JP2005114352A - Fluid heating device - Google Patents

Abstract

An object of the present invention is to provide a fluid heating apparatus capable of efficiently heating a fluid.
A cylindrical ceramic body in which a heating resistor is embedded is inserted into a double-bottomed cylindrical body that simultaneously covers an inner peripheral surface and an outer peripheral surface of the ceramic body, and a powder is sandwiched between the two. And a fluid heating device that allows fluid to pass through both the inner surface side and the outer surface side of the bottomed cylindrical body.
[Selection] Figure 6

Description

  The present invention relates to a liquid heating apparatus using a ceramic sheathed heater formed by inserting a ceramic heater into a metal bottomed cylindrical body.

  Conventionally, ceramic heaters in which a heating resistor is embedded in a ceramic body have been used in various fields. And when using as a heater for liquid heating, such as a water heater for bathtubs, putting the said ceramic heater directly in water and heating is performed.

  However, when there was water only partway through the ceramic heater, the water-free part generated abnormal heat and cracks were generated, or heat generation was uneven due to adhesion of scales, etc., and cracking was likely to occur due to heat shock. . Alternatively, when immersed in an alkaline solution or the like, ceramics may be eroded.

  As described above, when a crack or erosion occurs, the heating resistor is exposed to cause a leakage or an electric shock.

  Therefore, a ceramic sheathed heater in which the ceramic heater is covered with a metal bottomed cylindrical body is used. For example, as shown in Patent Document 1, Patent Document 2, etc., a rod-shaped ceramic heater in which a heating resistor is embedded in a ceramic body is inserted into a metal bottomed cylindrical body, The powder is filled in between.

  By adopting such a structure, it is possible to prevent the ceramic heater from coming into direct contact with water and to prevent generation of cracks.

Moreover, as a powder filled between a ceramic heater and a metal bottomed cylindrical body, it is common to use a metal powder in order to increase thermal conductivity.
JP-A-57-151187 Japanese Patent Application Laid-Open No. 60-127689

  However, even with the ceramic sheathed heater as described above, cracks may occur in the ceramic body in which the heating resistor is embedded depending on the use conditions and the like. In such a case, there is a problem that the current applied to the heating resistor flows into the water through the powder and the bottomed cylindrical body, and there is a risk of electric leakage or electric shock.

  That is, in the conventional ceramic sheathed heater, since the ceramic heater itself has high insulation, powder having low insulation such as metal powder is used as the powder interposed between the bottomed cylindrical body. . Therefore, in the event that a crack occurs in the ceramic heater, the effect of preventing current leakage is poor.

  Further, the conventional ceramic sheathed heater has a problem that the density of the powder filled between the ceramic heater and the bottomed cylindrical body is low and heat transfer is poor. Furthermore, there has been a problem that the position of the ceramic heater in the bottomed cylindrical body tends to shift during repeated use.

  Therefore, the invention of claim 1 inserts a cylindrical ceramic body in which a heating resistor is embedded into a double bottomed cylindrical body that simultaneously covers the inner and outer peripheral surfaces of the ceramic body, And a fluid heating device is configured by allowing fluid to pass through both the inner surface side and the outer surface side of the bottomed cylindrical body.

  That is, the ceramic sheathed heater itself is formed in a cylindrical shape, and the fluid can be efficiently heated by passing the fluid through both the inner surface side and the outer surface side.

  According to the present invention, a cylindrical ceramic body in which a heating resistor is embedded is covered with a double-bottomed cylindrical body that covers the inner peripheral surface and outer peripheral surface of the ceramic body, and a powder is sandwiched between the two. In addition, the fluid heating device is configured such that the fluid passes through both the inner surface side and the outer surface side of the bottomed cylindrical body, so that the fluid can be efficiently heated.

  Therefore, according to the present invention, it is possible to obtain a highly safe ceramic sheathed heater that is excellent in thermal efficiency and can prevent leakage and electric shock, and can be suitably used as a fluid heating device such as a water heater for a bathtub.

  Hereinafter, reference examples will be described with reference to the drawings to explain the present invention.

  As shown in FIGS. 1 and 2, the ceramic sheathed heater includes a cylindrical ceramic heater 1 inserted into a bottomed cylindrical body 3 made of metal, an insulating powder 2 interposed therebetween, and a ceramic heater 1. The rear end portion is constructed by arranging a metal cover 4 and caulking at the rear end portion of the bottomed cylindrical body 3. The ceramic heater 1 includes a heating resistor 12 embedded in a cylindrical ceramic body 11 and a rear end portion of the heating resistor 12 connected to a lead wire 13. Thus, the heating resistor 12 can generate heat.

