RU124103U1 - FLEXIBLE ELECTRIC HEATER - Google Patents

Abstract

1. A flexible electric heater, comprising two layers of a flexible electrical insulating film, between which a heating and radiating element is placed, equipped with a ground conductor for grounding and leads for connection to an electric network or another electric heater, and a reflective element mounted on the outside of one of the electrical insulating films, characterized in that the heating and radiating element has a specific resistance of 0.7-1.2 Ohm / (mmm), made in the form of strips of foil or threads of conductive material connected and arranged according to the bifilar scheme and having pairwise paired parallel segments forming bifilar branches, the distance between pairwise paired parallel segments of each bifilar branch of the heating and radiating element is 5-10 mm. 2. The flexible electric heater according to claim 1, characterized in that the reflective element is made in the form of a dacron foil film. The flexible electric heater according to claim 1, characterized in that a polyethylene terephthalate film is selected as the electrical insulating film. The flexible electric heater according to claim 1, characterized in that the reflective element is separated from the heating and radiating element by an electrical insulating film with a thickness of at least 120 μm. The flexible electric heater according to claim 1, characterized in that the heating and radiating element is made of high-resistance precision alloy. The flexible electric heater according to claim 1, characterized in that the distance between the bifilar branches is at least 25 mm. The flexible electric heater according to claim 1, characterized in that it is additionally equipped with a residual current device.

Description

The utility model relates to the field of electrothermics, in particular to flexible sheet heating elements for heating residential premises and industrial buildings as primary or secondary heating.

A film heater is known from the prior art that comprises a flat, meander-shaped resistive heating and radiating foil element in the form of a continuous tape of precision conductive material located between two flexible heat-resistant electrical insulating films and equipped with leads for connection to an electric network. The electric heater is equipped with a radiating element in the form of aluminum foil, installed between the external insulating film and the resistive heating and radiating element and separated from the resistive heating and radiating element by an electrically insulating film with a thickness of not more than 30 μm (see, for example, RU 2321188, publ. 20.06.2001 )

A flexible electric heater is also known from the prior art, which, according to the Applicant, is the closest analogue and includes two layers of a flexible electrical insulating film, between which a heating and radiating element of a meander shape is placed, equipped with an electrical conductor for grounding and leads for connection to an electric network or other electric heater , and a reflective element mounted on the outside of one of the insulating films (see, for example, RU 89795, publ. 10.12.2009 or RU 2443081, publ. 02.20.2012).

The disadvantage of the above flexible electric heaters is the lack of electrical safety of the device. When a film heater is connected to an electric network and electric current flows through parallel strips of a meander-shaped resistive element, electromagnetic induction occurs between parallel segments of the heating and radiating elements, and electric potential arises on the surface of the radiating element. In the event of damage to the device during operation of an external electrical insulating film, the potential difference can reach half the voltage of the supply network.

The task to which this technical solution is directed is to create a reliable device by increasing its electrical safety.

This problem is solved due to the fact that in a flexible electric heater, which includes two layers of flexible electrical insulation film, between which there is a heating and radiating element, equipped with a ground conductor for grounding and leads for connection to an electric network or other electric heater, and a reflective element mounted on the outside one of the insulating films according to the technical solution is heated and the radiating element has a resistivity of 0.7-1.2 ohms / mm ² m, is made in the form of foil strips yl filaments of a conductive material, connected and arranged in a bifilar circuit and having mutually paired parallel segments forming the bifilar branches, the distance between the mutually parallel segments each coupled bifilar heating branch and the radiating member is 5-10 mm.

The reflecting element can be made in the form of a lavsan foil film.

As an electrical insulating film, a polyethylene terephthalate film can be selected.

The reflecting element can be separated from the heating and radiating element by an electrical insulating film with a thickness of at least 120 microns.

The heating and radiating element can be made of high-resistance precision alloy.

The distance between the bifilar branches can be at least 25 mm.

A flexible electric heater can be optionally equipped with a residual current device.

The technical result provided by the above set of features is to ensure the reliability of the device by increasing its electrical safety by performing a flexible electric heater of the proposed design. A causal relationship of the features of the claimed technical solution and the resulting technical result is given below.

