JP3903339B2 - Fluid heating device by electromagnetic induction - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an electromagnetic induction heating device that heats a heating element with an eddy current generated in the heating element by electromagnetic induction and heats a fluid such as a gas or a liquid brought into contact with the heating element.
[0002]
[Prior art]
Conventionally, gas and liquid are heated by using oil or gas combustion energy as a heat source such as a boiler, using natural energy as a heat source such as sunlight, or using electric energy as a heat source. There is a way to do it.
[0003]
The method of using combustion energy as a heat source requires cost for auxiliary equipment such as a fuel supply system, and also requires extra cost for ensuring safety against combustion and proper processing of exhaust gas generated by combustion. . Furthermore, the responsiveness of temperature control is very poor.
[0004]
The method using natural energy as a heat source is not only high in cost but also directly affected by natural conditions, so that stable heating is difficult to obtain.
[0005]
As a method of using electric energy as a heat source, resistance heating, infrared heating, and the like are used for industrial purposes. Resistance heating or infrared heating is an indirect heating type in which a heat exchanger that heats a gas or liquid is heated by heat conduction from a heater that is a heating element, and heating efficiency and responsiveness of temperature control are poor.
[0006]
On the other hand, as one method of using electrical energy as a heat source, there is direct heating type electromagnetic induction heating in which the heat exchanger itself becomes a heating element.
[0007]
FIG. 6 is a diagram showing the principle of direct heating type electromagnetic induction heating.
This is composed of a heat generating element 11 having conductivity and an induction coil 12 in which a conductive wire is arranged around the heat generating element 11 in a coil shape. When a high-frequency current I is passed through the induction coil 12, an alternating magnetic flux φ is generated. Due to this alternating magnetic flux φ, an eddy current flows through the heating element 11, and the heating element 11 generates heat due to this eddy current. As a result, the gas or liquid fluid in direct contact with the heating element 11 is heated. This method is known to have good temperature control responsiveness and excellent thermal efficiency.
[0008]
The electromagnetic induction heating method can be expected to have a high heat exchange rate in principle. In order to further improve the heat exchange rate, there are the following technical proposals related to the fluid heating method using electromagnetic induction heating.
In the case of improving the heat exchange rate in an induction heating cell that performs electromagnetic induction heating, as described below, each method mainly uses multiple fine heating elements to increase the heat transfer area of the heating elements. It has been placed.
[0009]
For example, in Japanese Patent Application Laid-Open No. 9-260042, a fluid pipe is filled with a large number of granular, linear, and rod-like pieces serving as heating elements to increase the area of the small piece in contact with the fluid. A method is shown in which the small piece heated by electromagnetic induction heats the fluid by passing a current through the heating coil.
[0010]
In JP-A-9-167679, by laminating corrugated sheets, a large number of cylinders are formed as a whole, the heat transfer area is increased, and these are used as heating elements to improve thermal efficiency. A method is also shown.
[0011]
Furthermore, in Japanese Patent Application Laid-Open No. 8-264272, specific guidelines regarding the operating frequency band and heat transfer area of the electromagnetic induction heating device are shown.
[0012]
[Problems to be solved by the invention]
FIG. 7 shows a structure of a general induction heating cell serving as a fluid heating device.
FIG. 7A shows a cross section of a cylindrical induction heating cell, and FIG. 7B shows a cross section of a rectangular parallelepiped induction heating cell.
[0013]
The structure of the induction heating cells 13 and 14 shown in FIG. 7 includes a heating element 15 that generates heat by electromagnetic induction, a heating cell case 16 that houses the heating element 15, and an induction coil 17 that is disposed on the outer periphery of the heating cell case 16. The induction heating cells 13 and 14 have the same structure. The heating element 15 is composed of a plurality of fine conductive pipes, a lattice-like fine conductive plate, and the like. In order to protect the induction coil 17, the heating cell case 16 is made of an insulating material and is electrically and thermally insulated from the heating element 15. The fluid is allowed to flow in direct contact with the heating element 15 in the heating cell case 16, thereby heating the fluid.
