The claimed invention relates to heating elements for heating water or other liquids in household or industrial heating appliances .

Prior Art.

At present, there are several varieties of heating elements similar to the claimed one.

For example, CN101237797A discloses the unit design most typical of modern household kettles produced. The disadvantage of the unit is increased energy consumption and considerable noise when boiling caused by inefficiently organized boiling process.

Most units of similar purpose use the same or similar design for household appliances.

For example, GB2588888A discloses the unit design for cooking solid or consistent (non-liquid) foods. However, the unit has a design similar to the claimed one with bottom electric heating.

Its distinctive feature is the local heating of the bottom by a small part of the heating element surface (less than 50 %) and an additional ventilation system of the under-the-vessel area due to higher temperatures of cooking solid or consistent (nonliquid) foods in oil compared to boiling water.

There is a unit under claim No. CN200948065. The document discloses the heating element unit for household kettles. The heating element is of complex shape, stamped from sheet metal with an electric ring heater soldered into the cavity.

The disadvantage of the heating element is the bottom surface area which is very narrow and strongly heated by the tubular electric heater (TEH) . As a result, the heat exchange rate increases in this zone, which leads to active cavitation bubble formation and increased noise level.

The unit disclosed in CN200948065 is chosen as a prototype.

The technical result of the claimed invention consists in creating a highly efficient closed-type heating element with increased convection intensity and reduced noise level. Known units do not allow to achieve the claimed technical result .

The problem solved by the claimed unit is the use of existing TEHs .

AGREED NOTATIONS

1 - bottom of variable thickness

1.1 - central area

1.2 - transition area from the central area to the heating area

1.3 - heating area (area with the largest bottom thickness)

1.4 - peripheral area

2 - heater

3 - edges to increase the heat transfer surface

DESCRIPTION OF DRAWINGS

Fig. 1 shows the heated reservoir bottom design according to patent GB2588888A.

Fig. 2 shows the heated reservoir bottom design of a prototype unit according to patent CN200948065.

Fig. 3 shows the claimed bottom design a) isometric view, b) plan view, c) plan view showing areas 1.1, 1.2, 1.3, and 1.4.

Fig. 4 shows a scheme of liquid motion in known designs.

Fig. 5 shows a scheme of liquid motion in the claimed design.

Fig. 6 - a) , b) , c) , and d) - shows possible implementations of the claimed design.

Fig. 7 shows the claimed design in cross section.

Fig. 8 shows a thermographic diagram of a longitudinal section of the heating element according to patent CN101237797A.

Fig. 9 shows a thermographic diagram of a longitudinal section of the heating element according to patent CN200948065 with an intense heat exchange zone.

Fig. 10 shows a thermographic diagram of a longitudinal section of the claimed heating element with uniform heat exchange distribution . Fig. 11 shows a drawing of an experimental model.

BRIEF DESCRIPTION

There is a claim for a heating element which is a reservoir bottom for heating primarily liquids and includes a metal bottom of variable thickness with a linear heater, primarily electric, attached to it from below or built in the body of the bottom.

The special feature of the claimed heating element is that the bottom in and around the place of heater penetration is made thicker than the rest of the bottom surface.

There is a claim for a heating element, which is a reservoir bottom for heating primarily liquids. The heating element is made in the form of a metal bottom of variable thickness with a circular linear heater, primarily electric, attached to it from below or built in the body of the bottom.

The features of the claimed heating element are as follows.

The bottom radially includes several concentric areas with different characteristics.

The central area has the smallest bottom thickness. This is an area of downward convection flow.

The heating area above and around the ring heater has the thickest bottom. The thickness raises it upwards so that most of the heat-radiating surface is in a liquid. This is an area of upward convection flow.

The ring heater is often designed as an incomplete ring with a gap. Heating coil leads are made at the ends of the ring. When such ring heater heats the bottom of, for example, a kettle, this part is not heated.

Therefore, in order to improve convection, it is suggested to make the above-the-ring-heater area of variable thickness. The place where there is a gap in the heater ring is made of lesser thickness. And the opposite side where there is the middle of the heating element is made of greater thickness.

The area between the central part and the above-the-ring- heater area is of variable bottom thickness from minimum thickness adjacent to the central part to maximum thickness adjacent to the above- the-ring-heater area.

The peripheral area from the ring heater up to the area adjacent to the vessel wall, if any, is of near-minimum bottom thickness .

The central area has a curved upwards spherical or spherical- to-cone shape.

