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Tubular electric heater element
Feb 09, 2018

Tubular electric heating elements (electrothermal tubes) are electrical components that convert electrical energy into thermal energy.It was based on the metal pipe of the shell (including stainless steel, copper tube), along the axial uniform spiral tube center electric thermal bonding wire, nickel chromium, iron chromium alloy) the gap filling compaction with good thermal conductivity of insulating oxide magnesia, with silicone seal on both ends of the tube, the metal armoured electric heating element to heat the air, metal molds and all kinds of liquid.The common electric heat pipes are fin electric heat pipe, fin electric heat pipe, fin electric heat pipe, teflon electric heat pipe, quartz electric heat pipe and so on.Due to its low price, convenient use, convenient installation and no pollution, it is widely used in various heating occasions.


Introduction to edit

Electric heat pipe [2] is also known as heat pipe and heating tube, which is a tubular heater element, which is placed in a metal tube in a coil wire (resistance wire).

Electric heat pipe

Electric heat pipe

The insulation powder (MgO) with good heat resistance, thermal conductivity and insulation is filled in the surrounding and void parts, and the ends of the heating wire have the outlet rod or lead wire.It has the characteristics of simple structure, high mechanical strength, high thermal efficiency, safe and reliable, simple installation and long service life.It is widely used in all kinds of nitrite groove, trough, oil groove, acid base tank, fusible metal melting furnace, air heating furnace, drying oven, drying oven, hot pressing mould and so on.

Electric heat pipe is an electrical component that converts electrical energy into thermal energy. It is widely used in various heating situations because of its low price, convenient use, convenient installation and no pollution.

Functional features

Small size and high power [1] : the heater adopts cluster tubular electric heating element first.High heat response, high temperature control, high comprehensive thermal efficiency.High heating temperature: heater design task highest temperature can reach 850 ℃.Average temperature of medium outlet temperature and high temperature control.Using wide limits, and strong adaptability, the heater can be used in explosion-proof or popular place, explosion-proof grade of d Ⅱ class B and class C, pressure of 20 mpa.Long life and high reliability: this heater is made of special electric heat data, designed with low power load and multiple maintenance, so that the electric heater can be added safely and life.Fully active temperance: according to the requirements of the heater circuit design, the outlet temperature, flow, pressure and other parameters can be easily controlled, and can be connected with the computer computer.The energy saving results are obvious, and the heat generated by electric energy is almost 100% to the heating medium.

structure

Metal tube shape typical electric heating tube structure (the structure of the most popular) typically consists of five parts: insulator, sealing material, which leads to the rods, filling material, heating wire, metal protective casing, terminal [1].

Spiral heating wire and bar is located in the middle of the metal protective casing, derivation of its manufacturing process is to spiral heating wire wear into seamless steel pipe, copper or aluminum tube, the gaps through the tube filling machine more evenly fill both insulation and thermal oxidation of media, such as crystal magnesia powder (also available alumina or clean quartz sand, etc.).Then the pipe diameter is reduced by the tube, so that the oxide media is dense (the density is 3.3g/cm3), so that the electric heating wire is isolated from the air, and the center position is not offset and the wall is touched.Like this.The unit area heat can increase a dozen times.The service life can also be increased to more than 10 years.Compared with the electric heating elements of the same heat, the tubular electric heat pipe can save 5% of the electric heating material, and the thermal efficiency can reach over 90%.

Therefore, from the perspective of the structure of electric heat pipe, tube shape is currently the most widely used electric heating tube, simple structure, reliable performance, long service life and sealed electric heating element, can be successfully applied to industry, household electrical appliances, more and more widely used.It is hoped that more users have a clear understanding of the structure principle of electric heat pipe.

Unit power

Unit power of tube surface area in heating tube heating area:

Pipe diameter

Load value (Wcm square)

From 6 ~ 10

22 or less

From 10.1 ~ 14

20 or less

From 14.1 to 18

16 or less

From 18.1 ~ 22

12 or less

From 22.1 ~ 40

10 or less

The above surface load refers to metal mold heating and water heating can be multiplied by 2 ~ 2.5.Air heating is 50% ~ 60%.