The bifilar arrangement pattern of the heating and radiating element is a variation of the meander pattern. The meander is a geometric pattern with equally spaced parallel strips located along the heater plane, and the bifilar stacking pattern is a double laying of two parallel conductors dispersed over the surface of a flexible electric heater in the form of bifilar branches located at the minimum allowable distance. And according to one and another scheme, the heating and radiating element bends at a right angle so that the current directions in adjacent parallel segments are opposite. The difference is that in a bifilar arrangement, the branches with the opposite direction of current flow are paired, i.e. are at a distance from each other less than the distance between similar bifilar branches of the element. When electric current passes through conductors laid according to the meander scheme, there is no compensation of electromagnetic fields, since it is a flat coil. The interaction of currents is caused by their magnetic fields: the magnetic field of one current acts by the Ampere force on another current and vice versa. The experiments showed that the modulus F of the force acting on a segment of length Δl of each of the conductors is directly proportional to the current strengths I ₁ and I ₂ in the conductors, the length of the segment Δl and inversely proportional to the distance R between them.

,

,

where F is the ampere force module (H);

I ₁ , I ₂ - current strength in the segments of the conductors (A);

Δl is the length of the segments of the conductors (m);

R is the distance between the conductors (m).

Thus, Ampere’s law confirms that as the distance between the conductors increases, the interaction force between the electromagnetic fields decreases.

The authors of the claimed utility model conducted laboratory studies of the dependence of the magnitude of the electric and magnetic induction on the surface of a flexible electric heater, on the distance between the strips of the heating and emitting element with different pitch bifilar laying. The heating and radiating element is made in the form of strips of foil in one experiment and threads of conductive material in another and has a specific resistance of 0.7-1.2 Ohm / mm ² m. The voltage of the electric heater is -220 V. The current flowing through the heating and radiating element is -1 A. The heater power is 220 W. The measurement results are summarized in table.

Experience Number Track spacing [mm] Electric field strength E [Sq / m] Magnetic field strength B [μT] one 70 1.49 8.98 2 35 0.559 8.82 3 thirty 0.503 7.14 four 25 0.246 6,645 5 fifteen 0.183 3.75 6 10 0.123 0.838 7 5 0,0993 0.548

The measurements were carried out using the following electrical measuring instruments:

- digital multimeter - voltage, current value;

- an indicator of electromagnetic fields of industrial frequency type BE-50-I - the magnitude of the electric and magnetic fields.

Before starting the experiments, the background value of the electromagnetic field in the laboratory was measured. Background values were: electric field strength E = 0.092 Sq / m; magnetic field strength B = 0.511 μT. Reference limit levels: E = 500 V / m; B = 5 μT.

As a result of the described experiments, it was concluded that the result of applying a bifilar scheme of laying a heating and radiating element in the form of strips of foil or strands of conductive material having a specific electrical resistance of 0.7-1.2 ohm / mm ² m with a distance between the strips or threads of 5-10 mm is the practical absence of electromagnetic radiation in view of the compensation of electromagnetic fields of two paired segments of the conductors of the bifilar branch.

The essence of the claimed device is illustrated by drawings that do not cover and, moreover, do not limit the scope of claims for this decision, but are only illustrative materials of particular cases of the device. The drawings show:

figure 1 is a General view of a flexible electric heater in plan;

figure 2 is a section along the cross section A-A;

figure 3 is a connection diagram of a heating and radiating element.

A flexible electric heater includes two layers of a flexible electrical insulating film 1, between which a heating and radiating element 2 is placed. The heating and radiating element 2 is equipped with a current lead 3 for grounding and terminals 4 for connection to an electric network or other electric heater. The reflecting element 5 is placed on the outer side of one of the insulating films and connected to it. The heating and radiating element 2 is made in the form of strips of foil or threads of conductive material and has a specific resistance of 0.7-1.2 Ohm / mm ² m. The strips or threads are connected and laid according to a bifilar pattern and have pairwise paired parallel sections 6, 7 forming bifilar branches 8. The distance between pairwise paired parallel segments 6, 7 of each bifilar branch 8 of the heating and radiating element 2 is R = 5-10 mm (Fig. 3).

Flexible electric heater operates as follows. When applying electric current to the terminals 4 for connection to the electric network or other electric heater of Fig. 1, the current passes through the bifilar branches 8 of the heating and radiating element 2. Electromagnetic fields of pairwise paired parallel segments 6, 7 of each bifilar branch 8 in the form of foil strips or threads of conductive material are compensated, electromagnetic radiation does not occur. The reflecting element 5 reflects the heat flux of the infrared spectrum, the soft range in the direction opposite to its installation, provides heating of objects located in the heated room. The ground conductor 3 for grounding is connected to a grounding device to remove residual static electricity.

