DE102017128254A1 - Heat exchanger with design-side adaptation to increased load requirements, especially for a high-performance low-temperature Stirling engine - Google Patents

Abstract

The invention relates to a heat exchanger, in particular a thermal regenerator for a high-performance low-temperature Stirling engine (M) comprising at least one housing part (1A, 2A, 1A-2A), which forms an energy storage space in which a storage mass for heat storage is arranged. The heat exchanger characterized in that the storage mass is formed of a highly conductive, preferably metallic or non-metallic material.

Description

The invention relates to a heat exchanger which can be used in particular in combination with a high-performance low-temperature Stirling engine.

The growing use of renewable energies is taking place at different rates of development, depending on the type of energy in Germany. In this case, the expansion for generating electrical energy was more intensive, which u. a. at the better feed-in possibility in the area-wide available power grid lies. The use of solar radiant heat, on the other hand, is largely tied to the heat demand prevailing at the place of production.

When supplying energy in commercial and residential buildings, heat is generally required for heating purposes and hot water, as well as electrical energy for lighting, information, communication and propulsion. The demand varies depending on the time of the day and the season. The amount of energy for heat is generally about 4 times that of electrical energy.

When assessing the share of renewable energies, the total energy demand is considered to be open to development opportunities in the integration of environmental heat into the energy supply. On the way to a complete renewable energy supply, in addition to improving efficiency, the storage of large amounts of energy and the possibility of transformation between the different types of energy are fundamental requirements. So far, only the electrical energy offers the property of being able to be converted into all types of energy as universal energy. However, a direct storage of large amounts of energy is not economically viable in spite of the enormous international development effort.

On the other hand, heat can already be stored cost-effectively today in large quantities, but requires their conversion to a complex drive units z. As steam turbines, steam engines or high-performance low-temperature Stirling engines and on the other hand, the temperature must be so high that a direct use of environmental heat is prevented. Ultimately, it avoids the usual combustion of gas, oil or solids. Even the occasional use of solar-powered Stirling engines require temperature differences between the hot and cold side, which can only be achieved by optical concentration by means of elaborate concave mirrors and their constant tracking.

The economic use of solar heat for energy conversion requires that standard components can be used that work effectively at temperature levels of around 50 to 70 ° C. Solutions that can provide the waste heat of a thermal energy conversion process as useful heat are considered to be particularly effective.

Stirling engines are known which relate their power exclusively from the pressure and volume changes caused by temperature changes. Conventional Stirling engines require a complex mechanism to ensure this function. As a result, Stirling engines have to be very heavy and large in high pressure ranges.

Low-temperature Stirling engines that are used to generate electricity currently require temperatures well above 100 ° C. As a working medium, helium, air, nitrogen and similar gases are used. It uses media that come close to the theoretically ideal gases.

The publication DE 10 2009 057 210 B4 describes a Stirling evaporator thermal power plant consisting of at least one heat engine, which is mechanically constructed like a Stirling engine, wherein a working substance is used whose boiling point is selected such that it is gaseous in the warm areas of the thermal power plant and in the cold areas as liquid, is present as transcritical or as supercritical phase.

The publication EP 2 333 285 A1 discloses a Stirling evaporator thermal power plant with external heating, which operates on a Stirling-like principle. The thermal power plant consists of at least one heat engine, which is constructed mechanically like a Stirling engine. It is used a working fluid whose boiling point is selected such that it is present in the warm areas of the thermal power plant in gaseous and liquid in the cold areas, transcritical or supercritical. With the thermal power plant, the advantages of Stirling heat engines and the machines operating according to the Rankine principle, in particular a sustainable lowering of the minimum heater temperature to about 150 ° C., are achieved at the same time. The system is particularly suitable for use in combined heat and power plants, for uninterruptible power supply units, for emergency generators and for motor vehicle power supplies.

The publication CN 102 418 621A illustrates a Stirling engine having an eccentric shaft rolling ring. A cylindrical air cylinder comprises four spaces, namely two interior spaces and two exterior sides. A working fluid is high pressure carbon dioxide. Since at the same time carried out the thermal expansion and the cold contraction of the working fluid and the working fluid always flows in the same direction, the Stirling engine has a good stability of movement without pulsation.

Furthermore, the documents describes EP 1 592 8 75 B1 and US Pat. No. 6,701,721 B1 analogous to a stirling engine powered heat pump with a fluid connection. Disclosed is a heating and cooling apparatus, and more particularly, a Stirling engine based prime mover, which drives the compressor of a vapor compression heat pump system to pump heat from a cooler mass to a hotter mass. A single working fluid, preferably carbon dioxide, can be used both for the Stirling engine as a working fluid and also as a refrigerant.

The publication DE10 2006 061 509 A1 further illustrates a thermal displacement motor with external thermal energy supply. The thermal displacement motor is designed in the manner of a Stirling engine. It is proposed a novel working fluid heater, which makes it possible to heat a working fluid compared to a conventional working fluid heater to a much higher pressure and temperature level.

To ensure the performance of Stirling engines with low temperature difference between a hot and a cold side and small component size, the hot side of the necessary amount of heat must be brought by means of a relatively large volume flow, the flow resistance in the heat exchanger should be possible small.

The object of the present invention is to provide a heat exchanger which allows for a low flow resistance rapid heat exchange.

The starting point of the invention is a heat exchanger which has at least one housing part which forms an energy storage space in which a storage mass for heat storage is arranged.

According to the invention, the heat exchanger is a solid heat store whose storage mass is formed from a highly conductive, preferably metallic or non-metallic material.

In one embodiment, it is provided that the storage mass is formed from a porous aluminum body, which is arranged in the at least one housing part.

Preferably, it is provided in the second embodiment that the compact or hollow metallic or non-metallic beads of the same or different diameter of steel or aluminum or glass are formed.

In the second embodiment, it is provided that the surface of the beads is completely smooth or smooth and partially structured or completely structured.

Advantageously, in the second embodiment variant, it is ensured that the beads are embedded in an inner surface of the inner wall of the heat exchanger, so that edge flow channels in the heat exchanger are closed by a ball embedding in the edge region of the heat exchanger.

According to a first embodiment variant is provided that on the inner surface of the inner wall of the heat exchanger, a thread is arranged, the pitch between two thread crests is the largest diameter of the metallic or non-metallic beads, so that the spherical surface of the metallic or non-metallic beads at least partially in the thread of Internal thread is located, whereby the edge flow channels are closed in the heat exchanger.

