JP5766348B2 - Tubular heater - Google Patents

Description

  The present invention relates to a tubular heater used for a fluid heating heater or the like.

  As the tubular heater, as shown in FIG. 11, a tubular ceramic base 901 having a fluid flow path 902, and a wire embedded in the tubular ceramic base 901 and arranged substantially evenly around the flow path 902. Have been proposed (see Patent Document 1).

  However, in the tubular heater shown in FIG. 11, the cross-sectional shape of the channel 902 is constant from the upstream side to the downstream side, and it cannot be said that the heat transfer efficiency to the fluid flowing through the channel 902 is high. When the fluid is heated to a predetermined temperature, there is a problem that the fluid is hardly warmed up and it takes a relatively long heating time until the fluid reaches the predetermined temperature.

  Therefore, as shown in FIG. 12, the flow path 902 has a configuration in which a plurality of flow path portions having different diameters are connected, so that the fluid residence time is increased by reducing the flow rate of the fluid, and the heat transfer efficiency is increased. It has also been proposed to increase it (see Patent Document 1).

  However, even with the tubular heater shown in FIG. 12, when the fluid is a liquid, the heat transfer efficiency is not sufficiently improved, for example, bubbles at the time of boiling accumulate in an area with a large flow path diameter or the fluid stagnates. Absent.

  On the other hand, when a fluid to be heated is heated using a heater, there is an increasing demand for shortening the running time by supplying power only when necessary and reaching a desired temperature in a shorter time. Here, as one of the means for shortening the running time, preheating is performed in advance below the intended heating temperature, and the fluid is heated to the necessary temperature when necessary, thereby shortening the arrival time to the desired temperature. The means are mentioned. However, in view of recent energy saving requirements, it is desirable to supply power only when necessary and to heat more efficiently.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a tubular heater that has good heat transfer efficiency and can raise the temperature of a fluid to a predetermined temperature in a short time.

JP 2004-185929 A

  The tubular heater of the present invention includes a tubular insulating base having a space serving as a fluid flow path inside, and a resistor having a heat generating portion embedded in the insulating base, and the inner wall of the insulating base is And a change region in which the shape of the surface perpendicular to the length direction of the flow path changes while the cross-sectional area of the surface perpendicular to the length direction of the flow path remains substantially constant from the upstream side to the downstream side.

It is the schematic which shows an example of embodiment of the tubular heater of this invention. It is a left view of the tubular heater shown in FIG. It is a right view of the tubular heater shown in FIG. It is a schematic perspective view which shows the example of the resistor of the tubular heater shown in FIG. It is a cross-sectional view in the AA line shown in FIG. It is a cross-sectional view in the BB line shown in FIG. It is the schematic which shows the other example of embodiment of the tubular heater of this invention. It is a schematic perspective view which shows the other example of embodiment of the tubular heater of this invention. It is the schematic which shows the other example of embodiment of the tubular heater of this invention. It is a schematic longitudinal cross-sectional view of the tubular heater shown in FIG. It is a schematic perspective view which shows an example of the conventional heater. It is a schematic perspective view which shows the other example of the conventional heater.

  Hereinafter, the example of an embodiment about the tubular heater of the present invention is explained in detail with reference to drawings.

  1 is a schematic perspective view showing an example of an embodiment of the tubular heater of the present invention, FIG. 2 is a left side view of the tubular heater shown in FIG. 1, and FIG. 3 is a right side view of the tubular heater shown in FIG. is there. The tubular heater of the present embodiment includes a tubular insulating base 1 having a space serving as a fluid flow path 2 on the inside, and a resistor 6 having a heat generating portion 7 embedded in the insulating base 1 and insulated. The inner wall of the substrate 1 has a change region 10 in which the cross-sectional shape of the flow path 2 changes while the cross-sectional area of the flow path 2 is substantially constant from the upstream side to the downstream side.

  As the insulating substrate 1, for example, ceramics having insulation properties such as oxide ceramics, nitride ceramics or carbide ceramics can be used. Specifically, alumina ceramics, silicon nitride ceramics, aluminum nitride ceramics, silicon carbide ceramics, or the like can be used. Among these, alumina ceramics is preferably used from the viewpoint of oxidation resistance. From the viewpoint of thermal conductivity to the fluid to be heated, high-purity alumina ceramics or aluminum nitride ceramics may be used.

