FI118181B - A method for improving the fluid flow properties of a heat transfer surface - Google Patents

Description

1118181

METHOD IMPROVES THE LIQUID FLOW CHARACTERISTICS OF THE HEAT EXCHANGE SURFACE

This invention relates to a process for improving the fluid transfer properties of a heat transfer surface, such as wetting ability and capillary flow, by chemical oxidation of the heat transfer surface or by heating in an oxygen-containing atmosphere.

10 A heat transfer surface is any surface that participates in the transfer of heat energy by means of heat transfer fluid in a direction perpendicular to the surface or perpendicular thereto. The heat transfer fluid may be any liquid, especially a liquid consisting of electrically polarized molecules such as water. In an electrically polarized molecule, the positive and negative electrical charges are inhomogeneously distributed.

The heat transfer surface is usually substantially different from the smooth surface, whereby the heat transfer surface is provided by various methods with fine surface structure such as grooves, grates, mesh structure, powder-coated structure, foamed structure, depressions, grooves, various ribs. The heat transfer surface is metal, collector, polymer or composite material. Preferably, the metal used in the heat transfer surface is copper, copper, alloy, aluminum, aluminum alloy or steel. The surface structure of the heat transfer surface ♦ ♦ • · 25 can be fine-grained, eg by rolling, pulling, extruding, foaming, sandblasting or by attaching metal to the surface. a list of fine structures made of copper or copper alloy, such as powder, needles, chips, granules, yarns, mesh, or a combination thereof.

* ·· * "i The fine structure of the surface structure can also be created by a combination of the above methods. The bonding method may be sintering, brazing, softening, welding, gluing, rolling or mechanical. Welding, for example, by static mechanical compression The joining method 2 118181 may also be a combination of the above methods Various methods for obtaining and joining heat transfer surfaces are described, for example, in U.S. Patents 3821018 and 4064914, which describe the formation of a porous metal layer. surface, JP patent application 5 61228294 discloses a method of forming a porous surface on the inner surface of a heating pipe, JP patent application 2175881 describes forming a powdery material on the inner surface of a heat transfer tube, CN patent application 1449880 discloses a low temperature sintering process. and a Fl-10 patent application 20040760 discloses attaching a copper or copper alloy powder to a heat transfer surface by brazing alloy.

The fluid flow properties of the heat transfer surface include, for example, surface wettability, which refers to the behavior of the liquid on the surface, and capillary flow, which refers to the penetration of liquid into the capillary cavity and the flow of liquid by capillary force in the gap. The wetting ability is good if the liquid droplet spreads as a thin liquid film on the surface. The wetting ability is poor if liquid; "** · * The droplet forms a hemispherical droplet shape on the surface. The wetting ability is affected by the composition of the liquid, the surface microstructure and the chemical composition, • ·: '· 20, temperature and atmospheric quality and pressure. ... · Comes from the aiming of a liquid in a state where its surface energy is as high as possible · *:: small The critical width for the capillary flow is the gap width.

As the gap narrows, capillary force increases exponentially until the gap is small enough for the liquid to penetrate it. However, the prior art solutions do not pay much attention to the fluid flow properties of the heat transfer surface, such as wetting ability and capillary flow.

The object of the present invention is to remove the prior art | disadvantages and improves fluid flow properties of the heat transfer surface, such as · 30 wetting ability and capillary flow, by oxidizing the heat transfer surface chemically or by heating in an oxygen-containing atmosphere, and utilizing the heat barrier surface obtained by Method 3 118181. The essential features of the invention will be apparent from the appended claims.

When applying the process of the invention, the desired structure of heat transfer structure is first formed on the surface of a metal, collector, polymer 5 or composite material, or a combination thereof, preferably of copper, copper alloy, aluminum, aluminum alloy or steel, or a combination of these metals. According to the invention, a body having a heat transfer surface is oxidized using at least one chemical oxidant or heated in an oxygen-containing atmosphere to improve fluid flow properties such as wetting ability and capillary flow. The oxidation may also be carried out using partially at least one chemical oxidant and partly t heating in an oxygen-containing atmosphere to achieve the desired oxidation result.

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In the process of the invention, metal, collector, polymer or composite material, or a combination thereof, preferably metal, *: ·: such as copper, copper alloy, aluminum, aluminum alloy or steel or the like;: * combination, made of metal with heat transfer surface | The oxidation is carried out at a temperature of 50-1200 ° C, preferably 250-450 ° C and more preferably 300-400 ° C, with an oxidation time of 0.1-60 mi- / * · nuts, preferably 0.1-60 ° C. 15 minutes, more preferably 1 to 5 minutes, in an atmosphere having an oxygen content of 0.01 to 100% by volume, preferably 15 to 50% by volume, most preferably 20 to 30% by volume. One preferred embodiment of the invention is the use of an atmospheric atmosphere in the atmosphere.

