JP2000304485A - Heating tube for down-flow liquid film type heat exchanger - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a high performance heating tube without increasing the weight per length by providing, on the outer surface thereof, with a plurality of grooves of specified depth, at a specified interval, in the direction of the tube axis and a large number of fins of specified height at a specified pitch and providing, on the inner surface thereof, with a plurality of protrusions extending spirally and intermittently in the direction of the tube axis. SOLUTION: Fins 1 are formed, at a fine pitch, on the outer surface of a copper tube being employed as the heating tube for a down-flow liquid film type heat exchanger and a large number of grooves 2 extending in the longitudinal direction to divide the fins 1 in the circumferential direction are formed, at a constant interval, in the circumferential direction. The grooves 2 are formed larger (deeper) than the height of the fin 1. Spiral protrusions are formed intermittently in the tube by pressing the tube with a protruding die spirally and intermittently from the outside thereby recessing the tube wall inwardly. The groove 2 has a depth of 0.5-2.0 mm and a circumferential interval of 0.3-4.0 mm and the fin 1 between the grooves has a height of 0.3-1.5 mm and a pitch of 0.4-1.5 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 used for a falling film heat exchanger using an absorption refrigeration cycle such as an absorption refrigerator, an absorption chiller / heater, an absorption heat pump, and the like.

[0002]

2. Description of the Related Art A falling liquid film type evaporator is constituted by arranging a number of heat transfer tubes horizontally in a closed vessel. A heating fluid flows through the heat transfer tubes, and a liquid refrigerant is supplied from above the heat transfer tubes. The liquid refrigerant evaporates while flowing down in the form of a film along the outer surface of the heat transfer tube, and the superheated fluid is cooled by the latent heat. Therefore, since there is no evaporation suppression due to the hydrostatic head of the refrigerant as in a liquid-filled evaporator, it is suitable for a low-temperature heat source evaporator having a low evaporation pressure of the refrigerant. It has been widely used as an evaporator for a chemical process device or the like, and recently as a low temperature difference power generation plant utilizing an ocean temperature difference or the like, or as an evaporator for a heat pump device.

Recently, attempts have been made to use a processed tube having fins or projections on its outer surface for the purpose of increasing the heat transfer area as this type of heat transfer tube. And by this, while improving the wettability of the refrigerant liquid, the actual wet area is improved,
Excellent heat transfer performance can now be obtained.

In the falling liquid film type evaporation, the performance outside the pipe is equal to or higher than the performance inside the pipe. Therefore, by improving the performance inside the pipe, the performance as a whole can be further improved. Therefore, measures such as providing a spiral continuous projection on the inner surface of the pipe to improve the performance in the pipe have been adopted.

[0005]

As a recent trend, the need for weight reduction of a heat transfer tube has been increasing as well as performance improvement. Therefore, in the case where a helical continuous projection is provided on the inner surface of the pipe, the weight per unit length becomes heavier than that without the projection.

An object of the present invention is to provide a high-performance heat transfer tube for a falling film heat exchanger without increasing the weight per unit length in view of the above-mentioned circumstances. .

[0007]

The gist of the present invention is to form a large number of fine pitch fins on the outer surface of a heat transfer tube, form a plurality of grooves extending in the longitudinal direction between the fins, and By providing intermittent spiral protrusions in the pipe by deforming the pipe wall, the weight is reduced and the heat transfer performance is remarkably improved as compared with the conventional example.

[0008] The intermittent spiral projection provided in the tube becomes a depression outside the tube. Accordingly, there is substantially no increase in weight due to the projections in the tube. However, this projection
This is to make the refrigerant flowing in the pipe into a turbulent flow, thereby improving the performance in the pipe.

The fin pitch is a parameter that determines the wettability of the liquid. If the fin pitch is increased, the wettability decreases. On the other hand, if the diameter is reduced, it is difficult to form a high fin, and it becomes impossible to secure a heat transfer area. Therefore, the fin pitch is suitably 0.4 to 1.5 mm.

If the groove depth is not larger than the fin height, the effect of dispersing the liquid in the pipe axis direction cannot be improved. Furthermore, the higher the fin height, the larger the heat transfer area,
This is effective as a means for improving performance. However, when the fin height is increased, the inner diameter of the tube becomes smaller, which causes an increase in pressure loss of the fluid flowing through the tube. Therefore,
Considering this, the fin height should be 0.3 ~
1.5 mm and a groove depth of about 0.5 to 2 mm are appropriate. Further, the number of grooves has a deep relationship with the performance. If the amount is small, the effect of liquid dispersion in the tube axis direction is reduced, but if the amount is large, the area of the fin portion is reduced. In addition, it is desirable that the angle between the pipe axis and the groove be limited to about −10 ° to + 10 ° in consideration of the fact that the heat transfer tube is used horizontally.

