JPH0264374A - Heat transfer tube for absorber and manufacture thereof - Google Patents

Abstract

PURPOSE:To make absorbing liquid in respective troughs flow down effectively and prevent the stagnation of the same by a method wherein a plurality of crests and troughs, extending axially on the outer surface of a tube, is formed alternately while a multitude of slant grooves, crossing diagonally respective crests formed on the outer surface of the tube respectively, is formed. CONSTITUTION:When a heat transfer tube is manufactured by a non-worked cylindrical tube, the tube is passed through a die, in which a plurality of axially extending crests and troughs is formed alternately, to form objective crests and troughs on the outer surface of the cylindrical tube. An indenting tool, provided with projected spiral threads on the inner surface or the outer surface thereof, is employed to push the projected threads against the crests, formed on the outer surface of the heat transfer tube, and form slant grooves on the crests while the outer surface of the cylindrical tube is recessed at positions corresponding to the slant grooves to make protrusions on the inner surface of the cylindrical tube at positions corresponding to the recesses formed on the outer surface of the same tube.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field) The present invention relates to a heat exchanger tube for an absorber with excellent heat transfer performance and a method for manufacturing the same.

(Background Art) Absorbers such as absorption heat pumps and absorption refrigerators generally have a structure in which a large number of heat transfer tubes are arranged in parallel in a closed container in a horizontally extending state. While a cooling medium such as cooling water is allowed to flow through these heat transfer tubes, an absorption liquid such as an aqueous LiBr solution is dropped onto the outer surface of the heat transfer tubes, and the absorption liquid is evaporated in an evaporator. The heat absorbed when absorbing water vapor is carried away by the cooling medium.

By the way, in such an absorber, the heat transfer tube is
In general, smooth tubes with smooth inner and outer surfaces are used, but the heat transfer performance of such smooth tubes is low, so it is recommended that surfactants such as octyl alcohol be added to the absorption liquid to improve the absorption capacity of the absorption liquid. However, there were problems in that the heat transfer performance could not be sufficiently improved, and the absorber could not be sufficiently improved in performance or miniaturized. Therefore, in recent years, heat transfer tubes with various structures have been proposed in order to improve the heat transfer performance of heat transfer tubes and achieve higher performance and smaller absorbers. The reality is that it is difficult to say that a structure with an ideal structure has been proposed.

(Problem to be solved) The present invention has been made against the background of the above, and its object is to provide a material for absorbers that can significantly improve heat transfer performance compared to smooth tubes. It is an object of the present invention to provide a novel structure for a heat exchanger tube, and also to provide a method for suitably manufacturing a heat exchanger tube for an absorber having such a structure.

(Solution Means) In order to solve this problem, in the present invention, a plurality of peaks and troughs extending in the tube axis direction are alternately formed in the tube circumferential direction on the tube outer surface, and the tube A large number of diagonal grooves are formed so as to diagonally cross the winter mountain portions formed on the outer surface, and the tube outer surface is recessed at the portions where the diagonal grooves are formed, so that the tube inner surface corresponds to the recessed portions of the tube outer surface. A structure in which the portion is raised on the inside of the tube was adopted as the structure of the heat exchanger tube for the absorber.

In addition, when manufacturing an absorber heat exchanger tube having such a structure from an unprocessed cylindrical tube, (a) a die in which a plurality of peaks and valleys extending in the axial direction are alternately formed in the circumferential direction is used; a vertical groove forming step of forming peaks and valleys corresponding to the peaks and valleys of the heat transfer tube on the outer surface of the cylindrical tube by passing the cylindrical tube through a die; (b) an inner or outer surface; A stamping tool equipped with a spiral protrusion is used to press the spiral protrusion of the stamping tool against the peak formed on the outer surface of the cylindrical tube in the vertical groove forming step. At the same time as forming the diagonal groove in the mountain portion, the outer surface of the cylindrical tube is recessed at the region where the diagonal groove is formed, and the inner surface of the cylindrical tube corresponding to the recessed portion of the outer surface is raised toward the inside of the tube. This includes a groove stamping process.

