RU2059939C1 - Electric heater for fluid and loose media - Google Patents

Abstract

FIELD: power engineering, farming and domestic systems for heating water, air, sand, oil, etc. SUBSTANCE: secondary winding 8 of transformer is made in form of several turns of electric wire; ends of winding are connected with pipe 1 provided with dielectric hermetic insert 7 in section between points of connection of ends of winding 8 of transformer 3. EFFECT: enhanced reliability. 3 dwg

Description

 The invention relates to energy and can be used in industry, agriculture and household for heating water, air, sand, oil, antifreeze, etc.

 Known electric heater containing a detachable housing with an electric heating element and a labyrinth channel for water, and the electric heater is made in the form of electrode plates.

 The disadvantage of this device is the limited service life of the electric heater due to oxidation and destruction of the electrodes.

 The closest in technical essence is an electric heater containing a transformer, the primary winding of which is connected to an AC voltage source, the heating element is made in the form of an electrically conductive pipe, inside which the heated medium moves, and the pipe is the secondary winding of the transformer, and its ends are hermetically connected to the inlet and outlet pipes, and between themselves the ends of the pipe are electrically connected by a jumper.

 The disadvantage of this device is the low reliability of the heating elements. This is due to the small area of contact of the heater with the liquid and the need to set the high temperature of the element. This mode causes the heater thread to burn out.

 The aim of the invention is to increase reliability.

 This goal is achieved in that the secondary winding of the transformer is made in the form of several turns of an electric wire, the ends of the winding are electrically connected to a pipe of length L, and a non-conductive hermetic insert is introduced at the pipe section between the places where the ends of the transformer winding are electrically connected.

где ΔТ требуемое приращение температуры нагреваемой среды; М масса нагреваемой среды; t время, необходимое для нагрева С удельная теплоемкость вещества; ρ- удельное электрическое сопротивление трубы; S площадь сечения металлической части трубы; К коэффициент, учитывающий потери; U напряжение во вторичной обмотке трансформатора.The length of the pipe is determined from the expression
L

where ΔТ is the required temperature increment of the heated medium; M is the mass of the heated medium; t is the time required for heating; C is the specific heat of the substance; ρ - electrical resistivity of the pipe; S is the cross-sectional area of the metal part of the pipe; K coefficient taking into account losses; U voltage in the secondary winding of the transformer.

 In FIG. 1 shows the design of an electric heater according to claim 1; figure 2 the design of the device implemented in accordance with paragraph 2 of the claims; figure 3 equivalent circuit diagram of the transformer.

 The electric heater according to claim 1 of the invention consists of a metal pipe 1, an electric jumper 2, a transformer 3 with a primary network winding 4. 5 inlet pipe, 6 outlet pipe.

 The electric heater according to claim 2 of the claims consists of a pipeline 1, a jumper 2, a transformer 3 with a primary winding 4, a supply pipe 5, a discharge pipe 6, a non-conductive insert 7, a secondary winding 8.

 Inlet 5 and outlet 6 nozzles are a continuation of the pipeline 1 and are used to connect the consumer of the heated medium and source (figure 1). The pipeline 1 is the secondary winding of the transformer 3. The pipeline forms two to three turns, and the "turns" of the pipeline must be electrically isolated from each other, as well as from the core of the transformer. The secondary winding 4 of the transformer is connected to a source of electrical energy. Jumper 2 provides an electrical connection to the pipeline in order to create a closed electrical circuit in which the secondary current of the transformer 3 circulates.

 A distinctive design feature in FIG. 2 is that a dielectric insert 7 is inserted into the rupture of the pipeline 1, which hermetically connects the segments of the pipeline 1 and excludes the flow of the secondary winding 8 at the rupture of the pipeline. The winding 8 is made of a thick wire with low electrical resistance. The junction of the secondary winding 8 with the pipeline 1 are located near the ends of the dielectric insert 7.

 The electric heater operates as follows.

 When applying voltage to the primary winding of the transformer 3 in the circuit of the pipeline 1 having a large conductivity, a large current is established with a small electromotive force.

 This condition determines the effective dissipation of electrical power in the form of heat in the body of the pipeline.

 A distinctive and positive side of the proposed electric heater is the reduction of the effect of localized (concentrated in a small volume) heating of the medium, since in the proposed device the heating element has a relatively large area for heat exchange with a heated medium. In this case, the heating element additionally performs the function of a shirt separating the heated medium from the external environment.

 The consequence of increasing the active area of the heater is to reduce changes in the physical properties of the medium and increase reliability by reducing erosion of the metal of the heater, reducing the number of thermal cracks that occur with large temperature differences.

 In order to simplify the design of the electric heater, a variant of its execution is possible, characterized in that the transformer winding from the pipeline is replaced by a wire with high conductivity (Fig. 2). This eliminates the more difficult to manufacture unit from rolled up in the form of turns of a pipe segment. In this case, as shown in figure 2, the pipeline may have a U-shape. The tightness of the fluid channel is provided by introducing a pipe of dielectric material into the rupture site.

 The efficiency of the electric heater in the presence of thermal insulation of the pipeline is determined mainly by the efficiency of the transformer. In this case, the efficiency of the second variant of the electric heater is obviously less than the first variant due to losses in the secondary winding of the transformer.

