JP2013181719A - Superheated steam generating device and method of generating superheated steam - Google Patents

Abstract

PROBLEM TO BE SOLVED: To surely prevent fine powder and the like generated by frictional contact of a heating element and porous bodies, from being included in superheated steam without degrading heat efficiency, startability, controllability and responsiveness of a superheated steam generating device.SOLUTION: A superheated steam generating device supplies water (W) to hollow sections (7) of porous bodies by capillary action of porous bodies (40, 41). The porous bodies are composed of the first porous body (40) absorbing water, and the second porous body (41) disposed inside of the first porous body. The superheated steam generating device evaporates and superheats the water at pore outlet sections of the porous bodies by a heating element (42) kept into contact with an inner wall surface (46) of the hollow section, to generate superheated steam (S). The second porous body has spalling resistance and heat conductivity higher than those of the first porous body.

Description

  The present invention relates to a superheated steam generator and a superheated steam generation method, and more specifically, to generate superheated steam in a very short time using a capillary water supply action of a porous body and a heating action of a heating element. The present invention relates to a superheated steam generator and a superheated steam generation method.

  Superheated steam heated to a temperature equal to or higher than the saturated steam temperature is used industrially in various plant processes, or is used for drying, heating, sterilization, and the like of wood, food, medical equipment, and the like. In recent years, household cooking appliances and the like using such superheated steam are spreading in the market, and the use of superheated steam has been especially expanded in recent years. In this kind of household cooking appliances, the superheated steam is generated by immersing an electric heater in the water in the water tank to heat the water in the water tank, and reheating the water vapor generated by the vaporization of the water. For example, Japanese Unexamined Patent Application Publication No. 2004-186103 (Patent Document 1) discloses a steam generator for a cooker provided with a steam generating heater and a steam superheater. In this type of apparatus, a relatively complicated apparatus configuration is adopted in which a two-stage process consisting of a water vapor generation process for vaporizing water to generate water vapor and a water vapor superheating process for superheating water vapor is executed step by step. . However, when superheated steam is generated by such a method, the structure of the apparatus increases in size, and considerable time is required for the pre-process from the start of the apparatus to the generation of water vapor. For this reason, development of the apparatus which can generate superheated steam quickly with a simple apparatus or method is desired.

  The present inventors have developed a superheated steam generator and a superheated steam generation method that can quickly generate superheated steam without adopting a complicated apparatus configuration, and that are excellent in controllability and responsiveness. This is proposed in Japanese Patent Application No. 2007-15920 (Japanese Patent Laid-Open No. 2009-248042 (Patent Document 2)).

  11 and 12 are a schematic perspective view and a longitudinal sectional view showing a configuration of the superheated steam generator described in Patent Document 2. FIG.

  The superheated steam generator A has a porous body B, a liquid tank C, a superheated steam delivery pipe D, and a coiled heating element E. The heating element E is disposed in the hollow portion N of the porous body B. The hollow portion N constitutes a water vapor channel having a circular cross section. The upstream end of the superheated steam delivery pipe D is connected to the outlet opening of the hollow part N. The downstream end of the superheated steam delivery pipe D is connected to an external device (not shown) or communicates with an internal region of the external device. A lead wire F is connected to a heating element E made of a heating wire such as a coiled nichrome wire or a Kanthal wire. An electric circuit including a voltmeter and an ammeter is connected to the terminal of the lead wire F. The electrical circuit is connected to an AC power source. A water purification device G is provided in the superheated steam generator A in association with the liquid tank C. The water supply pipe J is connected to the inlet of the water purification device G, and the makeup water supply pipe K is connected to the outlet of the water purification device G.

  The water purification device G supplies purified water into the liquid tank C. The porous body B is at least partially immersed in the liquid bath of the liquid tank C. The replenishing water W of the liquid bath is absorbed by the porous body B due to the capillary phenomenon of the porous body B, and flows inward toward the heating element E in the porous body B. When the heating element E is energized, the surface temperature of the heating element E is heated to a high temperature of 500 ° C. or higher, and steep water evaporation occurs in the liquid film portion of the meniscus formed in the inner peripheral surface pore portion of the hollow portion N. . By adopting a material having a relatively low thermal conductivity as the porous body B, for example, a refractory heat-insulating brick, the heat release of the porous body B is suppressed, and the heat generation of the heating element E is concentrated and effective. Since the gas is vaporized, the time from the start of energization to the start of vaporization and overheating of water can be greatly reduced. The prototype of the superheated steam generator having this configuration has already been confirmed to generate superheated steam at 300 to 400 ° C. when about 10 seconds have elapsed after the start of energization. Thus, superheated steam can be generated in an extremely short time and efficiently.

JP 2004-186103 A JP 2009-248042

  Thus, in the superheated steam generator using the porous body, the heat insulating performance is inferior. Therefore, when a porous body having a dense structure having high thermal conductivity is used, a relatively large amount of heat generated by the heating element is generated. Since heat is dissipated to the outside of the porous body, the heating element is difficult to effectively vaporize and overheat water, and therefore it is difficult to ensure the thermal efficiency, startability, controllability and responsiveness of the device as desired. . For this reason, in such a superheated steam generator, it is required not only to ensure the capillary action of the porous body, but also to ensure the heat insulation performance (and hence low thermal conductivity) of the porous body. However, a porous body that exhibits a sufficient capillary action and has a low thermal conductivity generally has a low hardness or a relatively fragile surface, and therefore has a spalling resistance (peeling resistance). Generally inferior.