The area between the central area and the above-the-heater area can have a curved downwards shape.

There is a claim for a reservoir bottom unit of variable thickness for heating primarily liquids.

The bottom radially includes several concentric areas with different characteristics.

The central area has the smallest bottom thickness. This is an area of downward convection flow.

Then there is an area of variable bottom thickness from minimal thickness adjacent to the central part to maximum thickness .

Further from the center, there is a heating area - with the thickest bottom. This is an area of upward convection flow.

This area is supposed to be the heating area and heating is supposed to come from a linear heat source being an incomplete open ring.

Therefore, the heating area is made thicker and has variable thickness - smaller on the one side and larger on the opposite side .

The peripheral area up to the zone adjoining the vessel wall is of near-minimum thickness.

The minimum thickness of the bottom is chosen and implemented for structural and technological reasons or based on specific operating conditions, material properties, and a number of other factors. If sheet material is used, minimum thickness is equal to the thickness of the sheet used. If cast, minimum thickness is determined by the casting and strength properties of the material.

The central area has a curved upwards spherical or spherical- to-cone shape. The heating region with the largest bottom thickness is raised up due to its thickness so that the bottom surface remains on a level with the adjacent areas, while the protruding part and most of the heat-radiating surface are in a liquid.

The area between the central area and the area with the thickest bottom has a curved downwards shape.

The peripheral area up to the area adjacent to the vessel wall has a near-flat shape, but can have a cone, spherical, cylindrical shape or a combination thereof, depending on the particular unit implementation.

DETAILED DESCRIPTION

When water (water-containing solutions or mixtures) is being heated, cavitation bubbles containing airfree steam appear in nucleation sites of the intense heat exchange zone due to low pressure and high temperature. Breaking away from the surface and losing the thermal energy source in the form of a heating element, cavitation bubbles fall into denser and colder layers of liquid, where they violently collapse emitting a shock wave that resonates in the heating element. This process results in boiling noise. The smaller the area of intense heat exchange, the higher the temperature therein, the denser and faster the bubbles form and the louder the noise. Thereafter, when an intense convection flow heating the liquid more evenly is formed, the bubble separation rate drops, bubble size increases, and the pressure difference within a bubble and in the upper layers of the liquid ceases to be critical. Separated bubbles reach the surface without collapsing. The noise decreases. The process of boiling begins.

Thus, the claimed technical result is achieved through choosing parameters of the body and the shape of the heating reservoir bottom with a built-in heating element, which increase the area of intensive heat exchange zone and speed up the formation of convection flow levelling liquid temperature.

The claimed technical result is achieved for the heating element unit, which is a reservoir bottom for heating primarily liquids. The heating element includes a metal bottom of variable thickness with a linear heater, primarily electric, attached to it from below or built in the body of the bottom.

The special feature of the claimed heating element is that the bottom in and around the place of heater penetration is made thicker than the rest of the bottom surface.

In this case, the linear heating element can be made in any shape - round ring, oval ring, rectangular ring or square or triangular, serpentine, or any other shape. Open or closed. It is only important that the bottom is made thicker in and around the place of heater penetration (including heater mounting) compared to the rest of the bottom surface.

To further increase the effect, the shape of the bottom surface can follow the expected trajectory of convective motion of liquid during heating and boiling.

The claimed technical result is achieved for the heating element unit, which is a reservoir bottom for heating primarily liquids. The unit includes a metal bottom of variable thickness with a linear heater, primarily electric, of a closed ring shape attached to it from below or built in the body of the bottom.

The features of the unit are as follows.

Bottom 1 radially includes several concentric areas with different characteristics.

Central area 1.1 has the smallest bottom thickness and is round in shape.

Then there is area 1.2 of variable bottom thickness from minimum thickness adjacent to the central part to maximum thickness adjacent to heating area 1.3 — attachment of the linear ring heater.

Area 1.3 is the thickest area at the attachment point of the linear ring heater. The thickness raises it upwards so that most of the heat- transmitting surface is in a liquid. Above-the-heater area 1.3 can be up to 20 times or more thicker than the central area .

The shape of the bottom surface can follow the expected trajectory of convective motion of liquid during heating and boiling . The linear heater is often designed as an incomplete ring with a gap. Electrical leads of the heating coil leads are made at the ends of the ring. When such ring heater heats the bottom of, for example, a kettle, the part of the bottom between the leads is not heated.