According to the following design variants, it is provided that a layer of a shape-variable material with a predefinable layer thickness is arranged on the inner surface of the inner wall of the heat exchanger, which impose the beads their surface shape, whereby the edge flow channels are sealed in the heat exchanger.

In these embodiments, the layer is formed of a permanently elastic or a plastic or a thermally variable or a chemically variable material.

In particular, it is provided in a second embodiment variant that the layer is formed of a permanently elastic material, in particular rubber or soft plastic.

In a third embodiment variant, it is provided that the layer is formed from a plastic material, in particular tin.

In a fourth embodiment variant, it is provided that the layer is formed from a thermally variable material, in particular a plastic or wax.

Finally, it is provided in a fifth embodiment variant, that the layer of a chemically variable material, in particular made of an epoxy resin is formed.

In all embodiments, the layer thickness is preferably 0.1 to 0.5 times the maximum ball diameter used.

In addition, it is provided that the heat exchanger has at least one closable filling element, via which a working fluid and the beads formed from the metallic or non-metallic material can be filled into the interior of the heat exchanger.

The heat exchanger has two connection openings, through which a working fluid flows into adjacent work spaces.

Finally, it is provided in the second embodiment that the heat exchanger has two connection openings, through which the working fluid in adjacent working spaces and flows out, wherein the working space side or heat exchanger side in each case at least one grid element, in particular is arranged from a stainless steel wire mesh, the mesh size depending on the diameter of the metallic or non-metallic beads is smaller than the diameter of the metallic or non-metallic beads.

The invention further describes the use of the heat exchanger for a heat engine, in particular a high-performance, low-temperature Stirling engine, which has the following features:

The heat engine comprises a pressure chamber formed by at least one housing part, which is formed pressure-tight with respect to the environment and filled with a working fluid, and on a hot side by external heat input at higher temperature and by on a cold side by external heat dissipation at lower than the higher temperature Temperature mechanical output delivers, wherein the at least one pressure chamber is divided by periodically movable piston in two fluid-tight and pressure-tight working spaces.

It is envisaged that the working chambers are separated from each other by the pistons on the fluid side and are in operative connection via the pistons, wherein one of the pistons on the hot side is brought to a higher temperature by the external heat supply with respect to the other piston arranged on the cold side is maintained at a higher temperature, the other cold side piston being maintained at a lower temperature relative to the hot side piston or brought to a lower temperature, the pressure variations produced in the working spaces periodically acting on the movable pistons coaxial with mutually arranged eccentric shafts are in operative connection, wherein the coaxially arranged eccentric shaft seen in the longitudinal direction of the eccentric shafts are arranged eccentrically to each other in a predetermined offset.

In a preferred embodiment of the invention, it is provided that each of the pistons has parallel opposing piston end faces, wherein two piston end faces of the pistons located on the same side-between the piston end faces-each form an energy storage space lying between the hot side and the cold side.

The invention provides that the energy storage spaces of the heat exchanger are designed as thermal regenerators of the heat engine.

It is provided that the formed as energy storage spaces thermal regenerators are arranged integrated in one embodiment in the housing or are arranged outside the housing in another embodiment.

The movable pistons are arranged in cylinders which are connected on the pressure side via connection openings with the energy storage spaces designed as thermal regenerators.

In a preferred embodiment of the invention, integrally formed or multi-part cylinder each form a piston interior, in which each eccentric shaft is associated with an eccentric, which is arranged together with the eccentric shaft in the piston interior, the piston inner spaces are formed pressure-tight and fluid-tight with respect to the work spaces, the acting on the piston end faces of the respective piston forces to the periodic movement of the piston and the respective piston acts as a function of the position of the eccentric on the eccentric shafts.

According to the invention it is further provided that the eccentric shafts are mounted on the piston inner space adjacent bearing in the longitudinal direction with respect to their longitudinal axes coaxially with each other in the housing, wherein the eccentric shafts are led out at least one end side of the piston interior. In another embodiment, it is possible that to avoid possible leaks at the shaft output an encapsulated magnetic coupling is arranged, via which a power output to the generator or the generator shaft. In a further embodiment, the generator can also be integrated into the pressure range of the housing.

The eccentric of the eccentric shafts relative to the other eccentric shaft the predetermined offset of the eccentric shafts to each other, wherein the offset between an eccentric center of the eccentric and the center of the longitudinal axis of the one relative to the other eccentric shaft is formed to each other, wherein the predetermined offset of the eccentric between 90 ° and 170 °.

The heat engine is characterized in particular by the fact that the predetermined offset is fixed by arranged on the eccentric shafts outside the housing gears, which are interlocked with each other according to the predetermined offset.

Preferably, in each case a plain bearing bush is arranged in the respective piston interior between the eccentric of the eccentric shafts and the inner sides of the piston.

The forces acting on the respective pistons of the heat engine are aligned with respect to the longitudinal axes of the eccentric shafts, whereby the forces act orthogonally as transverse forces on the eccentric shafts.

It is envisaged that the working fluid in the pressure space is liquid supercritical carbon dioxide or xenon or ethene.

In particular, the working fluid is carbon dioxide CO ₂ , which is used in the working spaces and the energy storage spaces of the pressure chamber at an operating point which has a temperature of 30 ° C at a pressure of 7.2 MPa (72 bar), as in the description even closer is explained.

In one embodiment, a plurality of heat engines seen in the longitudinal direction of the eccentric shafts are arranged separately from each other as a cascade, as also explained in more detail in the description.

According to the invention, the heat engine is a Stirling engine, in particular a high-performance low-temperature Stirling engine, which is structurally changed according to the boundary conditions to be observed, the working temperature <50 ° C and reaches its optimum operating window already at 27 ° to 37 ° C, wherein temperature differences between a hot and cold side of the Stirling engine of less than 10K are needed, as explained below.

With an ideal gas, a temperature increase from 30 ° C to 31 ° C leads to a pressure change (p1 / p2 = T1 / T2) or a volume change (V1 / V2 = T1 / T2) of only approx. 0.3%.

