DE102009026322A1 - Method for producing a heat exchanger and heat exchanger - Google Patents

Abstract

The invention relates to a method for producing a heat exchanger, comprising molded parts made of ceramic material and having channels or delimiting them. In order to ensure good heat conduction with simple production, it is proposed that preforms be produced from at least cellulose fibers and at least one filler-containing paper and then the paper preforms are carbonized to form the molded parts or sections thereof.

Description

The The invention relates to a method of manufacturing a heat exchanger comprising in particular fluid-carrying channels having or limiting shaped parts made of ceramic material. Furthermore, the invention relates to a heat exchanger having in particular fluids leading channels or limiting shaped parts made of ceramic material, in particular Heat exchangers such as cross-flow heat exchanger or Rektifiziereinrichtung.

Of the DE-C-139 33 426 is to remove a heat exchanger, which consists of moldings made of ceramic. The ceramic moldings are assembled before firing and connected by burning.

heat exchangers serve the purpose of heat from a flow of material higher Temperature to transfer to a stream of low temperature. In order to achieve optimum efficiency, it is necessary that the components separating the streams a good Have heat conduction. Such is also in rectification facilities or -apparaten necessary, with which liquid mixtures be separated. This z. B. the liquid and the vapor of a mixture to be separated in countercurrent to each other, that both phases for material and heat exchange possible touch intimately. The facilities therefore exist basically from a vertical tubular apparatus, the internals in the form of spaced plate elements with breakthroughs or packing, contains.

Of the The present invention is based on the object, a method and a heat exchanger of the aforementioned To develop a way so that with simple production a good Heat conduction is ensured. It should also be given the opportunity be, aggressive substances through the heat exchanger to lead.

• – Herstellen von aus zumindest Zellulosefasern und zumindest einem Füllstoff enthaltendem Papier bestehenden Preformen und
• – Pyrolysieren der Papierpreformen zur Bildung der Formteile oder Abschnitte dieser.

According to the invention, it is proposed by the method:

• - Preparing consisting of at least cellulose fibers and at least one filler paper containing preforms and
• - Pyrolyzing the paper preforms to form the moldings or sections thereof.

there can the the moldings and thus the sections of the heat exchanger forming Papierpreformen after or preferably before pyrolysis or carbonizing be assembled. It can therefore the preforms are connected as before gluing. It is also possible to use the pyrolyzed preforms connect and bond, before a Silicierprozessschritt.

The Connecting the Papierpreformen before pyrolysis can by means of Glue with high carbon yield done. Will the Papierpreformen after connected to the pyrolysis and thus carbonization, this is done preferably in the context of siliciding the pyrolyzed preforms.

Suitable fillers are those which are carbonizable. But ceramic fillers such as Al ₂ O ₃ or ZiO ₂ can be used to load the paper accordingly. Another preferred filler is carbon black.

Of Further, additives can be added to the paper to be pyrolyzed in the form of binders such as phenolic resin and / or cellulose added become.

preferably, the weight fraction of the filler is 30% by weight to 95 wt .-% based on the cellulose fibers of the paper and Filler existing dry matter of the paper, wherein Additives are involved.

According to the invention in particular provided that the pyrolyzed, d. H. the carbonized paper is silicified. This can be done with hyperpure silicon, with excess or deficit is worked. Silicating is standard Perform procedure. In particular, however, the pyrolyzed Paper for siliconizing brought into contact with a silicon melt, z. B. by wicks, transfer plates or similar techniques.

The Pyrolized paper is preferably added in a reaction space Sub-atmospheric silicates in a range of 50 mbar to 0.05 mbar, in particular in the range of 0.1 mbar should be. After the reaction of the C with the Si to SiC then becomes the reaction space with inert gas atmosphere ventilated to provide the opportunity for excess silicon on the siliconized ceramic substrate can form as Si layer.

Becomes a corresponding Si layer desired, the process should be controlled such that the Si layer has a thickness d of 0.5 μm ≦ d ≦ 50 μm, in particular 10 μm ≤ d ≤ 20 μm having.

The Siliciding takes place in a temperature range of 1350 ° C ≤ T ≤ 2000 ° C, in particular in the range of 1650 ° C ≤ T ≤ 1700 ° C instead of.