[0014]
In order to improve the heat exchange rate, as shown in FIG. 7, it is necessary to use a plurality of fine conductors to increase the heat transfer area of the heating element and to transfer more heat generated by the heating element to the fluid. There is. This heat transfer amount is expressed by the following equation, and is determined by the heat transfer area, the heat transfer rate, and the temperature difference between the heat source and the fluid.
Q = S × h × ΔT
Here, Q is the heat transfer amount [W], S is the heat transfer area [m ² ], h is the heat transfer coefficient [W / (m ² · ° C.)], and ΔT is the temperature difference between the heat source and the fluid [° C. ].
[0015]
From the above formula, in order to improve the heat exchange rate (heat transfer amount), it is conceivable to increase the product of the heat transfer rate and the temperature difference in addition to increasing the heat transfer area.
Of these, the heat transfer coefficient is expressed by the following equation.
h = 1.93 × (v / x) ^1/2
Here, v represents the flow velocity [m / s] of the fluid, and x represents the distance [m] from the inlet of the heat transfer section.
[0016]
From the above formula, in order to improve the heat transfer rate, it is necessary to increase the flow rate of the fluid, but simply increasing the flow rate will increase the amount of fluid used, and when applied to an actual manufacturing device , Leading to a significant cost increase.
[0017]
Therefore, attention is paid to the temperature difference as a parameter related to an increase in the amount of heat transfer.
[0018]
When an electromagnetic induction heating cell is actually constructed, there is a variation in temperature distribution in the flow direction of the fluid of the heating element and the plane perpendicular to the flow. In general, in order to control the temperature distribution of a heating element by electromagnetic induction, it is conceivable to adjust the winding method of the induction coil. However, depending on the winding method, a large amount of space may be required. Even restrictions come out.
[0019]
Therefore, a method for controlling the temperature distribution of the heating element other than the method of winding the induction coil is required.
[0020]
As the method, a method of controlling the heating element with an optimal combination of a magnetic substance and a non-magnetic substance can be considered. As a method actually devised, there is a method of making the temperature distribution of the surface perpendicular to the fluid flow of the heating element uniform by optimizing the combination of the magnetic pipe and the non-magnetic pipe. However, there is no example of a method for optimizing the temperature distribution in the fluid flow direction of the heating element.
[0021]
FIG. 8 is a diagram showing a temperature distribution in the fluid flow direction of the heating element in the induction heating cell.
In FIG. 8, a cross section in the longitudinal direction of the induction heating cell is schematically shown at the top of the drawing so that the correspondence relationship with the graph of the temperature distribution can be easily understood.
[0022]
As shown in FIG. 8, the temperature distribution in the fluid flow direction of the heating element of the induction heating cell has a convex distribution whose central part is higher by about several tens of degrees C. than the end part of the heating element. This is because the upstream and downstream ends are affected by leakage magnetic flux and heat dissipation, and the temperature is lower than that at the center.
[0023]
Since the heating element has a temperature distribution as shown in FIG. 8, when the output of the power source is increased in order to increase the amount of heat transfer to the fluid, only the central part of the heating element approaches the limit temperature of the material of the heating cell case. Therefore, the heat resistance is governed by the center of the induction heating cell.
When the heat transfer amount from the heating element to the fluid exceeds the heat capacity of the fluid, the heat that has not been transferred to the fluid is transferred to the surrounding heating cell case or induction coil. This becomes a heat loss, which leads to a decrease in the heat exchange rate.
[0024]
Therefore, in view of the above problems, the present invention provides a fluid heating apparatus by electromagnetic induction that optimizes the temperature distribution in the fluid flow direction and improves the heat exchange rate.