However, the high-performance, low-temperature Stirling engine according to the invention uses a working fluid FL , in particular carbon dioxide CO _2, which alters its pressure by approximately 2.3% and its volume by approximately 16.5% even in a low temperature range, for example 30 ° C. to 31 ° C., thereby achieving approximately 400 times higher theoretical working capacity ,

The high-performance low-temperature Stirling engine according to the invention is characterized by a high degree of compactness, and enables a high power output even at temperatures below 50 ° C. As a working fluid FL Xenon or ethene can also be used.

The invention is described below with reference to the associated 1 to 8th explained.

• 1 eine perspektivische Darstellung eines Hochleistungsniedrigtemperatur-Stirlingmotor in einer möglichen Ausführungsform in einer Außenansicht;
• 2 einen Schnitt A-A gemäß 1 durch den Hochleistungsniedrigtemperatur-Stirlingmotor;
• 3 einen Schnitt B-B gemäß 2 durch den Hochleistungsniedrigtemperatur-Stirlingmotor;
• 4 einen Schnitt C-C gemäß 2 durch den Hochleistungsniedrigtemperatur-Stirlingmotor;
• 5 einen Schnitt F-F gemäß 2 durch den Hochleistungsniedrigtemperatur-Stirlingmotor;
• 6 einen Schnitt G-G gemäß 2 durch den Hochleistungsniedrigtemperatur-Stirlingmotor;
• 7 einen Schnitt H-H gemäß 2 durch den Hochleistungsniedrigtemperatur-Stirlingmotor;
• 8 einen Schnitt K-K gemäß 6 durch den Hochleistungsniedrigtemperatur-Stirlingmotor.

Show it:

• 1 a perspective view of a high-performance low-temperature Stirling engine in a possible embodiment in an external view;
• 2 a cut AA according to 1 by the high performance low temperature Stirling engine;
• 3 a cut BB according to 2 by the high performance low temperature Stirling engine;
• 4 a cut CC according to 2 by the high performance low temperature Stirling engine;
• 5 a cut F - F according to 2 by the high performance low temperature Stirling engine;
• 6 a cut GG according to 2 by the high performance low temperature Stirling engine;
• 7 a cut HH according to 2 by the high performance low temperature Stirling engine;
• 8th a cut KK according to 6 by the high-performance low-temperature Stirling engine.

The invention relates to a high-performance low-temperature Stirling engine M (see. 1 to 8th , which is able to convert amounts of heat already at a low temperature level into electrical energy, and thereby to achieve a level of performance for significant support of the electrical energy demand, in particular an exemplified building supply.

For a commercial building, a total solution is provided which combines the supply of heat and electricity. In this case, preferably first by means of a solar thermal system (not shown) received environmental heat and with respect to the high-performance low-temperature Stirling engine M stored in an external hot water buffer.

Additional heat demand of the building is covered by a gas condensing boiler or alternatively by a heat pump and also stored in the external hot water buffer.

For energy conversion according to the invention, the special behavior of a working fluid FL used which, unlike ideal gases, has a supercritical state.

When a liquid working fluid is heated above the boiling point, this working fluid generally changes to the gaseous state of matter. If the existing pressure does not permit vaporization, the substance assumes a special condition, which applies to both liquids and gases. When changing to this condition called "supercritical", it expands as a working fluid FL used material with extreme volume growth, as it otherwise only arises in the evaporation process, while at the same time unfolding a force that occurs comparatively in the expansion of liquids. From an energy-technical point of view, the so-called supercritical state thus combines technically exploitable advantages of liquids and also of gases.

For example, carbon dioxide CO _{2 forms} this supercritical state as a property already at an operating point at a temperature of 30 ° C. and a pressure of 7.2 MPa (72 bar) and is found to be particularly suitable for the invention described below.

A novel high-performance, low-temperature Stirling engine solution M , which will be discussed below, exploits the particular expansion characteristics of liquid carbon dioxide CO ₂ in the supercritical state and at the same time copes with the concomitant high load of the engine technical components by a novel construction.

The high performance low temperature Stirling engine M gets on the hot side HS (see. 1 ) operated at a minimum of 32 ° C. This is the hot side HS preferably heated by the external hot water buffer (not shown).

About a schematically indicated piping system L (see. 1 and 6 to 8th ) becomes the hot side HS high-performance low-temperature Stirling engine M Heat is supplied, as will be explained in detail.

A cold side KS high-performance low-temperature Stirling engine M (see. 1 ) is cooled by the cold water buffer to a maximum temperature of 30 ° C. For this purpose, the cold side KS is cooled by the external cold water buffer, for example, inactive and / or active.

About an analogous to the hot side HS executed piping system L (see. 1 and 6 to 8th ) is from the cold side KS high-performance low-temperature Stirling engine M Heat dissipated, as will also be explained.

This particular mode of operation according to the invention already allows for a minimal temperature difference .DELTA.T between the hot side HS and the cold side KS of 2 ° K the normal function of the high-performance low-temperature Stirling engine M ,

The required heat energy requirement on the hot side HS and the cold side KS of the high-performance low-temperature Stirling engine is realized by correspondingly high volume flows from at least the external hot water tank or two external buffer storage the external hot water tank and the external cold water tank.

As the high-performance low-temperature Stirling engine M continuously during operation its hot side HS cools and its cold side KS heated, heat is ultimately transported from the external hot water buffer to the external cold water buffer. It is inventively provided that a heating circuit of the building is supplied from the cold water buffer, so that the building works as a cooler.

In other words, on the cold side KS high-performance low-temperature Stirling engine M transported heat is dissipated, for example via the heating circuit of the building, which communicates with the cold water buffer. Thus, the waste heat of the cold side is used KS high-performance low-temperature Stirling engine M in an advantageous manner, finally, as useful heat for heating the building.

The heating of the building is designed to cover a large area, at one for the cold side KS high-performance low-temperature Stirling engine M provided temperature of max. 30 ° C as the flow temperature of the building heating to realize a sufficient heat transfer.

The high performance low temperature Stirling engine M In addition, in a preferred embodiment, drives a generator which feeds the generated electrical energy, in particular feeds it into a household grid.

The desired temperature of the hot side HS , in particular at least 32 ° C or greater can either by the mixture of the inflowing from the external hot water buffer medium L _TO (see. 1 and 7 ) and from the hot side HS back flowing medium L _AB , or through the flow rate of the medium flowing from the external hot water buffer L _TO - without admixture - be adjusted.

Using these temperature settings, the instantaneous power of the high-performance, low-temperature Stirling engine M or the feed power of the generator to be adapted to the desired needs.

