JP3566804B2 - Heat transfer tube with fins - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance stirring action and wettability with liquid of an outer surface so as to improve heat exchanging performance of an outer portion by providing a porous layer formed by thermal spraying on the outer surface of a heat exchanger tube which causes heat exchange between a fluid flowing through an interior thereof and a heat medium outside of the tube. SOLUTION: Pipe stock 2 used as material for heat exchanger tubes 1 installed in a variety of types of heat exchangers has on an overall outer surface thereof a thermally sprayed coating 3 corresponding to a porous layer. The thermally sprayed coating 3 has a porous structure and effective radii of capillaries between thermally sprayed particles 4 are extremely small so that large capillary pressure is induced. Portions protruding on an outer surface of the thermally sprayed coating 3 function as fins 5. As layered structures of the sprayed particles 4 there are structures such as a double structure wherein particles having large sizes are sprayed on a surface of the pipe 2 and then particles having small sizes are overlaid thereon, a gradation structure wherein particles having sizes decreasing from a surface side of the pipe toward outside are sprayed, and the like structures.

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a heat transfer tube used as a component element of various heat exchangers, and more particularly to a heat transfer tube having improved external heat transferability.
[0002]
[Prior art]
It is well known that fins are attached to increase the surface area as a means for improving heat transfer on the outer surface of the heat transfer tube. On the other hand, for example, a heat transfer tube arranged inside an absorber such as an absorption refrigerator or an absorption chiller / heater is used to absorb refrigerant vapor generated in an evaporator by an absorption solution circulated on the outer surface thereof. In addition, there is a demand for a stirring action on the absorbing solution and a wettability with the absorbing solution.
[0003]
As an example of a heat transfer tube that satisfies these conditions, a large number of narrow grooves (grooves) are formed along the longitudinal direction on the outer surface of the pipe, and a large number of thin fins are formed on the pipe surface between the narrow grooves. There is a configuration provided at a narrow interval. According to this heat transfer tube, the heat radiation area or heat absorption area on the outer surface of the pipe is increased by the surface area of the fins and the narrow grooves. Due to the generated capillary pressure (pump action), the liquid is dispersed and held in a stirred state over a wide area on the outer surface. As a result, heat and mass transfer are promoted.
[0004]
[Problems to be solved by the invention]
By the way, the narrow grooves and fins of the heat transfer tube having the above configuration are formed by performing a cutting process or a rolling process on a smooth tube.
[0005]
However, the cutting process and the rolling process not only require large-scale equipment, but also have poor productivity, so that the production cost is disadvantageously increased. Further, in this type of processing method, since a large load is applied in the radial direction of the pipe, there is a possibility that deformation may occur when a thin pipe or a pipe made of a soft material is used.
[0006]
On the other hand, in the above-mentioned conventional heat transfer tube, a groove or the like is formed in order to retain the liquid on the outer surface thereof. Even if the effective capillary radius of the wick is reduced by making it thinner, there is a limit for reasons such as an increase in cost. Was not.
[0007]
The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a heat transfer tube which is inexpensive to manufacture and has high liquid agitating action on the outer surface and high wettability with a liquid.
[0008]
Means for Solving the Problems and Their Functions
The invention to achieve the above object, the finned heat transfer tube Ru to perform the heat exchange between the fluid and the outside of the heat medium flowing inside, the outer surface, a porous layer formed by thermal spraying the Yusuke Rutotomoni and is characterized that you said fins projecting outwardly in the radial direction is formed by the porous layer.
[0009]
In the invention according to claim 2, the porous layer can be formed by a plurality of layers having different particle diameters of the sprayed particles.
[0010]
Further, in the invention of claim 3, the porous layer can have an inclined structure in which the particle diameter of the spray particles continuously changes in the thickness direction.
[0011]
According to the present invention, an amount corresponding radiator or heat absorption area of the surface area of the multi-porous layer comprising a fin that projects outward in the radial direction is increased relative to the outer surface of the base pipe. Also, so that since the multi-porous layer comprising a fin has a structure having pores between the adjacent spray particles, causing a large capillary pressure. Thus, when contacted with liquid on the outer surface of the heat transfer tube, the liquid is widely dispersed is moderate agitation while being held in the fins and multi-porous layer.
[0012]
Further, as described in claim 2, if the porous layer is formed by a plurality of layers having different particle diameters of the sprayed particles, the size of the pores between the sprayed particles is different for each layer, that is, the effective layer is formed. Since the capillaries have different radii, there is a difference in the magnitude of the capillary pressure in the thickness direction of the porous layer. This appears as a liquid retention characteristic and a liquid diffusion characteristic on the outer surface of the heat transfer tube. Therefore, if the particle diameter of the spray particles is set for each layer, the liquid retention characteristic and the liquid diffusion characteristic can be finely adjusted.
[0013]
Furthermore, if the porous layer has an inclined structure in which the particle diameter of the sprayed particles continuously changes in the thickness direction, the distribution of the difference in the capillary pressure in the thickness direction is provided. Becomes more gentle. Therefore, for example, when the liquid is brought into contact with the outer surface of the heat transfer tube, the transfer of the liquid from the upper layer to the lower layer side of the porous layer becomes more rapid.