[0025]
[Means for Solving the Problems]
Fluid heating device by electromagnetic induction according to the present invention to solve the above problems, as the temperature of the lower stream side and the upstream side of the heating element having a non-magnetic material approaches the temperature of the longitudinal center portion of the heating element , inserting the magnetic body of the nonmagnetic material shorter length, it is inserted into the lower flow side end and the upstream end of the heating element, the magnetic body and the upstream end to be inserted at the downstream end The length of the magnetic material is different . The above invention, the temperature of the lower stream side and the upstream side of the heating element, close to the temperature of the longitudinal center portion of the heating element, can be made equal.
[0026]
The fluid heating apparatus using electromagnetic induction according to the present invention that solves the above-described problems is characterized in that the length of the magnetic body inserted into the downstream end is shorter than the length of the magnetic body inserted into the upstream end. to.
[0027]
The fluid heating apparatus by electromagnetic induction according to the present invention for solving the above-mentioned problems is characterized in that the non-magnetic body and the magnetic body are made into fine pipes, and the magnetic body can be inserted into the non-magnetic body. And
According to the above invention, a fine pipe made of a magnetic material having an appropriate length can be appropriately arranged in a fine pipe made of a non-magnetic material.
[0028]
DETAILED DESCRIPTION OF THE INVENTION
Example 1
FIG. 1 shows the structure of a fluid heating apparatus (hereinafter referred to as induction heating cell) according to an embodiment of the present invention.
FIG. 1A is a diagram showing the structure of the upstream end of the fluid of the induction heating cell 1, and FIG. 1B is a diagram showing the structure of the induction heating cell 1 in the flow direction. 1 (c) is a diagram showing the structure of the downstream end of the fluid in the induction heating cell 1. FIG.
[0029]
The induction heating cell 1 has a rectangular parallelepiped shape, a non-magnetic fine pipe-like non-magnetic pipe 2a, and a cell case 3 containing the plurality of non-magnetic pipes 2a and having an insulating property. The heat insulating material 4 provided so as to cover the outer periphery of the cell case 3 and the induction coil 5 disposed on the outer periphery of the heat insulating material 4 are provided. The plurality of nonmagnetic pipes 2a serve as heating elements that generate heat by electromagnetic induction. Similarly to a general heating cell, electromagnetic induction is caused by passing an electric current through the induction coil 5, and the heating element is heated by electromagnetic induction to heat the fluid flowing in the cell case 3.
[0030]
Specifically, the material of the cell case 3 was an electrically insulating ceramic (Narumi ceramic neo-ceram). The dimensions are 254 mm width × 11.8 mm height × 80 mm length, and the wall thickness is 3 mm. Isolite-made kao wool is used for the heat insulating material 4 provided around the cell case 3, and the induction coil 5 installed on the outer periphery thereof has two 2.0mm ² sizes of KIF wires (heat-resistant wires) made by Hitachi Cable in parallel. Used and the number of windings was 9 turns.
[0031]
The heating element has a structure in which fine non-magnetic pipes 2a made of stainless steel are assembled. The nonmagnetic pipe 2a has dimensions of an outer diameter of 1.0 mm, an inner diameter of 0.9 mm, and a length of 70 mm. As a material, SUS316 which is a non-magnetic material is used.
[0032]
A fine magnetic pipe 2b using SUS430, which is a magnetic material, is inserted into some of the nonmagnetic pipes 2a. The magnetic pipe 2b uses a magnetic body that is efficiently heated even at a low frequency, and is combined with a non-magnetic body to form a heating element, so that the in-plane perpendicular to the fluid flow of the heating element of the induction heating cell 1 is obtained. It is possible to achieve both uniform temperature uniformity and temperature in the fluid flow direction and efficient heating.
[0033]
The power source frequency and the efficiency of induction heating can be considered using the current penetration depth d [cm]. The penetration depth of the current is expressed by the following equation. This equation is an important parameter in induction heating.
d = 5030 × (ρ / (μ × f)) ^1/2
Here, μ is magnetic permeability, ρ is resistivity [Ω · cm], and f is power supply frequency [Hz].