The solution according to the invention fulfills the following functions:

An economic energy storage via the hot water buffer is guaranteed. In addition, an effective conversion of environmental heat into electrical energy is realized. In addition, a temporal decoupling of heat generation and heat demand and the need for electrical energy is made.

The high performance low temperature Stirling engine M in detail:

The embodiments of conventional high-performance, low-temperature Stirling engines have a piston-crankshaft construction which receives the pressure of the working fluid through the piston crown of the piston. In the piston, a piston pin is used. This forwards the force via a bearing, in particular a sliding bearing or a needle bearing on the upper connecting rod eye. The connecting rod itself is supported against the crankshaft and passes the power from the lower connecting rod eye via bearings to the crankshaft. The resulting torque is applied to the crankshaft journal as a rotating work.

In the planned use of the carbon dioxide CO ₂ , in particular in the supercritical state of the working fluid, considerable, and in particular larger, pressures than with conventional working fluids (such as nitrogen, helium or air), which do not assume a supercritical state, causing immense forces acting on the piston crown of the piston.

In the conventional high-performance low-temperature Stirling engines, the components of the chain of action piston pin, piston pin bearing and the upper connecting rod are constructively designed relatively small, which is why the surface pressure, bending stresses and shear stresses applied there, at the now present greater pressures, leading to their overload.

To avoid this overload, the power can be reduced, but disadvantageously reduces the attractiveness of the high-performance low-temperature Stirling engine.

There is also the possibility to safely absorb the high forces, as has been done in practice so far, to oversize the components, which disadvantageously size, weight and cost are increased, so that the efficiency of the high-performance low-temperature Stirling engine decreases.

A novel construction of a high-performance, low-temperature Stirling engine M dispenses with piston pin, piston pin bearing and connecting rod.

The new high-performance, low-temperature Stirling engine M is in a perspective outside view in 1 and in a sectional view in 2 The following description is recommended in a synopsis of the 1 to 5 understand.

It is preceded with respect to the figures that the high-performance low-temperature Stirling engine M at a temperature difference .DELTA.T of the working fluid AF of 10K between hot side HS and cold side KS is formed as a compact component having a height x width x depth (H / B / T) of 25 cm.

With such a compact component of 25 cm x 25 cm x 25 cm can work with the high-performance low-temperature Stirling engine M (without cascading), a power that is approximately 2 kW when working as working fluid AF as explained supercritical carbon dioxide CO2 is used.

In high-performance low-temperature Stirling engine M (see. 1 ) becomes the compressed working fluid FL , in particular supercritical carbon dioxide CO ₂ alternately from a cold control cylinder 2 , by means of a control piston 4 and a working piston 3 a warm working cylinder 1 about the regenerators 9 . 10 in the warm working cylinder 1 and from the warm working cylinder 1 in the cold control cylinder 2 postponed. A first regenerator R1 has analogous to the warm working cylinder 1 a hot side R1 - HS and analogous to the cold control cylinder 2, a cold side R1- KS on.

A second regenerator R2 also analogous to the warm working cylinder 1 a hot side R2 -HS and analogous to the cold control cylinder 2 a cold side R2 -KS on.

The two regenerators R1 . R2 (see. 1 ) form the heat storage mass of the high-performance, low-temperature Stirling engine M the heat engine.

In principle, the operation of the Stirling engine is possible without regenerators, but is missing then the heat storage mass to operate the Stirling engine efficiently.

The high performance low temperature Stirling engine M is a device known per se, which consists of a temperature difference between one of two pistons 3 . 4 back and forth funded working fluid can generate mechanical energy.

This process requires a cold source and a heat source. The cold source is in the high-performance low-temperature Stirling engine according to the invention M realized by the cold side KS. The heat source is through the hot side HS realized.

The high performance low temperature Stirling engine M has the mentioned two cylinders 1 . 2 on, namely the cold control cylinder 2 (Cold side KS ) and the warm working cylinder 1 (Hot side HS ) see. the cut F - F according to 5 and the cut BB according to 3 ,

The cold and the heat is the two cylinders 1 . 2 through the cold sides assigned to them KS and hot sides HS the regenerators R1 . R2 provided with the respective cylinders 1 . 2 via connection openings 12 . 13 (see. 1 and 4 . 5 ) are connected.

According to the 6 to 7 (cuts GG and HH ), the heat supply and heat dissipation via at least one piping system L ensures which in the housing 1A of the working cylinder 1 or in the housing 2A of the control cylinder 2 to the respective accesses of the regenerators R1 and R2 around on the hot side HS and preferably also on the cold side KS in the case 1A and 2A high-performance low-temperature Stirling engine M is trained. According to 8th are in the cases 1A . 2A corresponding line branches L1 designed to increase the effect of heat and heat dissipation.

At least on the hot side HS is at least one inlet opening L _to and a drain hole L _AB intended to (cf. 1 ) the high performance low temperature Stirling engine M a heat-conducting medium, in particular to be able to supply water, which after its heat release via the drain opening L _AB is dissipated. Preferably, this heat, as already mentioned, taken from a cycle of a solar heating system, which is stored in a hot water buffer of the solar thermal system.

Additionally is on the cold side KS (see. 1 ) Also at least one inlet opening L _to and a drain hole L _AB intended to (cf. 1 ) the high performance low temperature Stirling engine M to be able to supply a heat dissipating medium, which after its heat absorption via the drain opening L _AB is dissipated. We prefer this waste heat, as mentioned the cold side KS high-performance low-temperature Stirling engine M used in an advantageous manner as useful heat for heating buildings.

In a preferred embodiment of the invention are (see. 2 ) in the two cylinders 1 . 2 each the pistons 3 . 4 arranged, which by their translational movement in each case an eccentric shaft 5 . 6 rotationally driving, each in a preferred embodiment of the invention in a piston interior 3A . 4A are arranged.

On each of the eccentric shafts 5 . 6 is each a gear 9 . 10 arranged, which interlock, are thus interlocked with each other.

According to the invention it is further provided that each of the eccentric shafts 5 . 6 an eccentric 5A . 6A having, wherein the eccentric 5A the first eccentric shaft 5 opposite the eccentric 6A the second eccentric shaft 6 - specifiable - between 90 ° and 170 °, in a so-called offset V , are arranged offset.

The default offset selected according to different boundary conditions V the eccentric 5A . 5B the eccentric waves 5 . 6 is through the two interlocking gears 9 . 10 fixed.

