JPH03230094A - Heat transfer medium - Google Patents

Abstract

PURPOSE:To obtain a heat transfer medium having high heat transfer characteristic by incorporating a plurality of cylindrical first recesses relatively narrowed at openings and second recesses of smaller diameter and respectively formed in the bottoms of the first recesses in a porous electrodeposited metal layer. CONSTITUTION:In a heat transfer medium, a porous electrodeposited metal layer is formed on a metal base, and the layer has a plurality of cylindrical first recesses narrowed at openings and second recesses of smaller diameter and respectively formed in the bottoms of the first recesses. Since a nucleate boiling occurs not only in the first recesses but also in the second recesses, the boiling feasibly occurs as in the case of the sole first recesses, thereby enhancing thermal conduction efficiency. That is, bubbles to become seeds of nucleate boiling are generated from the second recesses, and the first recesses are then filled with the bubbles. In other words, the recesses of the small diameter performs a function as an initial boiling nucleate, then continuous nucleate boiling occurs, and the degree of superheat for the nucleate boiling is lowered. Since the recesses of different diameters are present, the recesses of suitable size for various viscous fluids are present to generate nucleate boiling.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Fields] The present invention is applicable to, for example, evaporation tubes and condensation tubes of heat exchangers for air conditioning;
The present invention also relates to a heat transfer body used in a heat pipe having a wick, and in particular, to a heat transfer body that is inexpensive to manufacture and has excellent heat transfer properties.

[Prior Art] In order to increase the heat transfer efficiency of a heat transfer tube for exchanging heat between an internal medium and an external medium, (1) the heat transfer area must be increased;

(2) Facilitates capillary action.

(3) Make it easier to cause turbulence.

(4) Make it easier to cause nucleate boiling.

It is said that this is effective.

As a heat exchanger tube that satisfies some of these conditions,
Some examples include those in which spiral grooves are formed on the inner surface of the tube by a rolling method, and those in which granular or linear metal is attached to the inner surface of the tube by brazing or the like.

[Problems to be Solved by the Invention However, the above-mentioned conventional techniques have the following problems.

In other words, when forming spiral grooves, the nucleate boiling phenomenon, which is the most effective of the above methods for increasing heat transfer efficiency, is not used, and there are also However, due to limitations on the inner diameter of the tube, the number of spiral grooves, and the angle of twist, the thermal properties are about 1.2 to 1.5 times higher than ordinary grooveless tubes. However, the performance was unsatisfactory. In addition, during manufacturing, the frictional force between the rolling tool and the inner surface of the tube is large, so a large pressing force is required, which in turn requires large-scale equipment, shortens the life of the tool, and increases production costs. There was a problem.

On the other hand, in order to avoid adhesion of granular or linear metal to the inner surface of the tube, it is necessary to perform high-temperature work, and there is also the problem that it is difficult to apply it to small-diameter tubes. there were.

Furthermore, in order to solve these problems, a technique has been proposed in which a porous layer is formed by plating a metal surface. In other words, JP-A-53-! The method described in Japanese Patent No. 19553 forms fine grooves on the surface of a metal base, and then attaches a plating layer to this surface.
The opening of the narrow groove is relatively narrowed.

Furthermore, the method described in JP-A No. 53-138969 forms a plating layer on the inner surface of the tubular body and then electrolytically dissolves this plating layer to make it porous. .

However, in the former technique, the entire porous layer is not formed by plating, but rather the plating layer is placed on the top of the groove after forming narrow grooves by machining etc. However, the process of forming fine grooves is time-consuming and increases costs, and it is difficult to form a fine porous layer, resulting in insufficient heat transfer function.

On the other hand, the latter technique utilizes selective corrosion due to microscopic deviations in the structure of the base metal, so it has the disadvantage that the selection of base metals is limited.
Since it is difficult to shape the recess so that the opening is relatively narrower than the inside, it has not been possible to effectively cause the nucleate boiling phenomenon.

[Means for Solving the Problems] The present invention has been made to solve the above-mentioned problems, and a porous electrodeposited metal layer is formed on the surface of a metal substrate. The metal layer was a heat transfer body having a plurality of cylindrical first recesses each having a relatively narrow opening, and a second recess having a smaller diameter formed at the bottom of the first recess. It is something.