(Detailed Description of Function and Invention) In the heat exchanger tube according to the present invention, when an absorbent liquid is dropped on the outer surface of the tube, the dropped absorbent liquid penetrates the valleys (vertical grooves) formed on the outer surface of the tube. It is transmitted to the pipe and is effectively caused to flow in the axial direction of the pipe, and is also preferentially transmitted through the diagonal grooves formed in the peaks that separate the valleys to flow down in the pipe circumferential direction, effectively causing disturbance and convection phenomena. It is diffused over a wide area of the extraluminal surface while being stimulated. Therefore, over a wide area of the outer surface of the heat transfer tube, the good water vapor absorption effect of the absorption liquid is maintained stably, and the heat transfer performance is greatly improved.

Furthermore, in the heat exchanger tube according to the present invention, since the outer surface of the heat exchanger tube is recessed at the portion where the diagonal grooves are formed, dripping or flowing/flowing occurs in each trough compared to a case where such a recess is not provided. This makes it easier for the absorbed liquid to flow down through the diagonal grooves, and therefore, the disturbance and convection phenomena of the absorbed liquid are more effectively induced, resulting in a higher Excellent heat transfer performance can be obtained, and the absorption liquid in each valley can be made to flow down more effectively, thereby better preventing the absorption liquid from stagnation in each valley. .

In addition, in the heat transfer tube according to the present invention, since the inner surface corresponding to the concave portion on the outer surface of the tube is raised on the inside of the tube, the raised portion effectively prevents turbulence in the cooling medium flowing inside the tube. Therefore, the heat transfer performance of the heat transfer tube is improved by the effect of promoting turbulent flow of the cooling medium due to the raised portion.

Note that if the groove depth of the diagonal grooves formed in the peaks on the outer surface of the heat transfer tube is too shallow compared to the depth of the valleys, it will be difficult for the absorption liquid to flow down in the circumferential direction of the tube through the diagonal grooves. This causes problems such as the disturbance and convection promotion effect on the absorbent decreases, and the absorbent tends to accumulate in each valley.On the other hand, if the depth is too deep compared to the depth of the valley, the pipe wall thickness increases. The groove depth of such diagonal grooves is usually about 7 times the depth of the trough, since it inevitably becomes thicker and causes problems such as being economically disadvantageous.
The depth is set to about 0 to 130%, preferably the depth of the troughs and the depth of the gaps.

Further, it is desirable that the angle of inclination of the diagonal grooves with respect to the tube axis of the heat transfer tube is set to 5 to 45 degrees, and the formation interval in the tube axis direction is 0.7 to 2.0 degrees of the outside diameter of the heat transfer tube.
It is desirable to set the size to about 0 times. this is,
If the angle of inclination of the heat exchanger tube with respect to the tube axis becomes too small,
This is because it becomes difficult to form diagonal grooves, and the absorption liquid does not flow down efficiently through such diagonal grooves, making it difficult to expect much improvement in the heat transfer performance of the heat transfer tube. If it becomes too thick, the rigidity of the tube will decrease, especially in thin-walled heat exchanger tubes, making it easier to bend, as well as causing problems in the horizontal direction (
This is because the disturbance effect of the absorption liquid in the tube axis direction is reduced, which may lead to a decrease in heat transfer performance. Furthermore, if the interval between the diagonal grooves in the tube axis direction of the heat transfer tube is too narrow, the spread of the absorbed liquid in the tube axis direction will be extremely small, and conversely, if it is too wide, it will flow down through the diagonal grooves. Since there is a risk that the absorption liquid will be significantly reduced, as mentioned above, the outer diameter of the heat exchanger tube should be 0.7 to 2.0.
It is desirable to set it to about twice the size.