In the in the 1 to 5 illustrated embodiment is the eccentric 5A the first eccentric shaft 5 opposite the eccentric 6A the second eccentric shaft 6 arranged offset by 90 °.

By the offset V (In the embodiment according to 2 with a 90 ° offset V ) is a continuous translational movement of the working piston 2 . 4 because of the working piston 2 with the inner first eccentric shaft 5 and the eccentric 5A over the gears 9 . 10 with the in the control piston 4 inner second eccentric shaft 6 and the eccentric 6A and thus with the control piston 4 connected, in a rotational movement of the eccentric shafts 5 . 6 transformed. Thus, by the offset V the time delay of the control piston 4 opposite the working piston 2 Accounted for.

According to the known Stirling principle, during operation of the high-performance low-temperature Stirling engine M on the eccentric shafts 5 . 6 or on the gears 11 . 12 a usable torque can be removed.

In a preferred embodiment of the invention are in the piston interior 3A . 4A (see. 2 ) plain bearing bushes 7 . 8th , preferably with a Teflon inner coating 7A . 8A are provided, respectively between the eccentrics 5A . 6A the eccentric waves 5 . 6 and the piston 3 . 4 arranged. The plain bearing bushes 7 . 8th advantageously reduce the friction between the eccentric shafts 5 . 6 and the insides of the pistons 3 . 4 ,

Since no connecting rod is required by the inventive design, can be worked with this explained principle with higher working fluid pressures than before, as will be explained below.

The high performance low temperature Stirling engine M thus has at least one housing part 1A . 2A . 1A - 2A formed pressure chamber, which is pressure-tight with respect to the environment and with the working fluid FL is filled, and the one on the hot side HS by external heat input at higher temperature and by on the cold side KS by external heat dissipation - in relation to the higher temperature lower temperature - mechanical output power, the at least one pressure chamber by periodically movable piston 3 . 4 divided into two fluid-tight and pressure-tight work spaces.

The work spaces are through the pistons 3 . 4 Fluid side separated and are above the piston 3 . 4 on the pressure side in an operative connection, wherein one of the pistons 3 . 4 on the hot side HS through the external heat supply to the other on the cold side KS arranged piston 3 . 4 brought to a higher temperature and the other on cold side KS arranged piston 3 . 4 opposite to the one on the hot side HS arranged piston 3 . 4 is maintained at a lower temperature, wherein the pressure fluctuations generated in the work spaces periodically to the translationally movable piston 3 . 4 act, with coaxially arranged rotating eccentric shafts 5 . 6 are in operative connection, wherein the coaxially arranged eccentric shafts 5 . 6 in the longitudinal direction of the eccentric shafts 5 . 6 ) seen in a predetermined offset V are arranged eccentrically to each other.

It is envisaged that each of the pistons 3 . 4 parallel opposing piston end faces A3 . A4 having two piston faces located on the same side A3 . A4 The piston 3 . 4 one each between the hot side HS and the cold side KS form lying energy storage space.

The energy storage rooms are according to the invention as heat exchangers, in particular as thermal regenerators R1 . R2 (see. 1 and 2 ) educated.

The energy storage spaces of the thermal regenerators are preferred R1 . R2 (as in the 1 and 2 shown) in the housing 1A . 2A . 1A - 2A integrated, or they are outside the housing 1A . 2A . 1A - 2A (not shown) arranged.

In the operation of the high-performance low-temperature Stirling engine M prevails in the regenerators R1 and R2 using the working fluid carbon dioxide CO ₂ in said operating point at a temperature of 30 ° C, a pressure of about 7.2 MPa (72 bar).

Depending on the temperature on the hot side R1 -HS, R2-HS and the cold side R1 - KS . R2 - KS (see. 1 ) and the operating state of the high-performance low-temperature Stirling engine M the pressures are temperature dependent in the regenerators R1 and R2 between about 7.0 MPa (70 bar) and 7.5 MPa (75 bar), according to the Stirling principle between the opposite end faces A3 of the working piston 3 (see. 2 ) and the opposite end faces A4 of the control piston A4 (see. 2 ) there is a pressure difference Δp which ensures maintenance of the Stirling cycle.

It is envisaged that carbon dioxide as a working fluid FL in the working spaces of the pressure chamber and the energy storage spaces depending on temperature, preferably at a temperature difference .DELTA.T between 2K and 10K between the hot side HS and the cold side KS The piston 3 . 4 between 7.0 MPa (70 bar) and 7.5 MPa (75 bar) varies, with pressure fluctuations due to the temperature difference .DELTA.T between the hot and cold side HS . KS at a temperature on the hot side HS of a maximum of 37 ° C and a temperature on the cold side KS be caused by a minimum of 27 ° C.

The pressure differences Δp (p31-p32 and p41-p42) (cf. 1 ) are, however, by the structural design, on the front side opposite surfaces A3 of the working piston 3 adjacent pressures p31 . p32 or at the front side opposite surfaces A4 of the working piston 4 adjacent pressures p41 . p42 relatively low.

The by the remaining pressure difference Ap Acting force F In addition, it has a constructive effect on the high-performance low-temperature Stirling engine M on the respective piston 3 . 4 and not on the respective eccentric shaft 5 . 6 , The power F will depend on the position of the eccentric 5A . 6A (see. 2 . 3 . 4 . 5 ) on the eccentric shaft 5 . 6 transfer.

The longitudinal axes 5B . 6B the eccentric waves 6 . 7 lie across to the respective piston 3 . 4 on the eccentric 5A . 6A and the eccentric shafts 6 . 7 acting force F , So that's on the eccentric shafts 6 . 7 acting force difference relatively low. Thus, it is achieved in an advantageous manner that on the piston 3 . 4 acting transverse forces are minimized.

According to the invention, is thus due to the lower mechanical power transmission of the respective piston 3 . 4 on the eccentric 5A . 6A and the eccentric shafts 6 . 7 and thus on the eccentric shaft bearings 5D . 6D (see. 4 and 5 ) a component reduction of the respective components possible, whereby a total of a compact component can be formed, which withstands the high working pressures between 7.0 MPa (70 bar) and 7.5 MPa (75 bar).

This makes it possible to use the high-performance, low-temperature Stirling engine M with a working fluid FL to operate, which is in a supercritical state (eg, CO ₂ ), whereby the high-performance low-temperature Stirling engine M can be operated at high pressures and low temperatures and low temperature differences.