  On the other hand, the heating element in contact with the porous body repeats the thermal expansion / contraction behavior, and therefore repeatedly displaces relative to the porous body surface. The outer surface of the heating element rubs the inner wall surface of the porous body due to such relative displacement, and as a result, the porous material on the inner wall surface of the hollow part is scraped by frictional contact between the heating element and the inner wall surface of the hollow part. Is likely to occur. When the fine porous material particles or powder cut by the heating element are sent to the superheated steam delivery pipe together with the superheated steam, the superheated steam containing the fine powder of the porous body as an impurity is transferred to the external device or the like. In particular, the superheated steam generator with the above configuration is preferably used for heating and sterilizing foods, medical equipment, etc., and for drying precision machine parts and electronic parts. There are difficult circumstances.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide a superheated steam generator and a superheated steam generation method for generating superheated steam by a heating element built in a hollow portion of a porous body. Therefore, it is possible to reliably prevent the superheated steam from containing fine powder that can be generated by frictional contact between the heating element and the porous body without impairing the thermal efficiency, startability, controllability and responsiveness of the apparatus. The present invention provides a superheated steam generator and a superheated steam generation method.

In order to achieve the above object, the present invention has a porous body that absorbs water for water vapor generation from the outer surface by capillary action and supplies the water to the inner wall surface of the hollow portion, and contacts the inner wall surface of the hollow portion. In the superheated steam generator for generating superheated steam by evaporating and superheating the water in the pores of the porous body by a heating element that extends near or close to the inner wall surface,
The porous body has a first porous body that absorbs the water from the outer surface by capillary action, and a second porous body that is disposed inside the first porous body and forms the hollow portion. And
The second porous body has a spalling resistance and thermal conductivity that is higher or larger than the spalling resistance and thermal conductivity of the first porous body. A superheated steam generator, which is disposed inside the first porous body so that the water absorbed by the porous body is supplied toward the hollow portion by capillary action of the porous body. provide.

The present invention also absorbs water for water vapor generation by the capillary action of the porous body and supplies it to the inner wall surface of the hollow portion of the porous body so as to be in contact with or close to the inner wall surface of the hollow portion. In the superheated steam generation method in which the water is vaporized and heated in the pores of the porous body by a heating element extending along the wall surface to generate superheated steam,
The first porous body that absorbs the water from the outer surface by capillary action, and has a spalling resistance and thermal conductivity that is higher or greater than the spalling resistance and thermal conductivity of the first porous body. And the second porous body that forms the hollow portion, the first porous body is disposed outside the second porous body, and the water absorbed by the first porous body is porous. To the hollow part by the capillary action of
There is provided a method for generating superheated steam, characterized in that the heat of the heating element vaporizes and superheats the water in the pores of a porous body to generate superheated steam.

  In the present invention, superheat is performed by a composite structure formed by combining different porous bodies (first and second porous bodies) having different spalling resistance and thermal conductivity, or a porous body having a double tube structure or a multi-tube structure. Constructing a porous body of a water vapor generating device, forming the hollow portion by a second porous body (inner porous body) having relatively excellent spalling resistance and relatively high thermal conductivity, Water absorption and heat insulation are performed by the first porous body (outer porous body) having relatively low spalling resistance and thermal conductivity, thereby ensuring the desired water absorption action and heat insulation of the entire porous body. At the same time, it is intended to prevent generation of powder or the like due to frictional contact between the heating element and the porous body.

  That is, according to the above-described configuration of the present invention, water for generating water vapor can be supplied to the inner wall surface of the hollow portion using the capillary action of each porous body (first and second porous bodies). In addition, the use of a porous material having physical properties that are highly resistant to repeated thermal shocks as the inner porous material (second porous material) improves the spalling resistance (peeling resistance) of the inner wall surface of the hollow portion, and generates heat. It is possible to reliably prevent generation of fine porous material particles or powder in the hollow portion by frictional contact between the body and the inner wall surface of the hollow portion. Moreover, since the 2nd porous body is arrange | positioned inside the 1st porous body with relatively low heat conductivity, the heat insulation performance of the whole porous body can be ensured. According to the inventor's experiment, the superheated steam generator using the porous body having such a composite structure has substantially the same or equivalent thermal efficiency as the superheated steam generator using the porous body having a single structure. In addition, startability, controllability and responsiveness can be exhibited.

  The concept of the present invention is applicable not only to the generation of superheated steam but also to the vaporization and superheating of a liquid that can be sucked up by the capillary action of a porous body. Examples of usable liquids include various liquid fuels.

From such a viewpoint, the present invention has a porous body that absorbs liquid for generating steam from the outer surface by capillary action and supplies the liquid to the inner wall surface of the hollow portion, and contacts the inner wall surface of the hollow portion. In the superheated steam generator for generating superheated steam by vaporizing and superheating the liquid in the pores of the porous body by a heating element extending along or close to the inner wall surface,
The porous body includes a first porous body that absorbs the liquid from the outer surface by capillary action, and a second porous body that is disposed inside the first porous body and forms the hollow portion. Have
The second porous body has a spalling resistance and thermal conductivity that is higher or larger than the spalling resistance and thermal conductivity of the first porous body. The superheated steam generator is disposed inside the first porous body so that the liquid absorbed by the porous body is supplied toward the hollow portion by capillary action of the porous body. I will provide a.

Further, the present invention absorbs liquid for generating steam by the capillary action of the porous body and supplies it to the inner wall surface of the hollow portion of the porous body, and is in contact with or close to the inner wall surface of the hollow portion. In the superheated steam generation method in which the liquid is vaporized in the pores of the porous body by the heating element extending along the inner wall surface and is superheated to generate superheated steam.
The first porous body that absorbs the liquid from the outer surface by capillary action, and has a spalling resistance and thermal conductivity that is higher or greater than the spalling resistance and thermal conductivity of the first porous body. And the second porous body that forms the hollow portion, the first porous body is disposed outside the second porous body, and the liquid absorbed by the first porous body is porous. Supply toward the hollow part by the capillary action of the body,
There is provided a method for generating superheated steam, characterized in that the liquid is vaporized and superheated in the pores of a porous body by the heat of the heating element to generate superheated steam.