Therefore, in order to improve convection, it is suggested that the attachment area of the ring heater and the area around it be of variable thickness. The place where there is a gap in the heater ring is made of lesser thickness. And the opposite side where there is the middle of the heating element is made of greater thickness.

Consequently, the central area (with a smaller bottom thickness) is made slightly shifted away from the geometric center of the circular bottom to the circular heater gap.

Depending on heater power, the width and shape of the heattransmitting surface, and other features, the value of the required (necessary) thickening of area 1.3 may vary. As a consequence, the shift of the central area away from the geometric center of the circular bottom to the circular heater gap may also vary.

Due to the shift of the central area from the center to the edge, the central area having a circular shape can in some cases turn from almost circle to oval or ellipse. If there is a significant shift, an area of greater bottom thickness may become open, i.e., with a gap. The gap is in the place where the gap of the ring of the linear electric heater is placed.

The transition from small thickness to the large above-the- heater area can be smooth.

Peripheral area 1.4 from the ring heater all the way to the area adjacent to the vessel wall (if any) has near-minimum bottom thickness - approximately or exactly the same as central area 1.1.

Central area 1.1 can have a curved upwards spherical or spherical- to-cone shape to follow the directions of convection liquid motion. Area 1.2 between the central area and the heater attachment area has a curved downwards shape.

In the current experiments, the thickness of the central area was 1.2-2.5 mm.

Area 1.3 along the heater attachment can be up to 20 times thicker than the central area.

In the current experiments, the thickness of the peripheral area bottom was 1.2-2.5 mm.

Transitions between the areas can be smooth.

Radially-oriented edges can be added on the surface of the above- the-ring-heater area. In the current experiments, the height of the ribs was 1.2-2.5 mm.

To prevent surface oxidation and scaling, which also reduce the number of nucleation sites and therefore affect the technical result, a water-repellent, non-stick and/or any other coating can be additionally applied to the surface.

The shape of the bottom surface can follow the expected trajectory of convective motion of liquid during heating and boiling .

If there is an additional a peripheral area further (from the center) of the ring heater up to the area adjacent to the vessel wall, it can have a near-flat or cone or spherical shape.

In the current experiments, the thickness of the said peripheral area bottom was 1.2-2.5 mm.

The claimed technical result is achieved for the reservoir bottom unit for heating primarily liquids. The features of the metal bottom unit of variable thickness are as follows.

The bottom radially includes several concentric areas with different characteristics.

The central area has the smallest bottom thickness. This is an area of downward flow.

Then there is an area of variable bottom thickness from minimal thickness adjacent to the central part to maximum thickness .

The heater, including a linear ring heater or any other heat source, possibly electric or operating on any other principle, is brought, attached to or built in the body of the heating area - with the greatest bottom thickness.

This area is assumed to be a heating area and heating is assumed to come from any, inter alia, linear ring heat source, including those constituting a complete or open ring.

Therefore, depending on this, the heating area is made of constant or variable thickness - minimum thickness on the one side and the largest thickness on the opposite side.

The small-to-large thickness transition of the heating area can be made in a linear, exponential, power-law, or any other fashion as the developer or production engineer thinks fit.

Whether the trajectory of the heating element is closed or open, the central area with the smallest bottom thickness can be shifted slightly away from the geometric center of the circular bottom toward the heating line gap. At some parameter values, the shift of the central area can become significant, and the heating area can become open, with a gap.

The peripheral area from the area with the maximum bottom thickness up to the area adjacent to the vessel wall has nearminimum bottom thickness.

The central area can have a curved upwards spherical shape.

The above- the-heat-source area has the largest bottom thickness. The thickness raises it upwards so that most of the heat-radiating surface is in a liquid.

The area between the central area and the above-the-heater area can have a curved downwards shape.

The peripheral area further (from the center) from the area with the maximum bottom thickness (from the heating source) up to the area adjacent to the vessel wall can have a spherical, cylindrical, cone, or near-flat shape.

In the current experiments, the thickness of the central area bottom was 1.2-2.5 mm.

The bottom of the thickest area can be up to 20 times thicker than the central area. In the experimental studies, it was up to In the current experiments, the thickness of the peripheral area bottom was 1.2-2.5 mm.

Transitions between the areas can be smooth.

Radially-oriented edges can be made on the surface of the above- the-ring-heater area. In the conducted studies, their height was 1.2-2.5 mm.

To prevent surface oxidation and scaling, a water-repellent, non-stick and/or any other coating can be applied to the surface.

The surface shape can follow the expected trajectory of convective motion of liquid during heating and boiling.