The heat exchangers, in particular the regenerators R1 . R2 in detail:

To the performance of the high-performance low-temperature Stirling engine M with low temperature difference between hot and cold side HS . KS as well as to ensure small component size, the hot side needs HS the necessary amount of heat be introduced by means of a relatively large volume flow, the flow resistance in the regenerators R1 . R2 should be possible small.

A reduced temperature difference on both sides of the regenerator R1 . R2 proportionally reduces its transmission power.

A reduction of the regenerators R1 . R2 also causes a reduction of the transmission power, as less surface is available for heat transfer.

A smaller version of the regenerator R1 . R2 Although it can increase the transfer area, but generates increasing capillary effects and thus increases the mechanical resistance in the flow through the regenerators R1 . R2 with the working fluid FL ,

The following structural design according to the invention brings these resistive boundary conditions together as follows in an advantageous manner.

The in the 1 and 2 shown regenerator R1 . R2 allow the flow with a relatively high flow rate with low mechanical resistance and high surface area for heat transfer in a total compact design of the regenerators R1 . R2 ,

Proposed recuperative regenerators R1 . R2 , As they pass through the working gas, they withdraw thermal energy from the working gas heated by the supply of heat energy, cool it and store at least some of the heat energy withdrawn from it in the regenerators R1 . R2 arranged storage mass in the respective energy storage spaces.

The recuperatively stored heat energy is flowing through the, cooled by the withdrawal of heat energy working fluid FL , fed back from the heat energy stored in the storage mass.

Proposed is a heat exchanger, in particular as a thermal regenerator R1 . R2 a high-performance low-temperature Stirling engine M acts and the at least one housing part 1A . 2A . 1A - 2A in which an energy storage space is formed, in which a storage mass is arranged for heat storage, wherein the heat exchanger is a solid heat storage with the described recuperative properties, the storage mass of a highly conductive, preferably metallic material is formed.

In one embodiment, it is provided that the storage mass is formed from a porous aluminum body, which in the at least one housing part 1A . 2A . 1A - 2A The aluminum has pore sizes of 0.14 mm to 3.00 mm and an inner surface of between 20,000 and 2,500 m 2 / m 3. Between the aluminum porous body and an inner wall surface of the heat exchanger, it is ensured that the working fluid can not flow past the aluminum porous body.

In another embodiment, it is provided that the storage mass is formed from a bed of compact or hollow metallic or non-metallic beads of the same or different diameter, which is between 0.5 mm and 20 mm.

In the aforementioned size of H / W / T high performance low temperature Stirling engine of 25cm x 25cm x 25cm, metallic or non-metallic beads of preferably 0.5mm to 0.6mm are used, with a heat exchanger R1 . R2 an inner diameter of about 30 mm at a length of about 100 to 150 mm.

It is preferably provided that based on a maximum spherical packing with the same size beads (regardless of the ball diameter) about 73% of the heat exchanger volume of the spherical volume and about 27% of the heat exchanger volume of the fluid volume of the working fluid AF is taken.

These parameters result for each heat exchanger R1 . R2 a total spherical surface of about 1 m ² and thus with a heat transfer of CO2 to the metallic beads of 1000 J / m ² a thermal transfer performance of each of the heat exchangers R1 . R2 of about 1000 W / K. It has been found that in this size a good ratio between the desired low flow resistance and the desired high thermal transmission performance is achieved.

The invention provides that the compact or hollow metallic or non-metallic beads of the same or different diameter are made of steel or aluminum or glass.

With regard to a desired after rapid heat exchange sequences is preferred for the beads material side because of the good thermal conductivity metal (steel or aluminum) proposed.

In principle, however, non-metallic materials are also suitable for the beads.

In particular, less expensive materials such as glass is also suitable despite lower thermal conductivity.

Glass as a material can be used in particular when larger high-performance low-temperature Stirling engines are designed with slower heat exchange sequences and thus lower rotational speeds. A high performance low temperature Stirling engine M with a heat exchanger R1 . R2 in combination, filled with glass beads, can be made cheaper, and in particular with higher efficiency and lower temperature spread .DELTA.T of the working fluid AF be operated between hot and cold side.

It is preferably provided that the surface of the metallic or non-metallic beads is completely smooth or smooth and partially structured or completely structured. The formation of a surface structure of the beads increases the heat transfer and thus the possible frequency of the heat exchange sequences. The packing density of the beads slightly decreases depending on the surface roughness of the surface structure of the beads, but this effect is compensated for by the high-performance, low-temperature Stirling engine M can be operated at a higher speed by the increased heat transfer and the possible higher frequency of the heat exchange sequences.

It is further provided that the beads in an inner surface of the inner wall of the heat exchanger R1 . R2 are embedded so that edge flow channels in the heat exchanger R1 . R2 by a ball embedding in the edge region of the heat exchanger R1 . R2 are closed. This ensures that the working fluid FL between the inner wall of the heat exchanger and the bed can not flow past the ball bed.

In a preferred embodiment of the invention, a thread is arranged in a first embodiment variant on the inner surface of the heat exchanger whose pitch - as a distance between two thread crests - the diameter of the beads or at different diameters of the beads corresponds to the largest diameter, so that the spherical surface of the metallic or non-metallic beads is at least partially embedded in the thread of the internal thread.

An ideal sphere packing of the beads results in a tetrahedral, crystal-like structure that can follow the increasing course of the thread as far as possible.

Should occur in this first embodiment variant island-like impurities, which similar to the thread in a spiral both sides of the respective heat exchanger R1 . R2 connect with each other, further variants are proposed.

In a preferred embodiment of the invention it is provided that on the inner surface of the inner wall of the heat exchanger R1 . R2 a layer of a shape-variable material with a predetermined layer thickness is arranged, which impress the beads their surface shape, whereby the edge flow channels in the heat exchanger R1 . R2 are closed. In general, it is provided that a layer of a permanently elastic or a plastic or a thermally variable or a chemically variable material is formed.

Proposed is a ball embedding in the edge region of the heat exchanger R1 , R2

The inner wall of the respective heat exchanger R1 . R2 is preferably coated with a thin layer having a layer thickness of about 0.1 to 0.5 times the ball diameter with a shape-variable layer.

