JP2659831B2 - Boiling evaporation method and apparatus - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method and an apparatus for boiling evaporation.

(Prior art and its problems) Heat medium composed of a mixture of Freon R113 and ethanol or a mixture of Freon R11 and ethanol, that is, a dielectric having a high electric resistance and a dielectric having a lower electric resistance and a higher boiling point The heat medium formed by mixing with the body has a charge relaxation time smaller than the bubbling cycle at the time of boiling (time after bubbles are generated, they grow and separate from the heat transfer surface, and the next bubbles are generated). (The ratio between the dielectric constant of the heat medium and the electrical conductivity).

When a high voltage is applied between the electrode disposed in the heat medium and the heat transfer surface, the heat medium is heated through the heat transfer surface, and the heat medium is boiled and evaporated in the nucleate boiling region. It is known that boiling can be suppressed to promote heat transfer, and that boiling can be increased to promote heat transfer.

It is known that the heat transfer promotion rate is overwhelmingly large in the latter case, and the superheat degree of the heat transfer surface is reduced to 1/50 or less.

However, little has been known so far about the mechanism of the change of the foaming phenomenon or the heat transfer promoting phenomenon.

(Means for Solving the Problems) The present invention was invented to solve the above problems, and the gist of the first invention is that a charge relaxation time smaller than a foaming cycle at the time of boiling. In the boiling evaporation method, the heating medium is heated through the heat transfer surface in a state where a high voltage is applied between the electrode disposed in the heat transfer medium and the grounded heat transfer surface to thereby evaporate. In addition, the boiling evaporation method is characterized in that bubbles are supplied from an outer peripheral edge of the heat transfer surface.

The gist of the second invention is to provide an electrode disposed in a heat medium having a charge relaxation time smaller than the bubbling cycle at the time of boiling, and a portion having a high heat flow rate to heat the heat medium. And a means for applying a high voltage between the electrode and the heat transfer surface.

The gist of the third invention resides in that an electrode arranged in a heat medium having a charge relaxation time smaller than a foaming cycle at the time of boiling and an earthed ground made of a porous material for heating the heat medium. A heat transfer surface and means for applying a high voltage between the electrode and the heat transfer surface.

(Function) When the heat medium is heated via the heat transfer surface while a high voltage is applied between the electrode and the heat transfer surface, the bubbles supplied to the heat transfer surface become a so-called kind of fire and foaming is promoted. And promotes boiling heat transfer.

(Example) FIG. 1 shows an example of an experimental apparatus.

The heating medium 2 made of a mixture of Freon R113 and ethanol or a mixture of Freon R11 and ethanol is contained in the container 1. A disc-shaped heat transfer surface 3 is provided on the bottom of the container 1, and the heat transfer surface 3 is heated by energizing a sheath heater 4 from a power supply 5. A mesh electrode 6 is disposed in the heat medium 2 so as to be parallel to the heat transfer surface 3 at a slight distance (for example, 5 mm). The heat transfer surface 3 is grounded, and the electrode 6 is connected to the positive electrode of the DC high voltage power supply 7 so that a high voltage can be applied between the heat transfer surface 3 and the mesh electrode 6.

When the heating medium 2 is heated to a temperature higher than its boiling temperature via the heat transfer surface 3 without applying a high voltage between the heat transfer surface 3 and the mesh electrode 6, that is, without applying an electric field to the heat transfer surface 3. ,
The heating medium 2 boils and a large number of bubbles are generated from the heat transfer surface 3.

However, when a voltage is applied between the heat transfer surface 3 and the mesh electrode 6 in a state where the heat medium is heated to the boiling temperature or higher, and the applied voltage is gradually increased, the applied voltage is increased to 10 KV. Can suppress foaming from the upper surface of the heat transfer surface 3,
Bubbles are generated from the outer peripheral edge of the heat transfer surface 3, that is, a portion where heat transfer is poor and the heat flow rate is locally high.

When the applied voltage is further increased, the heat transfer surface 3 and the electrode 6
Air bubbles formed outside of the electric field, ie, the heat transfer surface 3
Bubbles generated from the outer peripheral edge are drawn into the electric field. When the applied voltage exceeds 10 KV, the bubbles are suppressed by the dielectrophoretic force on the heat transfer surface 3 and move around vigorously. When the applied voltage exceeds 20 KV, the bubble diameter becomes smaller and the rising speed of the bubble becomes faster. Then, at the same time as the movement of the bubbles on the heat transfer surface 3 becomes more intense, new foaming points are created one after another. Since the bubbles from these new foaming points cause the same phenomenon as described above, the heat transfer surface 3 is covered with the bubbles. Would. Thereafter, the bubbles are wiped out of the heat transfer surface 3 to reduce the number of bubbles on the heat transfer surface 3, but the remaining bubbles move vigorously on the heat transfer surface 3 again and repeat the above-described behavior.