In addition, although the diagonal grooves can be formed in an appropriate arrangement, they are usually formed in a staggered arrangement with a fixed interval (pinch) in the axial direction of the heat exchanger tube. .

In addition, the width of the diagonal groove is generally at least a width that does not cause retention of the absorbent liquid, and more specifically, the width in the direction parallel to the tube axis is 0.5, depending on the inclination angle of the diagonal groove. ~1
．． It will be set to be approximately 5 m111.

Incidentally, the heat exchanger tube for an absorber according to the present invention can be manufactured by any method, but when manufactured from an unprocessed cylindrical tube, a plurality of peaks and valleys extending in the axial direction may be formed. Using dies alternately formed in the circumferential direction,
A raw cylindrical tube is passed through such a die to form peaks and valleys corresponding to the peaks and valleys of the desired heat transfer tube on the outer surface of the cylindrical tube, and then a spiral shape is formed on the inner or outer surface of the cylindrical tube. Using a stamping tool equipped with a protrusion, press the spiral protrusion of the stamping tool against the ridge formed on the outer surface of the cylindrical tube, and then press the ridge diagonally onto the ridge formed on the outer surface of the cylindrical tube. At the same time as forming the groove, the outer surface of the cylindrical tube is recessed at the portion where the diagonal groove is formed, and the inner surface of the cylindrical tube corresponding to the recessed portion of the outer surface of the tube is raised toward the inside of the tube. This is desirable for stably manufacturing heat exchanger tubes with good productivity.

In addition, as a stamping tool with a spiral protrusion on the inner surface,
Dies with spiral protrusions on the inner surface can be mentioned.
Further, examples of the stamping tool having a helical protrusion on its outer surface include a roller having a helical protrusion on its outer surface.

When using a die with spiral protrusions on the inner surface as a stamping tool, the die is rotatably held and a cylindrical tube with peaks and valleys formed on the outer surface of the tube is inserted. Alternatively, if a roller with a spiral protrusion on the outer surface is used as an stamping tool, a plurality of rollers may be arranged so as to surround the cylindrical tube so that they can revolve around the cylindrical tube. The cylindrical tube may be moved in the axial direction of the cylindrical tube with the plurality of rollers pressed against the outer surface of the cylindrical tube.

In addition, when manufacturing such a heat exchanger tube, when passing an unprocessed cylindrical tube through a die to form peaks and valleys in the tube axis direction on the outer surface of the tube, generally the cylindrical tube is A plug will be inserted to regulate the amount of pipe contraction.

Hereinafter, in order to clarify the present invention more specifically,
Although the examples are shown below, it is understood that the present invention is not limited in any way by the description of the examples, and that the present invention can be implemented in other embodiments without departing from the spirit thereof. should be understood.

(Example) First, FIGS. 1 to 3 show an absorber heat exchanger tube 2 which is an example of the present invention. This heat exchanger tube 2 has 1
It has an outer diameter of 9.05 mm, and on its outer surface, 20 peaks 4 parallel to the tube axis direction are formed at equal intervals in the tube circumferential direction. As a result, valleys (vertical grooves) 6 having a depth of 0.45±0.05 mm are formed between the peaks 4.

The crests 4 formed on the outer surface of the heat exchanger tube 2 have 10 helical threads, each having a twist angle of approximately 13° with respect to the tube axis and separated by a distance of 30 mm from each other in the tube axis direction. Diagonal grooves 8 having approximately the same groove depth as the trough portion 6, specifically approximately 0.45+++ m, are formed in a staggered arrangement so as to diagonally cross each of the grooves 4. Then, as shown in FIG. 2, the outer surface of the heat transfer tube 2 at the portion where the diagonal grooves 8 are formed is slightly recessed inward in the radial direction, so that the outer surface of the tube corresponding to each diagonal groove 8 is Diagonal groove 8
Smooth recesses 10 slightly shallower than the depth of the recesses 10 are formed respectively, and smooth ridges with shapes corresponding to the recesses 10 are formed on the inner surface side of the heat exchanger tube 2 corresponding to the formation areas of the recesses 10. A portion 12 is formed respectively.