The balls on the edge of the heat exchanger R1 . R2 This layer has its own surface shape and closes edge flow channels. The imprinting of the surface shape can be achieved in various ways:

According to the invention, the layer is formed from a permanently elastic or a plastic or a thermally variable or a chemically variable material.

In a second embodiment variant, the layer is formed from a permanently elastic material, in particular rubber or soft plastic. The beads are slightly pressed during filling from above and / or from below to the inner wall, so that a coating-forming force is exerted by the beads on the layer in the edge region of the heat exchanger. When disassembling, the original coating starting state again sets in and the filling process can be repeated as desired and the adaptation can again be brought about, if necessary, in a different manner.

In a third embodiment variant, it is provided that the layer is formed from a plastic material, in particular tin. The balls are filled as explained to the second embodiment variant with coating-deforming force. The impressions of the spherical surfaces in the layer are now preserved. When refilling, the layer is reshaped. The filling process can be repeated several times.

In a fourth embodiment variant, it is provided that the layer is formed from a thermally variable material, in particular a plastic or wax. In this embodiment, the balls are filled without applying force. The respective heat exchanger R1 . R2 is heated so far that the coating softens and gives way to the pressure of the balls. A mechanical induced vibration of the heat exchanger R1 . R2 supports the expression of the maximum packing density of the beads within the respective heat exchanger R1 . R2 ,

In a fifth embodiment variant, it is provided that the layer is formed from a chemically variable material, in particular from an epoxy resin. The coating is adapted by chemical reaction. The coating is carried out by a viscous material, which sets within a certain time optionally with an increase in temperature. Within the setting time of the filling process takes place. The edge balls are advantageously with the inner wall of the respective heat exchanger R1 . R2 bonded. in this embodiment, only after removal of the edge balls and the old coating is a refilling of the respective heat exchanger R1 . R2 possible with the beads.

Furthermore, it is provided in particular that the heat exchanger has two connection openings 11 . 12 over which the working fluid FL flows into adjacent work spaces and flows out, wherein the working space side or heat exchanger side in each case at least one grid element 13 . 14 , In particular, is arranged from a stainless steel wire mesh whose mesh size is smaller than the diameter of the metallic or non-metallic beads depending on the diameter of the metallic or non-metallic beads.

The heat exchanger has at least one closable filling element R1 - 1 . R2 - 1 (see. 2 ), over which the working fluid FL and the beads formed of the metallic or non-metallic material are / can be filled into the interior of the heat exchanger.

Again, summarized some advantages of the high-performance low-temperature Stirling engine according to the invention M and the heat exchanger according to the invention R1 . R2 ,

An advantage consists in the very large expansion factor of liquid carbon dioxide CO ₂ even at low temperature changes of the carbon dioxide. For example, liquid carbon dioxide already has an expansion factor of 258% per Kelvin in the range from 30.0 ° to 30.06 °. This high expansion factor can already be caused by small temperature changes, a volume change in the operation of the high-performance low-temperature Stirling engine M leads to a high work capacity. In addition, the dynamic viscosity of liquid carbon dioxide CO ₂ in the described temperature ranges is extremely low, whereby flow rates, especially in the heat exchangers R1 . R2 are feasible. As a result, even at temperatures below 50 ° C high performance of the high-performance low-temperature Stirling engine M can be generated, which can otherwise be produced only with Stirling engines, which are much larger or are driven in other higher temperature ranges. The power range of the described high-performance low-temperature Stirling engines ranges from a few watts to several megawatts, whereby the performance can be influenced in a simple manner, inter alia, by the described cascading. The cascading is thus to be understood as a modular solution, which allows an adaptive adaptation of the described standard solution to the respective local conditions by the modular structure. The high performance low temperature Stirling engine M uses explained as least temperature differences between the hot side HS and the cold side KS at a low overall temperature level, so that increases the display of the possible heat sources used as a result. As a result, in particular heat sources can be used whose temperature level is generally not sufficient to operate a heat engine.

It can thus be used, for example, both environmental heat and waste heat, without the need for a prior concentration of heat.

In particular, the small size of the high-performance low-temperature Stirling engine according to the invention M with a power of 2 kW, in contrast to large and difficult known Stirling engines, ensures use in any application in which only a small space is available.

In the mentioned embodiment (size of 25 cm x 25 cm x 25 cm) have the cylinder piston 3 . 4 only a diameter of about 80 mm. The diameter of the eccentric shafts 5 . 6 is only about 30 mm, with the diameter of the eccentric 5A . 6A based on the respective outer ring of the eccentric is only about 61 mm.

In addition, the high-performance low-temperature Stirling engine M is very quiet and represents a closed system from which the once introduced supplies in the operation of the high-performance low-temperature Stirling engine M do not escape. The sealing of the housing is also possible in an advantageous manner by Elastomerabdichtungen, as prevail in system only temperatures of less than 50 ° C. A high-performance low-temperature Stirling engine requires no starter or starter system, no valves, no spark plugs and no exhaust system. In addition, a total of only a few components of small size are needed, so that a mass-produced high-performance low-temperature Stirling engine M is inexpensive to produce. The high-performance low-temperature Stirling engine according to the invention M It can be easily integrated into regenerative energy systems, eliminating the need for conventional fuels throughout the system to achieve the desired rated power, which is typically only available with conventional fuels.

The heat exchanger according to the invention also has, as explained, only a small component size. The heat exchanger R1 . R2 operates at low between the hot side HS and the cold side KS existing temperature difference .DELTA.T optimized by a relatively low flow rate at a relatively low flow resistance, since the surface of the storage mass is very high.