Main parameters of electric heat pipe.

1. Power supply voltage, V;[3] 2. Power frequency, Hz;

3. Rated voltage, V;

4. Rated power, kw;

5. Working temperature ℃;

6. External diameter, (die aperture of single electric heat pipe), mm;

7. Expand length, mm;

8. External dimension, mm;

9. Weight, kg.

How to develop more advanced electric heat pipe material is a difficult problem for many enterprises.Most electric heat pipes are commonly used as heating wires in alloys.High quality enterprise electric heat pipe is the best alloy electrothermal wire as the heating body.And there is also the elicitation rod in the tube is the encapsulation of the magnesium oxide insulating medium, with the fixed heating element.In the derivation bar, it is connected to the heating body for the components and the power supply, and the metal conductive parts connected with the components.The length of the expansion is the sum of the straight line and the bending length of the metal tube in the design of the component.

Calorific value

You can change the heat by changing the input voltage and current.

The heat is proportional to the voltage square, proportional to the current square.

When the voltage becomes 1/2, the heat becomes 1/4.

When the current becomes 1/2, the heat is also 1/4.

C(the specific heat capacity of the heating material)*M (the total mass of the material to be heated)* T (temperature difference) =P (power)* T (time)

Power calculation

1. Calculate the required power of heating to the set temperature from the initial temperature in the specified time [1]

2. Calculate the power of the maintenance temperature required to maintain the constant temperature of the medium.

3. According to the above two calculation results, select the type and quantity of heater.The total power takes the maximum of the above two types of power and considers the 1.2 coefficient.

Formula:

1. The power required for the initial heating is KW = (C1M1T + C2M2T), and 864/P + P/2.

Type: C1C2 respectively containers and the specific heat of the medium (Kcal/Kg ℃)

M1M2 is the mass of the container and the medium (Kg).

T for the required temperature and the difference between the initial temperature (℃)

H is the time required to heat the initial temperature to the set temperature (H).

The heat dispersion of the container at the final temperature of P (Kw)

2. The power required to maintain the temperature of the medium is KW=C2M3T/864+P.

In the formula: the media kg/h increased by M3 per hour.

Short circuit fault

Burning resistance wire [1]

Reason: A, the electric heat pipe burns to cause short circuit;

B. The lead of the electric heat pipe or the lead off will cause the short circuit;

C. small diameter of resistance wire and insufficient capacity;

D. The accumulation of fouling or carbonization of electric power sockets causes short-circuit.

E, power cord plug and electrical outlet short circuit;

Solution: A, replace the heating pipe;

B. re-welding;

C. Replace the appropriate resistance wire heat pipe. Normally, the resistance wire of iron chromium aluminum can be used.

D. remove dirt, repair or replace parts.

E. Repair or replace the power plug or electric socket;

No fever

The reason: A, for the adjustable temperature control heating tube, the temperature control device contact is bad or burn off.

B. Abnormal power supply or power failure;

C. The resistance wire has been fused;

D. The power cord plug is not in contact with the electrical outlet, or the power cord is broken;

E. The electric heat pipe has been burned;

F, electric heat pipe lead or lead off;

Solution: A, the heating tube is not well maintained, and it is recommended to be replaced;

B. Use after normal power supply;

C. The heating tube is scrapped, and the same type of resistance wire is remanufactured.

D. Inspect the wiring for repair or replacement;

E. Replace the installation with electric heat pipe;

F. Rewelding the primer or lead;

The leakage

Reason: A, the circuit wire falling off with the cup body;

B. Electric heat pipe burns and short circuit of cup body;

C, not connected to the ground;

D. there is too much dirt in the electric socket or power plug;

E. Insulation damage of electric heat pipe;

F, clean and improper, water into the cup;

Solve: A, check the loose wire, and weld again;

B. The electric heat pipe has been damaged and replaced with the same specification electric heat pipe;

C. Connect the ground wire as required and check whether it is correct;

D. Clean and dry properly;

E. Check and repair if there is any such event suggested to be replaced;

F. Clean and dry properly;

Classification of editing

1. According to the classification of outgoing lines, it can be divided into single-head electric heat pipe and double-head electric heat pipe [1].

