Patent ID: 12235018

DETAILED DESCRIPTION

A known heat exchanger with the structure that forms the basis of a heat exchanger according to one or more embodiments of the present disclosure may be included in a washing apparatus and include a hollow cylindrical heater including an internal water channel, and a water feeding line for feeding water into the water channel.

The heat exchanger is to efficiently heat a heating fluid. In a heat exchanger with the structure that forms the basis of the heat exchanger according to one or more embodiments of the present disclosure, water flowing through the water channel in the heater is likely to be laminar. This may reduce the efficiency of heat exchange between the water and the heater, possibly causing inefficient heating of the water.

The heat exchanger according to an embodiment of the present disclosure will now be described with reference to the drawings.

FIG.1is a perspective view of the heat exchanger according to the present embodiment.FIG.2is a perspective view of the heat exchanger according to the present embodiment as viewed from a viewpoint different fromFIG.1.FIG.3is a cross-sectional view of the heat exchanger according to the present embodiment.FIG.4is a development view of a ceramic body in the heat exchanger according to the present embodiment.FIG.5is an enlarged cross-sectional view of a main part of the heat exchanger according to the present embodiment.FIG.6is an enlarged cross-sectional view of a main part of a heat exchanger according to a modification of the present embodiment.FIG.7is an enlarged cross-sectional view of a main part of a heat exchanger according to another modification of the present embodiment.FIGS.1and2show a heater and a water receiver in the heat exchanger without showing other parts of the heat exchanger.FIGS.3and5to7schematically show the heat exchanger. The positions of a feedthrough conductor and an electrode pad shown inFIGS.3and5to7may be imprecise. InFIGS.2and4, a heat element and lead-out conductors are hatched.FIG.4is a development view of a surface of a surface layer facing a core.FIG.5. is an enlarged cross-sectional view of area A shown inFIG.3. Enlarged cross-sectional views shown inFIGS.6and7each correspond to the enlarged cross-sectional view of the main part shown inFIG.5.

A heat exchanger1includes a heater10and a water receiver20. The heater10includes a ceramic body11and a heat element12.

The ceramic body11is tubular and has an open first end11aand an open second end11b. The ceramic body11may be a triangular tube, a rectangular tube, a cylinder, or an oval tube, or may have another shape. As shown in, for example,FIGS.1and2, the ceramic body11in the heat exchanger1is cylindrical.

The ceramic body11is formed from an insulating ceramic material. Examples of the insulating ceramic material for the ceramic body11include alumina, silicon nitride, and aluminum nitride. Alumina may be used for its oxidation resistance and ease of manufacture. Silicon nitride may be used for its high strength, high toughness, high insulating performance, and high heat resistance. Aluminum nitride may be used for its high thermal conductivity.

At least either an inner peripheral surface11cor an outer peripheral surface11dof the ceramic body11may be coated with a coating layer formed from a metal material. The coating improves the corrosion resistance of the ceramic body11, thus improving the durability of the heat exchanger1. Examples of the metal material for the coating layer include silver, gold, copper, and nickel. An oxide film may be on the outer surface of the coating layer.

As shown in, for example,FIGS.1to3and5to7, the ceramic body11includes a core11eand a surface layer11f. The core11eis a cylinder having open ends. The surface layer11fis located on the outer peripheral surface of the core11e. The surface layer11fmay entirely or partially cover the outer peripheral surface of the core11e. In the heat exchanger1, the core11ehas both ends in the axial direction of the ceramic body11(hereafter simply referred to as the axial direction) exposed from the surface layer11f. The core11ehas, for example, an entire length in the axial direction of 30 to 150 mm, an outer diameter of 10 to 20 mm, and an inner diameter of 8 to 18 mm. The surface layer11fhas, for example, an entire length in the axial direction of 28 to 148 mm and a thickness of 0.2 to 1 mm.

The ceramic body11may have, on the outer peripheral surface11d, a recess11gextending in the axial direction. As shown in, for example,FIGS.1and2, the recess11gmay be defined by the surface layer11fpartially covering the outer peripheral surface of the core11eand the exposed portion of the outer peripheral surface of the core11e. The recess11gmay extend entirely or partially across the length of the surface layer11fin the axial direction.