  When this ceramic sheathed heater is used for water heating such as a bath water heater, the bottomed cylindrical body 3 is immersed in water and the lead wire 13 is energized to cause the ceramic heater 1 to generate heat. Water can be heated by telling. At this time, since the ceramic body 11 does not come into direct contact with water, generation of cracks and the like can be prevented.

  In such a ceramic sheathed heater, the insulating powder 2 serves as a cushioning material between the ceramic heater 1 and the bottomed cylindrical body 3 and transmits heat. However, the most important point in the present invention is that the insulation of the heating resistor 12 can be prevented from flowing into the bottomed cylindrical body 3 even if a crack or the like occurs in the ceramic body 11. This is to give the powder 2 sufficient insulation.

Specifically, even when a crack occurs in the ceramic body 11, the resistance value R at room temperature between the heating resistor 12 and the bottomed cylindrical body 3 may be set to 10 ⁴ Ω or more. . This is because if the resistance value R is set to 10 ⁴ Ω or more when a household voltage of 100 V is applied, even if a leakage current is generated, it becomes 10 mA or less and can be set to a level that does not adversely affect the human body.

Preferably, the leakage current is 0.5 mA or less. Therefore, even when a crack occurs in the ceramic body 11, the resistance value R at room temperature between the heating resistor 12 and the bottomed cylindrical body 3 is 2 ×. It should be 10 ⁵ Ω or more.

  When the resistance value R is measured, a voltage higher than a specified voltage is applied to the ceramic sheathed heater in advance to generate a crack in the ceramic body 1, and in this state, between the heating resistor 12 and the bottomed cylindrical body 3. The resistance value R may be measured at room temperature.

As such an insulating powder 2, one or more of boron nitride (BN), silicon nitride (Si ₃ N ₄ ), aluminum nitride (AlN), and silicon carbide (SiC) are used. As shown in Table 1, any of these has a large volume resistivity and can increase the insulation.

  At the same time, it is necessary for the insulating powder 2 to improve heat conductivity. However, since these materials have a high thermal conductivity of 0.06 cal / cm · sec · ° C. or more as shown in Table 1, the ceramic powder 1 The generated heat can be efficiently transferred to the bottomed cylindrical body 3.

These insulating powders 2 have an average particle diameter of 0.5 to 10 μm, and the thickness t ₂ when filled is preferably 1 mm or less. This is because the thermal conductivity when the thickness t ₂ is more than 1mm is lowered. Moreover, thermal conductivity can be improved by filling with a high density so that a filling rate may be 50% or more.

Furthermore, the thermal conductivity can be further increased by impregnating the insulating powder 2 with a liquid having good heat resistance and insulating properties such as silicon oil.

On the other hand, although the bottomed cylindrical body 3 uses a metal material such as copper or aluminum having a good thermal conductivity, stainless steel or other iron-based alloys can be used as necessary. In addition, the thickness t ₁ of the bottomed cylindrical body 3 is preferably 1 mm or less in order to increase the thermal efficiency.

  Furthermore, ceramics such as alumina and silicon nitride are used as the ceramic body 11 constituting the ceramic heater 1, and high-melting point metals such as W, Mo, and Mn and metal compounds such as TiC, TiN, and WC are used as the heating resistor 12. Use. When the cylindrical ceramic heater 1 is manufactured, for example, a material forming the heating resistor 12 is applied to a predetermined pattern as a paste on a ceramic sheet-shaped molded body, and the sheet-shaped molded body is applied to another circular shape. It can be obtained by overlapping the whole of the columnar molded body so as to cover the whole and firing and integrating the whole.

  In addition, although the column-shaped ceramic heater 1 and the cylindrical bottomed cylindrical body 3 were shown in the figure, it cannot be overemphasized that it can be set as various shapes, such as not only this but prismatic shape and plate shape. The ceramic sheathed heater of the present invention is particularly suitable for liquid heating such as a water heater for a bathtub, but can be suitably used for various other applications.

  Next, another reference example will be described.

  The ceramic sheathed heater shown in FIG. 3 is basically the same as the reference embodiment described above, but has a feature in the joining structure of the ceramic heater 1 and the bottomed cylindrical body 2.

  That is, a cylindrical flange member 20 is joined to the opening of the bottomed cylindrical body 2, and the ceramic heater 1 and the flange member are connected to the end of the flange member 20 opposite to the bottomed cylindrical body 2. A pressing member 21 is arranged between the two.