Note that the groove width of the diagonal groove 8 is set here so that the dimension in the direction perpendicular to the extending direction of the diagonal groove 8 is approximately 0.6 to 0.9 n+m. Furthermore, as is clear from the above description, here, the inclination angle α (see FIG. 1) of the diagonal groove 8 with respect to the tube axis of the heat exchanger tube 2 is set to approximately 13 degrees, and each peak Diagonal groove 8 in the tube axis direction in 4
The formation interval is set to 30 mm.

The heat exchanger tubes 2 having such a structure were set horizontally in an experimental absorber with an effective length of 500 mm and a pitch of 35+ nm in 1 row and 5 stages, and the cooling medium was applied in 5 passes starting from the bottom of the heat exchanger tubes 2. LiBr as an absorption liquid to which 250 PPM of octyl alcohol was added while flowing cooling water as
Pour the aqueous solution into the top heat transfer tube 2 through the dripping hole with a diameter of 2 mm.
For the heat exchanger tube 2 having such a structure,
Exchange heat defined by the following formulas (1) to (3) 1. Q, heat transfer coefficient 2, and tube outer surface heat transfer coefficient: ho were measured and calculated, and the results are shown in FIGS. 6 and 7. In addition, in order to compare with this, for smooth tubes with the same outer diameter, exchange heat i: Q, heat transfer rate: and tube outer surface heat transfer coefficient: ho were measured and calculated in the same manner in Figure 6 and It is also shown in Figure 7.

Q=Cp・W−ρ(Tc0−Tc,) ...(
1) K=Q/(S・ΔT) ...(
2) 1/h, -1/to 1/hi (d, /di)
...(3) However, Cpi specific heat (kcal/kg"c) W: Cooling water amount (m'/h) ρ: Specific weight (kg/m") Tcoi Cooling water absorber outlet temperature (°C) Te day Cooling water absorber inlet temperature (°C) S: Tube outer surface area (m2) ΔT: Logarithmic average temperature difference (°C) hii tube inner heat transfer coefficient (kcal/m 2h'C
) d o i tube outer diameter (m) d i i tube inner diameter (m) In addition, the tube outer surface area: S is obtained by the following formula (4), and the logarithmic average temperature difference: 8T is the LiBr concentrated solution absorption When the equilibrium temperature at the inlet of the vessel and the temperature at the outlet of the LiBr dilute solution absorber are respectively T its Two, it is expressed by the following (5) 2.

S=πX0.019 XO,'5 X5...
-(4) Table 1 below shows main experimental conditions other than those mentioned above.

As is clear from the measurement and calculation results in Tables 6 and 7, the heat exchanger tube 2 according to the present invention has a higher exchange heat N:Q, a higher heat transfer rate, and a higher heat transfer rate than a smooth tube. The tube outer surface heat transfer coefficient (ho) is significantly improved in all cases, and it is recognized that the heat transfer performance is extremely superior to that of a smooth tube.

In addition, when the side wall of the experimental absorber was constructed with a transparent glass plate and the LiBr aqueous solution as the absorption liquid was observed to flow down along the outer surface of the heat exchanger tubes 2, it was found that in each heat exchanger tube 2, the solution It is observed that the solution flows effectively in the tube axis direction through the section 6, and it is also observed that the solution flows preferentially through the diagonal groove 8, and the disturbance and convection phenomena are effectively caused to the solution. It was inferred that this was caused.

By the way, the heat exchanger tube 2 having the above structure was manufactured as follows. Hereinafter, an example of manufacturing such a heat exchanger tube 2 will be explained based on FIGS. 4 and 5.