  According to the superheated steam generator and superheated steam generation method of the present invention, in the superheated steam generator and superheated steam generation method for generating superheated steam by the heating element built in the hollow portion of the porous body, the thermal efficiency and startability of the apparatus , Preventing loss of fine powder due to frictional contact between the heating element and the porous body without impairing controllability and responsiveness, thereby ensuring that the fine powder is contained in superheated steam. Can be prevented.

  Further, according to the superheated steam generator and superheated steam generation method of the present invention, in the superheated steam generator and superheated steam generating method for generating superheated steam by the heating element built in the hollow portion of the porous body, the thermal efficiency of the apparatus, Without impairing the startability, controllability and responsiveness, it prevents the generation of fine powder due to frictional contact between the heating element and the porous body, so that the fine powder is included in the superheated steam. Can be reliably prevented.

FIG. 1 is a longitudinal sectional view showing a preferred embodiment of a superheated steam generator to which the present invention is applied. 2 is a cross-sectional view taken along the line II of FIG. FIG. 3 is a perspective view showing a configuration of the superheated steam generator shown in FIGS. 1 and 2. FIG. 4 is a perspective view showing the configuration of the vaporization / superheater. FIG. 5 is a cross-sectional view showing the relationship between the coiled heating element and the porous body. FIG. 6 is an enlarged view of a portion “a” shown in FIG. 7A is an enlarged cross-sectional view showing a contact portion between the coiled heating element and the inner wall surface of the hollow portion, and FIGS. 7B and 7C are partial enlarged cross-sectional views of FIG. 7A. It is. FIG. 8 is an enlarged view of a “b” portion shown in FIG. FIG. 9: is a schematic sectional drawing which shows the structure of the cooking appliance provided with the superheated steam generator which concerns on the Example of this invention. 10A, 10B, and 10C are a plan view, a front view, and a perspective view showing the structure of the vaporization / superheater that constitutes the superheated steam generator shown in FIG. FIG. 11 is a perspective view showing a configuration of a superheated steam generator according to the prior art. FIG. 12 is a longitudinal sectional view of the superheated steam generator shown in FIG.

  According to a preferred embodiment of the present invention, the outer surface of the second porous body has water or liquid absorbed or absorbed by the first porous body on the inner wall surface by the capillary action of the second porous body. Superheated steam delivery means or superheated steam that is in contact with or close to the inner side surface of the first porous body and feeds the superheated steam or superheated steam generated in the hollow portion from the hollow portion to the outside of the porous body so as to be supplied The delivery means is provided in the superheated steam generator or the superheated steam generator.

Preferably, the heating element is composed of a heating wire that is in contact with or close to the inner wall surface of the hollow portion at an interval, and the inner wall surface near the heating wire has a drying zone whose surface is dried by the heat of the heating wire. A wet inner wall zone is formed between the drying zones while being spaced apart. More preferably, the hollow portion has a circular cross section, and the heating element is made of a coil-shaped electric heater that is in contact with or close to the inner peripheral surface of the hollow portion and whose axis is oriented in the axial direction of the hollow portion. . Preferably, the heat flux at the contact portion between the inner wall surface and the electric heater is set to 1 MW / m ² or more.

According to a further preferred embodiment of the present invention, the second porous body is made of an alumina, mullite, or silicon carbide ceramic tube inserted or fitted into a hole or hollow portion of the first porous body. Become. Preferably, the first porous body has a heat conductivity of 0.5 W / m · K or less, a linear expansion coefficient of 10 × 10 ⁻⁶ / ° C. or more, and a porosity (porosity) of more than 50%. The porous body is made of a porous material such as brick, and the second porous body has a higher thermal conductivity, a lower linear expansion coefficient, and a lower porosity (for example, a porosity of 50% or less). Of) a relatively high strength ceramic tube. For example, the ceramic tube constituting the second porous body has a thermal conductivity of 10 times or more and a compressive strength of 30 times or more compared to the refractory heat-insulating brick constituting the first porous body. Note that the spalling resistance is generally higher as the thermal conductivity is higher, higher as the linear expansion coefficient is lower, higher as the porosity is lower, and higher as the compressive strength is higher. The test method for the spalling resistance of the refractory heat insulating brick is defined in “JIS R 2657 Spalling Test Method for Refractory Brick and Refractory Insulating Brick”.

  Preferably, the second porous body has an average pore diameter and / or mode diameter smaller than the average pore diameter and / or mode diameter of the first porous body, and the minimum diameter of the pores of the second porous body. Is smaller than the minimum diameter of the pores of the first porous body, the maximum diameter of the pores of the second porous body is larger than the minimum diameter of the pores of the first porous body, and the second porous body Has a pore size distribution smaller than the maximum pore size of the first porous body. For example, the first porous body has an average pore diameter of 5 μm or more, and the second porous body has an average pore diameter of less than 5 μm.

  In a preferred embodiment of the present invention, the first porous body at least partially includes a porous inorganic ion exchanger having a cation exchange capacity and heat resistance. The inorganic ion exchanger constituting at least part of the first porous body removes scale components contained in the water absorbed by the first porous body. The water purified by the scale removal action of the inorganic ion exchanger is supplied to the inner wall surface of the hollow portion by the capillary action of the second porous body. As the inorganic ion exchanger, a porous molded body mainly composed of natural or synthetic zeolite can be preferably used. According to such a configuration, it is possible to prevent scale deposition at the pore outlet portion of the second porous body and blockage of the pores associated therewith, and reduce the replacement frequency of the second porous body.