[0014]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, specific examples of the present invention will be described with reference to the drawings. The example shown here is an example in which a thermal spray coating is formed on the entire outer surface of a pipe material, and a fin is formed by projecting a part of the surface of the thermal spray coating. In FIG. 1, reference numeral 1 indicates a heat transfer tube. In this specific example, a smooth copper pipe having a general circular cross section is used as the pipe material 2 as a material of the heat transfer tube 1.
[0015]
A thermal spray coating 3 corresponding to a porous layer is formed on the entire outer surface of the pipe material 2. The thermal spray coating 3 has a porous structure having pores between the thermal spray particles 4, and generates a large capillary pressure because the effective capillary radius between the thermal spray particles 4 is extremely small. . As shown in FIG. 2, the surface of the thermal spray coating 3 projects outward in the radial direction at regular intervals in the longitudinal direction of the pipe material 2, and these projected portions function as fins 5. That is, each fin 5 is formed by the thermal spray coating 3. Therefore, the outer surface of the heat transfer tube 1 has an uneven shape due to the thermal spray coating 3 and the fins 5.
[0016]
Here, as an example of the laminated state of the thermal spray particles 4 in the thermal spray coating 3, as shown in FIG. 3, the thermal spray particles 4 having a large diameter are arranged on the surface of the pipe material 2, and the thermal spray particles 4 having a small diameter are further disposed thereon. Or a structure in which small-diameter spray particles 4 are arranged on the surface of pipe material 2 and large-diameter spray particles 4 are stacked thereon, as shown in FIG. Is mentioned.
[0017]
Furthermore, as shown in FIG. 5, a so-called gradient structure and in which is arranged a small diameter of the spray particles 4 gradually toward the outer side from the surface side of the pipe 2, and conversely, as shown in FIG. 6 which, An inclined structure in which the spray particles 4 having the smallest diameter are arranged on the surface of the pipe material 2 may be used. Although not particularly shown, a single-layer structure using spray particles 4 having a uniform size may of course be used. Such a change in the particle size can be achieved by changing the particle size of the material supplied during thermal spraying.
[0018]
Other examples of the pipe material 2 include a groove pipe having a plurality of narrow grooves along the longitudinal direction on the outer surface, a corrugated pipe having a continuous vertical wavy shape, or a large number of small pipes on the inner surface of the pipe. For example, a groove tube having a projection may be used. Further, as the thermal spraying material, other metals or ceramics or a cermet obtained by mixing them may be used as long as the material has excellent thermal conductivity and heat resistance, and the particle size can be appropriately set. Further, as the thermal spraying method, a conventionally known method such as a plasma thermal spraying method, a gas thermal spraying method or a flame thermal spraying method can be employed.
[0019]
Therefore, the heat transfer tube 1 configured as described above does not require large-scale equipment required for rolling and cutting, and is excellent in productivity. Therefore, the manufacturing cost is low. Further, the heat transfer tube 1 suitable for mass production can be obtained. Further, since thermal spraying is not a means for applying an excessive load to the pipe material 2 in the radial direction, there is an advantage that the material is soft and the wall thickness is small.
[0020]
Furthermore, according to the heat transfer tube 1 of this specific example, the heat radiation area or heat absorption area on the outer surface of the pipe member 2 is increased by the amount of the surface area of the thermal spray coating 3 including a large number of fins 5 as compared with a general smooth tube. I do. Moreover, since the thermal spray coating 3 and each fin 5 generate a large capillary pressure, for example, when a liquid is brought into contact with the outer surface of the heat transfer tube 1, a part of the liquid is applied to each fin 5 and the thermal spray coating 3. And is moderately dispersed. That is, the so-called wettability between the outer surface of the heat transfer tube 1 and the liquid is high.
[0021]
Here, the wettability between the heat transfer tube 1 and the liquid differs depending on the lamination state of the spray particles 4. For example, in the two-layer structure shown in FIG. Since the effective capillary radius on the upper layer side of the thermal spray coating 3 is larger than that on the lower layer side, the liquid moves from the upper layer to the lower layer quickly, while the liquid from the lower layer to the surface of the pipe material is relatively slow. And migrate. Further, since the pores formed in the lower layer are larger than those in the upper layer, the liquid comes into contact with the pipe member 2 in a large area.
[0022]
On the other hand, in the two-layer structure shown in FIG. 4 in which the arrangement of the thermal spray particles 4 is reversed, the liquid moves relatively slowly from the upper layer to the lower layer, while the liquid moves from the lower layer to the surface of the pipe material 2 quickly. Transition. Further, since the pores in the upper layer are small, the contact area between the liquid and the pipe member 2 is smaller than that of the structure shown in FIG.
[0023]
Further, the inclined structure shown in FIG. 5 in which the spray particles 4 having a smaller diameter are gradually arranged from the surface side of the pipe material 2 toward the upper layer side, and the spray structure shown in FIG. With the inclined structure, the structure shown in FIG. 5 has a larger contact area between the pipe member 2 and the liquid. This is due to the difference in the size of the pores near the surface of the pipe material 2.