  The insulating substrate 1 is formed in a tubular shape, and has a space serving as a fluid flow path 2 inside as shown in FIG. A resistor 6 having a heat generating portion 7 is embedded in the tubular insulating base 1 surrounding the flow path 2.

  Specifically, the insulating base 1 has a thin end region 11 and a thick central region 12, and the resistor 6 is embedded in the central region 12. For example, the length of the insulating substrate 1 (length of the flow path 2) is 40 to 200 mm, the length of the thin end region 11 is 0.5 to 15 mm, and the length of the thick central region 12 is 30. ~ 190 mm. Moreover, the diameter of the flow path 2 is 4-20 mm, for example. This shape is produced by a manufacturing method described later, but is not particularly limited to this shape.

  The resistor 6 is made of a conductor whose main component is a refractory metal such as tungsten, molybdenum or rhenium. For example, when the resistor 6 is formed by a screen printing method or a transfer method, a conductive paste mainly composed of these refractory metals is used.

  Here, as shown in FIG. 4, it is preferable that the resistor 6 includes a heat generating portion 7 serving as a heating region and a drawing portion 8 serving as a non-heating region.

  By providing the lead-out portion 8 which is a non-heated region, the temperature increase of the power feeding portion 3 to which the lead terminal 4 is connected to the pad 5 by means such as brazing or soldering is suppressed, and cracks are generated due to thermal fatigue. It is possible to suppress contact failure due to oxidation caused by heating. Therefore, it is possible to provide a long-life and highly reliable tubular heater in which failures such as electric leakage and disconnection are suppressed.

  This is not limited to the case where the power supply unit 3 is used at a low temperature such that the temperature of the power supply unit 3 is 50 ° C. or lower. However, in order to increase the connection reliability of the power supply unit 3, the heat generation unit 7 and the lead-out unit 8 are provided. It is good to have a configuration. In addition, it can be set as the wiring pattern which can distinguish the heat-emitting part 7 and the drawer | drawing-out part 8 clearly by varying the line width and thickness of a wiring pattern.

  Further, the heat generating portion 7 is provided on one end side of the insulating base 1, and the end of the resistor 6 is led out to the surface of the insulating base 1 on the other end side of the insulating base 1 from the position corresponding to the heat generating portion 7. It is preferable that With such a configuration, the temperature of the power feeding unit 3 connected to the end of the resistor 6 is not easily increased, so that stable heating is possible without contact failure, and there is a long life with no leakage or disconnection. A tubular heater with high reliability can be obtained.

  Further, as shown in FIGS. 4 to 6, the heat generating portions 7 that form the heating region are arranged at almost equal intervals over the circumferential direction of the tubular insulating base 1, for example. In addition to the heat generating portion 7, the resistor 6 has a drawing portion 8 that is a non-heated region, and the drawing portion 8 is also arranged at substantially equal intervals in the circumferential direction like the heat generating portion 7.

  Thereby, it has the effect of becoming a uniform temperature distribution and reducing the malfunction that a heat shock crack arises. Further, when firing the insulating substrate 1, there is an effect of reducing a problem that the sintering balance is lost and cracks are generated.

  The inner wall of the insulating base 1 has a change region 10 in which the cross-sectional shape of the flow path 2 changes while the cross-sectional area of the flow path 2 is substantially constant from one end side to the other end side of the insulating base 1. In this embodiment, the cross-sectional shape of the insulating substrate 1 continuously changes from one end to the other end of the central region 12. That is, in the present embodiment, the entire inner wall of the central region 12 is the change region 10. Therefore, as shown in FIGS. 2 and 3, the shape of one end surface of the insulating base 1 is different from the shape of the other end surface. Note that the change region 10 may be partially provided in the insulating substrate 1.

  Here, the change in the cross-sectional shape in the change region 10 does not change abruptly but changes gently. More specifically, the “cross-sectional shape is changing” state refers to the following state. That is, as shown in FIG. 5, in one surface of the cross section perpendicular to the length direction of the insulating base 1, the axis in the direction in which the inner diameter is maximum is the X axis, and the axis in the direction perpendicular to the axis is the axis. As the Y-axis, a value obtained by dividing the length in the X-axis direction by the length in the Y-axis direction is R1. Furthermore, as shown in FIG. 6, on the other surface of the cross section perpendicular to the length direction of the insulating base 1, the value obtained by dividing the length in the X-axis direction by the length in the Y-axis direction is R2. And At this time, when the value of R1 and the value of R2 differ by 0.5% or more, it is considered that “the cross-sectional shape has changed”.

