JPH0119747B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a fluid heater in which the tube carrying the fluid to be heated is itself part of the heating element. More specifically, the present invention relates to an electric fluid heater that does not require special electrical insulation between this tube and a tube connected before and after the tube that passes a fluid to be heated.

An invention that is closest to the present invention (a) JP-A-55-142200 "Electric heating pipeline" (b) Japanese Patent Publication No. 58-11344 "Insulation-saving flange fluid heating pipe device" There is.

These inventions (a) and (b) can of course be used for the purpose described above, but invention (a) has too small a heat load (amount of heat generated per unit area of heat generating part) to be used for the purpose of the present invention, Suitable for relatively long pipes such as lines. Invention (b) may be used in some cases for the purposes of the present invention, but is generally suitable for higher power applications.

Furthermore, since the invention (b) has a complicated structure, in the case of a relatively small output, it is desired that the structure be simpler and more economical.

SUMMARY OF THE INVENTION An object of the present invention is to provide a fluid heater having a relatively small scale, low output, moderate heat load, and simple structure.

The present invention provides a fluid heater in which a ferromagnetic outer tube enclosing a conductive inner tube through which a fluid to be heated passes is provided outside the inner tube, and an alternating current is passed through the inner and outer tubes. A transformer core having a primary winding is placed around the outside of the inner tube and inside the outer tube, and the inner and outer tubes are electrically connected at both ends of the outer tube to form a secondary current circuit. The gist of the present invention is a through-tube electric fluid heater.

An electrical insulator may be placed in the gap between the inner and outer tubes. This insulation may be a solid, liquid or gas filling and/or a spacer. It is also preferable that these fillers or spacers have better thermal conductivity than the atmosphere. Examples include heat transfer cement, cement, water, transformer oil, pressurized gas, etc.

Hereinafter, the present invention will be explained with reference to the drawings. FIG. 1 is a schematic cross-sectional view in the longitudinal direction of a tube of an example of the device of the present invention;
FIG. 2 is a schematic cross-sectional view of the X-Y section in FIG. 1.

In FIG. 1, 1 is an AC power source, 4 is a transformer core, and 2 is a primary winding wound around the core 4. 8 is a fluid to be heated, and 6 is a tube through which 8 flows, and together with the outer tube protruding portion 3 at the transformer and the outer tube portion 5 which is approximately coaxial with the tube 6, forms an electric circuit through which a secondary current _i2 flows. ing.

In the gap 10 between the outer tubes 3 and 5, the tube 6, the transformer winding 2, etc., there is a liquid that is electrically insulating but has better thermal conductivity than the atmosphere, such as transformer oil or a heating medium. If filled with , the temperature difference between each part will be reduced,
It can prevent the occurrence of thermal stress. For this purpose, between the outer tubes 3 and 5 and the tube 6, at both ends of the outer tube,
Means 11, 1 for electrically connecting the inner and outer tubes, respectively
It is necessary to use 2 as a closing member and perform welding 11', 12', etc. to prevent liquid leakage. Further, an insulating spacer 7 or the like may be provided between the outer tubes 3, 5 and the inner tube 6 to maintain the distance therebetween, if necessary.

9 is a bushing for passing a conductor connecting the primary winding 2 and the AC power source 1.

FIG. 2 is a schematic cross-sectional view taken along line XY in FIG. Symbols have the same meaning as in Figure 1.

Although the transformer core 4 is a circularly wound core in FIGS. 1 and 2, this is not an absolute condition.

Now, in such a heater, the inner tube 6, outer tubes 3, 5, etc. that form the secondary circuit are made of ferromagnetic steel, and their thickness t has a value called the skin depth of alternating current. S (cm), t≧2S (1) If we set the relationship as t≧2S (1), the secondary current i ₂ is the tube 6,
The flow concentrates on the epidermis on the side of the gap 10 of the outer tubes 3 and 5,
Substantially no voltage appears on the surfaces opposite them, and substantially no secondary current i ₂ flows out.

Here, S is expressed as S=5030√ (2) where the resistivity of the steel is ρ (Ωcm), the relative magnetic permeability is μ (−), and the power frequency is f (Hz).

In equations (1) and (2), even if ρ, μ, S, etc. differ due to different materials of each member, if equations (1) and (2) hold for each member, i ₂ It is possible to prevent the leakage of water to the outside. The tube 6 is made of non-ferromagnetic material such as aluminum or copper, and even if a voltage appears on the surface of the fluid to be transported, if the fluid to be heated is a gas and electrically insulating, current will not flow into this fluid. There is no problem because there is no. Also, even if it is a liquid, mercury
The relationships in equations (1) and (2) are not required unless you want to prevent electrical leakage to a metallic liquid such as molten sodium.