 FIG. 1 is a longitudinal sectional view showing a preferred embodiment of a superheated steam generator to which the present invention is applied, and FIG. 2 is a sectional view taken along the line II of FIG. FIG. 3 is a perspective view showing the configuration of the superheated steam generator, and FIG. 4 is a perspective view showing the configuration of the vaporization / superheater.

  The superheated steam generator 1 includes a casing 2 made of metal or latchac, a superheated steam feed pipe 3 extending outward from the end wall 21 of the casing 2, a vaporization / superheater 4 accommodated in the casing 2, It comprises a water supply device 5 for supplying makeup water to the vaporization / superheater 4.

  The casing 2 is formed of a box or a container having a rectangular parallelepiped shape as a whole, and has front and rear end walls 21, 22, a top wall 23, a bottom wall 24, and left and right side walls 25, 26. A pair of circular openings 20 are formed in the end wall 21 of the casing 2. The opening 20 has a diameter of 10 mm, for example. A raised portion 27 having an opening 28 is formed on the top wall 23 of the casing 2. A resin water supply bottle 51 constituting the water supply device 5 is inserted into the opening 28. The casing 2 has, for example, an external dimension of width 100 mm × height 60 mm × length 140 mm (the height excludes the height of the raised portion 27). Note that the casing 2 does not necessarily have to be a rectangular parallelepiped or a casing or container having a combination of rectangular parallelepipeds. Can be used as

  The superheated steam supply pipe 3 is made of a metal tube having a true circular cross section that is curved downward as a whole. The upstream end 31 of the superheated steam feed pipe 3 passes through the circular opening 20 of the casing 2 without contacting the end wall 21 and is connected to the downstream (discharge side) end of the inner pipe 41 described later. The downstream end 32 of the superheated steam feed pipe 3 is connected to an external device (not shown) such as a cooker, or is opened to an internal region of the external device. The superheated steam feed pipe 3 sends the superheated steam S generated by the vaporization / superheater 4 to an external device.

  The vaporization / superheater 4 includes a porous body 40 disposed in the casing 2, a porous inner tube 41 disposed in the porous body 40, and a coil-shaped heat generation disposed in the inner region of the inner tube 41. And a body 42. The porous body 40 and the inner tube 41 are made of a ceramic molded body having a large number of communicating voids, and have heat resistance and electrical insulation. The porous body 40 constitutes the aforementioned first porous body, and the inner tube 41 constitutes the aforementioned second porous body.

The porous body 40 has dimensions of, for example, width 90 mm × height 50 mm × length 90 mm. The porous body 40 is, for example, a commercially available fire-resistant insulating brick (product of Isolite Industry Co., Ltd., model B5, main component: SiO ₂ 55%, Al ₂ O ₃ 41%, thermal conductivity: 0.33 [W / (m K)]) and has various physical properties such as average pore diameter = 9 μm, mode diameter = 90.6 μm, porosity = 62.3%, bulk specific gravity of about 0.8, and compressive strength of about 1.7 MPa. A pair of through holes 43 are formed in the porous body 40. The through-hole 43 has a uniform true circular cross section over the entire length, and the diameter of the through-hole 43 is slightly larger than the diameter of the circular opening 20. The diameter of the through hole 43 is set to 12.5 mm, for example.

  As a modification, a porous inorganic ion exchanger having cation exchange capacity and heat resistance is used as the porous body 40, or the porous body 40 is partially formed by such a porous inorganic ion exchanger. You may comprise. In particular, in the present invention, as described later, a dense porous body having a relatively small pore diameter is used as the inner tube 41. Therefore, scale components (calcium, magnesium, etc.) contained in water supplied to the inner tube 41 are used. The removal of the compound) is an effective means for preventing the pores of the inner tube 41 from being blocked by the precipitation of the scale component and extending the life of the inner tube 41. For example, a porous molded body mainly composed of natural or synthetic zeolite is used as the porous body 40, and scale components contained in water flowing through the pores of the porous body 40 are removed by ion exchange. In addition, it is possible to prevent scale precipitation at the pore outlet portion of the inner tube 41 and blockage of the pores associated therewith, and reduce the replacement frequency of the inner tube 41.

  As shown in FIG. 2, the inner tube 41 is formed of a cylindrical body having a uniform cross section over the entire length. As the inner tube 41, an alumina ceramic tube having a wall thickness of 2 mm, an inner diameter of 8.8 mm, an outer diameter of 12.5 mm, a total length of 72 mm, and an average pore diameter of 3 μm can be suitably used. The inner tube 41 also has a mode diameter that is smaller than the mode diameter of the porous body 40. If all the pores of the inner tube 41 have a smaller pore diameter than the pores of the porous body 40, the flow resistance of water during water absorption increases in the inner tube 41, and the porous body 40 and the inner tube 41 Capillary action is reduced. Therefore, in the inner tube 41, the minimum diameter of the pores of the inner tube 41 is smaller than the minimum diameter of the pores of the porous body 40, and the maximum diameter of the pores of the inner tube 41 is smaller than the pores of the porous body 40. The pore diameter distribution is larger than the minimum diameter, and the maximum diameter of the pores of the inner tube 41 is smaller than the maximum diameter of the pores of the porous body 40.