  The pressing member 21 is a cylindrical body having an inner diameter that is substantially the same as the outer diameter of the ceramic heater 1, and includes a screw portion 21 a on the outer periphery of the tip, and also has a screw portion 20 a on the inner diameter on the flange portion 20 side. . The insulating powder 2 can be pressed and the filling density can be increased by screwing the pressing member 21 onto the screw portion 20a.

  Further, a notch 21 b is formed on the rear end side of the pressing member 21, and this portion is filled with an adhesive 22 and joined to the ceramic heater 1. At this time, in order to increase the bonding force, it is more preferable to form a recess 14 on the surface of the ceramic body 11 on the ceramic heater 1 side. For example, when the ceramic heater 1 is manufactured, holes are formed in the outermost ceramic green sheet and stacked, and the concave portion 14 can be formed on the surface as shown in FIG. In this case, it is preferable that the recess 14 has a diameter of 0.5 mm or more and a depth of 0.1 mm or more, and an epoxy resin, a silicone resin, or an inorganic adhesive is used as the adhesive 22.

  Thus, by providing the pressing member 21, the packing density of the insulating powder 2 can be increased to improve the thermal conductivity, and the ceramic heater 1 can be firmly positioned with respect to the bottomed tubular body 2. The position of the ceramic heater 1 can be prevented from shifting during use.

  Moreover, although the structure which screws the pressing member 21 in the said reference example was shown, what is necessary is just a joining structure which can press the insulating powder 2 other than screwing.

  Furthermore, the flange member 20 is also provided with a threaded portion 20b on the outer peripheral surface side to facilitate joining with other members. In addition, in this embodiment, although the bottomed cylindrical body 2 and the flange member 20 were joined as separate bodies, both can be integrally formed.

The material of the ceramic heater 1 and the bottomed cylindrical body 2 is the same as that of the embodiment of FIGS. 1 and 2, and the flange member 20 and the pressing member 21 are made of stainless steel, copper, It is made of a metal such as brass or titanium. Further, the material of the insulating powder 3 embodiment illustrates boron nitride (BN), silicon nitride (Si3 N4) of Fig. 1 and 2, aluminum nitride (AlN), is not limited to silicon carbide (SiC), Al ₂ O ₃ and MgO can also be used, and metal powder such as Cu and Al can be used instead of the insulating powder. Further, as the adhesive 22, an epoxy-based or silicon-based resin, glass, an inorganic adhesive, or the like is used.

  Next, a fluid heating apparatus using a ceramic sheathed heater will be described.

  In the fluid heating apparatus shown in FIG. 5, the ceramic heater 1 is inserted into the metal bottomed cylindrical body 3 through the insulating powder 2, and the bottomed cylindrical body 3 and the metal outer tube 30 are joined. Composed. In addition, a water inlet hose 31 and a water discharge hose 32 are joined to the metal outer pipe 30. When a fluid such as water is supplied from the water inlet hose 31 while the ceramic heater 1 is energized and heated, it is heated. It can be sent out from the water discharge hose 32 to the outside.

  At this time, since the ceramic heater 1 is covered with the bottomed cylindrical body 3, the fluid does not come into contact therewith. Therefore, it is possible to prevent generation of cracks due to heat shock and adhesion of scale.

  In FIG. 2, the opening of the bottomed cylindrical body 3 is closed with the packing 33, but it is more preferable if a pressing member as shown in FIG. 3 is provided.

  Next, an embodiment of the present invention will be described.

  In the fluid heating apparatus shown in FIG. 6, the ceramic body 11 constituting the ceramic heater 1 is formed into a cylindrical shape, and both the outer peripheral surface and the inner peripheral surface of the ceramic body 11 are provided with double existence through the insulating powder 2. The bottomed cylindrical body 3 is covered and the bottomed cylindrical body 3 and the metal outer tube 30 are joined. Of the bottomed cylindrical body 3, the inner tube 3 a covering the inner peripheral surface of the ceramic body 11 is led out to the rear end of the ceramic heater 1 and joined to the water inlet pipe 31, and the water discharge pipe 32 is a metal outer tube. 30.

  If a fluid such as water is supplied from the water intake hose 31 while energizing and heating the ceramic heater 1, the ceramic heater 1 is heated on the inner surface of the ceramic heater 1 when passing through the inner tube 3 a and passes through the outer metal tube 30. In this case, the outer surface of the ceramic heater 1 is heated, so that it can be heated efficiently.

Reference example 1
As a reference for the examples of the present invention, the ceramic sheathed heater shown in FIGS.