The heat element12is conductive and linear or strip-shaped. The heat element12generates heat upon receiving a current and heats a heating fluid with the ceramic body11in between. The heat element12is embedded in the ceramic body11and extends between the first end11aand the second end11b. As shown in, for example,FIGS.2,3, and5to7, the heat element12in the heat exchanger1is between the core11eand the surface layer11f. The heat element12may not be located on the exposed portions of the outer peripheral surface of the core11e.

The heat element12is formed from a conductive material mainly containing a metal having a high melting point. The conductive material for the heat element12mainly contains, for example, tungsten, molybdenum, or rhenium. The heat element12may contain the material for the ceramic body11. The dimensions of the heat element12are determined as appropriate depending on, for example, the heating temperature of the heat element12and a voltage applied to the heat element12. The heat element12may have, for example, a width of 0.3 to 2 mm, a thickness of 0.01 to 0.1 mm, and an entire length of 500 to 5000 mm. The ceramic body11may contain a compound containing a metallic element contained in the heat element12. For example, when the heat element12contains tungsten or molybdenum, the ceramic body11may contain tungsten silicide (WSi2) or molybdenum disilicide (MoSi2).

The heat element12may have a conductive pattern in which the heat element12is turned repeatedly between the first end11aand the second end11bof the ceramic body11. As shown in, for example,FIGS.2and4, the heat element12in the heat exchanger1has a conductive pattern in which the heat element12is turned repeatedly between the first end11aand the second end11bin the peripheral direction of the ceramic body11. In other words, the heat element12has a meandering conductive pattern having multiple linear portions12aand multiple turns12b. The linear portions12aextend in the axial direction and are parallel to one another with an interval. The turns12bextend in the peripheral direction of the ceramic body11as viewed in a cross section perpendicular to the axial direction. Each turn12bconnects ends of adjacent linear portions12a. The turns12bmay be linear as shown in, for example,FIGS.2and4or curved. The cross section of the heat element12may be circular, oval, rectangular, or in another shape.

The heater10further includes lead-out conductors13, feedthrough conductors14, and electrode pads15. The heat element12is electrically connected to an external circuit (external power source) with the lead-out conductors13, the feedthrough conductors14, and the electrode pads15.

Each lead-out conductor13is a linear or strip member. As shown in, for example,FIGS.3and5to7, the lead-out conductors13are between the core11eand the surface layer11fand extend in the axial direction. Each lead-out conductor13has a first end connected to the heat element12and a second end located nearer the first end11aof the ceramic body11than the first end connected to the heat element12.

The lead-out conductors13are formed from, for example, a conductive material mainly containing a metal having a high melting point. The conductive material for the lead-out conductors13mainly contains, for example, tungsten, molybdenum, or rhenium. The lead-out conductors13may contain the material for the ceramic body11.

The lead-out conductors13may have a lower resistance value per unit length than the heat element12. The lead-out conductors13may contain a lower amount of the material for the ceramic body11than the heat element12to have a lower resistance value per unit length than the heat element12. In some embodiments, the lead-out conductors13may have a larger cross-section area than the heat element12to have a lower resistance value per unit length than the heat element12.

The feedthrough conductors14are inside the ceramic body11and extend in the radial direction of the ceramic body11. The feedthrough conductors14in the heat exchanger1extend through the surface layer11fin the ceramic body11. Each feedthrough conductor14has a first end face connected to the second end of the corresponding lead-out conductor13not connected to the heat element12, and a second end face exposed on the outer peripheral surface11dof the ceramic body11.

The feedthrough conductors14are formed from, for example, a conductive material mainly containing a metal having a high melting point. The conductive material for the feedthrough conductors14mainly contains, for example, tungsten, molybdenum, or rhenium. The feedthrough conductors14may contain the material for the ceramic body11.

The electrode pads15are located on the outer peripheral surface11dof the ceramic body11. Each electrode pad15covers an end face of the corresponding feedthrough conductor14exposed on the outer peripheral surface11d. Each electrode pad15is joined with a lead terminal to electrically connect to an external circuit (external power source) through the lead terminal. The electrode pads15are formed from a conductive material containing, for example, tungsten or molybdenum. A plating layer formed from, for example, a nickel-boron alloy or gold may be on the outer surfaces of the electrode pads15. The electrode pads15each have, for example, a thickness of 10 to 300 μm and a length and a width of 1 to 10 mm.

