JPH0942875A - Heat transfer pipe - Google Patents

Abstract

PROBLEM TO BE SOLVED: To promote a dispersion of absorbing liquid toward an axial direction of a pipe and further promote an agitating action of an absorbing liquid film by a method wherein both banks at both sides of a liquid accumulating recessed part are formed with some slots spaced apart by a predetermined distance in an axial direction of a pipe and more shallow than the recessed part in a direction across the recessed part, and a central part of the lower surface of an outer surface is formed with a projection part for removing liquid which is continuous with an axial direction of the pipe. SOLUTION: A heat transfer pipe 11 is formed with a liquid accumulating recessed part 13 which is axially continuous with a central part of an upper surface of an outer surface under a state of horizontal arrangement. Both sides of this recessed part 13 form banks 15 and the banks 15 are formed with some slots 17 spaced apart by a predetermined distance across the recessed part 13 in an axial direction of the pipe. The slots 17 are formed to be more shallow than the recessed part 13. In addition, the central part of the lower surface of the outer surface is formed with a projection 19 for use in removing liquid which is continuous in an axial direction of the pipe. With such an arrangement as above, it is possible to perform a sufficient promotion of a spreading of absorbing liquid in an axial direction of the pipe and an agitating action of the absorption liquid film.

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 used for an absorber or a regenerator of an absorption refrigerator.

[0002]

2. Description of the Related Art An absorption refrigerator is basically composed of four heat exchangers, an evaporator, an absorber, a regenerator and a condenser. Of these, the absorber has the largest heat transfer area and volume, and the performance of the absorber has a great influence on the performance as a refrigerator. Generally, the absorber of an absorption chiller is equipped with a large number of heat transfer tubes arranged horizontally, and an absorption liquid such as an aqueous solution of lithium bromide is sprayed from the upper part of this heat transfer tube group to obtain this absorption liquid. While flowing down the outer surface of the heat transfer tube, the refrigerant vapor is absorbed and at the same time, heat exchange is performed with the cooling water flowing in the heat transfer tube.

In order to efficiently perform this heat exchange,
It is necessary to promote the mass transfer phenomenon that causes the absorption liquid to absorb the refrigerant vapor, and for that purpose, the absorption liquid must be spread efficiently on the outer surface of the heat transfer tube. Further, it is known that the absorbing liquid causes a disturbing phenomenon of the absorbing liquid film when absorbing the refrigerant vapor, and it is also necessary to efficiently promote this disturbing phenomenon.

As a heat transfer tube designed so that the absorbing liquid spreads on the outer surface of the heat transfer tube, particularly in the tube axial direction, for example, "a concave surface continuous in the tube axial direction is formed at the upper part of the outer surface,
A heat transfer tube having a large number of ridges or grooves formed on the outer surface in the circumferential direction is known (Japanese Utility Model Publication No. 48-47050).
In this heat transfer tube, the dispersed absorption liquid is accumulated in the concave surface of the upper surface of the heat transfer tube and spreads in the axial direction of the tube, and the absorption liquid overflowing from the concave surface spreads in the circumferential direction along the ridges or grooves formed in the circumferential direction. By so doing, the entire outer surface of the heat transfer tube is wetted with the absorbing liquid to enhance the ability to absorb the refrigerant vapor.

As a heat transfer tube aiming at the effect of promoting the disturbing action of the absorbing liquid, for example, "a heat transfer tube having a large number of fine spiral grooves formed on the outer surface" is known (Actual exploitation 5).
7-100161). This heat transfer tube is intended to spread the absorbing liquid adhering to the outer surface in the pipe axial direction along the spiral groove, and at the same time to promote the disturbing action of the absorbing liquid film by the unevenness of the numerous spiral grooves.

[Problems to be Solved by the Invention]

However, in the former heat transfer tube, the concave surface formed in the tube axial direction on the upper surface can be expected to spread the absorbing liquid in the axial direction of the tube, but the absorbing liquid overflowing from the concave surface is formed in the circumferential ridges or grooves. Since it will flow down smoothly along it, the disturbing action of the absorbing liquid film cannot be expected.

In the latter heat transfer tube, the absorbing liquid flows along the spiral groove in the upper half of the outer surface and spreads in the axial direction of the tube.
In the lower half of the outer surface, the absorbing liquid flows downward due to its own weight, which makes it difficult to flow along the spiral groove. Therefore, the spread of the absorbing liquid in the tube axis direction cannot be sufficiently obtained.