As preform, in particular one or more corrugated board having paper layers are used. It can be used as a preform one, the three layers with an inner first layer, one associated with this as bonded bonded a wave geometry intermediate layer and a connected with this as glued and covering the intermediate layer third layer comprises. In this case, the first and the second layers are spaced over the intermediate layer.

It However, there is also the possibility of being shaped as a preform To select paper layers, the so assigned to each other and supported and interconnected, that the desired channel training exists, if one such is needed. Other geometries, in particular for plate elements as a molding for rectification can be required, can also be produced how to be shaped.

Furthermore, the invention provides that the pyrolyzed and possibly siliconized liner has a thickness d _z with 50 microns ≤ d ≤ _z 1000 microns. The webs which provide the webs in the actual sense, the first and second layer provides a good heat transfer with a corresponding thickness, wherein the media flowing through the channels can have a temperature up to 1400 ° C, without causing damage. If silicon-free pyrolyzed preforms are used as molded parts for the heat exchanger, the fluids may have even higher temperatures.

Independently This should be used as a material for the preform used during the pyrolysis up to 60% shrinks and / or after carbonization a coke content in the Range between 20% and 55%.

End plates and / or funnels of the heat exchanger or possibly between individual layers of the moldings extending stabilizing plates can be made of cellulose and / or lignocellulose particles existing plate-shaped moldings, the exclusion of air at a temperature T with 400 ° C ≤ T ≤ 2000 ° C, in particular 800 ° C ≤ T ≤ 1600 ° C are pyrolyzed. In particular moldings should be used, which are made of wood fibers and / or vegetable fibers such as flax, hemp, sisal, miscanthus or nettle and after pyrolysis have a density between 500 kg / m ³ and 900 kg / m ³ . For this purpose, medium density fibreboards or high density fiberboards are preferably used as starting moldings to be pyrolyzed.

In that regard, recourse is made to carbon or ceramic components, such as these WO-A-03/050058 to be taken, the disclosure of which is expressly incorporated by reference.

A heat exchanger of the type mentioned above is characterized in that the molded parts consist of ceramized Papierpreformen. Standard papers or paperboard as starting material for the preform are included. In this case, the cellulose fibers and at least one filler-containing paper is carbonized. The filler should be selected from the group of carbon black, SiC, Si, ceramic filler such as Al ₂ O ₃ or ZiO ₂ . Carbonizable fillers are also suitable.

The ceramized Papierpreform can be converted from a SiC and consist of the filler and / or SiC loaded paper.

Especially the preform has a corrugated cardboard geometry, wherein the preform three layers with a flat first layer, one connected to this corrugated intermediate layer and one of these covering and with this may include interconnected planar second layer, wherein the intermediate layer limited with the first and second layer, the channels.

The Intermediate layer can consist of sections, which in average a S-shaped, V-shaped, U-shaped or have circular section geometry. Also exists the possibility of embossed paper for training to use the moldings, without necessarily the first and second Location are provided. In this case, the embossed Papers aligned with each other so that they are the desired Provide channel training.

Furthermore, the heat exchanger can have intermediate or end plates as well as fluid inlet or outlet elements in the form of a respective ceramic component, which is produced by pyrolysis of a cellulose-containing semi-finished molded part. The cellulosic semi-finished molded part is in particular a medium density fiberboard with an initial density between 600 kg / m ³ and 850 kg / m ³ or a high density fiberboard with an initial density between 850 kg / m ³ and 1050 kg / m ³ in question, which after pyrolysis have a density between 500 kg / m ³ and 700 kg / m ³ or 700 kg / m ³ and 900 kg / m ³ . The semifinished product should also be silicided after pyrolysis or carbonization.

Further Details, advantages and features of the invention do not arise only from the claims, the features to be taken from them - for themselves and / or in combination but also from the description below to be taken from the drawing preferred embodiments.

It demonstrate:

1 a first view of a cross-flow heat exchanger,

2 the crossflow heat exchanger according to 1 turned by 90 degrees,

3 a detail of a first embodiment of a molding,

4 a section of a second embodiment of a molding and

5 a section of a third embodiment of a molding.