The inner tube 41 has a hollow portion 7 having a true circular cross section, and the hollow portion 7 communicates with a tube inner region of the superheated steam supply tube 3. For example, the alumina ceramic tube constituting the inner tube 41 has a volume ratio of particles (aggregate) 40 to 45 vol%, binder 10 to 15 vol%, pores 30 to 50 vol%, and thermal expansion coefficient 7 to 8 ( 10 ⁻⁶ / ° C.), thermal conductivity 4 to 5 kcal / mhr ° C. (4.6 to 5.8 [W / (m · K)]), tensile strength (tensile strength) 150 to 200 kg / cm ² (15 to ²⁰ MPa), bending resistance It has various physical properties such as force (bending strength) 300 to 500 kg / cm ² (29 to 49 MPa), coercive pressure (compression strength) 700 to 1000 kg / cm ² (69 to 98 MPa), and bulk specific gravity 2.0 to 2.4. As the inner tube 41, a mullite ceramic tube having the same average pore diameter, mode diameter and physical properties (however, a coefficient of thermal expansion of 4 to 5 (10 ⁻⁶ / ° C.), a bulk specific gravity of 1.7 to 2.0), or , Silicon carbide ceramic tubes (however, thermal expansion coefficient 4 to 5 (10 ⁻⁶ / ° C.), thermal conductivity 7 to 8 kcal / mhr ° C., bulk specific gravity 1.6 to 1.9) may be used. . Such a ceramic tube has a thermal conductivity of 10 times or more that of the porous body 40 and a compressive strength of 40 times or more that of the porous body 40. As the ceramic tube constituting the inner pipe 41, a cylindrical filter medium available on the market as a filter for water treatment such as clean water may be used. Moreover, it is also possible to use a grindstone having water permeability as the inner tube 41.

  As shown in FIG. 1, the ceramic plug 44 is inserted into the through hole 43 of the porous body 40 from the water supply device 5 side. The plug 44 is fitted into the hollow portion 7 on the water supply device 5 side, and closes the upstream opening end of the hollow portion 7. On the other hand, the downstream opening of the hollow portion 7 located on the opening 20 side communicates with the in-pipe flow path of the superheated steam supply pipe 3. The outer diameter of the inner tube 41 is larger than the diameter of the opening 20, and the end surface 45 of the inner tube 41 is held on the end wall 21 of the casing via a heat insulating material (not shown).

  FIG. 5 is a cross-sectional view showing the relationship between the coiled heating element 42, the inner tube 41 and the porous body 40.

  As shown in FIG. 5, the coiled heating element 42 is composed of a coiled nichrome wire or Kanthal wire having a circular cross section that is in contact with or in close contact with the inner wall surface 46 of the inner tube 41 over the entire circumference, and generates heat when energized. For example, the heating element 42 is made of a heating wire (nichrome wire or Kanthal wire) having a diameter d (L 1) = 0.35 mm, and is arranged spirally along the inner wall surface 46, and is in close contact with the inner wall surface 46. The pitch interval of the heating elements 42 is set to about 2.5 mm, and the number of turns of the Kanthal wire is set to about 25 to 30 turns per length of about 70 mm in the axial direction.

  As shown in FIGS. 1 and 3, lead wires 61 are connected to the respective end portions of the heating element 42. Each lead wire 61 is connected to a power supply side terminal (not shown) of the power switch 60. The power switch 60 includes a manually operated ON-OFF switch that can be operated with a finger or a remote-operated ON-OFF switch. A power supply side terminal (not shown) of the power switch 60 is connected to the electric circuit 6 via a pair of lead wires 62. The electric circuit 6 includes a voltmeter and an ammeter, and is connected to an AC power supply (AC100V). If desired, the power switch 60 may be directly connected to the AC power source by a power cord or the like, or a voltage regulator or the like for dropping the voltage of the AC power source may be incorporated in the electric circuit 6. The electric circuit 6 applies an AC voltage to the heating element 42 by turning on the power switch 60 to cause the heating element 42 to generate heat.

  As shown in FIG. 1, the water supply device 5 includes a resin water supply bottle 51 that can store makeup water W, an automatic water supply valve device 53 connected to a water supply port portion 52 of the bottle 51, and a valve device 53. A heat-resistant sponge 54 made of resin that absorbs the replenished replenishing water W is formed. The heat-resistant sponge 54 has an open cell structure. The valve device 53 detects the water absorption state of the heat-resistant sponge 54 and automatically opens the water supply port portion 52 so that the makeup water W in the bottle 51 flows out to the heat-resistant sponge 54. When the replenishment water W in the bottle 51 decreases, after the bottle 51 is pulled out from the opening 28, another full bottle 51 is inserted into the opening 28 or refilled into the bottle 51. The water W may be refilled and reinserted into the opening 28, and the water supply port portion 52 may be connected to the valve device 53.

  As shown in FIG. 2, the heat-resistant sponge 54 is filled in a region between the inner surface of the casing 2 and the outer surface of the porous body 40. The makeup water W that has penetrated into the heat-resistant sponge 54 spreads over the entire outer surface of the porous body 40. The porous body 40 having a large number of communicating voids absorbs water from the heat-resistant sponge 54 by capillary action. The water W absorbed by the porous body 40 flows toward the hollow portion 7 as indicated by arrows in FIGS. 2 and 5.

  FIG. 6 is an enlarged view of a portion “a” shown in FIG. FIG. 6 schematically shows a large number of pores 47 and 48 formed inside the porous body 40 and the inner tube 41 by the communication gap.

  The inner tube 41 is also made of a ceramic molded body having a large number of communicating voids, and has heat resistance and electrical insulation. As described above, the average pore diameter and mode diameter of the inner tube 41 are smaller than the average pore diameter and mode diameter of the porous body 40, respectively. The outer peripheral surface of the inner tube 41 and the inner peripheral surface of the through-hole 43 partially contact with each other by fine unevenness or unevenness, and at least partially form a minute gap of about 5 μm that maintains the capillary action. If desired, such a minute gap may be formed uniformly over the entire outer periphery of the inner tube 41.