Further, in the absorber of the absorption refrigerating machine, since the horizontal heat transfer tubes are arranged in multiple stages in the vertical direction, the absorbing liquid dropped from the upper heat transfer tubes falls on the heat transfer tubes in the lower step. It is desirable that the heat transfer tube be spread again on the outer surface of the heat transfer tube. However, in the conventional heat transfer tube, the absorption liquid drip position (liquid separation position) is not constant, so the outer surface of the heat transfer tube in the stage below it As a result, the way in which the absorbing liquid spreads tends to be uneven or uneven.

The above problems also exist in the dropping liquid film type regenerator of the absorption refrigerator. The dripping liquid film type regenerator is similar to the above-mentioned absorber in that the heat transfer tube group is arranged horizontally, and the diluted absorption liquid that has become thin by absorbing the refrigerant vapor in the absorber is dropped onto the outer surface of the heat transfer tube. Hot water or steam is caused to flow inside the heat transfer tube to boil the rare absorption liquid on the outer surface of the heat transfer tube to convert it into a concentrated absorption liquid. Therefore, even in the dropping liquid film type regenerator, it is a key to high performance to promote the spreading of the absorbing liquid on the heat transfer tube and the disturbing action when the refrigerant vapor is expelled from the absorbing liquid.

In view of the above-mentioned problems, an object of the present invention is to sufficiently promote the spreading of the absorbing liquid in the tube axis direction and the disturbing action of the absorbing liquid film, and the liquid separating position on the lower surface side. It is to provide a heat transfer tube that stabilizes the heat transfer tube and allows the absorbing liquid to drip at an appropriate position of the heat transfer tube in the lower stage.

[0011]

In order to achieve this object, the heat transfer tube of the present invention has a recess for liquid storage which is continuous in the axial direction of the tube in the central portion of the upper surface of the outer surface when it is horizontally arranged. However, the bank portion on both sides of this recess has a slot shallower than the recess in the direction crossing the recess at a predetermined interval in the pipe axis direction,
It is characterized in that it has a convex portion for liquid separation which is continuous in the tube axis direction in the central portion of the lower surface of the outer surface (Claim 1).

Since the heat transfer tube of the present invention has the above-mentioned structure, the absorbing liquid dropped on the heat transfer tube collects in the concave portion on the upper surface, and sufficiently spreads along the concave portion in the axial direction of the tube. When the concave portion is filled with the absorbing liquid, a part of the absorbing liquid flows through the slots formed in the bank and over the other portions, flows over in the circumferential direction of the pipe, overcoming the bank. This allows the absorbing liquid to spread over the entire outer surface of the heat transfer tube.

Further, the film of the absorbing liquid flowing out from the concave portion in the circumferential direction is thicker in the portion passing through the slot than in the portion passing over the bank portion. Therefore, when the difference in the film thickness flows down the side surface of the pipe. The surface tension causes the disturbance of the absorption liquid.

Further, the absorbing liquid flowing down on both sides of the pipe is
It gathers on the convex portion formed in the central portion of the lower surface and drops from there. Therefore, the dropping position is stable, and the absorbed liquid that has been dropped can be reliably received by the recessed portion in the center of the upper surface of the heat transfer tube in the lower stage. Therefore, even in the lower heat transfer tube, heat exchange is performed in a state where there is no unevenness or variation in the absorbing liquid.

In the heat transfer tube of the present invention, since the flow of the absorbing liquid as described above is obtained, the absorption capacity is improved and the heat transfer performance can be improved.

The depth of the recess formed in the central portion of the upper surface of the heat transfer tube in the tube axial direction is preferably about 1.0 to 3.0 mm. If it is too shallow, the absorbent will overflow from the recess before spreading in the tube axis direction. On the other hand, if the depth is too deep, the amount of the absorbing liquid accumulated will be too large, and the absorbing liquid remaining on the heat transfer tubes will crystallize when the refrigerator is stopped, which will adversely affect the refrigerator.

