CN101128072A - Skin electrical heating part - Google Patents

Abstract

The utility model relates to a skin-effect heating component, comprising a carbon steel tube, a plurality of alloy heating wires, a plurality of magnesia powder, a leading bar, metal plug and an anti-corrosive stainless steel bushing, Which is applied for various large electric heating equipments in petrol, chemical, electric power and similar industries. The utility model has the advantages of simple structure, high reliability, long life and that no current passes through the whole surface of the carbon steel tube, thus the insulation problem of cluster large-power electric heating component is solved, enabling wide market prospect.

Description

Skin electrical heating part

Technical field

The present invention relates to electric pyrogenicity principle electric heating element, especially in conjunction with the electric heating element of kelvin effect, proximity effect, Joule effect one.

Background technology

At present, " tubular metal electric heating element JB/T2379-93 " mechanical industry standard of national industrial electroheat Standardization instrument technology committee member issue has been stipulated its use, replacing, reliable, durable safety, economical rationality and requirements of saving energy.It is big to require also should to propose power in addition for the industrial electroheat Element Technology, length is long, is fit to the requirement of the various conditions of high temperature or anti-corrosion medium, and wherein the 3.1.1b both-end is drawn, the electric heating element of one termination enclosure form is a kind of better suited ideal structure (in order to understand, seeing Fig. 1).Though that this structure can be made is long, religion is thick, higher, the simple installation of efficient changes industrial electroheat element easily, outer casing electrification during its shell (promptly claiming metal tube) work; When directly contacting, human body may cause electric shock fully; So abnormally dangerous, even the collection skin large power, electrically heater of form of flanges is made in the weldering of many electric heating elements, or change electric connection and will more can cause Personal Risk's possibility.As danger more in explosivity, gaseousness place or explosive dust place.

Summary of the invention

The objective of the invention is a kind of industrial electroheat element, is to utilize kelvin effect, proximity effect, and the Joule effect principle has thoroughly solved " shell " charged insulation complete problem simultaneously in above-mentioned " one termination enclosure structure " on the cost basis of equipment change structure.

1. known, the impedance of carbon steel pipe under industrial frequency AC is significantly greater than its D.C. resistance.General carbon steel pipe also can produce tangible kelvin effect.Electric current only flows through at the carbon steel pipe inwall when having spiral heating alloy two ends respectively to add power-frequency voltage by opposite current respectively in carbon steel pipe two ends and its hole, and outer wall does not have electric current process, no-voltage." proximity effect " and kelvin effect have appearred.Formed " collection skin conducting ring " at the carbon steel pipe inwall, its outside has formed " collection skin dead ring ".And current density changes decay from the interior nature index law of pressing outward, and its principle heats based on the eddy current of electromagnetism sense and heat that magnetic hysteresis produced.As the carbon steel pipe and the heating alloy other end are connected, the other end at both adds voltage, just JB/T2379-93 3.1.1b " both-end is drawn, the one termination enclosure " version is identical, and only its version is different and different with the principle of the invention.The former adopts the Joule heat principle, and the latter utilizes electromagnetic eddy and heat that magnetic hysteresis produces and Joule heat; The former electric loop current is through the gross section of heating alloy and common metal pipe, and the latter's electric loop current is through the inner wall section of heating alloy and carbon steel pipe.(resistance of ignoring eduction rod and plug can be set up equivalent-circuit model of the present invention and see Fig. 2.

According to Kirchhoff's second law:

＝I(r+R)+jI(X _L+X _C)…………………………(1)

In the formula:  is an input ac voltage;

I is the alternating current by heating alloy and carbon steel pipe;

R is the resistance of heating alloy;

R is the resistance of carbon steel pipe;

X _LInduction reactance for heating alloy;

X _CCapacitive reactance for carbon steel pipe;

By (1) formula as seen: real part r+R heating alloy resistance and carbon steel pipe active component have formed Joule heat, the X of portion of portion _L+ X _CAlloy taenidium induction reactance and carbon steel pipe capacitive reactance portion are at the heat of carbon steel pipe inwall electromagnetic eddy and magnetic hysteresis generation.(wherein carbon steel pipe is difficult to accurately calculate determine because of resistance and the capacitive reactance that relates to magnetic permeability, only measures meritorious electrical parameter and could calculate other parameter.)