  Thus, by providing the change area | region 10 in the insulation base | substrate 1, it can suppress that a bubble etc. accumulate in the flow path 2. FIG. Moreover, a turbulent flow is generated in the fluid (subject to be heated) flowing in the flow path 2, and the heat transfer efficiency to the fluid is improved. Therefore, the fluid is easily warmed and can be warmed to the target temperature in a short time.

  As used herein, the phrase “the cross-sectional area is substantially constant” means that the cross-sectional area is within a range of an area difference of ± 5% or less with respect to the average cross-sectional area. According to this configuration, since the flow path 2 has no irregularities and is a smooth change, when the fluid is a liquid, entrainment of bubbles or the like when the liquid flows is eliminated, and heat transfer efficiency is improved.

  The following method can be used to confirm that the cross-sectional shape is changing and that the cross-sectional area is constant. For example, the above-described R1 and R2 and the cross-sectional area may be measured by cutting the change region 10 at intervals of 5 mm and using the Measuring Microscope manufactured by Mitsutoyo.

  Moreover, as shown in FIG. 7, while the cross section of the one end side and the cross section of the other end side are each elliptical shapes, it may be the shape change that the cross section is circular in the center part. Further, the cross section on the one end side and the cross section on the other end side may be circular, and the shape may be changed so that the cross section changes most greatly from the circular shape at the center.

  In the case where the change region 10 is provided only in a desired region, for example, as shown in FIG. 8, the heat generating portion 7 is provided on one end side of the insulating base 1 and the change region 10 is provided on the insulating base 1. It may be provided on the other end side. Thereby, when the fluid is caused to flow from the other end side of the insulating base 1, the fluid can be heated in the heat generating portion 7 after the fluid becomes turbulent in the change region 10. Thereby, it is possible to easily heat the fluid, and it is possible to warm up to a target temperature in a shorter time.

  The more the portion where the shape provided in the flow path 2 provided inside the insulating substrate 1 changes, the greater the effect of generating turbulent flow on the fluid passing through the flow path 2 and the higher the heat transfer efficiency. An effect is obtained.

  Therefore, as shown in FIG. 9, there is a configuration in which there are a plurality of change regions 10, and the cross-sectional shape of the flow path 2 is maintained while the cross-sectional area of the flow path 2 is substantially constant from one end side to the other end side of the insulating base 1. Preferably it has changed. 9 is a schematic perspective view showing another example of the embodiment of the tubular heater of the present invention, and FIG. 10 is a longitudinal sectional view of the tubular heater shown in FIG.

  Since the change region 10 in which the cross-sectional shape is repeatedly changed from one end side to the other end side of the insulating base 1 is provided, there are more portions where the shape provided in the flow channel 2 changes. This is because the effect of generating turbulent flow on the fluid passing through the cylinder becomes larger and the heat transfer efficiency is improved.

  1 to 10, the outer shape of the insulating base 1 is changed in accordance with the change in the cross-sectional shape of the flow path 2, but the insulating base 1 is not limited to such a configuration. The outer shape may not change (a straight shape as viewed in the longitudinal section).

  Further, the heat generating portion 7 may be provided on one end side of the insulating base 1, and the change region 10 may be provided in a region corresponding to the heat generating portion 7. In this case, since the turbulent flow can be generated in the heat generating portion 7, it is possible to easily heat the fluid in a portion where the temperature in the flow path 2 is relatively high.

  Next, the manufacturing method of the tubular heater of this Embodiment is demonstrated.

  Here, an example in which the insulating substrate 1 is made of an alumina ceramic will be described.

First, the alumina which has alumina (Al ₂ O ₃ ) as a main component and is prepared so that silica (SiO ₂ ), calcia (CaO), magnesia (MgO) and zirconia (ZrO ₂ ) are within 10 mass% in total. A ceramic green sheet is produced.