  The pores 47 and 48 of the porous body 40 and the inner tube 41 communicate in series, or communicate via a liquid film formed at the boundary portion (micro gap) between the porous body 40 and the inner tube 41. . The water W sucked into the pores 47 by the capillary phenomenon of the porous body 40 is further sucked into the pores 48 by the capillary phenomenon of the inner tube 41.

  7A is an enlarged cross-sectional view showing a contact portion between the coiled heating element 42 and the inner wall surface 46 of the inner tube 41. FIGS. 7B and 7C are shown in FIG. FIG. FIG. 8 is an enlarged view of a “b” portion shown in FIG.

  As shown in FIG. 8, the water in the pores 48 is bent by the surface tension at the opening 49 to form a meniscus M. The meniscus M is formed as a thin water film all around the opening 49. When the heating element 42 is energized, the surface temperature of the heating element 42 reaches 500 ° C. or higher, for example, 700 ° C. The heat H of the heating element 42 conducted from the heating element 42 to the inner tube 48 is transferred to the water of the meniscus M, and heats the water of the meniscus M. The water of the meniscus M is also heated by the radiant heat of the heating element 42. Since the meniscus M is a minute mass of water or a thin water film located at the edge of the outlet of the pore 48, the heat capacity is extremely small. Therefore, the water of the meniscus M is instantly vaporized by the heat of the heating element 42. To do. The water vapor S generated in the pores 48 by the vaporization of water of the meniscus M flows along the surface of the heating element 42, exchanges heat with the surface of the heating element 42, and further receives the heat of the heating element 42. The steam S in the hollow portion 7 flows in the hollow portion 7 as shown in FIGS. 7A and 5 and flows out to the superheated steam feed pipe 3 (FIG. 1) as described above.

  As shown in FIG. 8, when the vaporization of the water W starts, a vapor layer is formed in the pores 48 in and around the inner wall surface 46 in contact with the heating element 42, and the inner wall surface 46 is locally dried. Occurs. In the pores 48 in the vicinity of the heating element 42, the liquid level of the water W moves back into the pores 48 from the outlet opening (opening 49) of the pores 48 as shown in FIG. As a result, the heat generated by the heating element 42 overheats the water vapor S generated in the pores 48. That is, when the water vapor S generated in the pores 48 flows out of the pores 48 and flows in the hollow portion 7, it flows in the vicinity of the heating element 42, Due to the convective heat transfer action in the region near the surface of the heating element 42, it is rapidly heated. Thus, superheated steam is generated in the hollow portion 7 and flows out to the superheated steam feed pipe 3 (FIG. 1).

  As shown in FIG. 7, an inner wall surface zone α in the vicinity of the dried heating element 42 and an inner wall surface zone β between the wet heating elements 42 are formed on the inner wall surface 46 by local heating of the inner wall surface 46. . By forming the drying zone (zone α) at an interval, three-dimensional movement of the water W to the vicinity of the heating element 42 occurs, so that the entire inner tube 48 is prevented from drying, and the water W is capillary. By the action, the heat source 42 is smoothly replenished in the vicinity.

  FIG. 9 is a schematic cross-sectional view of a cooking device using the superheated steam generator 1 having the above-described configuration, and FIGS. 10A, 10B, and 10C show the superheated steam generation shown in FIG. FIG. 2 is a plan view, a front view, and a perspective view showing a structure of a vaporization / superheating device 4 constituting the device 1. 9 and 10, the same reference numerals are assigned to the same or equivalent components or components as those shown in FIGS. 1 to 8.

  The cooker 70 includes a dew receiving tray 71 for receiving condensed water, a draining tray 72 having a large number of openings, a transparent or translucent dome-shaped cover 73, and a superheated steam generating unit disposed on the top surface of the cover 73. 75. The superheated steam generator 1 is accommodated in the housing 76 of the superheated steam generation unit 75. The food Q or the like to be cooked is placed on the draining tray 72. The superheated steam generator 1 is connected to the auxiliary machine 80. The auxiliary machine 80 includes a control unit 81 that controls the operation of the superheated steam generator 1 and a water supply unit 82 that supplies water W such as distilled water to the superheated steam generator 1.

  The superheated steam generator 1 includes a casing 2 that houses a vaporization / superheater 4. The lower region of the casing 2 constitutes a liquid tank capable of storing make-up water W, and the porous body 40 of the vaporization / superheater 4 is at least partially immersed in a liquid bath of water W. A water supply pipe 83 of the water supply unit 82 is connected to the casing 2, and a discharge port of the water supply pipe 83 opens into the casing 2. The water supply unit 82 includes a water supply pump 84, and the discharge port of the water absorption pump 84 is connected to the upstream end of the water supply pipe 83. A water level gauge 85 such as a float switch is disposed in the casing 2. The water level meter 85 detects the water level of the makeup water W stored in the casing 2. The detection value of the water level meter 85 is input to a detection unit (not shown) of the control unit 81 via the control signal line 86. Moreover, the superheated steam generator 1 includes a steam temperature detector 87 such as a thermocouple for detecting the temperature of superheated steam discharged from the superheated steam feed pipe 3. The detection value of the water vapor temperature detector 87 is input to the detection unit of the control unit 81 via the control signal line 88.

  A pair of feeders 90 are connected to the heating element 42 of the superheated steam generator 1. The power supply line 90 is connected to a drive unit (not shown) of the control unit 81. The control unit 81 includes a control unit (not shown) that sets the voltage to be applied to the heating element 42 based on the detection values of the water level meter 85 and the water vapor temperature detector 87, and is used to empty the superheated steam generator 1. A safety device (not shown) such as an earth leakage breaker is provided. The control unit 81 is connected to an AC power source by a power cord 91 or the like, applies a voltage set by the control unit to the heating element 42, operates the water supply pump 84 based on the detected value of the water level gauge 85, and the casing 2 The replenishing water W is appropriately supplied to the liquid tank.