The water receiver20is a cylinder having open ends. The water receiver20draws a heating fluid, for example, water from an external source into the ceramic body11. The ceramic body11has an internal space defined by the inner peripheral surface11cof the ceramic body11. The water receiver20has one end (hereafter also referred to as the first end)20aplaced inside the ceramic body11and fixed to the heater10. The water receiver20may be fixed to the heater10with an adhesive between an outer peripheral surface20bof the water receiver20at the first end20aand the inner peripheral surface11cof the ceramic body11, or with another method. The water receiver20has a second end, opposite to the first end20a, connected to an external source of a heating fluid.

The water receiver20may have the outer peripheral surface20bat the first end20aalong the entire periphery in contact with the inner peripheral surface11cof the ceramic body11. The first end20amay have an end face inclined with respect to the axial direction of the ceramic body11, as shown in, for example,FIGS.3and5. The first end20amay have an end face orthogonal to the axis of the ceramic body11, as shown in, for example,FIGS.6and7.

The water receiver20is formed from, for example, a resin material or a metal material. Examples of the resin material for the water receiver20include a fluororesin and a silicone resin. Examples of the metal material for the water receiver20include stainless steel. The water receiver20has, for example, an outer diameter of 8 to 18 mm and an inner diameter of 3 to 13 mm. The length of the water receiver20is determined as appropriate depending on the distance between the heater10and the external source of a heating fluid.

The heat exchanger1includes a heat exchange channel through which a heating fluid flows. The heat exchange channel includes a first channel F1defined by the inner peripheral surface of the water receiver20and a second channel F2defined by the inner peripheral surface11cof the ceramic body11and having a larger cross-sectional area than the first channel F1. The second channel F2is downstream from the first channel F1in the flow direction of a heating fluid (from left to right inFIGS.3and5to7). During the operation of the heat exchanger1, streamlines of the heating fluid in the second channel F2in a part adjacent to the first channel F1(upstream part of the second channel F2) leave the inner peripheral surface11c, allowing turbulence of the heating fluid to be more likely to occur. With turbulence, a part of the heating fluid after exchanging heat with the inner peripheral surface11cflows apart from the inner peripheral surface11c, and another part of the heating fluid yet to exchange heat with the inner peripheral surface11cflows nearer the inner peripheral surface11c. Thus, the heat distribution of the heating fluid is more likely to be uniform in the radial direction of the ceramic body11. The heat exchanger1thus enables efficient heat exchange between the heating fluid and the heater10.

In the heat exchanger1, the first end20ais at least partially located nearer the second end11bof the ceramic body11than an end of the heat element12nearer the first end11aof the ceramic body11. In other words, as shown in, for example,FIGS.3and5, the first end20ais at least partially placed in a part inside the ceramic body11that reaches high temperatures due to the embedded heat element12during operation. The upstream part of the second channel F2in which turbulence is likely to occur thus includes a part that reaches high temperatures during operation. The heat exchanger1thus enables efficient heat exchange using turbulence in a part of the heat exchange channel that reaches high temperatures. The heat exchanger1heats the heating fluid efficiently with lower power consumption.

As shown inFIG.6, the entire periphery of the first end20aof the water receiver20may be located nearer the second end11bof the ceramic body11than an end of the heat element12nearer the first end11aof the ceramic body11. This structure causes turbulence in a part of the ceramic body11that reaches high temperatures during operation and thus enables efficient heat exchange in the part, enabling more efficient heating of the heating fluid. Thus, the heat exchanger1having the structure shown inFIG.6further reduces power consumption.

As shown inFIG.7, the first end20aof the water receiver20may have an inner diameter increasing toward the second end11bof the ceramic body11. This structure reduces the decrease in the flow velocity of the heating fluid caused by, for example, a pressure drop in the first channel F1. This allows the heating fluid flowing from the first channel F1into the second channel F2to maintain a flow velocity for effective generation of turbulence in the upstream part in the second channel F2. This structure effectively causes turbulence in a part of the ceramic body11that reaches high temperatures during operation and enables efficient heat exchange in the part, thus enabling more efficient heating of the heating fluid. The heat exchanger1having the structure shown inFIG.7further reduces power consumption.