  A predetermined pattern to be the resistor 6 is formed on the surface of the alumina ceramic green sheet. As a method of forming the resistor 6, a screen printing method, a transfer method, a resistor embedding method, or as another method, a method of forming a metal foil by an etching method or the like, or a nichrome wire formed in a coil shape and embedded However, it is easy to use the screen printing method in terms of quality stability and manufacturing cost. Moreover, although the resistor 6 consists of the heat generating part 7 and the drawer | drawing-out part 8, you may form each with a separate formation method.

  Further, the pad 5 is formed in a predetermined pattern shape on the surface of the ceramic green sheet opposite to the surface on which the resistor 6 is formed in the same manner as the resistor 6 is formed.

  Moreover, the ceramic green sheet is filled with a conductor paste for forming a through hole conductor 9 and a through hole conductor 9 for electrically connecting the resistor 6 and the pad 5.

  For the resistor 6, the pad 5, and the through-hole conductor 9, for example, a conductive paste whose main component is a refractory metal such as tungsten (W), molybdenum (Mo), or rhenium (Re) can be used.

  On the other hand, a cylindrical alumina ceramic molded body is formed by extrusion molding.

  Then, the above alumina ceramic green sheet is wound around this cylindrical alumina ceramic molded body, and an adhesive liquid in which the alumina ceramic of the same composition is dispersed is applied and brought into close contact, whereby alumina serving as the insulating substrate 1 is obtained. A quality-integrated molded body can be obtained. The integral molded body is deformed by applying a load with a mold having various shapes in a humidified state of 80% RH at 30 ° C., and then dried in a drying chamber at 70 ° C., so that the cross-sectional area is substantially uniform. As a result, an integrally molded body having the change region 10 in which the cross-sectional shape is changed can be formed.

  By firing the integrally molded body thus obtained in a reducing atmosphere (nitrogen atmosphere) at 1500 to 1600 ° C., an alumina-based integrated sintered body (insulating base 1) can be produced.

  Next, plating is applied on the pad 5 formed on the insulating substrate 1 as a base for forming the power feeding portion 3. As the plating, nickel plating, gold plating, tin plating and the like are generally used. As a plating method, a plating method such as electroless plating, electrolytic plating, or barrel plating may be selected according to the purpose. The power feeding unit 3 can be obtained by a method of forming terminals and leads by brazing or a method of soldering twisted wires. Considering the current value when using the tubular heater, it is better to select from the thickness and material.

  The tubular heater of the present invention is obtained by the above method.

An alumina ceramic green sheet having Al ₂ O ₃ as a main component and adjusted so that SiO ₂ , CaO, MgO and ZrO ₂ are within 10 mass% in total is prepared, and tungsten and molybdenum are used as main conductive components on the surface. The resistor conductive paste was printed by a screen printing method. Also, a pad conductive paste having tungsten as a main conductive component was similarly printed on the back surface by a screen printing method.

  Specifically, the resistor formed a heat generating portion in a 5-reciprocating meandering shape with a width of 1 mm, and was led out at the position of the power feeding portion through a lead portion 8 with a width of 3 mm connected to both ends thereof.

  A through hole having a diameter of 0.4 mm was formed at the end of the lead portion, and a paste having tungsten as a main conductive component was injected to form a through hole conductor that electrically connected the pad and the resistor. Here, four through-hole conductors were provided on the diagonal line of a 5 mm × 6 mm square pad so that the distance between each through-hole conductor was 1 mm or more.

  Next, an adhesive liquid in which alumina ceramics having substantially the same composition are dispersed is applied to the side of the prepared alumina ceramic green sheet on which the conductive paste for resistor is formed, and a cylindrical shape serving as an insulating base prepared separately is applied. An alumina-based integral molded body was produced by closely contacting the periphery of the alumina-based ceramic molded body. The alumina ceramic molded body to be an insulating substrate is produced by extrusion molding and dried. Specifically, an alumina ceramic molded body is extruded, and the molded body is deformed by applying a load with a mold having various shapes in a humidified state of 80% RH at 30 ° C., followed by drying at 70 ° C. By drying in a chamber, an insulating substrate having a change region in which the cross-sectional shape was changed while the cross-sectional area was substantially uniform was obtained.

  The length of the insulating base was 90 mm, the length of the thick central region was 70 mm, and the length of the thin end region was 10 mm at both ends of the central region. The inner diameter (diameter of the flow path) of the insulating substrate was 6.5 mm, the thickness of the central region was 2.75 mm, and the thickness of the end region was 2.25 mm.