  As shown in FIG. 10, the superheated steam generator 1 includes eight superheated steam feed pipes 3. Four inner pipes 41 with heating elements 42 are arranged in the through holes of the porous body 40, and the superheated steam feed pipe 3 is connected to both ends of the inner pipe 41. As shown in FIG. 9, the superheated steam feed pipe 3 passes through the cover 73 and opens into the cooking region 77, and the superheated steam generator 1 responds to the heat generated by the heating element 42 as described above. S is supplied to the cooking area 77.

  As shown in FIG. 9, the control unit 81 includes a manual operation unit 89 for manually setting the temperature and supply amount of the superheated steam S. An operation mode changeover switch (not shown) is further provided in the manual operation unit 89. The operation mode changeover switch automatically controls the temperature and supply amount of the superheated steam S by the control unit, and manually supplies the superheated steam S to the cooking region 77 based on the set temperature and set supply amount set manually. Switch operation of superheated steam generator 1 to setting mode

  The control unit 81 controls the voltage of the heating elements 42 based on the automatically set or manually set temperature and supply amount of the superheated steam S, or controls the number of the heating elements 42, thereby the cooking area 77. The superheated steam S supplied to the is controlled. In the prototype of the cooking device 70 configured as described above, superheated steam at 300 to 400 ° C. is supplied to the cooking area 77 when about 10 seconds elapse after starting, and therefore, cooking is started very quickly and efficiently. Is possible. Moreover, the superheated steam S supplied to the cooking region 77 by the superheated steam generator 1 provided with the inner pipe 41 does not contain fine porous material particles or powders, and therefore clean superheat without impurities. The steam S can be continuously supplied to the cooking region 77.

  The preferred embodiments of the present invention have been described in detail above, but the present invention is not limited to the above-described embodiments, and various modifications or changes can be made within the scope of the present invention described in the claims. Is possible.

  For example, the material and porosity of the porous body, the pore diameter of the porous body and the inner tube, the cross-sectional dimension of the hollow part, the number of through holes or the number of hollow parts, etc. can be appropriately changed in accordance with the purpose of the present invention .

  In the above embodiment, the first porous body (porous body 40) is configured to completely surround the outer surface of the second porous body (inner tube 41). As long as a sufficient water absorption path can be secured, it is not always necessary to completely surround the outer surface of the second porous body. Similarly, in the above-described embodiment, the heat-resistant sponge completely surrounds the outer surface of the first porous body (porous body 40), but the heat-resistant sponge is not necessarily the second as long as a sufficient water absorption path can be secured. It is not necessary to completely surround the outer surface of the porous body.

  Furthermore, in the above embodiment, a porous body having a double structure is used, but it is also possible to form the whole porous body with more different types of porous bodies.

  Moreover, in the said Example, the inner surface of a 1st porous body (porous body 40) and the outer surface of a 2nd porous body (inner pipe | tube 41) are contacting or adjoining, and each porous The pores of the body are in fluid communication via a liquid film formed at the boundary portion (micro gap) between the first and second porous bodies, and the water sucked up by the capillary action of the first porous body It is further sucked up by the capillary action of two porous bodies. However, the inner surface of the first porous body (porous body 40) and the outer surface of the second porous body (inner tube 41) are separated from each other, and water vapor or vapor is provided between the first and second porous bodies. May be formed. In this case, the water or liquid receives the heat generated by the heating element as radiant heat on the outer surface of the second porous body (inner tube 41), and also receives heat by the convective heat transfer action in the flow region, and the first porous body (porous Vaporizes on the inner surface of the material 40) and flows out from the pores of the first porous material into the flow region. The water vapor or steam in the flow region flows into the hollow portion of the second porous body through the pores of the second porous body (inner tube 41), and is superheated by heat transfer contact with the second porous body. .

  According to the present invention, there are provided a superheated steam generator and a superheated steam generation method that have a small and inexpensive structure that can be employed in various devices that use superheated steam, and that generate superheated steam very quickly. . In particular, the superheated steam generator and the method of generating superheated steam according to the present invention are preferably used in household or industrial equipment using superheated steam such as household cooking appliances, steamers, sterilizers, and dryers. Can do. When the present invention is applied to such a device, the present invention is very advantageous because it enables downsizing and cost reduction of the superheated steam generating mechanism. In addition, the configuration of the present invention can be applied to superheated steam generating means for generating superheated steam by vaporizing liquid fuel or the like, and its practical effect is remarkable.

DESCRIPTION OF SYMBOLS 1 Superheated steam generator 2 Casing 3 Superheated steam feed pipe 4 Vaporization / superheater 5 Water supply device 6 Electric circuit 7 Hollow part 40 Porous body (1st porous body)
41 Inner pipe (second porous body)
42 Coiled heating element 43 Through hole 44 Ceramic plug 46 Inner wall surface 47, 48 Fine hole 60 Power switch 70 Cooker 80 Auxiliary machine W Supplementary water M Meniscus S Superheated steam

Claims (14)

