JPS5986898A - Heat exchanging wall and manufacture thereof - Google Patents

Abstract

PURPOSE:To improve boiling heat transferring properties in a heat exchanger wall by decreasing the entrance resistance to liquid which flows into the cavities under the surface of a wall, by providing a porous layer, consisting of laminated fiber, to the top of a number of slender cavities formed in the surface of a heat exchanger wall, and by interconnecting the inside of cavities with the surface of a wall by through-holes in the porous layer. CONSTITUTION:First, a number of cavities 2 in the shape of slender grooves are provided to the surface of a heat exchanger wall by a plastic work such as a mechanical cutting or a rolling. The proper size of a cavity is above 0.2mm. up to 2mm. in width, above 0.4mm. up to 2.2mm. for a pitch, and above 0.2mm. up to 1mm. in depth. Copper wire fiber of 0.18mm. in diameter and of 5mm. in length are scattered and laminated on the above-mentioned cavities, and they are sintered in vacuum at 915 deg.C by heating. By constituting the heat exchanger wall in such a manner, steam bubbles are generated in the cavities, and they are filled with the steam bubbles, when the heat exchanger wall is heated up to the higher temperature than liquid which contacts to the wall. When the pressure of steam bubbles bebecomes higher tha the liquid outside, part of the steam bubbles is discharged from the through-holes which are comparatively large among the ones in the porous layer. The other steam bubbles are left in the cavities as residual steam bubbles. At this time, a change in pressure is produced in the cavities, and liquid can easily flow into the cavities passing through a number of through-holes other than ones through which steam bubbles are discharged.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a heat exchange wall suitable for use in a refrigerator, and the present invention also relates to a method of forming such a heat exchange wall. It is.

[Prior art]

As a conventional heat exchange wall, the heat exchange wall shown in Figure 1 has been proposed in an attempt to transfer heat with high efficiency from the surface of a pipe or plate to a liquid that comes into contact with it, such as fluorocarbon liquid, liquid nitrogen, or liquid oxygen. . It is provided with a number of elongated cavities 2 in the skin zone of the heat exchange wall 1 in contact with the liquid,
This cavity 2 is communicated with the outside through a large number of minute holes 3. The cavity 2 of the heat exchange wall 1 is generally formed by forming grooves in the base material of the heat exchange wall 1 by mechanical cutting or plastic processing using rolls, etc., and then a large number of through holes 3 smaller than the side walls 5 of the cavity 2 are formed. A perforated plate 4 having a large number of through holes 3 is placed over the groove and bonded so as to be directly above the cavity.

With a heat exchange wall having such a structure, when the wall is heated to a higher temperature than the liquid in contact with the wall, vapor bubbles 6 are generated in the cavity 2 and grow as shown in a boiling state in FIG. 2. When the vapor pressure inside the cavity 2 becomes higher than that outside, some of the vapor bubbles 6 are released from the through hole 3 and separated. The remaining vapor bubbles remain within the cavity 2 and are retained. At this time, a pressure change occurs in the cavity 2, and liquid enters the cavity from the through hole 3 from which the steam 6 was released and another through hole 3' as shown by the arrow. The infiltrating liquid flows into the four corners of the cavity 2 by capillary force, forming an extremely thin liquid film 8. Evaporation occurs from the surface of this thin liquid film 8, causing vapor bubbles 6 to grow within the cavity 2, and this process is repeated. However, since the liquid flowing into the cavity 2 through the through-hole 3 flows through the back surface of the perforated plate 4, the liquid cannot directly flow into the four corners of the cavity 2. Therefore, when the degree of superheating of the heat exchange wall 1 is large, the flow resistance for the infiltrating liquid is large, so that the liquid in the cavity 2 cannot be replenished by the liquid film 6.
The liquid cannot keep up with the evaporation of the liquid, and the inside of the cavity eventually dries up. Therefore, the heat transfer performance of the heat exchange wall cannot be improved.

[Purpose of the invention]

The object of the present invention is to overcome the above-mentioned drawbacks and to provide an efficient and inexpensive heat exchange wall.

[Features of the invention]

In order to achieve this objective, the present invention provides a porous layer made of stacked fibers on top of a large number of elongated cavities formed on the surface of the heat exchange wall, and communicates the interior and surface of the cavities with the communicating holes of this porous layer. It is characterized by being connected.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to FIG. Third
The figure is a photograph and a schematic cross-sectional view of a porous layer in which copper fibers are laminated on the groove-like elongated cavity on the surface of the heat exchange wall shown in FIG. 1, observed from the surface. A heat exchange wall having such a structure can be easily manufactured.

First, a large number of elongated groove-shaped cavities 2 are provided on the surface of the heat exchange wall by mechanical cutting or plastic processing such as roll processing. The size of the cavity is 0.2 m or more in width and up to 2 brains, the pitch is 0.4 tm or more and up to 2.2 m, and the depth is 0.2 r.
rrm, up to the first pharynx above IJ is appropriate. Copper wire fibers each having a diameter of 0.18 mm and a length of 5 mm were individually laminated on the above-mentioned cavity, and then sintered by heating to 915C in a vacuum. At this time, a pressure of 2 Kg/cm 2 per unit area was applied to the fiber lamination surface.

As a result, the porosity of the porous layer is 60% by volume.
The surface and the groove-shaped cavities communicate with each other through the pores of the porous layer 9. The fiber diameter must be greater than 0.05 mm. 74% smaller than this diameter is desirable for heat transfer.
It becomes difficult to obtain pores larger than 0.05WrIn. On the other hand, the length of the fiber must be two or more torsos. If it is too short, the fibers will accumulate excessively in the groove-like cavity, significantly impairing the effectiveness of the cavity.