2. According to the material classification, it can be divided into stainless steel electric heat pipe, quartz electric heat pipe, ferrofluoroelectric heat pipe and titanium electric heat pipe.

3. According to the appearance classification, it can be divided into direct electric heat pipe, u-type electric heat pipe, l-type electric heat pipe, w-type electric heat pipe, fin electric heat pipe and special electric heat pipe.

4. According to the classification of USES, it can be divided into dry heat and water heating pipes.

5. According to the heating mode, it can be divided into conventional resistance heating tube and radiant heating tube.

Common type editor

Finned tube.

The fin electric heat pipe is a kind of energy consumption which is converted into heat energy to heat the heating materials.

Work in cryogenic fluid through the pipe under the action of pressure into the input port, along the electric heating container within specific in hot runner, the path of the design with the principle of fluid thermodynamics, take away the heat energy produced by electric heating element work, make the heating medium temperature, fin export get technological requirements of high temperature medium electric heating tube.

Finned tubular electric heating elements, winding metal heat sink is a common element in the surface, compared with the common components heat dissipation area expanded 2 ~ 3 times, namely the fin element is allowed to the surface of the power load 3 ~ 4 times that of ordinary elements.

Due to shorten the length of the element, making itself reduce heat loss, under the condition of the same power, has quick heating, high thermal efficiency, long service life, heating device is small in size, low cost advantages.

It can be installed in the air duct or other stationary, flowing air heating occasions [4].

Flanged electric heat pipe

Flange (also called plug-in electric heating tube electric heater) : is a u-shaped tubular electric heating element, according to the different heating medium design specifications, in accordance with the requirements for the power configuration on the flange cover assembly, insert the heating material, heating elements work to a lot of heat conduction is heating medium to medium temperature, to achieve the required process requirement.

When the medium temperature reaches the set value of technical requirement, the control system according to the temperature sensor signal, after PID arithmetic to adjust electric heater power output, the resistive load to realize temperature control of the heating element.

Make the medium temperature even and meet the required requirements;

When the heating element exceeds the temperature or low level, the interlock protection device of the heating element will immediately cut off the heating power to prevent the heating element from burning and prolong the service life.

Flange electric heat pipe mainly for oil, chemical, food, machinery and other industries of various types of storage tanks, containers, oil tank materials heat preservation and heating.

The connection mode can be sealed by flanged or threaded end face [1].

Titanium heating tube

Titanium electric heating tube is titanium pipe shell, along the axial uniform electric thermal bonding wire tube center the gap filling compaction with good thermal conductivity of insulating oxide magnesia, with silica gel or ceramic seal on both ends of the tube, the metal electric heating element for high corrosive liquid.

Titanium heat pipe has the characteristics of simple structure, high mechanical strength, high thermal efficiency, safe and reliable, simple installation and long service life.

It is widely used in all kinds of highly corrosive liquids.

Titanium with a small specific gravity, are widely applied to heat water, nitrate solution, acid solution, alkali solution, practice has proved that the titanium in the applications of anticorrosive equipment production, high efficiency, long service life, in the applications of electroplating equipment, does not affect the plating solution can greatly improve the efficiency of the electroplating industry.

The effective length of the electric heating element must be completely immersed in the liquid [1].

teflon

Teflon tube is a new type of electric heating tube with strong corrosion resistance. It is used for the heating of various corrosive liquids.

With good aging resistance and good winding performance, low surface load design is adopted.

The joint adopts fully enclosed anti-acid base, no heating section and overheat safety protection system, according to the customer's requirement.

It ensures that the heater is not easy to burn, long service life, full seal, no corrosion, no leakage, ground protection, safe and reliable.

Suitable temperature below 110 ° C.

Anticorrosion iron fluoride Long Dian heat pipe has high thermal efficiency, energy saving save electricity, the advantage of cost-effective, can design a variety of structural forms, such as spiral, L, U, W, mosquito-repellent incense, portfolio, etc.

It has been recognized by several listed companies as a long-term supplier of its mosquito-repellent teflon heater.