The oxidation of a body having a heat transfer surface according to the invention may also be carried out using at least one chemical oxidant. The oxidizing agents suitable for the process of the invention:: ··: are preferably sodium chloride: sodium chloride, potassium permanganate or hydrogen peroxide, for example, with an oxidation time of between 0.1 and 15 minutes.

118181 '4

Comparing the oxidized surface with the non-oxidized surface by the process of the invention, it was found that the wetting capacity of the water, which acts as a heat transfer fluid for the oxidized surface, was significantly better than that of the non-oxidizing surface. As a result of this procedure, the water wetting ability of the structured surface was further improved compared to the non-oxidized surface, which was poorly wetted by water. In addition, the capillary flow was enhanced so that the liquid flow occurred not only on the horizontal but also on the vertical surface. Capillary flow on the non-oxygenated surface was much slower.

The method of the invention can advantageously be used to enhance the fluid flow properties of a heat transfer surface, for example in the following applications: electrical and electronic applications such as heat pipes, vapor chambers, heat spreaders, boiling surfaces, air conditioning freezing applications such as air conditioning tubes (ACR tubes), solar collectors, various heat exchangers and coolers such as plate heat exchangers, auto coolers, casting dies, drain coolers, microcoolers.

The invention will be described in more detail below with reference to the accompanying drawings, in which: Figure 1 shows the results of the measurement of time / water travel in the travel coordinate system forming the heat transfer surface of Example 1 of the present invention. with a grain size of between 71 and 90 µm, Figure 2 shows the measurement results of ai-25 ka / water travel of ai-25 ka / water of the powdered powder forming a heat transfer surface of 125-160 µm in the coordinate system, and · · * ': ** Figure 3 shows the measurement results of Example 1 of the present invention, the time / water travel in the travel coordinate system of the heat transfer surface forming * · · • · '*: ** with a grain size of copper powder between 180 and 250 µm.

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Example 1

Six strips of cut copper-free (Cu-OF) were cut. On all strips, thick porous layers of 149, 319, and 330 μΓη of gas-atomized copper powder were sintered at 900 ° C for 1 hour to form a heat transfer surface. The average grain sizes of the copper powder were 80, 140 and 215 µm. Each coated size was matched by two coated strips. After coating, the surfaces of the strips were completely clear and non-oxidizing.

One strip corresponding to each particle size was oxidized in a tube oven at an air-10 atmosphere of 350 ° C and annealing time of 3 minutes. After annealing, the strips were allowed to cool in an air atmosphere. After annealing, the surfaces of the strips were oxidized to dark brown. The effect of oxidation on the capillary flow of water in a porous coating was investigated by placing the strips perpendicular to the ground surface. The lower ends of the strips were contacted with deionized water. The distance traveled by the water front in the porous coating was measured as a function of time. In the oxidized coatings, the water rose significantly faster and longer distance than the corresponding non-oxidative coatings, such as the accompanying Figures 1-3, with average copper powder sizes of 80, 140 and 215 µm, respectively.

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Example 2 1 «· · · · 1 · * 1 ·

The unoxidized and oxidized strips of Example 1 were subjected to a corresponding capillary flow test by positioning the strips in a horizontal position relative to the surface of the earth with the planar surface of the strip perpendicular to the surface of the earth. A second drop of ion-exchange water was dropped on the other ends of the tapes. In non-oxidizing tapes, water droplets were slowly absorbed into the · · ♦ 'porous coating and the water front proceeded slowly toward the other end of the tape. In the oxidized tapes, water droplets were immediately absorbed into the porous surface *: ··: 30 wadding and the water front proceeded much faster toward the other end of the tape than in the corresponding non-oxidized tapes.

6 118181

Example 3 -

The corresponding test of Example 1 was performed on longitudinally extensively ribbed ribbons and other ribbed ribbons where the grooves formed a 15 degree 5 angle (pitch) with respect to the longitudinal axis of the ribbon. At 350 ° C oxidized strips, the water front advanced rapidly in a vertical direction. In oxygen-free tapes, the water front did not rise at all vertically.

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Claims (3)

1. A process further enhances the fluid flow characteristics, such as wetting ability and capillary flow, of a heat transfer surface formed on a piece made of copper, in which process til at least 3 minutes. ς Process according to claim 1, characterized in that the oxidation) - Λ is carried out in an atmosphere whose oxygen content is up to 15-50% by volume. - -¾ 10 Process according to claim 1, characterized in that the oxidation is carried out in an atmosphere whose oxygen content is up to 20-30% by volume. : 1 '| ·····. ' • * • · * • · * · · • · 'p • · • · · • * • * • * *. :: 1- • · * ··· · • · * • «> • · • · · · · Φ · • ·· • · · · · · · · · ♦ ·; ··· i • · · • »• · ··· • · / • · · • · * ♦ · '• * · ···' • · • · • · · /'.v