The heat exchanger1further includes a flange30. The flange30facilitates attachment of the heater10to an external device. The flange30is annular and has a hole30ato receive the ceramic body11as shown in, for example,FIGS.3and5to7. The flange30is formed from, for example, a metal material. Examples of the metal material for the flange30include stainless steel and an iron-nickel-cobalt alloy. Stainless steel may be used for its high corrosion resistance. The surface of the flange30may be coated with a plating layer mainly containing a metal such as nickel, tin, or gold to improve the corrosion resistance of the flange30.

The flange30is fixed to the heater10with an inner peripheral surface30aaof its hole30ajoined to the outer peripheral surface11dof the ceramic body11. As shown in, for example,FIGS.3and5to7, the inner peripheral surface30aamay be joined to the outer peripheral surface11dof the ceramic body11with a metal layer34in between. The metal layer34is located nearer the second end11bof the ceramic body11than the electrode pads15in the axial direction. Examples of the metal material for the metal layer34include tungsten and molybdenum.

The flange30may be joined to the outer surface of the metal layer34with a bond35. The bond35may be any appropriate material that joins the flange30to the metal layer34. The bond35may be, for example, a brazing material such as a silver brazing material and a silver-copper brazing material. A plating layer formed from, for example, nickel, tin, or gold may be on the outer surface of the metal layer34. This improves the wettability of the metal layer34with the bond35, thus increasing the bonding strength between the ceramic body11and the flange30.

In the heat exchanger1, as shown in, for example,FIGS.3and5to7, the first end20aof the water receiver20is at least partially located nearer the second end11bthan an edge30abof the inner peripheral surface30aaof the hole30anearer the first end11a. In other words, the first end20aoverlaps the inner peripheral surface30aaas viewed in a direction perpendicular to the axial direction. This structure allows heat dissipation from the flange30to reduce the likelihood of the temperature of the first end20aincreasing excessively under heat generated by the heat element12. With the water receiver20formed from a resin material as well, this structure reduces deformation and deterioration of the first end20aunder heat generated by the heat element12, allowing reliable generation of turbulence in the second channel F2. Thus, the heat exchanger with this structure is durable and enables efficient heating of a heating fluid over a long period. More specifically, the heat element12meandering as shown in, for example,FIG.4, has turns12bthat reach the highest temperature in the heat element12at ends12cof the heat element12nearer the first end11a. With this structure as well, the heat exchanger1reduces deterioration of the water receiver20under heat generated by the heat element12. Thus, the heat exchanger1is durable and enables efficient heating of a heating fluid over a long period.

As shown in, for example,FIGS.3and5to7, the flange30may have a first portion31, a second portion32, and a third portion33. The first portion31stands upright and radially outward from the metal layer34. The second portion32extends from the outer peripheral edge of the first portion31toward the first end11aof the ceramic body11. The third portion33extends radially outward from an end of the second portion32nearer the first end11a. In other words, as shown in, for example,FIGS.3and5to7, the flange30has two bends between its inner periphery and outer periphery as viewed in a cross section including the axis of the ceramic body11.

As shown in, for example,FIGS.3and5to7, the metal layer34may have a length in the axial direction greater than the length of the inner peripheral surface30aain the axial direction. This structure allows the bond35to form a meniscus extending from the metal layer34to the first portion31in the flange30, thus increasing the bonding strength between the heater10and the flange30and improving the durability of the heat exchanger1.

The heat exchanger1further includes a connection member40and an annular member50. The connection member40is tubular and has open ends. The connection member40continuously covers the outer peripheral surface of a portion of the ceramic body11adjacent to the first end11aand an outer peripheral surface20cof a portion of the water receiver20exposed from the ceramic body11. As shown in, for example,FIGS.3and5to7, the connection member40may include multiple cylindrical members with different sizes connected coaxially with each other. The inner peripheral surface of the connection member40may be in contact with the outer peripheral surface11dof the ceramic body11and the outer peripheral surface20cof the water receiver20.