[0034]
In SUS430, from μ >> 1, ρ = 60 × 10 ⁻⁶ [Ω · cm], when the power supply frequency is 50 kHz, the current penetration depth is 0.05 mm or less. Since the penetration depth of the current is equal to or less than the thickness (0.05 mm) of the magnetic pipe 2b, the SUS430 can be efficiently heated at a power supply frequency of 50 kHz or more.
[0035]
As shown in FIG. 1 (c), in the induction heating cell 1, the magnetic pipe 2b is used to make the temperature in the plane perpendicular to the fluid flow of the heating element and the temperature in the fluid flow direction uniform and to improve the heating efficiency. Is inserted downstream of the induction heating cell 1, and every other magnetic pipe 2b having an outer diameter of 0.88 mm, an inner diameter of 0.68 mm, and a length of 20 mm is inserted into the non-magnetic pipe 2a. This means that the magnetic pipe 2b is inserted with a dense and uniform density on the surface of the heating element perpendicular to the fluid flow.
[0036]
Further, as shown in FIG. 1A, the cross section perpendicular to the fluid flow direction of the cell case 3 being used is a rectangle having a large aspect ratio, so that the temperature distribution in the longitudinal direction of the cross section is made uniform. Therefore, the magnetic pipe 2b is also inserted at an appropriate position in the nonmagnetic pipe 2a on the upstream side. The magnetic pipe 2b has a size of an outer diameter of 0.88 mm, an inner diameter of 0.68 mm, and a length of 50 mm.
[0037]
FIG. 2 is a diagram showing a temperature boundary layer of a fluid flowing on a flat heating element having a constant temperature, and a graph showing changes in the amount of heat transfer with respect to the temperature of the heating element and the flow direction of the fluid in the lower part. The induction heating cell is heated at a power supply frequency of 50 kHz, air is used as a fluid gas, and its flow rate is 5 l / min.
[0038]
In FIG. 2, the surface of the heating element has a constant temperature Th in the fluid flow direction, and a fluid having an initial temperature T0 flows on the surface of the heating element. As shown in FIG. 2, the temperature boundary layer, which is a region having a temperature different from that of the fluid and the heating element, has a wide region on the downstream side of the fluid. In general, in the heat transfer from a flat plate having a constant temperature, the temperature difference between the heating element and the fluid decreases toward the downstream side due to the temperature boundary layer, and the amount of heat transfer decreases.
[0039]
In the conventional induction heating cell, the surface of the heating element is not constant, and has a convex temperature distribution as shown in FIG. Therefore, the heat transfer amount from the heating element to the fluid is significantly reduced on the downstream side.
[0040]
On the other hand, in the induction heating cell 1, since the magnetic body having a very large electromagnetic induction effect is densely inserted on the downstream side, the temperature of the heating element is higher on the downstream side than that of the conventional induction heating cell. . For this reason, on the downstream side, the temperature difference between the heating element surface and the fluid becomes large, and the total heat transfer amount can be increased.
[0041]
FIG. 3 is a graph showing the temperature distribution and heat transfer amount of the heating element in the induction heating cell 1 with respect to the fluid flow direction. For comparison, the temperature distribution and heat transfer amount of the heating element in the conventional induction heating cell are also shown.
[0042]
As shown in the graph of FIG. 3, in the induction heating cell 1, the temperature of the heating element on the downstream side of the induction heating cell can be brought close to and equal to the temperature of the central portion in the longitudinal direction of the heating element. The amount of heat transfer to the fluid on the downstream side of the heating cell can be increased.
[0043]
This is because the temperature on the downstream side of the heating element is increased by using the magnetic flux (leakage magnetic flux) on the downstream side of the induction heating cell 1 that could not be used in the prior art. The amount of transmission increases, which is effective in improving the heat exchange rate.