It has a porous body that absorbs water for water vapor generation from the outer surface by capillary action and supplies it to the inner wall surface of the hollow portion, and is in contact with or close to the inner wall surface of the hollow portion along the inner wall surface In the superheated steam generator for generating superheated steam by evaporating the water in the pores of the porous body and heating it with a heating element that extends,
The porous body has a first porous body that absorbs the water from the outer surface by capillary action, and a second porous body that is disposed inside the first porous body and forms the hollow portion. And
The second porous body has a spalling resistance and thermal conductivity that is higher or larger than the spalling resistance and thermal conductivity of the first porous body. The superheated steam generator, which is disposed inside the first porous body so that the water absorbed by the porous body is supplied toward the hollow portion by capillary action of the porous body. The outer surface of the second porous body is arranged so that the water absorbed by the first porous body is supplied to the inner wall surface by the capillary action of the second porous body. In contact with or close to the side,
2. The superheated steam generator according to claim 1, further comprising superheated steam delivery means for delivering superheated steam that has flowed out of the pores into the hollow portion from the hollow portion to the outside of the porous body.   The heating element is composed of a heating wire in contact with or close to the inner wall surface at an interval, and the inner wall surface in the vicinity of the heating wire is formed with a drying zone whose surface is dried by the heat generation of the heating wire. The inner wall surface zone is formed on the inner wall surface between the drying zones, and the superheated steam generator according to claim 1 or 2.   The hollow portion has a circular cross section, and the heating element is made of a coil-shaped electric heating element that is in contact with or close to the inner peripheral surface of the hollow portion and whose axis is oriented in the axial direction of the hollow portion. The superheated steam generator according to any one of claims 1 to 3.   2. The second porous body is made of an alumina, mullite, or silicon carbide ceramic tube inserted or inserted into a hole or hollow portion formed in the first porous body. The overheated steam generator of any one of thru | or 4. The first porous body has a thermal conductivity of 0.5 W / m · K or less, a linear expansion coefficient of 10 × 10 ⁻⁶ / ° C. or more, and a porosity (porosity) of more than 50%. The material according to any one of claims 1 to 5, wherein the material has a relatively large thermal conductivity, a small linear expansion coefficient, and a low porosity as compared with the first porous body. Superheated steam generator.   The second porous body has an average pore diameter and / or mode diameter smaller than the average pore diameter and / or mode diameter of the first porous body, and the minimum pore diameter of the second porous body. Is smaller than the minimum diameter of the pores of the first porous body, the maximum diameter of the pores of the second porous body is larger than the minimum diameter of the pores of the first porous body, and The superheated steam according to any one of claims 1 to 6, wherein the maximum pore diameter of the two porous bodies has a pore size distribution smaller than the maximum diameter of the pores of the first porous body. Generator.   8. The first porous body according to claim 1, wherein the first porous body at least partially includes a porous inorganic ion exchanger having a cation exchange capacity and heat resistance. Superheated steam generator. Water for generating water vapor is absorbed by the capillary action of the porous body and supplied to the inner wall surface of the hollow portion of the porous body, and is in contact with or close to the inner wall surface of the hollow portion and extends along the inner wall surface. In the superheated steam generation method of generating superheated steam by vaporizing and superheating the water in the pores of the porous body by a heating element,
The first porous body that absorbs the water from the outer surface by capillary action, and has a spalling resistance and thermal conductivity that is higher or greater than the spalling resistance and thermal conductivity of the first porous body. And the second porous body that forms the hollow portion, the first porous body is disposed outside the second porous body, and the water absorbed by the first porous body is porous. To the hollow part by the capillary action of
A method for generating superheated steam, characterized in that the water is vaporized and superheated in the pores of the porous body by the heat of the heating element to generate superheated steam.   The outer surface of the second porous body is brought into contact with or close to the inner side surface of the first porous body, and as the heating element, a heating wire that is in contact with or close to the inner wall surface at a distance is used. The drying zone is formed on the inner wall surface near the heating wire by heat generation of the heating wire, and the wet inner wall zone is formed on the inner wall surface between the drying zones. Method for generating superheated steam. The method for generating superheated steam according to claim 10, wherein a heat flux at a contact portion between the inner wall surface and the heating wire is set to 1 MW / m ² or more.   Supplying at least partly the first porous body with an inorganic ion exchanger, and supplying water from which scale components have been removed by the inorganic ion exchanger to the inner wall surface by capillary action of the second porous body. The superheated steam generation method according to claim 10 or 11, characterized in that It has a porous body that absorbs liquid for vapor generation from the outer surface by capillary action and supplies it to the inner wall surface of the hollow portion, and is in contact with or close to the inner wall surface of the hollow portion and along the inner wall surface In the superheated steam generator for generating superheated steam by evaporating the liquid in the pores of the porous body by a heating element extending in a superheated manner,
The porous body includes a first porous body that absorbs the liquid from the outer surface by capillary action, and a second porous body that is disposed inside the first porous body and forms the hollow portion. Have
The second porous body has a spalling resistance and thermal conductivity that is higher or larger than the spalling resistance and thermal conductivity of the first porous body. The superheated steam generator is disposed inside the first porous body so that the liquid absorbed by the porous body is supplied toward the hollow portion by capillary action of the porous body. . The liquid for vapor generation is absorbed by the capillary action of the porous body and supplied to the inner wall surface of the hollow portion of the porous body, and is in contact with or close to the inner wall surface of the hollow portion along the inner wall surface. In the superheated steam generation method in which the liquid is vaporized and superheated in the pores of the porous body by a heating element extending to generate superheated steam,
The first porous body that absorbs the liquid from the outer surface by capillary action, and has a spalling resistance and thermal conductivity that is higher or greater than the spalling resistance and thermal conductivity of the first porous body. And the second porous body that forms the hollow portion, the first porous body is disposed outside the second porous body, and the liquid absorbed by the first porous body is porous. Supply toward the hollow part by the capillary action of the body,
A method for generating superheated steam, characterized in that the liquid is vaporized in the pores of the porous body by the heat of the heat generating body and heated to generate superheated steam.

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