The connection member40is formed from, for example, a metal material or a resin material. Examples of the metal material for the connection member40include stainless steel and an iron-nickel-cobalt alloy. Examples of the resin material for the connection member40include a fluororesin and a silicone resin.

The connection member40at the connection between the heater10and the water receiver20improves the durability of the mechanical connection between the heater10and the water receiver20. The heat exchanger with this structure is durable.

The annular member50is an annular member (O-ring) including a resin material. The annular member50is between the inner peripheral surface of the connection member40and the outer peripheral surface11dof the ceramic body11. Examples of the resin material for the annular member50include a fluororesin and a silicone resin.

The annular member50between the ceramic body11and the connection member40reduces stress caused by the difference in thermal expansion between the ceramic body11and the connection member40, thus reducing cracks in the ceramic body11. The heat exchanger with this structure is durable.

As shown in, for example,FIGS.3and5to7, the annular member50may be in contact with a portion of the outer peripheral surface11dof the ceramic body11with no heat element12embedded. This structure reduces deterioration of the annular member50under heat generated by the heat element12. The heat exchanger with this structure is durable and enables efficient heating of a heating fluid.

The heat exchanger1further includes a case60. The case60is tubular and has a closed first end and an open second end. The case60may be a triangular tube, a rectangular tube, a cylinder, or an oval tube, or may have another shape. The case60in the heat exchanger1is cylindrical. The heater10and the case60may be arranged to have the ceramic body11and the case60being coaxial.

The case60is formed from a highly heat-resistant resin material. Examples of the resin material for the case60include a fluororesin. The case60has, for example, an entire length in the axial direction of 40 to 160 mm and an inner diameter of 10 to 25 mm.

The case60has an opening60aat the open second end in which the heater10is held. As shown inFIGS.3and5to7, the case60accommodates a portion of the ceramic body11nearer the first end11b. As shown inFIGS.3and5to7, the heater10may be held in the case60with the second portion32of the flange30press-fitted in the opening60a. The second portion32may be press-fitted in the opening60awith an annular member (O-ring) formed from a resin material in between.

In the heat exchanger1, the first channel F1, the second channel F2, and a third channel F3defined by the outer peripheral surface11dof the ceramic body11, an inner surface60bof the case60, and a surface of the flange30exposed inside the case60are connected to each other to define a channel for the heating fluid to pass through. The heating fluid exchanges heat with the heater10in the second channel F2and the third channel F3. As shown in, for example,FIGS.3and5to7, the case60includes an outlet61that allows the third channel F3to be open outside. The outlet61allows ejection of the heating fluid heated by the heater10. The outlet61has, for example, an inner diameter of 1 to 5 mm. As shown in, for example,FIGS.3and5to7, the outlet61may be at a position in the side wall of the case60nearer the first end11aof the ceramic body11. This structure facilitates heat exchange between the heating fluid and the heater10in the third channel F3, thus enabling efficient heating of the heating fluid.

An example method for manufacturing the heat exchanger1will now be described. In the example described below, the ceramic body11is formed from alumina ceramic.

First, an alumina ceramic green sheet to be the surface layer11fof the ceramic body11is prepared with alumina (Al2O3) as a main component and silica (SiO2), calcium oxide (CaO), magnesia (MgO), and zirconia (ZrO2) in a combined total amount less than or equal to 10% by mass. Predetermined patterns to be the heat element12and the lead-out conductors13are formed on the alumina ceramic green sheet. The predetermined patterns are formed by, for example, screen printing, a transfer process, or embedding a resistor. The predetermined patterns may be formed by, for example, etching a metal leaf or shaping nichrome wire into a coil and embedding the wire. Screen printing may be used for stable quality and lower manufacturing costs. The heat element12and the lead-out conductors13may be formed with different methods.

Subsequently, predetermined patterns to be the electrode pads15and the metal layer34are formed on the surface opposite to the surface of the ceramic green sheet on which the heat element12and the lead-out conductors13are formed, in the same manner as with the heat element12and the lead-out conductors13. Holes for forming the feedthrough conductors14that electrically connect the lead-out conductors13and the electrode pads15are punched in the ceramic green sheet and filled with a conductive paste to be the feedthrough conductors14. A conductive paste mainly containing a metal having a high melting point such as tungsten, molybdenum, and rhenium may be used for the heat element12, the lead-out conductors13, the feedthrough conductors14, and the electrode pads15.

