is provided so as to intersect with the fin 2. The notch 4 has a pitch Q in the circumferential direction of the tube.

In this embodiment, the height H of the fin 2 is substantially the same as the depth of the notch 4 provided in the fin. Therefore, the grooves 3 formed between the fins 2
And the bottom of the notch 4 provided in the fin 2 are at the same height, and there is no step between them.

As described above, in this embodiment, since there is no step between the bottom of the groove 3 and the bottom of the notch 4, the refrigerant dropped on the outer surface of the pipe is not only in the pipe circumferential direction but also in the pipe axial direction. , So that extremely high heat transfer efficiency can be obtained.

The present invention relates to a copper or copper alloy tube, an iron tube,
And a heat transfer tube of various materials such as a titanium tube and the like, and all have the same effect.

[0019]

Next, the results of tests performed to demonstrate the effects of the present invention will be described.

First Example A phosphor-deoxidized copper tube of JIS H3300 C1201T was used, and fins were formed on the outer surface thereof. Note that the inner surface remains smooth. In the heat transfer tube of the example, the outer diameter of the heat transfer tube before fin formation is 16 mm and the thickness is 1.0 mm. The number of fins is 26 peaks per inch and the fin height is 0.3
mm. The pitch of the notch of the fin is 0.62 mm. The fin height is the same as the depth of the notch.

The heat transfer tube of the comparative example has a fin height of 0.5 m.
m, and the tip of the fin is disclosed in Japanese Unexamined Patent Publication No. 7-71889.
As described in the publication, a groove extending in the longitudinal direction of the fin is formed. The bottom surface and the side surface of the inner surface of this groove are orthogonal to 90 °. Other conditions are the same as in the embodiment. The pitch of the fin notch is 0.62 mm.

The heat transfer properties of these heat transfer tubes were examined. FIG. 3A is a schematic view showing a test device for wet spreadability. In order to sufficiently degrease the surface of the test tube, immerse in trichloroethane for 1 hour, and further in an oxidizing atmosphere for 20 hours.
A heat treatment of heating to 0 ° C. for 1 hour was performed. The test tube 10 was set with the axial direction being horizontal, and the pipette 7 was fixed so that its tip was located at a position 20 mm above the substantially central portion of the tube 10. 2 cc of colored water 8 was dropped onto the test tube 10 by adjusting the cock 9. Then, FIG.
The wet spreading length at eight positions P1 to P8 in the circumferential direction of the test tube 10 shown in (b) was measured, and the average wet length was calculated.

This average wet length is 10 in the case of the comparative example.
In contrast to 0 mm, the wetting length of the heat transfer tube of this embodiment is 150 mm, and it can be seen that in this embodiment, the wettability of the refrigerant is significantly improved. In the case of a bare pipe (a pipe without fins), the average wet length is 25 m.
m.

FIG. 2 is a graph showing the heat transfer performance of the heat transfer tubes of the present example and the comparative example, with the horizontal axis representing the amount of refrigerant sprayed and the vertical axis representing the overall heat transfer coefficient. As shown in this figure,
The heat transfer performance of this example is extremely high as compared with the comparative example. The values of the overall heat transfer coefficient thus obtained are as shown in Table 1 below.

[0025]

[Table 1]

Second Embodiment Using the same phosphorous deoxidized copper tube as in the first embodiment, fins having the shapes shown in the following Tables 2 and 3 were formed on the outer surface thereof. The outer diameter of the fin is 15.8 mm, and the bottom thickness is 0.85 m.
m and the inner surface remains smooth.

[0027]

[Table 2]

[0028]

[Table 3]

Then, in the same manner as in the first embodiment, wetting and spreading properties of each heat transfer tube were examined. Further, the heat transfer coefficient of each heat transfer tube was measured.

In the measurement of the heat transfer coefficient, the internal pressure was set to 6 (mm).
Hg), the amount of refrigerant sprayed is 1.00 (kg / m · min), the flow rate of cold water is 1.5 (m / sec), the test tubes are arranged in four rows in one row, the cold water outlet temperature is 7 (° C.), and the The number was 4 passes.

The results are shown in Tables 4 and 5 below and FIG.
(A) to (d) and FIGS. 5 (a) to (d). FIG. 4 is a graph showing the heat transfer performance of the heat transfer tubes of this embodiment and the comparative example, with various variables taken along the horizontal axis and heat transfer coefficients taken along the vertical axis. The axis is the notch depth, the horizontal axis in (b) is the notch pitch, the horizontal axis in (c) is the fin pitch,
The horizontal axis of (d) is the fin height. FIG. 5 is a graph showing the wetting and spreading properties of the heat transfer tubes of the present example and the comparative example, with various variables being plotted on the horizontal axis and the wet length on the vertical axis. Is the notch depth, the horizontal axis of (b) is the notch pitch, the horizontal axis of (c) is the fin pitch, and the horizontal axis of (d) is the fin height. 4 (a) to 4 (d) and 5 (a) to 5 (d), ● shows the result of the example, and Δ shows the result of the comparative example.

[0032]

[Table 4]

[0033]

[Table 5]

As shown in Tables 4 and 5, and FIGS. 4 (a) to (d) and FIGS. 5 (a) to 5 (d), the heat transfer performance and the refrigerant wetting and spreading property of each of the examples are comparative examples. It turns out that it is much higher than that of.

[0035]

As described above, the liquid dropped on the outer surface of the tube has an excellent spreading property in the axial direction of the tube, and the evaporation heat transfer performance can be improved. Thereby, the amount of the dripping liquid can be reduced, the amount of the refrigerant as the dripping liquid in the evaporator can be reduced, and the size of the spray pump and the like can be reduced.

[Brief description of the drawings]

FIG. 1 is a perspective view showing a part of an outer surface of a heat transfer tube according to an embodiment of the present invention.

FIG. 2 is a graph showing the effect of the present invention.

FIG. 3A is a schematic diagram of an apparatus for measuring the wetting and spreading property of a heat transfer tube, and FIG. 3B is a schematic diagram showing points for measuring the wetting and spreading property of a heat transfer tube.

FIG. 4 is a graph showing heat transfer performance.

FIG. 5 is a graph showing the wet spreading property of the refrigerant.

[Explanation of symbols]

 1: Heat transfer tube body 2: Fin 3: Groove 4: Notch 7: Pipette 8: Water 9: Cock 10: Test tube

Claims (2)

[Claims] A downflow having a pipe main body, a fin provided on an outer surface of the pipe main body and extending in a direction orthogonal or inclined to a pipe axis direction, and a notch extending in a direction intersecting the fin and notching the fin. In the heat transfer tube for a liquid film type evaporator, the depth of the notch is substantially the same as the height of the fin. 2. The fin has a pitch of 0.6 in the tube axis direction.
The pitch of the notch portion in the circumferential direction of the tube is 0.50 to 0.9 mm, and the height of the fin is 0.2 to 0.4 mm. 2. The heat transfer tube for a falling liquid film type evaporator according to 1.