In a preferred embodiment of the device for increasing the degree of electrical safety, the reflecting element 5 is separated from the heating and radiating element 2 by an electrical insulating polyethylene terephthalate film 1 with a thickness of at least 120 μm. Any flexible film electric heater is also a flat capacitor, one of the plates of which is a heating and radiating element distributed over the surface of the heater, separated from the second plate - a reflecting element, by a dielectric (polyethylene terephthalate film). The most widely used electrical insulation film is 30 microns thick. At the same time, the heater capacity is too large. Since the electric field is concentrated inside the capacitor, the lines of tension begin on one plate of the capacitor and end on the second (another), so the free charges that arise on different plates are equal in magnitude and opposite in sign. This is illustrated in the diagram below.

A capacitor’s capacity is understood to mean a physical quantity equal to the ratio of the charge q accumulated in the capacitor to the potential difference φ1-φ2 between its plates.

,

,

where C is the capacitance of the capacitor, (C / V);

q is the charge-pendant (C);

φ ₁ -φ ₂ is the potential difference (B);

ω ₀ = 8.854185x10 ^-12 is the electric constant;

ω is the relative dielectric constant;

S is the area of one lining (m ² );

d is the distance between the plates (m).

Then the energy of the capacitor:

,

,

where W is the energy of the capacitor (C);

c is the electric capacity of the capacitor (F);

u is the voltage across the capacitor plates (B).

From these considerations, we can conclude that the use of an insulating film with a thickness of at least 120 μm, ceteris paribus, reduces the heater capacity by 4 times (120: 30 = 4), while the capacitor energy decreases by 4 times and, accordingly, the induced static electricity by reflective element (potential). No measurements were made due to obviousness.

Also, in order to increase electrical safety, a flexible electric heater can be additionally equipped with a residual current device. In some embodiments, the reflective element 5 is made in the form of a Mylar foil submarine or Alumoflex film, the heating and radiating element 2 is made of a high-resistance precision alloy, and the distance m between the bifilar branches is at least 25 mm (Fig. 3).

A prototype of a flexible electric heater with a size of 510 × 2000 mm and a thickness of 360 μm was made of two layers of electrical insulation polyethylene terephthalate film 1 according to TU 6-495761763-334-90 with a thickness of 125 μm with a heating and radiating element 2 in the form of a conductive foil of high-resistance precision alloy with a thickness of 13 microns and a width of 5.2 mm. The foil strips are connected and arranged according to a bifilar pattern and have pairwise paired parallel segments 6 and 7 forming bifilar branches 8 distributed along the plane of the heater web with a step m = 30 mm, and the distance between pairwise paired parallel segments 6 and 7 of each bifilar branch 8 R = 10 mm (12 strips). Radiating power - 120-150 W / m ² , surface heating temperature 47 degrees Celsius. The heat flux reflecting element 5 is made of a lavsan foil-coated Alumoflex film 100 μm thick. The prototype was tested and showed a high degree of electrical safety and the absence of static electricity on its surface.

Claims (7)

1. A flexible electric heater, comprising two layers of a flexible electrical insulating film, between which a heating and radiating element is placed, equipped with a ground conductor for grounding and leads for connection to an electric network or other electric heater, and a reflective element mounted on the outside of one of the electrical insulating films, characterized in that the heating and the radiating element has a resistivity of 0.7-1.2 ohms / (mm ² m) is in the form of foil strips or filaments of a conductive material and connected aspolozhennyh of bifilar circuit and having mutually paired parallel segments forming the bifilar branches, the distance between the mutually parallel segments each coupled bifilar heating branch and the radiating member is 5-10 mm. 2. The flexible electric heater according to claim 1, characterized in that the reflective element is made in the form of a lavsan foil film. 3. The flexible electric heater according to claim 1, characterized in that a polyethylene terephthalate film is selected as the electrical insulating film. 4. The flexible electric heater according to claim 1, characterized in that the reflective element is separated from the heating and radiating element by an electrical insulating film with a thickness of at least 120 μm. 5. The flexible electric heater according to claim 1, characterized in that the heating and radiating element is made of high-resistance precision alloy. 6. The flexible electric heater according to claim 1, characterized in that the distance between the bifilar branches is at least 25 mm. 7. The flexible electric heater according to claim 1, characterized in that it is additionally equipped with a residual current device.

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