A cylindrical alumina ceramic molded body to be the core11ein the ceramic body11is formed by extrusion molding. The cylindrical alumina ceramic molded body is wrapped in the alumina ceramic green sheet described above. An adhesion liquid containing an alumina ceramic material having the same composition as the green sheet in a dispersed manner is then applied and stuck tightly to the molded body to obtain an integrally molded alumina body to be the ceramic body11. The alumina ceramic green sheet may be wrapped around the alumina ceramic molded body with a predetermined area on the outer peripheral surface of the alumina ceramic molded body left uncovered with the alumina ceramic green sheet to obtain an integrally molded alumina body including a groove to be the recess11g. The integrally molded alumina body is fired in a reducing atmosphere (nitrogen atmosphere) at 1500 to 1600° C. and thus shrinks to form a sintered integral alumina body (ceramic body11).

Subsequently, the electrode pads15and the metal layer34on the ceramic body11are plated. The plating typically uses, for example, nickel, gold, or tin. A plating technique may be selected from, for example, electroless plating, electroplating, and barrel plating, in accordance with use.

The flange30may be manufactured from a stainless-steel plate, which undergoes processes such as cutting, punching, and pressing to have a shape including the first portion31, the second portion32, and the third portion33, as well as the hole30ato receive the ceramic body11.

Subsequently, the ceramic body11is set on a fixture. The flange30is then positioned to have the hole30aaligned with the metal layer34on the outer peripheral surface11dof the ceramic body11. The ceramic body11is then brazed using the bond35at about 1000° C. in a furnace with a reducing atmosphere.

Subsequently, an annular member (O-ring) formed from, for example, rubber is attached to the outer peripheral surface of the second portion32in the flange30. The case60formed from a resin is prepared. The case60receives and holds the heater10with the annular member attached. The water receiver20formed from, for example, a resin material or a metal material is then placed inside the ceramic body11. The heat exchanger1may be thus manufactured.

A washing apparatus according to an embodiment of the present disclosure will now be described.

The washing apparatus according to the present embodiment includes the heat exchanger1described above. The washing apparatus heats, with the heater10, water drawn from an external water source through the water receiver20and ejects the heated water outside. The external water source may be, for example, a public water supply system. The water flows from the first channel F1into the second channel F2and then into the third channel F3, and is ejected through the outlet61. While passing through the second channel F2and the third channel F3, the water is heated by the heater10to a predetermined temperature. The heated water may be used for, for example, washing a part of a human body. The washing apparatus according to the present embodiment including the heat exchanger1heats water efficiently with lower power consumption.

The present disclosure may be implemented in the following forms.

A heat exchanger according to one aspect of the present disclosure includes a heater including a ceramic body being tubular and having a first end being open and a second end being open and a heat element embedded in the ceramic body, and a water receiver being tubular and having a first end being open and a second end being open. The first end of the water receiver is through the first end of the ceramic body and is located inside the ceramic body. The first end of the water receiver is at least partially nearer the second end of the ceramic body than an end of the heat element nearer the first end of the ceramic body.

The heat exchanger according to the above aspect of the present disclosure heats a heating fluid efficiently with lower power consumption. A washing apparatus according to one aspect of the present disclosure includes the heat exchanger described above. The washing apparatus heats water efficiently with lower power consumption.

Although the embodiments of the present disclosure have been described in detail, the present disclosure is not limited to the above embodiments, and may be modified or changed variously without departing from the spirit and scope of the present disclosure. The components described in the above embodiments may be entirely or partially combined as appropriate unless any contradiction arises.

REFERENCE SIGNS LIST

1heat exchanger10heater11ceramic body11afirst end11bsecond end11cinner peripheral surface11douter peripheral surface11ecore11fsurface layer11grecess12heat element12alinear portion12bturn12cend13lead-out conductor14feedthrough conductor15electrode pad20water receiver20aone end (first end)20bouter peripheral surface20couter peripheral surface30flange30ahole30aainner peripheral surface30abedge31first portion32second portion33third portion34metal layer35bond40connection member50annular member60case60aopening60binner surface61outlet