JP2013088004A - Method for manufacturing heat transfer tube and heat transfer tube - Google Patents

Abstract

An object of the present invention is to improve the heat transfer function of a heat transfer tube by forming fine water-repellent irregularities of μm units on the surface of the heat transfer tube in a short time.
A heat transfer tube manufacturing method for forming a water-repellent fine uneven shape by irradiating a surface of a heat transfer tube with a pulsed electron beam, wherein the irradiation current of the pulsed electron beam ( mA) * The irradiation rate (sec) is set to 0.002 to 0.008.
[Selection] Figure 1

Description

  The present invention relates to a method of manufacturing a heat transfer tube, and more particularly to a method of manufacturing a heat transfer tube by electron beam irradiation and a heat transfer tube.

  In cooling equipment used in conventional power equipment and heat exchangers, in order to increase the heat radiation area and improve cooling efficiency, cooling fins are installed, and uneven shapes etc. are formed on the inner and outer surfaces of the cooling equipment. Forming. When the material of the cooling device is made of copper or aluminum, since the body or aluminum is a material that can be easily processed, the uneven shape can be easily formed by machining or the like.

  Further, a heat transfer tube used in a heat exchanger or the like is also provided with a number of protrusions in order to increase the contact area with the coolant and to impart wettability (hydrophilicity) (Patent Document 1). However, the heat transfer tubes used in the heat exchangers of various plants are often made of stainless steel, and it is not easy in processing to give a desired uneven shape by machining or the like. Therefore, it is known to form an uneven hydrophilic layer on the surface of the heat transfer tube by performing a coating process or a blasting process on the surface of the heat transfer tube (Patent Document 2).

By the way, there is a Young's formula shown by the formula (1) for evaluating the wettability of the solid surface 2 of the structural material to the liquid.
cosθ = (α13−α12) / α23 (1)
Here, α12, α13, and α23 are the solid-liquid interface, the solid-gas interface (solid surface free energy), and the interfacial tension (liquid surface tension) of the gas-liquid interface, respectively, as shown in FIG.

  The contact angle between the solid surface 2 of the structural member 6 and the droplet 1 is small on the hydrophilic surface because the interfacial tension α13 at the solid-gas interface is large. On the other hand, since α13 is small on the water-repellent surface, the contact angle θ is large. However, even if a solid surface of the same material has a fine uneven surface 3 smaller than the droplet 1 as shown in FIG. 7, the contact angle θ of the droplet 1 is the contact angle on a flat surface. It is known that it is different from θ.

The contact angle θr of the droplet 1 on the fine uneven surface 3 is expressed by the following equation by the contact angle θ on the plane.
cosθr = r · cosθ (2)
Here, r is a surface area doubling factor, and indicates the increase ratio of the surface area of the fine uneven surface 3 to the surface area of the smooth surface of the solid surface 2. Since this factor is larger than 1, the contact angle θr of the droplet 1 on the fine uneven surface 3 is larger than θ when θ> 90 degrees, and smaller than θ when θ <90 degrees. That is, it suggests that the geometric shape is important in making the solid surface 2 uneven, and the rougher the surface, the more water-repellent surface becomes water-repellent and the hydrophilic surface becomes more hydrophilic. It is known to be.

  In general, θr is water repellency when it is 90 degrees or more, high water repellency when 110 degrees to 150 degrees, and super water repellency when it is 150 degrees or more. On the other hand, the direction in which the angle decreases is referred to as hydrophilicity, and 40 degrees or less is considered hydrophilic.

Cassie-Baxter theory is applied when the grooves of these concavo-convex structures become deep and water cannot reach the bottom of the deep groove due to capillary action and air remains below the water droplet 1. That is, assuming that the fine uneven surface 3 is composed of two kinds of fine mosaic-like substances A and B, if the contact angles of each of the pure component liquids are θ ₁ and θ ₂ , the equation (3) is obtained. It holds.
cosθr = f ₁ cosθ ₁ + f ₂ cosθ ₂ (3)
Here, f ₁ and f ₂ are area fractions of the substances A and B on the solid surface 2 and f ₁ + f ₂ = 1.