5 Effect J In the heat transfer body of the present invention, nucleate boiling occurs not only in the first recess but also in the second recess, so nucleate boiling occurs more easily than in the case of a single recess, and the heat transfer efficiency improves. It gets expensive.

That is, bubbles that become seeds of nucleate boiling are generated from the second recess, and then the first recess is filled with air bubbles. In other words, the small-diameter concavity functions as an initial boiling nucleus, and then continuous nucleate boiling occurs, reducing the degree of superheating for nucleate boiling.

Furthermore, since there are recesses of different diameters, there are recesses of suitable sizes for fluids of various viscosities, thereby causing nucleate boiling.

"Example" Hereinafter, an example of a heat exchanger tube of the present invention will be described with reference to the drawings.

(Example 1) Figures 1 and 2 show the cross section and surface properties of a copper pipe according to the first example of the present invention, which has a pipe length of 1000 mm, an outer diameter of 9.35 mm, and a wall thickness of 0.35 mm. Homogeneous narrow pores with a pore diameter of 250 μm are formed on the inner surface of the steel pipe with a porosity of 18%. The heat exchanger tube in this example was manufactured by forming a hydrophobic thin film on the surface of a steel tube, and then electroplating using the steel tube as a cathode and an insoluble anode. This will be explained with reference to Figure 3.

The hydrophobic thin film 2 on the surface of the copper tube I was formed by diluting Noricon oil three times with ethanol, applying it to the inner surface of the copper tube II, and then evaporating the ethanol. The anode wire (made of Ti-Pt) 3 is stretched with tension on the axis of the copper tube I, and insulating spacers 4 are provided around the wire 3 at appropriate intervals to connect the copper tube I and the wire. 3. This prevents short circuits due to contact. Then, copper sulfate plating solution (copper sulfate 2
A storage tank 5 for storing 00g/Q, sulfuric acid 50gA2) and a chemical pump 6 for flowing this plating solution into the copper pipe 1 are provided, and this storage tank 5 is replenished with basic copper carbonate in an amount corresponding to the copper ions reduced by plating. I try to use it repeatedly.

As the plating current, a pulse current such as an intermittent current, a normal pulse current, or a PR current is appropriately used. Such a pulsed current makes it easier to transport metal ions into the pores compared to direct current, so it can increase the deposition rate.6. It is possible to suppress vertical deposition and prevent short circuits caused by deposited metal. Further, in the PR current, since positive and reverse currents are passed alternately and periodically, the growth of the deposited film can be made uniform.

Using the apparatus described above, plating was performed for 10 minutes under the conditions of a plating solution temperature of 30°C, a cathode current density of 33 A/dm', and a plating solution flow rate of 2 m/s. An electrodeposited metal layer with holes formed therein was obtained.

The mechanism by which narrow pores are formed on the substrate surface in the above manufacturing method is considered to be as follows.

First, since plating is performed using an insoluble anode, water in the plating solution is electrolyzed and oxygen scum is generated at the anode. A part of this oxygen gas is carried to the surface of the cathode substrate as the plating solution moves, but the hydrophobic thin film formed on the surface impairs the wettability of the substrate to the plating solution. The gas adheres to the surface of the substrate as bubbles.

Therefore, the deposited metal grows to envelop these air bubbles, forming uniform and fine interspaced pores.

Therefore, the diameter and number of bubbles adhering to the substrate can be controlled by changing the anode current density or the relative moving speed of the plating solution with respect to the substrate.

After washing the inner surface of this copper tube I with water and drying it, a test was conducted by crushing the copper tube 1 with a vise.
After annealing for 0 minutes, tube expansion using a mandrel was attempted, but no peeling or falling off of the electrodeposited metal layer was observed in either case, demonstrating excellent adhesion and strength.

Thermal properties of the steel pipes manufactured as described above were measured using a thermal property testing apparatus as shown in FIG. 4 under the conditions shown on the next page.

In this device, T is a temperature sensor, P is a pressure gauge, PD is a differential pressure gauge, IO is a pump, 11 is a valve, 12 is a flow meter, 13
1 is an expansion valve, 14 is a compressor, 15 is a sub-condenser, 16 is a sub-evaporator, 17 is a constant temperature water tank, and 1
8 is a #J tube as a test tube. In this thermal property testing apparatus, a refrigerant supplied from a compressor 14 is flowed inside the test tube I8, and hot water from a constant temperature water tank 17 is flowed outside against the refrigerant. The temperature of the constant-temperature water was controlled according to each refrigerant flow rate so that the refrigerant system was stable.