FIG. 3 shows a heating circuit according to the invention (a) described above, in which 1 is an AC power source, 6' is an inner pipe 5' for transporting the fluid to be heated 8, and an outer pipe is connected to the heating circuit by conductive connecting members 11 and 12. ′、
6' are connected to form a current circuit to the power source 1. 9 is an electric bushing, 10 is a gap between the inner and outer tubes, and 7 is an insulating spacer. Comparing this circuit with the circuit of the present invention, if the connecting member 1
The length between 1 and 12 is 25 m, and the diameter of pipe 6' is 20 cm.
If the frequency of this circuit is 50Hz and it generates about 120KW of heat, the power factor is set to 0.8 and the power supply is
The voltage is 25V, which corresponds to a length of 25m ÷ 2 = 12.5m.
The current from the power supply is 3000A on one side, and on both the left and right sides.
It will be about 6000A. The 6000A electric bushing 9 has a complicated structure, and the bus bar from the power source 1 is also large, and if the location is a dangerous place, the cost for disaster prevention will increase.

However, according to the present invention, the connecting member 1 in FIG.
If the length between 1 and 12 is 25 m, the same as in Figure 3, and the diameter of pipe 6 is 20 cm, the voltage of pipe 6, which is the secondary circuit, will be 50 V and 3000 A, corresponding to the pipe length of 25 m.
The busbar between the bushing 9 and the power supply 1, which is the problem, is
The voltage of power supply 1 can be set arbitrarily, so if the power supply voltage (primary voltage) is 400V, the current flowing from the power supply to primary winding 2, which is the primary circuit, is 375A.
Therefore, it is possible to use something much simpler than the case of invention (a).

Next, whereas in the known case of FIG. 3, the position of the power source or electric bushing 9 had to be approximately in the center of each section of the tube 6', in the present invention, as shown in FIG. , can be provided at one end or at any arbitrary position. It is also possible to connect several sets of the units shown in FIG. 1 in the direction of the tube 6, that is, in the direction of the flow of the fluid 8, as shown in FIG.

Furthermore, as is clear from this figure, the device shown in FIG. 1 differs from the device shown in FIG. Not only can the connection bus between the power source and the heater be omitted, but there is no energy loss that would otherwise occur due to the bus, and the loss in the transformer core 4 and winding 2 can be used to heat the fluid 8, reducing energy consumption. It also has the advantage of increasing efficiency.

[Brief explanation of drawings]

FIG. 1 is a schematic longitudinal cross-sectional view of the heater of the present invention;
FIG. 2 is a schematic partial cross-sectional view taken along the line X-Y in FIG. 1, and FIG. 3 is a schematic diagram of the known invention (a). In Figures 1 and 2, 1 is an AC power source, 2 is a primary winding wound around the transformer core 4, 8 is a fluid to be heated, and 6 is a primary winding wound around a transformer core 4.
is a pipe through which 8 flows, 3 and 5 are pipes 6, outer pipes containing transformers 2 and 4, 7 is an insulating spacer, 10 is a gap, 9
is electric bushing. In FIG. 3, 6' is a tube through which the fluid to be heated 8 passes, 5' is an outer tube substantially coaxial with 6', and other symbols are the same as in FIGS. 1 and 2.

Claims (1)

[Claims] 1. A ferromagnetic outer tube enclosing the conductive inner tube is provided outside the conductive inner tube through which the fluid to be heated passes, and an electrical insulator is provided in the gap between the inner tube and the outer tube. In a fluid heater, which may or may not be arranged and in which an alternating current is passed through the inner tube and the outer tube, a transformer core that surrounds the outside of the inner tube and has a primary winding inside the outer tube. A through-tube type characterized in that an inner tube and an outer tube are electrically connected at both ends of the outer tube so that the inner tube and the outer tube form a secondary current circuit. Electric fluid heater. 2. The heater according to item 1, wherein a portion of the outer tube protrudes more outward in the core portion than in other portions in order to accommodate the transformer core. 3. The heater according to item 1 or 2, wherein the electrical insulator disposed in the gap between the inner tube and the outer tube is a filler and/or a spacer. 4. The heater according to item 3, wherein the filler or spacer has a higher thermal conductivity than air.