Now, when the water droplet 1 cannot reach the bottom of the groove on the water-repellent surface having a deep concavo-convex structure, the second component can be regarded as air. In that case, equation (3) becomes equation (4).
vcos θr = f−1 + f cos θ (4)
This is because the contact angle between air and water can be regarded as 180 °.

  Thus, when water cannot reach the bottom of the groove on the water-repellent surface having a deep concavo-convex structure, that is, the ratio of the solid area is lower and the area ratio of the tip of the protrusion is smaller, the air trap layer is formed in the groove. Improves water repellency.

JP 2002-372390 A JP 2007-155219 A

The above-described conventional unevenness forming means by machining has a problem that machining is difficult when the object is stainless steel. Also, the unevenness forming means by the coating process has a problem that the uneven layer is worn and peeled over time by the fluid flowing on the surface of the structural material, and also requires periodic inspection and recoating. It is necessary to stop a plant or the like equipped with the structural material, and there are problems that the operability of the plant is reduced, the maintenance cost is increased, and the maintenance period is prolonged.
In addition, it is difficult to form a fine water-repellent uneven shape in units of μm with deep grooves on the surface of the heat transfer tube by means of the unevenness forming means by blasting.

  The present invention has been made in order to solve the above-described problems. By using an electron beam, it is possible to form a fine water-repellent uneven shape of μm units on the surface of the heat transfer tube in a short time. It aims at providing the manufacturing method of a heat exchanger tube which can improve the heat transfer function of a heat exchanger tube, and a heat exchanger tube.

  In order to solve the above-described problems, a method of manufacturing a heat transfer tube according to the present invention is a method of manufacturing a heat transfer tube that forms a water-repellent fine uneven shape by irradiating the surface of the heat transfer tube with a pulsed electron beam. The pulsed electron beam irradiation current (mA) * irradiation rate (sec) is 0.002 to 0.008.

  Further, the method of manufacturing a heat transfer tube according to the present invention is a method of manufacturing a heat transfer tube that forms a water-repellent fine uneven shape by irradiating the surface of the heat transfer tube with a pulsed electron beam, The irradiation current (mA) * irradiation speed (sec) of the electron beam is controlled so that the surface roughness is 50 to 220 μm.

  According to the present invention, it is possible to improve the heat transfer efficiency of the heat transfer tube by forming a fine water-repellent uneven shape in units of μm on the surface of the heat transfer tube.

The graph which shows the correlation of the contact angle which concerns on 2nd Embodiment, and irradiation conditions. The graph which shows the correlation of the surface roughness and contact angle which concern on 3rd Embodiment. The graph which shows the correlation of the surface roughness and irradiation conditions which concern on 3rd Embodiment. The schematic perspective view which shows the manufacturing method of the heat exchanger tube which concerns on 4th Embodiment. The schematic sectional drawing which shows the manufacturing method of the heat exchanger tube which concerns on 5th Embodiment. The droplet model figure on the solid surface of structural material. The droplet model figure on the fine uneven surface of a structural material.

  Hereinafter, a heat transfer tube manufacturing method and a heat transfer tube embodiment according to the present invention will be described with reference to the drawings.

(First embodiment)
The manufacturing method of the heat exchanger tube which concerns on the 1st Embodiment of this invention is demonstrated.
In a heat exchanger or the like used in a power plant, steam used in a steam turbine comes into contact with the surface of a number of heat transfer tubes cooled with seawater to condense into water, and is returned to a boiler or the like again. There are two main forms of condensation at this time: film condensation and drop condensation. Film condensation occurs when the contact angle between the cooling surface of the heat transfer tube and the cooling liquid is small, and the cooling liquid condenses into a film on the cooling surface. On the other hand, liquid condensation occurs when the contact angle between the cooling surface and the cooling liquid is large, and the cooling liquid condenses in the form of droplets on the cooling surface.

Due to the difference in the condensation form, the heat transfer coefficient of the droplet condensation is 20 times or more that of the film condensation. Therefore, heat transfer is promoted by generating droplet condensation on the surface of the heat transfer tube.
The present invention has been made on the basis of the above findings, and in order to promote droplet condensation on the surface of the heat transfer tube, a fine water-repellent uneven shape of μm unit is formed on the surface of the heat transfer tube by electron beam irradiation. Features.