In this figure, arrows A and A'' indicate the flow directions of refrigerant and water, respectively, in the case of the evaporation test, and arrows B and B' indicate the flow directions of the refrigerant and water, respectively, in the case of the condensation test. .

As a result of this test, the copper tube I of Example 1 of the present invention showed a film heat transfer coefficient on the inside as shown as C in FIG. It was found that the thermal properties were 7 to 8 times more excellent than that of the previous one.

(Example 2) A spiral groove was formed on the inner surface of a steel pipe having the same shape as the material of Example 1 by rolling, and then, by the method of Example 1, a plating layer having narrow holes in the inclined wall of the spiral groove was formed. was formed. The heat transfer properties were measured using the same method, and the results showed that the heat transfer properties were approximately 10 times higher than those of ordinary steel pipes.

(Example 3) A heat exchanger tube was manufactured in which a concave portion with a smaller diameter was formed at the bottom of a narrow hole (see FIG. 6). Heat exchanger tubes with smaller-diameter recesses like this are formed when lubricating oil for processing is used as a hydrophobic thin film, and because the film is thin, fine bubbles are formed first, and then After the plating progresses and a small-diameter concavity appears, the bubbles gather and become large-diameter.
Furthermore, surrounding this is plated to form four parts with a larger diameter. This heat transfer tube has approximately 20% better heat transfer characteristics than B, which does not have a recess at the bottom.3 (Example 4) Pipe length: 500 mm, outer diameter: 9.35 mm, wall thickness: 1], 35 m
Electroplating was performed at a cathode current density of 2 OA/di2 and a high flow rate of the plating solution (4 m/s) at 1 of m, and a sandwich plate was formed at an angle of about 20 degrees with respect to the axis or the normal to the heat transfer surface. H the mouth cavity
A plated metal layer was obtained (see FIG. 7).

When such a heat transfer tube was set so that the flow direction of the internal fluid or the inclination of the narrow opening was the same, the heat transfer characteristics were improved by about 30% compared to a tube without an inclination.

In the above manufacturing method, the diameter and number of the sandwiched holes can be controlled by changing the cathode current density and the flow rate of the plating solution. It is possible to control the inclination angle of the mouth cavity.

Note that the present invention is of course not limited to heat exchanger tubes.

[Effects of the Invention] As detailed above, in the present invention, a porous electrically conductive metal layer is formed on the surface of a metal substrate, and this porous electrically conductive layer has relatively defined openings. Since the configuration has a plurality of cylindrical first four parts and a second four part with a smaller diameter formed at the bottom of the first recess, the small diameter recess at the bottom of the recess serves as an initial boiling nucleus. This allows nucleate boiling to occur more easily than a heat transfer body with a single-diameter concavity, resulting in high heat transfer performance. Furthermore, the concavities with diameters corresponding to fluids of various viscosity can induce nucleate boiling, increase the heat transfer area, and provide a heat transfer body with good heat transfer characteristics, and can be manufactured on a large scale. Since it does not require expensive equipment or high-temperature work, the production cost is low, and secondly, it has excellent effects such as easy production of small-diameter heat exchanger tubes.

[Brief explanation of drawings]

Fig. 1 is a drawing showing the cross-sectional shape of the first embodiment of the present invention, Fig. 2 is a drawing showing the surface shape, Fig. 3 is a schematic diagram showing the manufacturing method of the first embodiment, and Fig. 4 is a heat transfer diagram. A schematic diagram of an apparatus for measuring characteristics, FIG. 5 is a graph showing the heat transfer characteristics of the first embodiment, FIG. 6 is a drawing showing the cross-sectional shape of the third embodiment of the present invention, and FIG. 7 is a graph showing the heat transfer characteristics of the first embodiment. It is a drawing which shows the cross-sectional shape of 4th Example.

Claims (2)

[Claims] (1) A porous electrodeposited metal layer is formed on the surface of a metal substrate, and this porous electrodeposited metal layer has a plurality of cylindrical first recesses in which openings are relatively sandwiched, and 1. A heat transfer body comprising: a second recess having a smaller diameter formed at the bottom of the first recess. (2) The heat transfer body according to claim 1, wherein the base body is a tube body.