2. the wall thickness of carbon steel pipe is the key of decision safety, determines the current density obedience physical index rule decay of carbon steel pipe wall thickness from the inwall to the outer wall quantitatively $j=j_{o}e\frac{d}{\mathrm{ds}}......\left(2\right)$

J wherein _o: the current density in carbon steel pipe cross section;

J: the current density of carbon steel pipe;

D: the thickness of carbon steel pipe;

Ds: current density has been reduced to j from inwall outside pipe _o37% the degree of depth be called " skin depth ".

Under power frequency, skin depth is directly proportional with square newspaper of resistivity, is inversely proportional to the square root of relative permeability.Because the carbon steel pipe relative permeability is very high, and not a nonlinear constant, 10#, 20# carbon pipe or pure iron pipe for production caliber inequality " 3/4～3 " specification just have relative permeability inequality, (getting about 100) actual uses that to recommend to get the carbon steel pipe wall thickness be more than 3 times of skin thickness that become for safe in utilization about the about hundreds of of scope.

$j=5030\sqrt{\frac{\mathrm{\ρ}}{u.f}}................................................\left(3\right)$

In the formula: j: skin depth cm;

P: carbon steel pipe resistivity Ω .cm;

U: relative permeability;

F: frequency HZ.

Description of drawings

Fig. 1, be " JB/T2379-93 gold tubular electrothermal element " mechanical industry standard, the 3.1.1.b both-end is drawn, the structure chart of one termination enclosure.

Fig. 2, be equivalent-circuit model schematic diagram of the present invention.

Fig. 3, be examination slowdown monitoring circuit of the present invention.

Fig. 4, the skin thickness map that becomes of the present invention.

Among the figure: 1. heating alloy; 2. magnesia powder; 3. metal tube

4. metal plug; 5. end seal material; 6. eduction rod

7. the resistance of heating alloy, symbol R;

8. the induction reactance of heating alloy, symbol X _L

9. the resistance of carbon steel pipe, symbol r;

10. the capacitive reactance of carbon steel pipe, symbol X _C

11. collection skin conducting ring, S; 12. collection skin dead ring, T;

13. the carbon steel pipe internal diameter, d; 14. the carbon steel pipe external diameter, D; 15. carbon steel pipe wall thickness δ;

16. critical potential  for the skin thickness that becomes ₀17. zero line is to tail end current potential  _W

18. the head end phase line to other each hole of tail end at the bottom of current potential  _X19. AC power ;

20. for the current potential  of carbon steel pipe from internal diameter to external diameter _Z21. surrounding environment;

22. carbon steel pipe resistance  _C23. platform gold heating wire resistance  _L

Embodiment

Now use an industrial skin electrical heating part, 20# carbon steel pipe specification is  18*3.5mm, and long 7.5m wears a right hand helix silk in its hole, and material is Cr20Ni80,  1.3mm, and resistivity is 1.05 Ω mm ²/ m, taenidium external diameter are  5mm, and pitch is 8.4mm, length of run 8.16mm, D.C. resistance 6.45 before making.Press Fig. 1 structure, two ends two eduction rods of burn-oning, an eduction rod connects heating alloy, another eduction rod connects, metal plug and the welding of carbon steel pipe tail end, the eduction rod that connects heating alloy is received the power frequency supply phase line, and the head end surface of carbon steel pipe is received the power frequency supply zero line and is linked to be the heating of electric loop.Isometric being positioned in the middle of the carbon steel pipe closely filled crystal magnesium oxide between carbon steel pipe and taenidium.Make dress taenidium eduction rod in the carbon steel pipe through draw technology, crystal magnesium oxide makes pipe range 7.5m, and elongation 8.2m makes former D.C. resistance 6.45 Ω increase 7.3 Ω, heating wire surface thermal load 17w/cm ², electrothermal tube surface thermal load 1.8w/cm ²The skin electrical heating part of this enforcement is connected the 220V50HZ power frequency supply, and its power is 5588W, electric current 25.4A.Measuring voltage at the carbon steel pipe two ends is  _CBe 0.4V, measure voltage  at the voltage at heating alloy two ends _LBe 216V, can rated output factor (216V+0.4V) * 25.4A/220V*25.4A=0.98.By the above-mentioned carbon steel pipe AC resistance rate 0.33 Ω mm that calculates ²/ m.This skin electrical heating part attribute ohmic load.And be connected into hookup by Fig. 3.As seen from Figure 3, skin electrical heating part is identical from head end to tail end collection skin conducting ring thickness, can get by getting the hole that  5mm is bored at 8 positions respectively near the tail end, its degree of depth gets 0.5,1.0,1.5,2.0,2.3,2.7,3.0 respectively from carbon steel pipe from the outer radial internal diameter, 3.3mm, and measure at the bottom of the pore respectively and the current potential  numerical value on carbon steel pipe head end surface, Fig. 4 such as following table:

Degree of depth mm	Dead ring							Conducting ring
										0.5	1.0	1.5	2.0	2.3	2.7	3.0	3.3	 W
	Drain voltage (V) between at the bottom of carbon steel pipe head end phase line and each hole	0.01	0.01	0.03	0.03	0.03	0.04	0.04	0.35										0.6

On the other hand, the drain voltage  on Φ 18 * 3.5 carbon steel pipe surfaces _WMeasure the rule to find out increase in direct ratio to tail end from the head end 2mm of whenever being separated by.The tail end maximum can see Table down:

Length m	2	4	6	8.2
					Drain voltage V	0.09	0.17	0.24	0.33

Show that by Fig. 4 collection skin dead ring and collection skin conducting ring are very obvious, though because the outer drain voltage of carbon steel pipe exists, and it is very faint can not to cause danger to human body, just carbon steel pipe self has insulated.For safe and reliable, it is " skin thickness becomes " 5 times that carbon steel pipe thickness should be got, i.e. safety economical rationality again.Though self has insulating properties steel pipe, the objective drain voltage of carbon steel pipe exists, must be with its ground protection (see figure 2).Obviously as seen find " skin thickness becomes " for about 0.4mm from the last table and the skin thickness chart 4 that becomes.Check with (3) formula and to have directiveness.

$j=5030\sqrt{\frac{\mathrm{\ρ}}{u.f}}=5030\sqrt{\frac{{0.33\mathrm{\Ωmm}}^2/m\×{10}^{-6}}{100\×50\mathrm{HZ}}}=0.4\mathrm{mm}$

Meet with present embodiment.

In addition, this skin electrical heating part can put corrosion-resistant and high-temperature resistant at carbon steel pipe, and stainless steel such as Incolog600, Monel400 etc. adopt draw technology closely to put and polish.

Claims (4)

1. the present invention is a kind of skin electrical heating part, by carbon steel pipe, heating alloy, magnesia powder, eduction rod, the metal plug is formed, two eduction rods are arranged, an eduction rod connects heating alloy, another eduction rod connects the metal plug, metal plug and the welding of carbon steel pipe tail end, between heating alloy and carbon steel pipe, be magnesia powder, the eduction rod of heating alloy is drawn the phase line of receiving carbon steel pipe head end power frequency power frequency supply continuously, the zero line of power frequency supply is received on the head end surface of carbon steel pipe, is linked to be the heating of electric loop, and it is characterized in that: current circuit is through heating alloy, the inwall of metal plug and carbon steel pipe, the whole surface of carbon steel pipe does not have electric current to pass through.

2. skin electrical heating part according to claim 1 is characterized in that: the conductor material through the inwall current circuit is a carbon steel pipe.

3. skin electrical heating part according to claim 1 is characterized in that: carbon steel pipe is that thickness is taken as the collection skin thickness more than 3 times.

4. skin electrical heating part according to claim 1 is characterized in that the corrosion-resistant stainless steel sheath is arranged above the carbon steel pipe.

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