LIST OF REFERENCE NUMBERS

M

High-performance low-temperature Stirling engine

FL

working fluid

1

Arbeitszylinder (Heißseite)

1A

Gehäuse

3

Arbeitskolben (Heißseite)

3A

Kolbeninnenraum

A3

Kolbenstirnflächen des Arbeitskolbens 3

p31

Arbeitsdruck einer Kolbenstirnfläche

p32

Arbeitsdruck einer Kolbenstirnfläche

5

erste Exzenterwelle (Heißseite)

5A

Exzenter

5B

Längsachse der erste Exzenterwelle 5

5C

Exzentermittelpunkt

5D

Exzenterwellenlager

7

Gleitlagerbuchse (Heißseite)

7A

Innenbeschichtung

9

erstes Zahnrad

11

Verbindungsöffnung

13

Gitterelement

Hot side:

1

Working cylinder (hot side)

1A

casing

3

Working piston (hot side)

3A

Piston interior

A3

Piston end faces of the working piston 3

p31

Working pressure of a piston end face

p32

Working pressure of a piston end face

5

first eccentric shaft (hot side)

5A

eccentric

5B

Longitudinal axis of the first eccentric shaft 5

5C

Exzentermittelpunkt

5D

eccentric shaft bearing

7

Plain bearing bush (hot side)

7A

internal coating

9

first gear

11

connecting opening

13

grid element

2

Steuerzylinder (Kaltseite)

2A

Gehäuse

4

Steuerkolben (Kaltseite)

4A

Kolbeninnenraum

A4

Kolbenstirnflächen des Steuerkolbens 4

p41

Arbeitsdruck einer Kolbenstirnfläche

p42

Arbeitsdruck einer Kolbenstirnfläche

6

zweite Exzenterwelle (Kaltseite)

6A

Exzenter

6B

Längsachse der zweiten Exzenterwelle 6

6C

Exzentermittelpunkt

6D

Exzenterwellenlager

8

Gleitlagerbuchse (Kaltseite)

8A

Innenbeschichtung

10

zweites Zahnrad

12

Verbindungsöffnung

14

Gitterelement

Cold side:

2

Control cylinder (cold side)

2A

casing

4

Control piston (cold side)

4A

Piston interior

A4

Piston end faces of the control piston 4

p41

Working pressure of a piston end face

p42

Working pressure of a piston end face

6

second eccentric shaft (cold side)

6A

eccentric

6B

Longitudinal axis of the second eccentric shaft 6

6C

Exzentermittelpunkt

6D

eccentric shaft bearing

8th

Plain bearing bush (cold side)

8A

internal coating

10

second gear

12

connecting opening

14

grid element

R1

erster Regenerator

R1-HS

Heißseite des Regenerators

R1-KS

Kaltseite des Regenerators

R1-1

Befüllelement

R1-2

Innengewinde

R2

zweiter Regenerator

R2-HS

Heißseite des Regenerators

R2-KS

Kaltseite des Regenerators

R2-1

Befüllelement

R2-2

Innengewinde

F

Kraft

1A-2A

Innengehäuseteil

Heat exchanger:

R1

first regenerator

R1-HS

Hot side of the regenerator

R1-KS

Cold side of the regenerator

R1-1

filling element

R1-2

inner thread

R2

second regenerator

R2-HS

Hot side of the regenerator

R2-KS

Cold side of the regenerator

R2-1

filling element

R2-2

inner thread

F

force

1A-2A

Inside housing part

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 102009057210 B4 [0009]
• EP 2333285 A1 [0010]
• CN 102418621 A [0011]
• EP 1592875 B1 [0012]
• US Pat. No. 6,701,721 B1 [0012]
• DE 102006061509 A1 [0013]

Claims (17)

Heat exchanger, in particular as a thermal regenerator (R1, R2) of a high-performance low-temperature Stirling engine (M), comprising at least one housing part (1A, 2A, 1A-2A), which forms an energy storage space in which a storage mass for heat storage is arranged, characterized the heat exchanger is a solid heat store whose storage mass is formed from a highly conductive, preferably metallic or non-metallic material. Heat exchanger after Claim 1 , characterized in that the storage mass is formed of an aluminum porous body, which is arranged in the energy storage space of the at least one housing part (1A, 2A, 1A-2A). Heat exchanger after Claim 1 , characterized in that the storage mass is formed from a bed of compact or hollow metallic or non-metallic beads of the same or different diameters, wherein the diameter is between 0.5 mm and 20 mm. Heat exchanger after Claim 3 , characterized in that the compact or hollow metallic or non-metallic beads of the same or different diameter are made of steel or aluminum or glass. Heat exchanger after Claim 3 or 4 , characterized in that the surface of the beads is completely smooth or smooth and partially structured or completely structured. Heat exchanger after Claim 3 , characterized in that the beads are embedded in an inner surface of the inner wall of the heat exchanger (R1, R2), so that edge flow channels in the heat exchanger (R1, R2) are closed by a ball embedding in the edge region of the heat exchanger (R1, R2). Heat exchanger after Claim 6 , characterized in that on the inner surface of the inner wall of the heat exchanger (R1, R2) a thread is arranged whose pitch between two thread crests is the largest diameter of the metallic or non-metallic beads, so that the spherical surface of the metallic or non-metallic beads at least partially in the Thread of the internal thread is, whereby the edge flow channels in the heat exchanger (R1, R2) are closed. Heat exchanger after Claim 6 , characterized in that on the inner surface of the inner wall of the heat exchanger (R1, R2) a layer of a shape-variable material with a predetermined layer thickness is arranged, which impress the beads their surface shape, whereby the edge flow channels in the heat exchanger (R1, R2) are closed , Heat exchanger after Claim 8 , characterized in that the layer is formed of a permanently elastic or a plastic or a thermally variable or a chemically variable material. Heat exchanger after Claim 8 , characterized in that the layer is formed of a permanently elastic material, in particular rubber or soft plastic. Heat exchanger after Claim 8 , characterized in that the layer of a plastic material, in particular tin is formed. Heat exchanger after Claim 8 , characterized in that the layer is formed of a thermally variable material, in particular a plastic or wax. Heat exchanger after Claim 8 , characterized in that the layer is formed of a chemically variable material, in particular of an epoxy resin. Heat exchanger after Claim 8 , characterized in that the layer thickness is 0.1 to 0.5 times the maximum ball diameter. Heat exchanger after Claim 1 , characterized in that the heat exchanger (R1, R2) has at least one closable filling element (R1-1, R2-1), via which a working fluid (FL) and that of the metallic or non-metallic material according to Claim 3 trained beads can be filled in the interior of the heat exchanger is / are. Heat exchanger after Claim 1 , characterized in that the heat exchanger (R1, R2) has two connecting openings (11, 12) through which the working fluid (FL) flows into adjacent working spaces and flows out. Heat exchanger after Claim 16 , characterized in that the heat exchanger (R1, R2) has two connection openings (11, 12) via which the working fluid (FL) flows into and out of adjacent work spaces, wherein at least one grate element (13, 14), respectively on the working space side or on the heat exchanger side, in particular from one Stainless steel wire mesh is arranged whose mesh size is smaller than the diameter of the metallic or non-metallic beads depending on the diameter of the metallic or non-metallic beads.

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