[0024]
Further herein, in an inclined structure shown in two-layer structure as in FIG. 5 and 6 shown in FIGS. 3 and 4, the effective capillary radius towards the structure shown in FIGS. 5 and 6 are in the middle portion of the sprayed skin layer 3 for small, migration of the liquid from the surface side of the sprayed skin layer 3 to the outer surface of the pipe 2 is more quickly performed. That is, if the laminated state of the thermal spray particles 4 is set, the wettability on the outer surface of the heat transfer tube 1 can be finely adjusted. Further, since the outer surface of the heat transfer tube 1 (the surface of the thermal spray coating 3) has an irregular shape due to each fin 5, the liquid is easily stirred. Therefore, for example, the heat transfer tube 1 is suitable for an absorber of a heat pump.
[0025]
Next, another specific example of the present invention will be described with reference to FIGS. The same members as those in the first specific example are denoted by the same reference numerals, and detailed description thereof will be omitted. A plurality of ring-shaped fins 5 formed by the thermal spray coating 3 are provided on the outer surface of the pipe member 2 at regular intervals in the longitudinal direction of the pipe member 2. Therefore, as shown in FIG. 7, a portion provided with the fins 5 and a portion where the base 6 is exposed alternately appear on the outer surface of the pipe member 2. Therefore, the outer surface of the heat transfer tube 1 is uneven in the radial direction.
[0026]
Here, in forming the fins 5 having the above-described shape, for example, a masking is provided in a portion of the outer surface of the pipe material 2 other than where the fins 5 are formed, and the exposed bare ground 6 is formed. The thermal spraying is performed to form a thermal spray coating 3 having a predetermined thickness. Thereafter, the masking may be removed, and cleaning or the like may be performed as usual.
[0027]
Therefore, according to the heat transfer tube 1 configured as described above, the wettability with a liquid can be improved almost in the same manner as in the first specific example, and the heat radiation and heat absorption area can be increased. In addition to the effect, the amount of the sprayed material used in the first embodiment is reduced by the area of the exposed bare ground 6, so that advantages such as lower cost and weight reduction are obtained.
[0028]
In each of the above specific examples, the ring-shaped fins 5 are illustrated, but the present invention is not limited to the above specific examples, and the fins 5 protrude in the radial direction on the surface of the pipe material 2, and What is necessary is just to consist of the thermal spray coating 3, therefore, the individual shape, the layout as a whole, etc. can be set appropriately.
[0029]
【The invention's effect】
As apparent from the above description, according to the present invention, in the finned heat transfer tube Ru to perform the heat exchange between the fluid and the outside of the heat medium flowing inside, the outer surface, which is formed by thermal spraying because a multi-porous layer containing fins protruding outward in the radial direction, as compared with the conventional heat transfer tube which has been made by cutting or rolling process, possible to reduce the production costs Can be. Further, it is possible to improve the liquid stirring action on the outer surface of the pipe material and the wettability with the liquid.
[0030]
Further, the multi-porous layer including the fin, be formed by a plurality of layers different from each other in the particle size of the spray particles, it is possible to finely adjust the liquid retention characteristics and liquid diffusion characteristics at the outer surface of the pipe material.
[0031]
Furthermore , in the heat transfer tube with fins of the present invention , if the porous layer has an inclined structure in which the particle diameter of the spray particles continuously changes in the thickness direction, the liquid holding characteristics on the outer surface of the pipe material and The liquid diffusion characteristics can be adjusted more finely.
[Brief description of the drawings]
FIG. 1 is a schematic diagram showing a specific example according to the present invention.
FIG. 2 is a cross-sectional view showing a surface of a fin and a pipe material according to the specific example.
FIG. 3 is a schematic view showing a fin having a two-layer structure in which spray particles having a large diameter are provided on the surface side of a pipe material.
FIG. 4 is a schematic diagram showing a fin having a two-layer structure in which spray particles having a small diameter are provided on the surface side of a pipe material.
FIG. 5 is a schematic view showing a fin having an inclined structure in which spray particles having a smaller diameter are gradually arranged outward from the surface of a pipe material.
FIG. 6 is a schematic diagram showing a fin having an inclined structure in which spray particles having a gradually larger diameter are arranged outward from the surface of the pipe material.
FIG. 7 is a schematic diagram showing another specific example.
FIG. 8 is a cross-sectional view showing the surface of a fin and a pipe material according to the specific example.
[Explanation of symbols]
1 ... heat transfer tube, 2 ... pipe material, 3 ... thermal spray coating, 4 ... thermal spray particles.

Claims (3)

In finned heat transfer tube Ru to perform the heat exchange between the fluid and the outside of the heat medium flowing inside,
The outer surface, Rutotomoni that having a porous layer formed by thermal spraying, the porous finned heat transfer tubes wherein you characterized that you fins are formed protruding outward in the radial direction by the layer. The finned heat transfer tube according to claim 1, wherein the porous layer is formed by a plurality of layers having different diameters of the sprayed particles. The porous layer, finned heat exchanger tube according to the particle size of the thickness direction to spray particles are continuously changed to have inclined structure to claim 1 shall be the feature.

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