We can undertake non-standard products, in terms of voltage, power, size and shape of products, as well as the wiring way, can be designed according to the customer's requirements, welcome to the sample to customize production.

Quartz tube

Quartz heating tube, most commonly used for carbon fiber quartz heating tube.

Carbon fiber heating pipe [3], also known as carbon fiber electric heat pipe, infrared heating tube, infrared electric heat pipe, carbon fiber infrared electric heat pipe, carbon fiber infrared heating tube, etc.

It consists of a carbon fiber wire in a quartz tube, a vacuum seal in the tube, and a voltage on the carbon fiber wire that heats the carbon fibers and generates heat.

The company's products adopt imported carbon fiber heating body, which has the advantages of high power balance, high temperature resistance, high thermal capacity, long service life, and adjustable power.

Radiant tube

Radiation heating tube inside the electric heating elements enclosed in a protective sleeve is electric heating and the heat radiation from casing indirect to furnace lining and processed workpiece, widely used in heat treatment industry of various kinds of heating furnace.

The electrothermal alloy material used in radiant heating tube should have high resistivity and high electric conversion rate.

Because the radiation tube is placed in the tube, the heat transfer process is different from the general electric heating element. The heat shield is large, and the temperature of the element must be controlled in the heating process to prevent the element from overheating.

Radiant tube closed heating, electric heating element surface temperature higher than the furnace temperature about 100 ℃ to 150 ℃.

Therefore, when selecting materials, we should analyze the temperature atmosphere in furnace and furnace, and choose the correct heating materials [1].

Attention editor

1. Components are allowed to work under the following conditions [3] : A.

Air relative humidity is not greater than 95%, no explosive and corrosive gases.

B.

The working voltage shall be no more than 1.1 times the rated value, and the enclosure shall be effectively grounded.

C.

Insulation resistance 1 m or more Ω dielectric strength: 2 kv / 1 min.

2. The electric heat pipe shall be fixed in position, and the effective heating zone must be completely immersed in liquid or metal solids, and it is strictly prohibited to burn.

When the surface of the tube has scale or carbon, it should be cleaned and reused in time so as not to shorten the service life [3].

3. When heating the fusible metal or solid nitrite, alkali, leaching and stone wax, the voltage should be reduced first, and then the rated voltage can be reached after the medium is melted.

4. When heating air, the components should be arranged evenly, so that the components have good heat dissipation conditions, so that the air flowing through can be fully heated.

5. Safety measures should be taken into account when heating the nitric salt to prevent explosion accidents.

6. The wiring part shall be placed outside the insulation layer, avoiding corrosive, explosive medium and moisture contact;

The connection should be able to withstand the temperature and heating load of the connection part for a long time.

7, components should be stored in a dry place, if long-term placed below 1 m Ω insulation resistance, can be in around 200 ℃ oven drying, or lower voltage electric heat, until the insulation resistance.

8. Magnesium oxide powder on the outlet of the electric heat pipe shall avoid contamination and water infiltration in the use of the site to prevent the occurrence of leakage accidents.

Validation standard editing

The specific test and verification method of electric heat pipe can check the national standard "JB/T 2379-1993 metal tubular electric heating element", "GB/T 23150-2008 water heater tube heater", "JB/T 4088-1999 daily tubular electric heating element";

The main standard [5] specifies the technical requirements of electric heating tube, experiment method, testing, packaging, storage and so on a series of regulations by the quality of electric heat pipe depends mainly on the following aspects: the electric strength, insulation, leakage current, power accuracy, life, corrosion resistance, size, etc.

Power input detection

The power deviation of the rated voltage shall not exceed the following table.



Rated input power (W)

deviation

W ≦ 200

Plus or minus 10%

W > 200

Positive: +5% negative: -10%.

Electric strength test


A. Electrical strength in cold state: it should be able to withstand 50Hz,1min withstand voltage, cut current 5mA, no breakdown, flashover phenomenon.

Rated voltage test voltage [5]

250 v, 1250 v

B. Electrical strength at work temperature: withstanding 50Hz,1min withstand voltage, cutting current 5mA, no breakdown, flashover phenomenon.

Rated voltage test voltage.