The pores obtained by the above method have a diameter of 0.05 mm or more and up to 1 lung, preferably 0.1 fi to 0.3 mm. This is because if the diameter is less than 0.05ttan, it will be difficult for the liquid to flow into the cavity, and if the diameter is more than 1 cylinder, it will be easy for the liquid to flow in, so the liquid will fill the cavity, making it difficult to generate vapor bubbles. be. Moreover, the thickness of the porous layer 9 is 0
．． To obtain a 0.05 mm pore, at least 0.2 cylinder or more is required.

When the heat exchange wall constructed in this manner is heated to a higher temperature than the liquid in contact with it, vapor bubbles are generated within the cavity and fill the cavity. When the pressure of the vapor bubbles becomes higher than that of the external liquid, some of the vapor bubbles are released through the relatively large communication holes in the porous layer, and other vapor bubbles are retained within the cavity as residual vapor bubbles. At this time, pressure changes occur within the cavity,
The waste easily flows into the cavity through a large number of communication holes other than the communication hole from which the vapor bubbles were released. The inflowing liquid is transported by capillary action, forming an extremely thin liquid film. At this time, since the fibers at the corners of the cavity are directly connected, the liquid can easily flow in due to capillary action, and the liquid can be smoothly replenished against evaporation from the thin liquid film. Additionally, since the diameters of the communicating holes are different, the flow resistance is different for each hole, and the steam generated within the cavity is always released from the large holes in the communicating holes, while the liquid flows in through the small holes. Because it is stable, it ultimately improves heat transfer performance.

〔Effect of the invention〕

According to the present invention, boiling heat transfer characteristics are improved by reducing the inflow resistance of liquid flowing into the cavity under the heat exchange skin, and high performance heat transfer walls with different characteristics can be manufactured. effective.

Figure 4 is an experimental example showing the effects of the present invention, comparing the boiling performance (using Freon R-11 reagent) of a heat transfer wall manufactured by the method of the present invention and a conventional heat transfer wall. It shows. The horizontal axis is the degree of superheating ΔT (tZ') of the heat transfer wall surface from the saturation temperature of the refrigerant liquid, and the vertical axis is the heat flux q (W/cnr2).
shows. Curve A has the structure shown in Figure 1 and has a cavity pitch of 0.5.
This is a case where the through hole size is 0.1 m, the pitch is 0.7 mm, and the depth is 0.4 RAN. Curve B is for the structure of the present invention shown in Fig. 3, and the fiber diameter is 0.18 on the groove in Fig. 1.
m+++, length 5m+n, porous layer thickness 1g, porous layer cavity volume ratio 60%.

As is clear from this figure, when the heat flux is the same, curve B has a smaller degree of superheating, and this tendency becomes more pronounced as the heat flux increases. Thus, it is clear that the heat exchange wall of the present invention has higher heat transfer performance than conventional heat exchange walls.

[Brief explanation of drawings]

Fig. 1 is a partially sectioned perspective view showing a conventional heat exchange wall, Fig. 2 is a perspective view illustrating the boiling state of the heat exchange wall in Fig. 1, and Fig. 3 is a porous heat exchange wall according to the present invention. A photograph and a schematic cross-sectional view of the layer from above, and FIG. 4 are graphs showing the boiling heat transfer performance of the heat exchange wall of the present invention and the conventional heat exchange wall. 1... Heat exchange wall, 2... Cavity, 3... Through hole. Atsushi 1 Figure 1? Figure 3 Figure 4 Figure b9-7 poverty + 1 AT (-B) Procedural amendment (method) Display of 1 case 1982 6 Permission No. 195994 Bow. 3. The person who makes the correction, I・'51□]
1st Manufacturing Company” '-'
-Ill if A) 1'Katsu 4 Representative Person 7 Contents of Amendment 3 Drawing 1, page 4 of the specification, lines 16-17, the phrase "the porous layer ... and the cross section" is replaced with "the cross section of the porous layer." do. 2. On page 5, instead of ``1 fiber in 4 lines,'' use ``10 fibers.''
shall be. 3. On page 8, line 3 of the same page, the phrase ``... and cross-section of the porous layer'' is defined as ``the cross-section of the porous layer.'' 4. Correct the concave man figure 3 as shown in the attached sheet. Above 3rd area 0

Claims (1)

[Claims] Technique 6: A permeable porous layer composed of aggregation of individual metal fibers or inorganic fibers is bonded to the surface of a non-permeable base material having a large number of irregularities on the surface. Features a heat exchange wall. 2. Claim 1 (in which the metal fibers or inorganic fibers forming the permeable porous layer have a diameter of 0.05++
rm and longer than 1rrrm in length, these fibers are bound to each other in a random stacking relationship, and are bound to the uneven surface of the base material, 0.
A heat exchange wall characterized by a porous layer having a pore radius of 03+n+n to 1 pore, forming gaps between fibers, and having pores that communicate with each other. 3. A thickness of 0.2 rran or more can be obtained by individually distributing metal fibers or inorganic fibers alone or with a binder or auxiliary agent added to the surface of a non-permeable base material having many irregularities on the surface. A method for producing a heat exchange wall, which is characterized in that after laminating the layers as described above, sintering is performed in a predetermined atmosphere and temperature with no load or a predetermined load applied to the laminated surfaces.