The The teaching according to the invention is described below a cross-flow heat exchanger or molded parts described, used to make the crossflow heat exchanger be, without thereby limiting the inventive Teaching takes place. Rather, this can also be used for other heat exchangers which also include rectifiers, which does not necessarily contain channels delimiting molded parts, the are flowed through by fluids. Rather, the invention applies Teaching for all heat-transferring moldings.

In the 1 and 2 is a cross-flow heat exchanger 10 represented, by means of which heat is transferred from a stream of higher temperature to a stream of low temperature. Each material stream has its own delimited flow path, wherein the material flows are guided at right angles to each other. Typical application cases of cross flow heat exchangers are pipe registers or finned tube registers for heating and cooling tasks.

The flow directions of the fluids passing through the cross-flow heat exchanger 10 pour in, are in 1 and 2 through the arrows 12 and 14 symbolizes, with the flow direction of the one substance in 1 runs perpendicular to the drawing plane.

The individual channels of the cross-flow heat exchanger 10 are formed by pyrolyzed, ie carbonized Papierpreformen that are optionally silicided. Consequently, ceramized preforms are used, which form the channels or delimiting shaped parts of the heat exchanger 10 form.

When Materials for paper preforms are also standard papers and cardboard in question.

The paper preforms may be those of different geometries, portions of which 3 - 5 can be seen. So is in 3 a section of a preform 16 represented, which has a corrugated cardboard geometry. There is the preform 16 from a first and second level position 18 . 20 , between which a section having a wave geometry and the first and second position 18 . 20 spacing liner 22 runs. The liner 22 consists of juxtaposed sections that show an S-geometry.

An appropriate preform 16 extends over the effective heat exchanger length of the heat exchanger 10 , where appropriate preforms 16 spaced apart from each other. In the intermediate spaces preferably geometrically identical preforms are arranged, which, however, run rotated by 90 ° to the first preforms to allow the desired cross flow.

In 4 is a section of molded parts 21 a cross-flow heat exchanger, wherein the individual molded parts of semi-circular embossed sections 23 . 24 made of paper, which are joined together in their edges. This is due to the thickened areas 26 . 28 indicated. Corresponding embossed sections forming a tube geometry on average 23 . 24 are strung together to form a first series of channels. Above this are corresponding rows of embossed paper preforms rotated 90 degrees to form the intersecting channels of the heat exchanger. The adjacent channels rotated by 90 ° are denoted by the reference numerals 30 . 32 characterized.

But other geometries for forming the moldings or the fluids leading channels are possible. This is based on the 5 clarified. So are V-shaped embossed strips of paper 34 . 36 interconnected (connection points 38 . 40 ) and strung together to form channels. The adjacent channels rotated by 90 ° have the reference numerals 42 . 44 on.

Next the three exemplified geometries of preforms and However, sections of these are z. B. also U-geometries or a open oval shaped embossed papers or paper webs or strip possible to moldings of a heat exchanger to build.

According to the invention, the moldings forming the channels consist of at least cellulose-containing paper, such as standard paper or paperboard, and at least one filler. This may be carbon black, a carbonizable filler, a reactive filler such as boron or Si or a ceramic filler. Preferred fillers are carbon black or A ₂ O ₃ or ZiO ₂ as ceramic fillers.

The Paper can also be loaded with SiC or Si + SiC.

Regardless, the weight should be part of the filler 30 wt .-% to 95 wt .-% based on the consisting of cellulose fibers of the paper and filler dry matter of the paper. Also, other additives such. As binders such as phenolic resin or cellulose are added.

A suitable preform, like the one 3 can be found or by embossing paper webs or strips formed and assembled preforms z. B. according to the 4 and 5 are then pyrolyzed in a temperature range between 800 ° C and 1400 ° C, ie carbonized. Subsequently, a siliconizing of the carbonized paper in a temperature range between 1350 ° C and 2000 ° C, in particular between 1650 ° C and 1700 ° C take place. In particular, siliconizing by means of a wick with a silicon melt is preferred. During siliconizing, the carbonized preform should be arranged in a reaction space in which a negative pressure in the range of 0.1 mbar prevails.