Further, it is desirable that the depth of the slots formed on the bank portions on both sides of the recess is about 0.5 to 2.0 mm. If it is too shallow, the difference between the thickness of the absorbent film passing through the slot and the thickness of the absorbent film passing over the bank is small, and the disturbing action cannot be sufficiently obtained. On the other hand, if it is too deep, the absorbing liquid in the recess flows out only from the slot, the vicinity of the top of the bank is not wetted, and the effective heat transfer area is reduced.

Further, the slots formed on the bank portions on both sides of the concave portion serve to let the absorbing liquid accumulated in the concave portion flow out in the circumferential direction of the pipe, and therefore, in the circumferential direction of the pipe (direction orthogonal to the concave portion). It is desirable to form. However, the direction of the slot may be slightly inclined with respect to the circumferential direction of the tube, and if the inclination is within 10 ° with respect to the circumferential direction, there is no problem in performance.

It is desirable that a plurality of ridges or grooves extending in the tube axis direction or a direction close to the tube axis be formed on both side surfaces of the tube (claim 2). When such protrusions or grooves are formed, the heat transfer area can be increased, and the disturbing action of the absorbing liquid film flowing down is promoted by the protrusions or grooves. The direction of the ridge or groove is preferably the same as the tube axis, but may be slightly inclined with respect to the tube axis direction within 10 °.

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described in detail below with reference to the drawings.

[First Embodiment] FIG. 1 shows a first embodiment of the present invention. The heat transfer tube 11 has a recess 13 for holding a liquid, which is continuous in the axial direction of the tube, in the central portion of the upper surface of the outer surface when the heat transfer tube 11 is horizontally arranged. Both sides of the recess 13 are bank portions 15
The bank portion 15 is formed with slots 17 extending in the direction crossing the recess 13 at predetermined intervals in the pipe axis direction. The slot 17 is formed shallower than the recess 13. A convex portion 19 for separating the liquid is formed in the central portion of the lower surface of the outer surface and is continuous in the tube axis direction. Because of the above-described shape, the cross section of the heat transfer tube 11 is substantially heart-shaped, and is symmetrical with respect to the vertical plane passing through the center of the concave portion 13 and the center of the convex portion 19.

FIG. 2 shows a state in which the heat transfer tubes 11 of FIG. 1 are arranged in multiple stages in the vertical direction within the absorber of the absorption refrigerator. When the absorbing liquid is sprayed and applied to the heat transfer tube 11, the absorbing liquid is collected in the recess 13 on the upper surface of the heat transfer tube 11 and spreads along the recess 13 in the tube axial direction. When the concave portion 13 is filled with the absorbing liquid 21, a part of the absorbing liquid 21 passes through the slots 17 and the other portions pass over the bank portion 15 and flow out in the circumferential direction of the heat transfer tube 11. As a result, the absorbing liquid 21 spreads over the entire outer surface of the heat transfer tube 11. The cooling water 23 flows in the heat transfer tube 11.

The film of the absorbing liquid 21 flowing out from the recess 13 is
Since there is a difference between the film thickness of the portion that has passed over the bank 15 and the film thickness of the portion that has passed through the slot 17, the disturbing action of the absorbing liquid is promoted by the surface tension. Therefore, the absorbing liquid efficiently absorbs the refrigerant vapor when flowing down both side surfaces of the heat transfer tube 11, and is cooled by the cooling water flowing in the heat transfer tube 11.

Further, the absorbing liquid flowing down on both side surfaces of the heat transfer tube 11 gathers on the convex portion 19 in the central portion of the lower surface, and the droplet 2 is discharged from there.
It becomes 1a and falls. The convex portion 19 of the upper heat transfer tube 11
Is located directly above the concave portion 13 of the heat transfer tube 11 in the lower stage, so that the absorbing liquid dropped from the convex portion 19 is reliably received by the concave portion 13 of the heat transfer tube 11 in the lower stage. Therefore, the same phenomenon as above is repeated in the lower heat transfer tube.

[Second Embodiment] FIG. 3 shows a second embodiment of the present invention. The heat transfer tube 11 has a plurality of ridges 25 extending in the tube axis direction on both sides of the outer surface.
Other than that, since it is the same as the heat transfer tube of FIG. 1, the same reference numerals are given to the same portions. When the protrusion 25 is formed as described above, the absorbing liquid flowing down the side surface of the pipe is further spread by the protrusion 25 in the pipe axial direction, and the disturbing action is promoted. The same applies when a groove is formed instead of the protrusion 25.