In the first embodiment, a pulsed electron beam is used to form a fine water-repellent uneven shape on the surface of the heat transfer tube in a short time.
According to the first embodiment, by using a pulsed electron beam, it is possible to form a fine concavo-convex shape having water repellency even on a material that is difficult to machine. The droplet condensation is promoted, and the heat transfer efficiency can be greatly improved.

(Second Embodiment)
A method of manufacturing a heat transfer tube according to the second embodiment will be described with reference to FIG.
FIG. 1 is a graph showing a correlation obtained by experiments on irradiation conditions and contact angles when a target material for pulsed electron beam irradiation is a heat transfer tube made of SUS304 material. According to FIG. 1, the contact angle is increased by setting the product (irradiation current (mA) * irradiation rate (sec)) of the irradiation current (mA) and the irradiation rate (sec: 1 / irradiation frequency) to 0.002 or more. It becomes possible to form a fine uneven shape having water repellency of 90 degrees or more on the surface of the heat transfer tube.

  Under such a pulsed electron beam irradiation condition, the amount of energy irradiated onto the material surface is relatively high, so that the unevenness of the material surface, that is, the depth of the concave surface is deep. Therefore, if the concave surface has a deep shape, it becomes easy to trap the air layer there, and the irradiation condition (product of irradiation current (mA) and irradiation speed (sec)) is set to 0. 0 as shown in FIG. By setting it to 002 or more, water repellency having a contact angle of 90 degrees or more can be imparted.

In addition, since the power and position control of an electron beam become difficult if irradiation conditions (product of irradiation current (mA) and irradiation speed) become large, the upper limit value is desirably about 0.008.
According to the second embodiment, by appropriately controlling the irradiation condition (product of irradiation current and irradiation speed), a heat transfer tube having a water-repellent fine uneven shape can be manufactured in a short time. .

(Third embodiment)
The manufacturing method of the heat exchanger tube which concerns on 3rd Embodiment is demonstrated with reference to FIG.
One of the indexes indicating the degree of water repellency and hydrophilicity is surface roughness (μm). In general, when the roughness is large, the water repellency is improved, and when the roughness is small, the hydrophilicity is improved. The reason for this is that, as described in the first and second embodiments, when the air layer is trapped in the concave and convex portions, and the air layer becomes larger due to the area ratio of the solid to the air layer, the droplet and the air layer The ratio of contact with the water increases and water repellency is improved. FIG. 2 is a graph showing the correlation between the contact angle and the surface roughness (μm).

  In the third embodiment, the surface of the heat transfer tube 5 made of stainless steel is irradiated with a pulsed electron beam to form a fine irregular surface in units of μm in a short time and in a simple manner. μm) as an index.

FIG. 3 is a graph showing the correlation between the irradiation conditions of the heat transfer tube made of SU304 material and the surface roughness.
As shown in FIGS. 2 and 3, the irradiation condition (product of irradiation current and irradiation speed) is appropriately controlled so that the surface roughness (μm) is 50 to 220 μm.

  According to the third embodiment, by using the correlation between the contact angle and the surface roughness and the correlation between the irradiation condition (product of the irradiation current and the irradiation frequency) and the surface roughness, the surface roughness is used as an index. A heat transfer tube with improved water repellency can be produced.

(Fourth embodiment)
A method of manufacturing a heat transfer tube according to the fourth embodiment will be described with reference to FIG.
In order to irradiate the outer surface of the heat transfer tube 5 with the pulsed electron beam 4 and create a fine uneven shape, it is necessary to irradiate the electron beam 4 while oscillating in the longitudinal direction of the heat transfer tube 5. However, since the heat transfer tube 5 is a cylinder, when the outer diameter is small, it is difficult to form an uneven structure similar to a flat plate from both ends to the outer surface of the lower region.