The Preforms, which include the embossed papers such as paper sections conceptually include or orbits or strips be assembled prior to pyrolysis or after pyrolysis. If the latter happens, the preforms become silicified with each other connected.

Become the preforms connected before pyrolysis, so takes place this by means of preferably a high-yield C adhesive.

As is clear from the 1 and 2 shows, the cross-flow heat exchanger 10 at its 1 opposite ends fluid inlet and outlet funnel 44 . 46 on, by flanges 48 . 50 be limited, over which the cross-flow heat exchanger 10 can be installed in a system and fixed in this system.

Both the funnels 44 . 46 as well as the flanges 48 . 50 may consist of appropriately cut or shaped medium-density or high-density cellulosic, in particular lignocellulosic semifinished moldings which are ceramized by carried out in non-oxidizing gas atmosphere pyrolysis. The pyrolyzed, ie carbonized semi-finished molded parts are in particular siliconized such that the ceramic component is a SiSiC ceramic component with a defined free C content. So there are ceramic components for the flanges 48 . 50 and the funnel-shaped end portions 44 . 46 used according to the doctrine of WO-A-03/050058 are made, the disclosure of which is referenced. The connection between the channels delimiting molded parts of the cross-flow heat exchanger 10 and the funnel-shaped components 44 . 46 can be done in a siliciding process. It is also possible to connect components by means of adhesive with high C-yield prior to the siliconizing process.

For the dimensioning of the molded parts is to indicate that they can have a planar extension of readily 1 m ² , so the length or cross section of the cross-flow heat exchanger can pretend. The wall thicknesses of the channels delimiting moldings may be due to the existing paper. Preform below 100 microns, so that a good heat transfer is ensured. Preferred thicknesses of the paper layers are between 50 μm and 1000 μm after carbonization and optionally siliconizing.

The paper layer itself should have a weight of 50 g / m ² to 1000 g / m ² .

The The invention will be further described below with reference to three examples explains which make up for themselves characteristics and / or Feature combinations that characterize the invention.

Example 1:

It is used a paper web with a basis weight of 200 g / m ² , which is loaded with a carbon black filler. The proportion by weight of the filler is about 75%, based on the existing of cellulose fibers and filler dry matter of the paper. The thus loaded paper is then further processed into a paper semi-finished product, which has a corrugated cardboard geometry and wound into a preform and glued. The resulting preform is pyrolyzed in an inert atmosphere at a temperature between 800 ° C and 1400 ° C. Then, the carbonized paper is siliconized by means of a wick with a silicon melt at a temperature in the range between 1650 ° C and 1700 ° C. In the reaction space itself, there is a negative pressure in the range between 1650 ° C and 1700 ° C. In the reaction space itself, there is a negative pressure in the range of 0.1 mbar. The siliconizing takes place with excess of silicon. After reaction of the silicon with carbon to form SiC, the reaction space is vented to avoid that the excess silicon is discharged. As a result, an Si layer is formed on the ceramic substrate, the process being controlled such that the thickness is in the range between 10 .mu.m and 20 .mu.m. The solidified layer is then remelted at a temperature just above the melting point of silicon and recrystallized. For the silicization itself hyperpure silicon is used.

It resulted in a thin-walled highly stable structure. Micrographs show that the substrate consists essentially of free silicon surrounding SiC. Unreacted C in the vanishing um catch can be included.

The Ceramics can be used as heat exchangers such as cross-flow heat exchangers or rectification device.

Example 2:

A paper web with a weight per unit area of 200 g / m ^{2 is} used, which is loaded with a filler consisting of SiC powder. The proportion by weight of the filler is about 75%, based on the existing of cellulose fibers and filler dry matter of the paper. The thus loaded paper is then further processed into a paper semi-finished product, which has a corrugated cardboard geometry and wound into a preform and glued. The resulting preform is pyrolyzed in an inert atmosphere at a temperature between 800 ° C and 1400 ° C. Then, the carbonized paper is siliconized by means of a wick with a silicon melt at a temperature in the range between 1650 ° C and 1700 ° C. In the reaction space itself, there is a negative pressure in the range of 0.1 mbar. The siliconizing takes place with excess of silicon. After reaction of the silicon with carbon to form SiC, the reaction space is vented to avoid that the excess silicon is discharged. As a result, an Si layer is formed on the ceramic substrate, the process being controlled such that the thickness is in the range between 10 .mu.m and 20 .mu.m. The solidified layer is then remelted at a temperature just above the melting point of silicon and recrystallized. For siliconizing itself, solar grade poly-silicon is used.