 Evaluation of the efficiency can be given using the equivalent circuit (figure 3) and a specific numerical example, the parameters for which are taken from the specific design of the electric heater, made according to claim 2 of the claims.

In FIG. 3 resistors R ₁ , R ₂ , R ₃ display respectively the active resistances of the primary, secondary windings and the resistance of the pipeline.

1000 A.If you set, for example, (in accordance with the actual design of the shower) the electric power dissipated in the pipeline 4 kW, then with a 4-meter pipe length with a resistance of R ₃ 0.004 Ohms, a current is required
I _n =

1000 A.

The voltage at the ends of the pipe
UR ₃ P ₃ / I _n 4000/1000 = 4 V.

For the secondary winding, a stranded wire with a thickness of 14 mm was used. This winding was wound simultaneously in three wires and had 2 turns with a total resistance of R _{2 of} 0.00017 Ohms.

The current consumed from the 220 V network was
I _c I _n • U _n / U _c 1000 • 4/220 18.2 A.

The primary winding was wound with a copper wire with a cross section of 4 mm. Its resistance was 0.65 ohms. Electric heater efficiency
η = P ₃ / (P ₁ + P ₂ + P ₃ ) P ₃ / ( $\genfrac{}{}{0ex}{}{\text{2}}{\text{Ic}}$ • R ₁ + I $\genfrac{}{}{0ex}{}{\text{2}}{\text{n}}$ x xR ₂ + P ₃ ) 4000 / (1.82 • 0.65 • 1000 ² • 0.00017 + + 4000) 0.91, where P ₁ , P _{2 are} power losses, respectively, on the primary and secondary windings of the transformer.

 From the calculations it is seen that even for the device according to claim 2 of the claims, the efficiency is quite large.

 In order to get a detailed idea of all the parameters of the electric heater, we will carry out its calculation.

Suppose that using the device you want to heat 10 kg of water in 5 minutes, changing its temperature by 30 ^about .

To heat the water, you must do the work
Q ΔT • C • M 1200 kJ, where C is the specific heat of water; M mass; ΔТ is the required temperature increment.

The power supplied by the system (excluding the energy required for a single heating of the pipe) should be
PQ / t 1200 / (5 • 60) 4 kW, where t is the time of heating the water.

Given that the number of turns in the primary winding of the transformer is W ₁ 110 a in the secondary W ₂ 2, the voltage in the secondary winding
U 220 • W ₂ / W ₁ 4 V.

For the manufacture of an electric heater, we use a pipe in which the cross section of the metal part is 0.0001 m ² .

4 M где ρ- удельное электрическое сопротивление стали.Find the required pipe length by the formula
L

4 M where ρ is the electrical resistivity of steel.

 The last formula is obtained on the basis of the following relations.

To heat a substance of mass M and heat capacity C by ΔТ ^, heat is required to complete the work
Q ΔT • C • M.

On the other hand, the power of electric energy released in the resistor with resistance R is
PI ² • RU ² / R, where I is the current flowing through the resistor; U is the voltage applied to the resistor.

During the time t of heating the substance, an energy equal to A P • t will be required, we take into account the heat and electric losses by introducing the coefficient K
QK • AK • U ² • t / R.

Hence, the electrical resistance of the pipeline should be
RK • U ₂ • t / Q. (one)
The electrical resistance of a conductor of length L, section S, and with specific resistance ρ is found from the relation
Rρ • L / S.

Подставляя в (1), получим
L

Технико-экономические преимущества.To ensure the necessary resistance, the length of the pipeline should be
L

Substituting in (1), we obtain
L

Technical appraisal and economic benefits.

 1. Improved reliability of the device by reducing the likelihood of failure of the heater, which is a pipe with a large inner surface, in contact with which there is heating. An increase in the active area of the heater leads to a decrease in metal erosion, a decrease in the likelihood of thermal cracks, mechanical stresses, and corrosion intensity.

 2. Application safety is achieved by reducing the voltage in the secondary winding.

 3. This device can give impetus to the creation of new designs of electric heaters, the principle of operation of which is based on the use of a short-circuited coil in the secondary winding of the transformer.

Claims (1)

ELECTRIC HEATER OF FLUID AND BULK MEDIA, containing a transformer, a heating element connected to the secondary winding of the transformer with the formation of a closed electrical circuit and made in the form of an electrically conductive pipe in which the heated medium moves, while the ends of the pipe are electrically interconnected by a jumper and hermetically connected to the supply and outlet pipes, characterized in that the secondary winding of the transformer is made in the form of several turns of an electric wire, the ends of the winding are connected They are connected with the pipe, moreover, in the pipe section between the points of connection of the ends of the transformer winding with the pipe, a non-conductive sealed insert is installed, the pipe length L is determined from the expression

where ΔT T is the required increase in temperature of the heated medium;
M is the mass of the heated medium;
t time required for heating;
C is the specific heat of the substance;
ρ electrical resistivity of the pipe;
S is the cross-sectional area of the metal part of the pipe;
K coefficient taking into account losses;
U voltage in the secondary winding of the transformer.

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