FIG. 4 shows an example of a method of manufacturing the heat transfer tube of FIG. The tube used as the material for the heat transfer tube 11 is a tube having a circular cross section, into which a plug 27 having a substantially heart-shaped cross section is inserted, and three roller dies 29A, 29B are provided on the outer circumference.
29C, and press each roller die 29A, 29
Molding is performed by rotating B and 29C with a motor.

The roller die 29A forming the concave portion 13 and the bank portion 15 on the upper surface of the tube has a protrusion 31, and the protrusion 31 forms the slot 17 (see FIG. 3). Further, the two roller dies 29B and 29C for molding both side surfaces and the lower surface of the tube have a peripheral surface corresponding to the protrusion 25.

Both ends of the pipe are provided with roller dies 29.
The cross section remains circular without being processed by A, 29B, and 29C. This is due to the assembly of the heat exchanger. The heat transfer tubes of other embodiments can be manufactured by the same manufacturing method.

[Third Embodiment] FIG. 5 shows a third embodiment of the present invention. The heat transfer tube 11 is attached to the bank 15 on the upper surface of the tube.
The deep slots 17A and the shallow slots 17B are alternately formed. The depth of the deep slot 17A is smaller than the depth of the recess 13. Other than that, it is the same as the heat transfer tube of FIG. 3, and thus the same portions are denoted by the same reference numerals. As described above, the slots 1 having different depths in the bank portion 15
When 7A and 17B are formed, the number of types of film thickness of the absorbing liquid flowing out to the side surface of the tube increases, so that the disturbing action can be further promoted.

[Fourth Embodiment] FIG. 6 shows a fourth embodiment of the present invention. The heat transfer tube 11 has irregularities 33 formed on the inner surface of the tube corresponding to the irregularities on the outer surface of the tube. The irregularities 33 on the inner surface of the tube are opposite to the irregularities on the outer surface of the tube. Other than that, it is the same as the heat transfer tube of FIG. 3, and thus the same portions are denoted by the same reference numerals. When the unevenness 33 is formed on the inner surface of the tube as described above, the thickness of the tube wall becomes substantially uniform and the heat transfer area of the inner surface of the tube increases, so that the heat transfer performance from the inside to the outside of the tube is improved.

[Fifth Embodiment] FIG. 7 shows a fifth embodiment of the present invention. The heat transfer tube 11 has a large number of protrusions 35 formed on both side surfaces of the outer surface and extending obliquely in a direction close to the tube axis direction (direction within 10 ° with respect to the tube axis direction).
Other than that, since it is the same as the heat transfer tube of FIG. 1, the same reference numerals are given to the same portions. Even with such a structure, the absorption liquid flowing down the side surface of the pipe can be spread in the axial direction of the pipe and a disturbing action can be produced. The ridge 35 as described above can be formed by cutting.

[0032]

Example A heat transfer test was performed on the following three types of heat transfer tubes when used in an absorber. Heat transfer tube of FIG. 1 (Example 1): The material is phosphorus deoxidized copper, the outer diameter of the raw tube before processing is 19.05 mm, and the depth of the recess 13 is 1.
0 mm, the direction of the slot 17 is perpendicular to the direction of the concave portion 13, the depth of the slot 17 is 0.7 mm, the interval between the slots 17 is 10 mm, and the radius of curvature of the lower end of the convex portion 19 is 1 mm. Heat transfer tube of FIG. 5 (Example 2): depth of slot 17A 0.7 mm, depth of slot 17B 0.5 mm, ridge 2
The height from the groove bottom of No. 5 is 0.5 mm, the number of the ridges 25 is three per one side, and the others are the same as in the first embodiment. Heat transfer tube described in Japanese Utility Model Laid-Open No. 57-100161 (conventional example): The material and the raw tube are the same as in Example 1, the twist angle of the groove with respect to the tube axis is 30 °, the groove depth is 0.35 mm, and the number of grooves is 61.
Book.