[0044]
(Example 2)
In the induction heating cell 1 according to the first embodiment, the magnetic pipe 2b is additionally inserted densely and uniformly at the downstream side of the nonmagnetic pipe 2a. However, as another embodiment, the magnetic pipe is disposed upstream of the nonmagnetic pipe 2a. It is conceivable to additionally insert 2b at a dense and uniform density. The insertion position of the magnetic pipe is on the upstream side of the induction heating cell, and every other magnetic pipe 2b is inserted into the non-magnetic pipe 2a. Further, since the cross section perpendicular to the fluid flow direction of the cell case 3 being used is a rectangle having a large aspect ratio, the nonmagnetic pipe 2a on the downstream side is made uniform in order to uniformize the temperature distribution in the longitudinal direction of the cross section. In addition, the magnetic pipe 2b is inserted at an appropriate position.
[0045]
FIG. 4 is a graph showing the temperature distribution and heat transfer amount of the heating element in the induction heating cell of Example 2 with respect to the fluid flow direction. For comparison, the temperature distribution and heat transfer amount of the heating element in the conventional induction heating cell are also shown.
[0046]
As shown in FIG. 4, compared with the conventional induction heating cell, the temperature of the heating element on the upstream side can be brought close to and equal to the temperature of the central portion in the longitudinal direction of the heating element, so that the fluid on the upstream side The amount of heat transfer to can be increased. Similarly to the induction heating cell 1 of the first embodiment, this can use the conventional leakage magnetic flux and is effective in improving the heat exchange rate.
[0047]
(Example 3)
As yet another embodiment, it is conceivable to additionally insert the magnetic pipe 2b with a dense and uniform density on both the upstream and downstream sides of the nonmagnetic pipe 2a. The insertion positions of the magnetic pipe 2b are upstream and downstream of the induction heating cell, and every other magnetic pipe 2b is inserted into the non-magnetic pipe 2a.
[0048]
FIG. 5 is a graph showing the temperature distribution and heat transfer amount of the heating element in the induction heating cell of Example 3 with respect to the fluid flow direction. For comparison, the temperature distribution and heat transfer amount of the heating element in the conventional induction heating cell are also shown.
[0049]
As shown in FIG. 5, both the upstream side and downstream side of the induction heating cell are additionally inserted with magnetic pipes 2b with a dense and uniform density, so that the heating elements upstream and downstream of the conventional induction heating cell. Can be made equal to the temperature of the central portion in the longitudinal direction of the heating element, and as a result, the heat exchange rate can be further improved.
In addition, since the temperature distribution of the heating element is made uniform in the fluid flow direction, only part of the heating element will not reach the limit temperature of the cell case as the temperature is increased. Even the induction heating cell can be used up to a higher output area.
[0050]
In the above-described Examples 1, 2 and 3, and FIG. 1, a rectangular parallelepiped induction heating cell having a width of 254 mm × height 11.8 mm × length 80 mm has been described. However, the shape and size of the induction heating cell according to the present invention are described. However, the present invention is not limited to this, and can be appropriately changed according to the type of fluid, the flow rate, and the like.
[0051]
In addition, the length, number, insertion position, etc. of the non-magnetic pipe as the heating element and the additional magnetic pipe to be inserted also depend on the shape and size of the induction heating cell. The temperature of the heating element can be appropriately changed so that the temperature of the heating element can be kept uniform in the fluid flow direction, and the shape of the heating element itself is not limited to the pipe shape, but other granular, linear, rod-like, plate-like, etc. Can also be applied.
[0052]
【The invention's effect】
According to the invention of claim 1, 2, so that the temperature of the lower stream side and the upstream side of the heating element having a non-magnetic body approaches the temperature of the longitudinal center portion of the heating element, said non-magnetic material the length of the magnetic member to insert the shorter length magnetic material, is inserted into the lower flow side end and the upstream end of the heating element, the magnetic body and the upstream end to be inserted at the downstream end In addition, since the length of the magnetic body inserted into the downstream end is shorter than the length of the magnetic body inserted into the upstream end , the heating element the temperature of the lower stream side and the upstream side of, close to the temperature of the longitudinal center portion of the heating element, can be equal, it is possible to increase the heat transfer to the fluid. In addition, since the temperature at the end of the heating element is increased by using the leakage magnetic flux at the end of the induction heating cell that could not be used in the past, the amount of heat transfer can be increased with the power output equivalent to the conventional one, As a result, the heat exchange rate can be improved. In addition, since the temperature distribution of the heating element is made uniform in the fluid flow direction, only a part of the heating element does not reach the limit temperature of the cell case, and can be used up to a higher output area. .