That is, when manufacturing the heat exchanger tube 2, first, as shown in FIG. Die 18 was prepared. Note that the troughs 14 and the peaks 16 are formed by the die 1.
8, and alternately formed in the circumferential direction. Then, an unprocessed cylindrical tube (smooth tube) 17 having an outer diameter slightly larger than the outer diameter of the heat transfer tube 2 is passed through the die 18, and while the cylindrical tube 17 is being shrink-processed, the heat transfer is applied to the outer surface of the tube. heat tube 2
A peak portion 4 and a valley portion 6 corresponding to the above were formed. When forming the peaks 4 and valleys 6, as shown in FIG. 4, a plug 19 is inserted into the cylindrical tube 17, and the amount of contraction of the cylindrical tube 17 is controlled by the plug 19. I decided to do so.

On the other hand, in addition to the die 18, a die 22 is prepared which is provided with ten spiral protrusions 20 having a weeping angle of approximately 13 degrees with respect to the axis at equal intervals, and the die 22 is rotatably held. Then, the cylindrical tube 17 passed through the die 18, that is, the cylindrical tube 17 having peaks 4 and troughs 6 similar to those of the heat transfer tube 2 on its outer surface, is passed through, and each protrusion 20 of the die 22 is inserted into the cylindrical tube. 17 into the diagonal groove 8 of the heat exchanger tube 2.
was formed by stamping. As a result, it was possible to obtain the heat exchanger tube 2 having the above-described structure, in which the portion where the diagonal groove 8 was formed on the outer surface of the tube was recessed, and the raised portion 12 was formed on the inner surface of the tube corresponding to the recessed portion 10.

Note that, as is clear from the above description, here, the unprocessed cylindrical tube 17 is passed through the die 18, and the cylindrical tube 1 is
The step of forming the peaks 4 and valleys 6 on the outer surface of the tube 7 is the vertical groove forming step, and the cylindrical tube 17 with the peaks 4 and valleys 6 formed on the outer surface thereof is passed through the die 22 to form a cylindrical tube. The process of forming the diagonal grooves 8 on the peak portion 4 of the tube 17 is a diagonal groove stamping process. Further, as is clear from this, here, the die 22 having the spiral protrusion 20 on its inner surface plays a role as a stamping tool.

It is believed that the heat exchanger tube 2 manufactured by such a method has excellent dimensional accuracy and is also excellent in productivity.

In addition, in the upper heat exchanger tube 2, the peak part (4) and the valley part (
6) is only formed on the outer surface of the heat exchanger tube, but the inner surface of the heat exchanger tube has troughs and ridges corresponding to the ridges and troughs on the outer surface of the tube, giving the heat exchanger tube a corrugated cross-sectional shape. It is also possible to do this.

If the cross-sectional shape of the heat exchanger tube is corrugated, the tube wall thickness will be thinner compared to a tube with only peaks and valleys formed on the outer surface of the tube.
It is possible to effectively reduce the weight of the pipe.
In addition, the groove depth of the diagonal groove (8) can be set deeper.Furthermore, by forming the diagonal groove (8), the outer surface of the tube can be more effectively depressed, and the inner surface of the tube can be more effectively recessed. The effect of inducing disturbance and convection phenomena on the absorbent liquid is further improved.
Moreover, it becomes possible to more effectively induce turbulence in the cooling medium flowing inside the tube.

In addition, such a heat exchanger tube employs, for example, a plug 19 in FIG. 4 that has peaks and valleys corresponding to the peaks 16 and valleys 14 of the die 18, so that the peaks on the outer surface of the tube are It is manufactured by forming peaks and valleys on the inner surface of the tube at the same time as forming the peaks and valleys, and then forming diagonal grooves on the peaks on the outer surface of the tube according to the method shown in FIG. becomes.