It resulted in a thin-walled highly stable structure. micrographs show that the substrate is essentially surrounded by free silicon SiC exists. Unreacted C in the vanishing extent may contain be.

The Ceramics can be used as heat exchangers such as cross-flow heat exchangers or rectification device.

Example 3:

It is used a paper web with a basis weight of 100 g / m ² , which is loaded with a filler consisting of carbon black. The proportion by weight of the filler is about 50% based on the consisting of cellulose fibers and filler dry matter of the paper. The thus loaded paper is then further processed into a paper semi-finished product, which has a corrugated cardboard geometry and wound into a preform and glued. The resulting preform is pyrolyzed in an inert atmosphere at a temperature between 800 ° C and 1400 ° C. Then, the carbonized paper is siliconized by means of a wick with a silicon melt at a temperature in the range between 1650 ° C and 1700 ° C. In the reaction space itself, there is a negative pressure in the range of 0.1 mbar. The siliconizing takes place with excess of silicon. After reaction of the silicon with carbon to form SiC, the reaction space is vented to avoid that the excess silicon is discharged. As a result, an Si layer is formed on the ceramic substrate, the process being controlled such that the thickness is in the range between 10 .mu.m and 20 .mu.m. The solidified layer is then remelted at a temperature just above the melting point of silicon and recrystallized. For siliconizing itself, solar grade poly-silicon is used.

It resulted in a thin-walled highly stable structure. micrographs show that the substrate is essentially surrounded by free silicon SiC exists. Unreacted C in the vanishing extent may contain be.

The Ceramics can be used as heat exchangers such as cross-flow heat exchangers or rectification device.

QUOTES INCLUDE IN THE DESCRIPTION

This list The documents listed by the applicant have been automated generated and is solely for better information recorded by the reader. The list is not part of the German Patent or utility model application. The DPMA takes over no liability for any errors or omissions.

Cited patent literature

• - DE 13933426 C [0002]
• WO 03/050058 A [0020, 0050]

Claims (38)