If there is an additional a peripheral area further (from the center) of the thickest area up to the area adjacent to the vessel wall, it can have a near-flat shape.

The bottom thickness of such peripheral area can be minimal, and in the conducted studies it was 1.2-2.5 mm.

The unit operates as follows.

When water (water-containing solutions or mixtures) is being heated, cavitation bubbles containing airfree steam appear in nucleation sites of the intense heat exchange zone due to low pressure and high temperature. Breaking away from the surface and losing the thermal energy source in the form of a heating element, cavitation bubbles fall into denser and colder layers of liquid, where they violently collapse. This process results in boiling noise. The smaller the area of intense heat exchange, the higher the temperature therein, the denser and faster the bubbles form and the louder the noise. Thereafter, when an intense convection flow heating the liquid more evenly is formed, the bubble separation rate drops, bubble size increases, and the pressure difference within a bubble and in the upper layers of the liquid ceases to be critical. Separated bubbles reach the surface without collapsing. The noise decreases. The process of boiling begins. Thus, the claimed technical result is achieved through choosing parameters of the body and the shape of the heating reservoir bottom with a built-in heating element, which increases the area of intensive heat exchange zone and speeds up the formation of convection flow levelling liquid temperature. Thus, the claimed technical result is achieved through choosing parameters of the body and the shape of the heating reservoir bottom with a built-in heating element, which increase the area of intensive heat exchange zone and speed up the formation of convection flow levelling liquid temperature, and arranging the necessary surface properties, for example, by applying a water-repellent, non-stick or any other coating, which in this case act as a protective layer that prevents surface oxidation and contaminants which close and thus reduce the number of steam generation sources.

The claimed heating element, which is reservoir bottom 1 for heating primarily liquids, operates as follows.

The unit includes metal bottom 1 of variable thickness with a linear ring heater, primarily electric, attached, mounted to, or built into it.

In order to enhance convection, the bottom is shaped as described and includes heating areas that form an upward flow and areas excluding heating that form a downward flow.

When heating 2 is turned on in area 1.3 with the largest bottom thickness, the temperature rises and local liquid heating takes place. Above this area, the liquid begins to move upwards.

Central area 1.1 has the smallest bottom thickness and is away from the heater, which make the liquid move downwards above this area.

Fig. 4 shows the liquid trajectory.

In order to improve convection efficiency, area 1.3 with the largest bottom thickness is raised upwards so that most of the heat-radiating surface is in a liquid.

Area 1.3 above the heater line gap is of the smallest thickness. The thickness gradually increases along the heating line of area 1.3. The part of area 1.3 opposite to the area above the linear heater gap is made of the largest thickness. The thickness gradually decreases along area 1.2 until it reaches its minimum above the linear heater gap.

When the heater is attached from below, the heat from electric heater 2 is transferred to the thickened part of bottom 1.3 through the lower surface. If the heater is built in the body of thickened area 1.3, the heat is transferred directly.

If there is peripheral area 1.4 from the thickened part of bottom 1.3 up to the area adjacent to the vessel wall, a downward flow that also increases convection is also formed there due to small bottom thickness.

In order to improve heat transfer, central area 1.1 can have a curved upwards spherical or spherical-to-cone shape.

Transitions between the areas can be smooth.

In order to improve heat transfer, radially-oriented edges 3 can be added on the surface of the heated above-the-ring-heater area .

To prevent surface oxidation and scaling, heating element 1 can be additionally coated with a composition having non-stick, anti- friction, and hydrophobic properties. Such coating effectively prevents the oxidation of the heating element body and ensures a significant increase and even distribution of nucleation sites.

The shape of the bottom surface can follow the expected trajectory of convective motion of liquid during heating and boiling .

The claimed technical result can also be achieved for the reservoir bottom unit for heating primarily liquids. Besides, the specific feature of a unit using a metal bottom of variable thickness is that heating should only take place in the area with the greatest bottom thickness.

Example of a comparative test of classic and claimed heating elements built in the reservoir bottom.

Input Parameters

Bottom diameter - 138 mm (see Fig. 11)

Thickness of area 1.1 1.3 - 1.5 mm

Thickness of area 1.3 10 - 15 mm

Thickness of area 1.4 1.3 - 1.5 mm

Height of edges 3 1.5 - 3.5 mm

TEH power - 1800-2200 W.

Water temperature: 60 degrees Air temperature: 30 degrees

TEH power: 2000 W

The lower part of the heating element is in contact with air.