The test machine is as shown in FIG. Reference numeral 41 denotes an evaporator, in which heat transfer tubes 37 are arranged in two rows and five stages, the upper and lower heat transfer tubes 37 are connected to each other, and water is passed through them.
Refrigerant (pure water) was sprayed from these spray pipes 45 to these heat transfer tubes 37. Reference numeral 39 denotes an absorber, in which the test heat transfer tubes 11 are arranged in five rows in one row, the upper and lower heat transfer tubes 11 are communicated with each other, and cooling water is allowed to pass through them. The absorbing liquid (lithium bromide aqueous solution) was sprayed through the spray pipe 43. Reference numeral 47 is a dilute solution tank for absorbing the refrigerant vapor in the absorber 39 and storing the diluted absorption liquid. The absorbing solution in the dilute solution tank 47 is supplied to the concentrated solution tank 49, lithium bromide is added in the concentrated solution tank 49 to adjust the concentration, and the absorbing solution after the concentration is adjusted by the pump 53 through the pipe 51 and the spray pipe. It was sprayed on the heat transfer tube 11 through 43.

The test conditions are as follows. Absorbing liquid: LiBr aqueous solution Inlet concentration: 58 ± 0.5 wt% Inlet temperature: 40 ± 1 ° C. Flow rate: 50 to 150 kg / h Surfactant: No addition Absorbing liquid spraying device Pore diameter: 1.5 mm Interval: 24 mm Absorber cooling Water inlet temperature: 28 ± 0.3 ° C. Flow velocity: 1 m / s Pressure inside absorber and evaporator: 15 ± 0.5 mmHg Arrangement of test heat transfer tubes: Heat transfer tubes of length 500 mm are arranged in 5 rows in one row in the vertical direction

As a result of the above-mentioned tests, the heat transfer coefficient of each test heat transfer tube was as shown in FIG. According to this result,
It can be seen that the heat transfer tubes of Examples 1 and 2 of the present invention have better heat transfer performance than the conventional heat transfer tube with the spiral groove.

The above description is for the case where the heat transfer tube of the present invention is used in the absorber of the absorption refrigerator, but the heat transfer tube is also used in the dropping liquid film type regenerator of the absorption refrigerator. Therefore, the heat transfer tube of the present invention can also be used as a heat transfer tube of a dropping liquid film type regenerator.

[0037]

As described above, according to the present invention, the absorbing liquid can be efficiently spread over the entire outer surface of the heat transfer tube, and the disturbing action of the absorbing liquid film can be sufficiently promoted. Further, the absorbing liquid dripping from the upper heat transfer tube is surely received by the concave portion of the lower heat transfer tube so that the sufficient absorbing liquid spreading and the disturbing action can be repeated many times. Therefore, a heat transfer tube having high heat transfer performance can be obtained, which can contribute to downsizing or improvement in capacity of the refrigerator.

[Brief description of drawings]

FIG. 1 is a perspective view showing a first embodiment of a heat transfer tube of the present invention.

FIG. 2 is a sectional view showing a usage state of the heat transfer tube of FIG.

FIG. 3 is a perspective view showing a second embodiment of the heat transfer tube of the present invention.

FIG. 4 is a sectional view showing a method of manufacturing the heat transfer tube of FIG.

FIG. 5 is a perspective view showing a third embodiment of the heat transfer tube of the present invention.

FIG. 6 is a perspective view showing a fourth embodiment of the heat transfer tube of the present invention.

FIG. 7 is a perspective view showing a fifth embodiment of the heat transfer tube of the present invention.

FIG. 8 is an explanatory diagram showing a heat transfer tube testing device.

FIG. 9 is a graph showing test results of heat transfer tubes.

[Explanation of symbols]

 11: Heat transfer pipe 13: Recessed portion 15: Bank portion 17, 17A, 17B: Slot 19: Convex portion 21: Absorbing liquid 23: Cooling water 25: Ridge

Claims (2)

[Claims] 1. A heat transfer tube which is horizontally arranged and used, wherein a recess for liquid storage which is continuous in the axial direction of the tube is formed in the central portion of the upper surface of the outer surface, and the tube is provided on both sides of the recess. A slot that is shallower than the concave portion in a direction crossing the concave portion at a predetermined interval in the axial direction is formed, and a convex portion for liquid separation that is continuous in the axial direction of the pipe is formed in the center of the lower surface of the outer surface. Heat transfer tube. 2. The heat transfer tube according to claim 1, wherein a plurality of ridges or grooves extending in the tube axis direction or a direction close to the tube axis are formed on both side surfaces of the outer surface.