As a result, as shown in FIG. 2, as the applied voltage increases, the degree of superheat at the same heat flux decreases, and
As shown in FIG. 3, the heat transfer promotion rate for the same heat flux increases as the applied voltage increases, and the heat transfer promotion rate reaches up to about 50 times.

When the heat transfer surface 3 is integrated with the container 1, or when the container 1 forms the heat transfer surface 3, the heat transfer surface 3 is locally formed by forming irregularities on the surface of the heat transfer surface 3 or bonding a heat insulating material. Therefore, a portion having a high heat flux can be formed. In a portion where the heat flow rate is high, the suppression of boiling by the electric field is small, and bubbles remain in this portion. Therefore, the bubbles can be continuously supplied to the heat transfer surface in the electric field as a kind of fire.

Further, if the heat transfer surface 3 is made of a porous material, the same voltage as the voltage applied to the heat transfer surface 3 is maintained until bubbles existing in a large number of holes of the porous material come out of the heat transfer surface 3. Since it is not affected by the electric field, it is possible to always supply the air bubbles which are the kind of fire.

As shown in FIG. 4, when a large number of linear electrodes 10 are provided around the heat transfer tube 11 with the insulating spacer 9 interposed therebetween, the portion of the heat transfer tube 11 facing the spacer 9 has a local heat flux. And a small gap between the heat transfer tube 11 and the spacer 9 generates bubbles serving as a kind of fire.

(Effects of the Invention) In the present invention, by supplying bubbles serving as a fire source to the heat transfer surface in the electric field, foaming can be promoted and the boiling heat transfer coefficient can be dramatically improved.

If a portion having a high heat flow rate is formed on the heat transfer surface, the portion having a high heat flow rate has a small amount of suppression of boiling by the electric field and bubbles remain in this portion, so that the bubbles can be continuously supplied to the heat transfer surface in the electric field .

If the heat transfer surface is made of a porous material, it is maintained at the same voltage as the voltage applied to the heat transfer surface until bubbles existing in many holes of the porous material come out to the heat transfer surface, and the heat transfer surface is affected by the electric field. Since there are no such bubbles, the bubbles can be supplied as a fire to the heat transfer surface in the electric field.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic cross-sectional view showing an example of an experimental apparatus that can be used for an experiment of the present invention, and FIG. 2 is a diagram showing a relationship between a degree of superheat, an applied voltage, and a heat flux. , FIG. 3 is a diagram showing the relationship between electric conductivity, applied voltage and heat transfer promotion rate, FIG. 4 shows an example of a heat transfer tube which can be used for carrying out the present invention, and FIG. FIG. 4 (b) is a sectional view. Electrodes: 6, heat transfer surface: 3, high voltage applying means: 7, bubble supply means: 8, 1 ... container, 2: heat medium, 4 ...
Sheath heater, 5 ... Power supply

 ──────────────────────────────────────────────────続 き Continuation of the front page Examiner Tetsuo Sekiguchi (56) References JP-A-2-19453 (JP, A) JP-JP-2-3918 (JP, B2)

Claims (3)

(57) [Claims] 1. A method in which a high voltage is applied between an electrode disposed in a heat medium having a charge relaxation time smaller than a bubbling cycle at the time of boiling and a grounded heat transfer surface. In the boiling evaporation method, the heating medium is heated to evaporate by boiling, wherein bubbles are supplied from an outer peripheral edge of the heat transfer surface. 2. An electrode disposed in a heat medium having a charge relaxation time smaller than a bubbling cycle at the time of boiling, and a grounded heat transfer having a portion having a high heat flow rate for heating the heat medium. A boiling evaporator, comprising: a surface; and means for applying a high voltage between the electrode and the heat transfer surface. 3. An electrode arranged in a heat medium having a charge relaxation time smaller than a bubbling cycle during boiling, a grounded heat transfer surface made of a porous material for heating the heat medium, and Means for applying a high voltage between the electrode and the heat transfer surface.