The upper part is in contact with water.

Air convection coefficient - 5, water convection coefficient - 3600 W/ (m2*S) (which corresponds to the water coefficient at 60 de . C .

Cavitation occurs approximately at 60 deg.C, increases at 70 deg.C, and disappears at 80 deg.C.

Results .

Given that the heater power is the same and the temperature difference is the same, the amount of energy transferred per unit of time will also be the same. Water will receive the same amount of energy per unit of time. Only in the first case it will be transferred to water across a small area equal to the contact area of the heating element with the bottom. In the second case, energy is distributed across a larger surface of the thickened part of the body. It is obvious that the same amount of energy is transferred across a smaller area with more heat.

Thermal cavitation occurs when there is a strong temperature change. Therefore, the smaller the change, the milder the cavitation .

It seems that in this case a wavy, thick-walled, and preferably aluminum heating element will be preferential.

It is also worth reminding that the claimed unit additionally solves the problem of using existing TEHs .

The unit is industrially applicable because each part can be manufactured on industrial equipment in large-scale and mass production . ADDITIONAL EXPLANATIONS

When water (water-containing solutions or mixtures) is being heated, cavitation bubbles containing airfree steam appear in nucleation sites of the intense heat exchange zone due to low pressure and high temperature. Breaking away from the surface and losing the thermal energy source in the form of a heating element, cavitation bubbles fall into denser and colder layers of liquid, where they violently collapse and emit a hydraulic shock wave. This process results in boiling noise. At the same time, the more powerful the heating element and the smaller the area of intense heat exchange, the denser and faster the cavitation bubbles and the louder the noise. Thereafter, when an intense convection flow heating the liquid more evenly is formed, the bubble separation rate drops, bubble size increases, and the pressure difference within a bubble and in the upper layers of the liquid ceases to be critical. Separated bubbles reach the surface without collapsing. The noise decreases. The process of boiling begins.

Thus, the claimed technical result is achieved through choosing parameters of the body and the shape of the heating reservoir bottom with a built-in heating element, which increase the area reduce the temperature of intensive heat exchange zone and speed up the formation of convection flow levelling liquid temperature more intensively.

The unit includes metal bottom of variable thickness 1 with ring heater 2, preferably electric, attached to it. In order to enhance convection, the bottom is shaped as described above and has downward convection flow area 1.1, pre-heating area 1.2, and crest-shaped upward convection flow area 1.3. Radially-oriented edges 3 can be added on the surface of crest 1.3 above ring heater 2 to increase the heat transfer area. If there is peripheral area 1.4 from the thickened part of bottom 1.3 up to the area adjacent to the vessel wall, a downward flow that also increases convection is also formed there due to small bottom thickness . When heater 2 is turned on in area 1.3 with the largest bottom thickness, temperature rises and a heat exchange zone appears, temperature in pre-heating zone 1.2 partially rises increasing the effective heat exchange area. Liquid begins to move up above upward convection flow area 1.3. Due to a thicker heating element body, high heat capacity and high thermal conductivity of body material, heat is distributed more evenly over areas 1.3 and 1.2 reducing the risk of intense heat exchange zones and, therefore, zones of intensive cavitation bubble formation .

Downward convection flow area 1.1 has the smallest bottom thickness and is not heated by heater 2. Due to this, an effective downward flow of liquid is formed in this zone. Passing through concave pre-heating area 1.2, the liquid is heated and sent upwards to upward convection flow area 1.3, where it gets into the intense heat exchange zone, heats up, and rises upward. This is how a closed convection flow is formed resulting in rapid mixing and even liquid heating.

In order to prevent oxidation, reduce friction, and form a uniform surface, heating element 1 in the upper part that is in contact with liquid can be further coated with a composition with non-stick, anti-friction, and hydrophobic properties. This coating effectively prevents the oxidation of the heating element body and ensures a significant increase and even distribution of nucleation sites.

The unit includes metal bottom of variable thickness 1 with ring heater 2, preferably electric, attached to it. In order to enhance convection, the bottom is shaped as described above and has downward convection flow area 1.1, pre-heating area 1.2, and crest-shaped upward convection flow area 1.3. Radially-oriented edges 3 can be added on the surface of crest 1.3 above ring heater 2 to increase the heat transfer area. If there is peripheral area 1.4 from the thickened part of bottom 1.3 up to the area adjacent to the vessel wall, a downward flow that also increases convection is also formed there due to small bottom thickness .