  Therefore, as shown in FIG. 4, the pulsed electron beam 4 is repeatedly irradiated in the longitudinal direction, and the radial direction of the heat transfer tube 5 is irradiated in the radial direction by rotating the heat transfer tube 5 itself. The rotation of the heat transfer tube 5 is variably controlled according to the irradiation speed of the electron beam 4.

  According to the fourth embodiment, by irradiating the electron beam while rotating the heat transfer tube, a uniform fine uneven shape is formed on the entire surface of the cylindrical heat transfer tube, thereby repelling the surface of the heat transfer tube. The water transfer can be improved and the heat transfer characteristics of the heat transfer tube can be improved.

(Fifth embodiment)
A method for manufacturing a heat transfer tube according to the fifth embodiment will be described with reference to FIG.
In the present embodiment, the heat transfer tube 5 is cut in half in the axial direction to form a semi-cylindrical structure, so that the heat transfer tube 5 can be obtained only by changing the irradiation direction of the pulsed electron beam 4 without rotating the heat transfer tube 5. An uneven shape is formed on the outer surface of 5.

  The irradiation control of the electron beam 4 is performed by inputting CAD data or the like in which the shape of the irradiated portion of the heat transfer tube 5 is recorded. Beam 4 is irradiated. The irradiation angle of the electron beam 4 is applied in accordance with the cylindrical end of the divided heat transfer tube 5. A plurality of divided heat transfer tubes 5 are each irradiated with an electron beam 4 to form a fine uneven shape, and then a cylindrical heat transfer tube 5 is manufactured by a joining process such as brazing material or welding.

  According to the fifth embodiment, since a fine uneven shape can be formed on the heat transfer tube without rotating the heat transfer tube, it is possible to improve the efficiency of irradiation control and simplify irradiation equipment and the like. .

(Sixth embodiment)
A method for manufacturing a heat transfer tube according to the sixth embodiment will be described.
When creating a fine uneven shape on the outer surface of the heat transfer tube 5, the flat plate shape can improve the efficiency of electron beam irradiation control and irradiation efficiency rather than the curved cylindrical shape.

In the sixth embodiment, after forming a fine uneven shape by irradiating a flat material surface (not shown) with a pulsed electron beam 4, the fine uneven shape of the flat plate becomes the outer surface. The heat transfer tube 5 is manufactured by processing into a cylindrical shape.
According to the sixth embodiment, the electron beam irradiation control and the irradiation efficiency can be further improved.

  As mentioned above, although some embodiment of this invention was described, these embodiment is shown as an example and is not intending limiting the range of invention. These novel embodiments can be implemented in various other forms, and various omissions, combinations, replacements, and changes can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

DESCRIPTION OF SYMBOLS 1 ... Droplet, 2 ... Solid surface, 3 ... Fine uneven surface, 4 ... Electron beam, 5 ... Heat transfer tube, 6 ... Structural material, 7 ... Base.

Claims (6)

  A method of manufacturing a heat transfer tube that forms a water-repellent fine uneven shape by irradiating a surface of a heat transfer tube with a pulsed electron beam, wherein the pulsed electron beam irradiation current (mA) * irradiation rate (sec) ) Is set to 0.002 to 0.008.   A method of manufacturing a heat transfer tube in which a water-repellent fine uneven shape is formed by irradiating a surface of a heat transfer tube with a pulsed electron beam, wherein the surface roughness of the heat transfer tube is 50 to 220 μm. A method for producing a heat transfer tube, wherein the beam irradiation current (mA) * irradiation rate (sec) is controlled.   The method of manufacturing a heat transfer tube according to claim 1 or 2, wherein the electron beam is irradiated while rotating the cylindrical heat transfer tube.   The method for manufacturing a heat transfer tube according to claim 1 or 2, wherein a cylindrical heat transfer tube is divided in the axial direction, and the surface of the divided heat transfer tube is irradiated with the electron beam.   3. The heat transfer tube according to claim 1, wherein one surface of a flat plate is irradiated with the electron beam, and then the irradiated surface is processed into a cylindrical shape so as to become an outer surface. 4. Production method.   A heat transfer tube manufactured by the method of manufacturing a heat transfer tube according to any one of claims 1 to 5.

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