250 v, 1000 v

Leakage current at work temperature.


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The electric heat pipe is input with 1.15 times the rated power, and the leakage current is 0.5m A[5].

Overload test


The electric heat pipe is rated at 1.27 times the rated power of 1hrs under sufficient heat release, and the power failure is cooled by 0.5 HRS to room temperature (allowing forced cooling). This is repeated for 30 cycles without damage [6].

Sealing test of electric heat pipe shell.


The electric heat pipe is immersed in the acidified water (2%~3% hydrochloric acid, sulfuric acid or nitric acid) 3hrs. The two terminals of the electric heat pipe should be exposed to at least 5mm of the liquid surface, and the second ~3 performance requirements should be satisfied after the test.

Sealing test of seal.


Puts the electric heat pipe temperature of 60 ℃, 95% humidity environment 24 HRS, placed shall meet after 2 ~ 3 items of performance requirements.

Life test


The electric heat pipe is supplied with a rated voltage of 1hrs under sufficient heat release, and the power failure is cooled by 0.5 HRS to room temperature (allowing forced cooling), and the cumulative working time is up to 3000hrs.

The performance requirements

According to the relevant standards of the root country, electric heat pipe has the following requirements [6] :

1. Heating time

Under the test voltage, the temperature of the element from the ambient temperature to the test temperature should not be greater than 15min.

2. Rated power deviation.

Under the condition of full heating, the deviation of the rated power of the element shall not exceed the range specified below;

The components with rated power less than or equal to 100W are: plus or minus 10%.

For components with rated power greater than 100W, it is +5% ~ -10% or 10W, which is the larger value of both.

Some enterprises have good power, for example, taizhou jia single terminal electric heat pipe factory;

Yancheng district, some enterprises can do + 5% ~ 5%, resistance value deviation was only 1 Ω, such as electric resistance.

3. Leakage current

The leakage current should not exceed 0.5mA after the cold leakage current and water pressure and sealing test.

The hot state leakage current at working temperature should not exceed the calculated value in the formula, but the maximum is no more than 5mA.

I = 1/6 (tT x 0.00001)

I - thermal leakage current mA.

T - heat length mm.

T - working temperature ℃

When multiple components are connected to the power supply, the leakage current test should be carried out as a whole.

4. Insulation resistance

Factory inspection when cold insulation resistance shall be not less than 50 m Ω

After sealing test, after long-term storage or use of insulation resistance should be needless and M Ω

Under the working temperature of hot insulation resistance shall be not less than calculated value in the formula, but should not be less than 1 m Ω minimum

R= "(10-0.015T)/T" * 0.001.

R - hot M Ω insulation resistance

T - heat length mm.

T - working temperature ℃

5. Insulation pressure strength.

The components shall be maintained for 1min under specified test conditions and test voltages without flashover and breakdown.

6. Ability to withstand power failure.

The component shall be able to undergo 2,000 power failure tests under specified test conditions without damage.

7. Overload capacity

The components shall be subjected to 30 cycles of overload test without damage under specified test conditions and input power.

8. Heat resistance

The components shall be subjected to 1000 cycles of heat resistance test under the specified test conditions and test voltages without damage.

Black processing editor.

Sometimes used in the process of the production of electric heating tube, black finish, heat treatment is stainless steel and other metal objects of a process of heat treatment, treatment after surface have a layer of oxide film in order to achieve the purpose of anticorrosion.

After heating treatment, the surface of the heating tube will be improved, and the surface hardness will be improved, and the components [1] will not be affected.

Under normal working conditions, the most convenient method for blackening of electric heat pipe surface is as follows:

1. First, clean the surface of the metal tube and keep it clean;

2. Second, the surface is degreased. This process can completely place the metal tube in the degreasing fluid.

The PH value of degreasing solution should be around 13, not less than half an hour.

Skim and rinse with water.

3. After the acid washing, the PH value of the acid lotion is about 3, and the processing time is not longer than 10 minutes.

4. Black treatment: the PH value of the pool solution is 2-4, and the processing time is 10 minutes.

5. Finally dry and oil;

It is a very effective method to deal with the blackening of electric heat pipe according to the above five points.









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