The higher the height of the projection, the higher the performance tends to be. However, the thickness is preferably 0.05 to 0.5 mm for the purpose of preventing an increase in pressure loss and erosion. The smaller the pitch of the projections in the tube axis direction, the higher the performance tends to be, but this causes an increase in pressure loss. Also,
When the pitch is small, the heat transfer area outside the tube decreases. On the other hand, if the pitch is too wide, the pressure loss decreases, and it is possible to suppress the decrease in the extra-tube heat transfer area.However, since this impairs the promotion of the turbulent flow effect, the total performance is not improved.
The pitch is suitably from 20 to 100 mm.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is an explanatory view showing the external appearance of a heat transfer tube according to the present invention, and FIG. 2 is an explanatory view showing the external appearance of the inside of the heat transfer tube. In FIG. 1, reference numeral 1 denotes fins formed at a fine pitch on the outer surface of a copper tube, for example, and 2 extend in the longitudinal direction so as to divide the fins 1 in the circumferential direction, and are formed at equal intervals in the circumferential direction. This groove 2 is the fin 1
Is formed to be larger (deeper) than the height. Reference numeral 3 denotes an intermittent spiral projection provided inside the pipe, and the projection 3 is formed by pressing a predetermined projecting die spirally and intermittently from the outside of the pipe so that the wall of the pipe is depressed inward. .

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS As a specific example, an outer diameter of 15.20 mm and an inner diameter of 1
The fins 1 are formed in a copper tube body of 4.00 mm in a spiral shape at a pitch of 1.0 mm, a height of 0.3 mm and an angle close to a right angle to the axis, while a depth of 0.05 mm in a circumferential direction and a circumferential interval. 1.0
A groove 2 having a height of 0.3 mm and a flat area of 1.85 mm ^{2 having} a circular shape with a plane area of 1.85 mm 2 was formed at an angle of 40 ° with respect to the pipe axis in the direction of the pipe axis. A heat transfer tube formed at a pitch of 40 mm was prepared.

With respect to the heat transfer tubes 4, nine were installed in an evaporator 5 of a performance measuring device as shown in FIG. In the measurement, while the liquid refrigerant (water) was dropped by the dropping nozzle 8, 1
The flow rate and the temperature of the water flowing through the condenser 5 were controlled such that cold water of 2 ° C. (flow velocity in the pipe was 2 m / s) was flown and the evaporation temperature of the liquid refrigerant was 5 ° C. In addition, in FIG. 3, 6 shows a refrigerant tank and 7 shows a scatter pipe.

FIG. 4 shows the results. In FIG. 4, the comparative example is a low fin tube (4.
0 peaks / inch). The liquid film flow rate on the horizontal axis indicates the mass flow rate per unit length flowing on one side of the tube.

As is apparent from the results shown in FIG. 4, the heat transfer tube according to the present invention has 1.3 to 1.5 times or more the vaporization performance as compared with the low fin tube widely used in the past. You can see that it is doing.

[0017]

As is apparent from the above description, according to the heat transfer tube of the present invention, the effect of dispersing the liquid refrigerant in the pipe axis direction is extremely excellent, and the generation of dryout is suppressed even in the lower heat transfer tube. It becomes possible. In addition, since the turbulence effect of water flowing in the pipe is promoted, the performance of an evaporator such as a seawater desalination apparatus, an absorption refrigerator, and a chemical process apparatus using the same can be improved.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing an outer surface of a heat transfer tube according to the present invention.

FIG. 2 is an explanatory view showing an inner surface of a heat transfer tube according to the present invention.

FIG. 3 is a schematic view of an apparatus for measuring the evaporation performance of a heat transfer tube.

FIG. 4 is a diagram showing performance measurement results.

[Explanation of symbols]

 1 Fin 2 Groove 3 Projection

Continued on the front page (72) Inventor Ken Horiguchi 3550 Kida Yomachi, Tsuchiura-shi, Ibaraki Hitachi Cable, Ltd.

Claims (5)

[Claims] 1. A heat exchanger of the type wherein a liquid film is formed on the outer surface of the heat transfer tube by dropping or spraying a refrigerant, an absorbing liquid or the like outside the heat transfer tube, and performing heat transfer through the liquid film. In the heat transfer tube, the outer surface has a depth extending in the tube axis direction of 0.5 to 2.
A plurality of grooves having a height of 0.3 mm to 1.5 mm and a pitch of 0.4 mm to 1.5 mm provided between the grooves having a diameter of 0.3 mm to 4.0 mm and a gap of 0.3 mm to 4.0 mm in the circumferential direction. And a plurality of projections extending intermittently spirally in the pipe axis direction on the inner surface of the heat transfer tube for a falling liquid film heat exchanger. 2. The heat transfer tube according to claim 1, wherein the intermittent projections are formed by deforming a tube wall from an outer surface side. 3. The heat transfer tube according to claim 1, wherein the bottom of the groove is formed deeper than the root of the fin. 4. The angle of the groove with respect to the tube axis is -10 ° to +10.
The heat transfer tube according to claim 1, wherein the heat transfer tube is in a range of degrees. 5. The height of the intermittent projection is 0.05 to 0.5 mm.
The heat transfer tube according to any one of claims 1 to 4, wherein the pitch in the tube axis direction is 20 to 100 mm.