JPS5939679B2 - boiling heat transfer surface - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a boiling heat transfer surface capable of advantageously transferring heat to a liquid with which it comes in contact.

In general, as a method to promote boiling heat transfer, a micro-space 2 (so-called reentrant cavity) with a large interior and a small opening 1 is placed on the heat-transfer surface of a metal tube or plate, as shown in Figure 1. ) is used as stable boiling bubble nuclei.

In order to protect the promoting effect from clogging, it is said that it is preferable that the above-mentioned minute spaces communicate internally with adjacent spaces.

Such a heat transfer surface has much better boiling heat transfer characteristics than a normal smooth surface, so it has great industrial value in the field of heat exchangers such as evaporators. Many ideas have been made regarding its production method.

For example, a porous layer is formed by sintering metal powder on the surface of a tube or plate, or a groove is formed by cutting a metal plate 3 as shown in Fig. 2, and then knurled to form a protrusion. Crush 4,
Then, as shown in FIG. 3, a bell-shaped or tapered hole is made in the thin metal plate 5 by electron beam processing or laser processing, and then a number of narrow grooves (internal grooves) are formed on the dog side of the hole diameter. Examples include those in which a porous layer is provided by bonding to a metal surface 6 having a hole (for communication).

However, with the sintering method, it is difficult to control the atmosphere and bonding agent during sintering, and the shape is complicated because the metal powders are fused together, so it is difficult to produce uniform products in large quantities. The drawback was that process control became extremely complex.

Furthermore, in the manufacturing method using hole-let processing after cutting, it is difficult to control the hole shape, and it is particularly difficult to process materials with poor malleability such as titanium.

In addition, the method of making a perforated plate by electron beam processing or laser processing and joining it to a surface with narrow grooves is limited to special methods such as electron beam processing, and this In order to form an endrant cavity using the method described above, it had a major drawback, such as the necessity of making the perforated plate a certain thickness.

The present invention has been made in consideration of the above circumstances, and its purpose is to form a reentrant cavity, which is conventionally known as a reentrant cavity, on the surface of a heat transfer surface using a very simple method. forms many small micro-spaces,
The object of the present invention is to easily provide a high-performance boiling heat transfer surface.

That is, when the present invention forms a boiling heat transfer surface by bonding a porous material having a large number of holes penetrating through the thickness to a grooved surface, the holes are made into long holes having an elongated shape. The length in the direction is at least larger than the width of the tips of the ridges sandwiching the grooves of the grooved surface, and the elongated holes are joined so as to intersect with the ridge direction of the ridges of the grooved surface, The aim was to achieve the above objective.

Hereinafter, one embodiment of the present invention will be described with reference to the drawings.

FIG. 6 is an external view showing a schematic configuration of the boiling heat transfer surface of the present invention, and the porous material 7 (length t of long hole 8, 6 mm, gap δ11) shown in FIGS. 4 and 5, respectively. =Q, 17WJ
Pitch p1=Q, 211i[, p2=-0,8mtn
, plate thickness t=0.15mm) and grooved surface 9 (groove gap δf
= 0.67W7m, groove depth h=o, 6mm, and width W of the tip 10 of the crest 10=0.2mm).

Possible joining methods include crimping, seam welding, etc., but sufficient performance can be achieved by simply mechanically fixing and contacting.

Since it is constructed in this way, its surface is shown in Figure 7 (
An ideal space 11 as shown in the cross section taken along arrow a-a in FIG. 6) is formed, and the
As shown in cross section b), the pores of the porous material are located at the tip of the crest 1 of the grooved surface.
Even when it is located at 0, it does not block that part and helps to remove bubbles, so very good boiling heat transfer characteristics are achieved.

Of the above two advantages, the latter is particularly effective when the width of the tip of the crest of the grooved surface becomes relatively large due to processing constraints.

A porous material 14 is wound around a heat exchanger tube 12 (a fluted tube 13 having an outer diameter D=25.4 mm and having grooves in the tube axis direction and having a groove in the tube axis direction) as shown in FIG. 9 to which the boiling heat transfer surface according to the present invention is applied. The pool boiling heat transfer coefficient of Freon R113 (the dimensions of the porous material and the grooved surface are almost the same as those described above) was investigated, and the result was as shown by the solid line P in FIG.

However, in the characteristic diagram in Figure 10, the horizontal axis is the average heat flow rate q
(W/y4), and the vertical axis is the pool boiling heat transfer coefficient α (W/y4).
y4K) are shown on a logarithmic scale, and the solid line Q in the figure shows the results for a fluted pipe without a porous material wrapped around it for reference.

As is clear from this characteristic diagram, the boiling heat transfer surface according to the present invention reliably promotes boiling heat transfer.

As described above, in a boiling heat transfer surface constructed by bonding a porous material having a large number of holes penetrating in the thickness direction to a grooved surface, the holes are long holes having an elongated shape. Ideally, the length in the longitudinal direction is at least larger than the width of the tips of the crests sandwiching the grooves of the grooved surface, and the long holes intersect with the direction of the ridges of the ridges of the grooved surface. This makes it possible to form bubble nuclei, providing an extremely high-performance boiling heat transfer surface.

The arrangement of the elongated holes is preferably such that the lateral gaps of the elongated holes are smaller than the groove dimensions of the grooved surface and the groove depth.

Note that the effects of the present invention can be obtained as long as the above conditions are satisfied, and are not limited by the method of manufacturing the porous material or the grooved surface, or the method of joining the two elements.

To be more specific, the porous material only needs to have elongated holes penetrating the material in the thickness direction, and the shape of the holes may, of course, be net-like instead of plate-like.

[Brief explanation of drawings]

Figure 1 is a sectional view showing an ideal boiling heat transfer surface shape, Figure 2 is a sectional view of a conventional heat transfer surface, Figure 3 is a sectional view of another conventional heat transfer surface, and Figure 4 is a cross-sectional view of a conventional heat transfer surface. FIG. 5 is a plan view of a porous material used for a heat transfer surface according to an embodiment of the present invention, FIG. 5 is a diagram showing a grooved surface constituting the heat transfer surface of the present invention, and FIG. 7 is a cross-sectional view taken along arrow a-a in FIG. 6, FIG. 8 is a cross-sectional view taken along arrow bb-b in FIG. 6, and FIG. 9 is a diagram illustrating the present invention. A diagram showing a heat exchanger tube, and FIG. 10 is a characteristic diagram showing experimental data. 7... Porous material, 8... Long hole, 9...
...Grooved surface.

Claims (1)

[Scope of Claims] 1. In a boiling heat transfer surface constructed by joining a porous material having a large number of holes penetrating in the thickness direction to a grooved surface, the holes are long holes having an elongated shape, and the long holes are The length in the longitudinal direction is at least larger than the width of the tip of the ridges sandwiching the grooves of the grooved surface, and the longitudinal direction of the elongated hole is joined so as to intersect with the ridge direction of the ridges of the grooved surface. A boiling heat transfer surface characterized by comprising: 2. The boiling heat transfer surface according to claim 1, characterized in that a grooved surface is formed on a tube body, and grooves are formed in the tube axis direction of the tube body.