  Here, as a sample of the produced tubular heater, an alumina-integrated molded body (sample 1) having the form shown in FIG. 1 was first produced. In this tubular heater, a heat generating portion is provided on one end side of the insulating base, the cross section on one end side is circular, and the shape is changed from a circular shape to an elliptical shape toward the other end side.

  Further, an alumina-based integral molded body (sample 2) having the form shown in FIG. 7 was produced. This tubular heater has an elliptical shape in cross section on one end side and a cross section on the other end side, and has a change region in which the cross section is circular in the center.

  Further, by using a mold partially provided with a change region, an alumina-integrated molded body (sample 3) having a form shown in FIG. 8 was produced. This tubular heater is provided with a heat generating portion on one end side of the insulating base and has a change region only on the other end side.

  Further, by using a mold provided with a change region as a whole when applying a load in a humidified state, an alumina integrated molded body (sample 4) having a form shown in FIG. 9 was produced.

  Furthermore, as a conventional structure for comparison, after the fluid flow path is formed by extrusion processing, it is uniformly processed by inner diameter processing to produce an alumina integrated molded body (sample 5) having a certain cross-sectional shape. did.

  The various alumina-based molded bodies thus prepared were fired in a reducing atmosphere (nitrogen atmosphere) at 1500 to 1600 ° C. to produce an alumina-based integrated sintered body. The aforementioned pad was formed on the surface of the alumina integrated sintered body. The pad was subjected to nickel plating by electroless plating, and a φ1.2 mm nickel wire was brazed with silver brazing to produce a tubular heater for evaluation.

  About the produced tubular heater, the water to be introduced was passed at a temperature of 5 ° C. and a flow rate of 500 ml / min, and the water thus passed was once put into a constant temperature water tank and then returned to the inlet side again to be circulated repeatedly. Each of the fabricated ceramic heaters was given a power at which the heater power at 45 ° C. was 1000 W, and the time until 5 liters of water reached 45 ° C. was comparatively evaluated. The water temperature was measured by installing K-type thermocouples at five locations in the thermostatic water tank, and taking the average of the five temperature measurements as the water temperature after heating.

  As a result, in the tubular heater of Sample 5 as a comparative example, it took 3 minutes and 10 seconds until the water temperature reached 45 ° C.

  On the other hand, in the tubular heaters of Samples 1 to 4 which are examples of the present invention, 2 minutes and 30 seconds (Sample 1), 2 minutes and 10 seconds (Sample 2), 1 minute and 40 seconds (Sample 3), and 1 minute, respectively. In 10 seconds (Sample 4), 5 liters of water could be heated to 45 ° C each.

  As described above, the tubular heaters of Samples 1 to 4 have higher heat transfer efficiency than the tubular heater of Sample 5 as a comparative example, and were able to warm the fluid to be heated to the target temperature in a short time. This is presumably because the turbulent flow is generated in the fluid due to the change in the shape of the flow path provided inside the insulating substrate, and the heat transfer efficiency is improved.

  In addition, although the tubular heater of this invention can obtain the effect mentioned above by flowing a fluid, it can be used also when heating the solid or gas containing powder.

  Moreover, a hot water washing toilet seat etc. are mentioned as a use of the tubular heater of this invention.

1: Insulating substrate 2: Flow path 3: Power feeding part 4: Lead terminal 5: Pad 6: Resistor 7: Heat generating part 8: Leading part 9: Through-hole conductor 10: Change region

Claims (4)

  A tubular insulating base having a space to be a fluid flow path on the inside, and a resistor having a heat generating portion embedded in the insulating base, the inner wall of the insulating base being the length of the flow path A tubular heater having a change region in which the shape of the surface perpendicular to the length direction of the flow path changes while the cross-sectional area of the surface perpendicular to the direction is substantially constant from the upstream side to the downstream side.   2. The tubular heater according to claim 1, wherein the heat generating portion is provided on one end side of the insulating base, and the change region is provided on the other end side of the insulating base.   The heat generating portion is provided on one end side of the insulating base, and the end of the resistor is led to the surface of the insulating base on the other end side of the insulating base from a position corresponding to the heat generating portion. The tubular heater according to claim 1, wherein:   The tubular heater according to claim 1, comprising a plurality of the change regions.

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