[0054]
According to the invention of claim 3, the non-magnetic body and the magnetic body are formed as fine pipes, and the magnetic body can be inserted into the non-magnetic body. A fine pipe made of a magnetic material can be appropriately arranged in a fine pipe made of a non-magnetic material, whereby the above temperature distribution can be easily realized.
[Brief description of the drawings]
FIG. 1 is a structural diagram of an induction heating cell according to an embodiment of the present invention. (A) is a structural diagram at the upstream end of the induction heating cell, (b) is a structural diagram of a cross section in the longitudinal direction of the induction heating cell, and (c) is a downstream end of the induction heating cell. FIG.
FIG. 2 is a diagram showing a temperature boundary layer of a fluid flowing on a flat heating element having a constant temperature, and a lower part is a graph showing the heat transfer amount of the heating element with respect to the temperature of the heating element and the flow direction of the fluid.
FIG. 3 is a graph showing a temperature distribution and a heat transfer amount of a heating element with respect to a fluid flow direction in the induction heating cell of Example 1 according to the present invention.
FIG. 4 is a graph showing a temperature distribution and a heat transfer amount of a heating element with respect to a fluid flow direction in the induction heating cell of Example 2 according to the present invention.
FIG. 5 is a graph showing a temperature distribution and a heat transfer amount of a heating element with respect to a fluid flow direction in an induction heating cell of Example 3 according to the present invention.
FIG. 6 is a diagram showing the principle of direct heating type electromagnetic induction heating.
FIG. 7 is a diagram showing the structure of an induction heating cell. (A) is sectional drawing of a cylindrical induction heating cell, (b) is sectional drawing of a rectangular parallelepiped induction heating cell.
FIG. 8 is a schematic diagram in the longitudinal direction of an induction heating cell and a diagram showing a temperature distribution of a heating element with respect to a fluid flow direction.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Induction heating cell 2a Nonmagnetic pipe 2b Magnetic pipe 3 Cell case 4 Heat insulating material 5 Induction coil 11 Heating body 12 Induction coil 13 Cylindrical induction heating cell 14 Rectangular induction heating cell 15 Heating body 16 Heating cell case 17 Induction coil

Claims (3)

It has a cell case having an insulating property, a plurality of nonmagnetic materials accommodated in the cell case, and an induction coil wound around the outer periphery of the cell case, and is caused by passing a current through the induction coil In the fluid heating device that heats the non-magnetic body as a heating element by electromagnetic induction and heats the fluid flowing in the cell case,
Wherein the temperature of the lower stream side and the upstream side of the heating element, so as to approach the temperature of the longitudinal center portion of the heating element, wherein the magnetic material of the nonmagnetic shorter length, the lower flow side of the heating element is inserted into the end portion and the upstream end, a fluid by electromagnetic induction, characterized in that the length of the magnetic material inserted into the magnetic body and the upstream end to be inserted into the downstream end portion different Heating device. The fluid heating apparatus by electromagnetic induction according to claim 1,
A fluid heating apparatus using electromagnetic induction, wherein a length of the magnetic body inserted into the downstream end is shorter than a length of the magnetic body inserted into the upstream end. In the fluid heating apparatus by electromagnetic induction according to claim 1 or 2,
A fluid heating apparatus using electromagnetic induction, wherein the non-magnetic body and the magnetic body are made into fine pipes, and the magnetic body can be inserted into the non-magnetic body.

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