(Effects of the Invention) As is clear from the above description, in the heat exchanger tube for an absorber according to the present invention, a plurality of peaks and valleys extending in the tube axis direction are alternately formed in the tube circumferential direction on the tube outer surface. At the same time, a large number of diagonal grooves are formed diagonally across the winter mountain area, and the outer surface of the tube is recessed at the portion where the diagonal grooves are formed, and the inner surface of the tube corresponding to the recess is raised on the inside of the tube. Because of its unique structure, it can significantly improve heat transfer performance compared to smooth tubes, and therefore can greatly contribute to higher performance and smaller size absorbers.

Further, when manufacturing the heat exchanger tube for an absorber according to the present invention from an unprocessed cylindrical tube, first, a die in which a plurality of peaks and valleys extending in the axial direction are formed is used, and the unprocessed cylindrical tube is attached to the die. After forming a plurality of peaks and valleys on the outer surface of the cylindrical tube, a stamping tool having a spiral protrusion on the inner or outer surface is used to form a plurality of peaks and valleys on the outer surface of the cylindrical tube. By stamping diagonal grooves on the ridges and simultaneously making the diagonal grooves concave and raising the inner surface of the tube, the heat exchanger tube for an absorber according to the present invention can be stabilized with good dimensional accuracy. Moreover, it can be manufactured at low cost with good productivity.

[Brief explanation of the drawing]

FIG. 1 is an external view showing an example of an absorber heat exchanger tube according to the present invention, and FIGS. 2 and 3 are enlarged views of main parts of the transverse and longitudinal sections, respectively. 4 and 5 are explanatory diagrams for explaining the manufacturing process of the heat exchanger tube shown in FIG. 1, respectively. FIG. 6 is a graph showing a comparison of the measurement results of the amount of heat exchanged between the heat exchanger tube and the smooth tube shown in FIG. 1, and FIG. 3 is a graph showing a comparison of the measurement results of the heat transfer coefficient and the tube outer surface heat transfer coefficient. 2: Heat transfer tube 4: Peak part 6: Valley part (vertical groove) 8: Diagonal groove 10: Concave part 12: Ridge part 14: Valley part (of the die) 16: Peak part (of the die) 17: Cylindrical tube (smooth Pipe) 18: Die 2o: Projection 22: Die (stamping tool) Figure 1 Applicant: Sumitomo Light Metal Industries, Ltd. Figure 2, Figure IiB] 2 Figure 6, i Br Molten rinser 1 iBr: @- L Taki Senl

Claims (2)

[Claims] (1) A heat exchanger tube for an absorber in which a cooling medium is allowed to flow inside and an absorption liquid is dripped on the outer surface, and the outer surface of the tube has a plurality of peaks and valleys extending in the tube axis direction in the tube circumferential direction. A large number of diagonal grooves are formed so as to diagonally cross each peak formed on the outer surface of the tube, and the outer surface of the tube is recessed at the portion where the diagonal grooves are formed, 1. A heat exchanger tube for an absorber, characterized in that an inner surface portion of the tube corresponding to a concave portion on the outer surface of the tube is raised on the inner side of the tube. (2) A method of manufacturing the heat exchanger tube from an unprocessed cylindrical tube, using a die in which a plurality of peaks and valleys extending in the axial direction are alternately formed in the circumferential direction, and the method includes: a step of forming vertical grooves corresponding to the peaks and valleys of the heat transfer tube on the outer surface of the cylindrical tube by passing the cylindrical tube; and a step of forming a spiral protrusion on the inner or outer surface. The helical protrusions of the stamping tool are pressed against the peaks formed on the outer surface of the cylindrical tube in the vertical groove forming step, thereby forming the diagonal grooves into the peaks. and at the same time, recessing the outer surface of the cylindrical tube at the portion where the diagonal groove is formed, and protruding the inner surface of the cylindrical tube corresponding to the recessed portion of the outer surface toward the inner side of the tube. 2. The method of manufacturing a heat exchanger tube according to claim 1, further comprising: .