  A heating resistor 12 made of W was embedded in a ceramic body 11 made of alumina ceramic to produce a cylindrical ceramic heater 1 having a diameter of 10 mm and a length of 120 mm. On the other hand, the ceramic heater 1 is inserted into a bottomed cylindrical body 3 made of stainless steel and having an outer diameter of 11.5 mm, an inner diameter of 10.5 mm, and a length of 122 mm, and the two are held so as not to contact each other. The gap is filled with the insulating powder 2 made of boron nitride or silicon carbide, and the bottomed cylindrical body 3 is vibrated to increase the packing density of the insulating powder 2. Finally, an insulating pipe (not shown) was provided on the lead wire 13 of the ceramic heater 1, and a metal cover 4 was arranged at the rear end portion, and was fixed by caulking at the rear end portion of the bottomed cylindrical body 3.

  In addition, when filling with the insulating powder 2, it can also be performed as follows. That is, the gap between the bottomed cylindrical body 3 and the ceramic heater 1 can be filled with a slurry in which the insulating powder 2 is dispersed in a solvent using a dispersant, and then heated to evaporate the solvent. .

  As described above, as this reference example, a ceramic sheathed heater was obtained in which the insulating powder 2 was made of boron nitride or silicon carbide, and the thickness t2 when filled was 0.25 mm.

  On the other hand, as a comparative example of this reference example, a metal (copper) powder was filled instead of the insulating powder 2, and a sheathed heater was manufactured in the same manner as in the above-described example.

  About these invention examples and comparative examples, after applying a voltage of 100 V and comparing the heating efficiency when used for water heating, a voltage exceeding a specified value is applied to each ceramic heater 1 consciously. Cracks were generated. At this time, a resistance value R between the heating resistor 13 and the bottomed cylindrical body 3 and a leakage current generated in water during use were measured.

  The results are as shown in Table 2. From this result, in the comparative example, the resistance value between the heating resistor 13 and the bottomed cylindrical body 3 when the crack occurred was low, and a leakage current exceeding 10 mA flowed in water, so there was a risk of electric shock or the like.

On the other hand, in this reference example, even if a crack occurs, the resistance value R between the heating resistor 13 and the bottomed cylindrical body 3 exceeds 10 ⁴ Ω, so that the leakage current in water should be 10 mA or less. There was no fear of electric shock. Moreover, since the insulating powder 2 has sufficient thermal conductivity, water could be heated satisfactorily.

Example 1
Next, as an example of the present invention, a fluid heating apparatus shown in FIG. 6 was prototyped. An alumina ceramic heater 1 having an outer diameter of 8 mm, an overall length of 120 mm, and a heating part length of 85 mm was inserted into a bottomed cylindrical body 3 having an outer diameter of 12 mm and an inner diameter of 10 mm. In this apparatus, 3 liters of water was poured and the temperature was raised from 25 ° C. to 45 ° C. over 5 minutes.

  The average power at this time was 906.1 W, and the thermal efficiency was 92.4%. As a comparative example, the same measurement was performed on an apparatus that does not include the bottomed cylindrical body 3. The average power was 902.2W and the thermal efficiency was 92.8%. From this result, it can be seen that the fluid heating device of the present invention exhibits excellent thermal efficiency similarly to the conventional example, even when the bottomed cylindrical body 3 is provided.

It is a longitudinal cross-sectional view of the ceramic sheathed heater which shows the reference example of this invention. It is the XX sectional view taken on the line in FIG. It is a longitudinal cross-sectional view which shows the ceramic sheathed heater which shows the reference example of this invention. FIG. 4 is a partial side view of the ceramic heater shown in FIG. 3. It is sectional drawing of the fluid heating apparatus using the ceramic sheathed heater which shows the reference example of this invention. It is sectional drawing of the fluid heating apparatus using the ceramic sheathed heater of this invention.

Explanation of symbols

1: Ceramic heater 11: Ceramic body 12: Heating resistor 13: Lead wire 14: Recess 2: Insulating powder 3: Bottomed cylindrical body 4: Cover 20: Flange member 21: Press member 22: Adhesive 30: Metal Outer tube

Claims (2)

A cylindrical ceramic body with a heating resistor embedded therein is inserted into a double-bottomed cylindrical body that simultaneously covers the inner and outer peripheral surfaces of the ceramic body, and a powder is interposed between the two. A fluid heating apparatus characterized by allowing fluid to pass through both the inner surface side and the outer surface side of the bottomed cylindrical body. Insulating powder is interposed between the heating resistor and the bottomed cylindrical body, and the resistance at room temperature between the heating resistor and the bottomed cylindrical body when a crack occurs in the ceramic body. The fluid heating device according to claim 1, wherein the value is 10 ⁴ Ω or more.

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