Method for producing a heat exchanger comprising in particular fluid-carrying channels having or limiting shaped parts of ceramic material, marked by the process steps: - manufacture of at least cellulose fibers and at least one filler containing existing paper preforms and - Carbonize the Papierpreformen to form the moldings or sections of these. Method according to claim 1, characterized in that that the paper preform before or after carbonation for formation the heat exchanger or at least a part be connected by this. Method according to claim 1 or 2, characterized that the carbonized Papierpreform is silicided. Method according to at least one of the preceding Claims, characterized in that as a filler a carbonizable filler is used. Method according to at least one of the preceding Claims, characterized in that as a filler Soot is used. Method according to at least one of the preceding Claims, characterized in that as a filler a reactive filler such as Si or B is used. Method according to at least one of the preceding claims, characterized in that a ceramic filler such as Al ₂ O ₃ or ZiO _{2 is} used as the filler. Method according to at least one of the preceding Claims, characterized in that the carbonisierendem Paper as an additive, a binder such as phenolic resin and / or cellulose is added. Method according to at least one of the preceding Claims, characterized in that the filler with a weight proportion G of 30% by weight ≦ G ≦ 95 Wt .-%, in particular 60 wt .-% ≤ G ≤ 80 wt .-%, based on the cellulose fibers and the filler existing Dry substance of the paper is introduced into the paper. Method according to at least one of the preceding Claims, characterized in that the carbonized Paper preform is siliconized with hyperpure silicon. Method according to at least one of the preceding Claims, characterized in that the pyrolyzed Paper preform with hyperpure silicon in excess or deficit is silicified. Method according to at least one of the preceding Claims, characterized in that the carbonized Paper preform is siliconized by means of a silicon melt. Method according to at least one of the preceding Claims, characterized in that the pyrolyzed Papierpreform in a reaction chamber at a pressure p with 50 mbar ≤ p ≤ 0.05 mbar, preferably p is silicated in about 0.1 mbar. Method according to at least one of the preceding Claims, characterized in that the reaction of carbonized Papierpreform with Si to SiC at a temperature T at 1350 ° C ≤ T ≤ 2000 ° C, preferably with 1650 ° ≤ T ≤ 1700 ° C performed becomes. Method according to at least one of the preceding Claims, characterized in that as Papierpreform a corrugated paper having paper or paper layers be used. Method according to at least one of the preceding Claims, characterized in that as Papierpreform an embossed paper is used. Method according to at least one of the preceding Claims, characterized in that as Papierpreform One such is used, the three layers with a flat first Location, associated with this having a wave geometry Liner and one associated with this and covering it level third layer includes. Method according to at least one of the preceding Claims, characterized in that as paper for the preform is one used during the Pyrolysis up to 60% shrinks and / or coke yield between 20% and 55%. Method according to at least one of the preceding claims, characterized in that the heat exchanger end z. B. is provided with a funnel-shaped feed or discharge opening, which consists of a ceramic component, which by pyrolyzing a cellulosic, in particular lignocellulosic semi-finished molded part preferably in the form of a fiberboard ke is ramisiert. Method according to at least one of the preceding Claims, characterized in that as a fiberboard a medium density fiberboard is used. Method according to at least one of the preceding Claims, characterized in that as a fiberboard a high density fiberboard is used. Method according to at least one of the preceding claims, characterized in that the medium-density or high-density fiberboard as semi-finished molded part has an initial density of in particular 600 kg / m ³ to 850 kg / m ³ for the medium-density fiberboard, in particular 850 kg / m ³ to 1050 kg / Having m ³ for the high density fiberboard and that the semi-finished molded parts after pyrolysis have a density between 500 kg / m ³ and 700 kg / m ³ and 700 kg / m ³ and 900 kg / m ³ . Heat exchanger ( 10 ) comprising in particular fluid-carrying channels having or limiting molded parts ( 16 . 21 . 33 ) made of ceramic material, in particular heat exchangers such as cross-flow heat exchanger or rectifier, characterized in that the molded parts ( 16 . 21 . 33 ) consist of ceramised paper preforms, Heat exchanger according to claim 23, characterized in that the paper of the preform at least Cellulose fibers and at least one filler contains. Heat exchanger after at least one of claims 23 or 24, characterized in that the filler is a reactive filler such as silicon or Boron is. Heat exchanger according to at least one of claims 23 to 25, characterized in that the filler from the group carbon black. SiC, Si, B and ceramic filler such as Al ₂ O ₃ or ZiO _{2 is} selected. Heat exchanger after at least one of claims 23 to 26, characterized that the ceramized Papierpreform converted into SiC and with the filler and / or SiC loaded paper is. Heat exchanger after at least one of claims 23 to 27, characterized that the preform has a corrugated cardboard geometry. Heat exchanger according to at least one of claims 23 to 28, characterized in that the preform three layers ( 18 . 20 . 22 ) with a flat first layer ( 18 ), an intermediate layer ( 22 ) and a level second layer ( 20 ), wherein the intermediate layer spaced the first and the second layer over web-like sections. Heat exchanger according to at least one of claims 23 to 29, characterized in that the intermediate layer ( 22 ) consists in section of sections of an S-shaped, V-shaped, U-shaped or circular section geometry. Heat exchanger according to at least one of claims 23 to 30, characterized in that the preform ( 21 ) of embossed paper ( 23 . 24 . 34 . 36 ) consists. Heat exchanger after at least one of claims 23 to 31, characterized that the preform on average of circular section, triangular or U-shaped and / or oval shaped sections of paper like paper strips. Heat exchanger after at least one of claims 23 to 32, characterized that the heat exchanger intermediate and / or end plates such as floor or cover plates in the form of a ceramic component, produced by pyrolysis of a cellulosic semi-finished molding is. Heat exchanger after at least one of claims 23 to 33, characterized that the semi-finished molded part is siliconized. Heat exchanger according to at least one of claims 23 to 34, characterized in that the heat exchanger at opposite end faces preferably funnel-shaped openings ( 44 . 46 ), which are made of a ceramized cellulosic semi-finished molded part. Heat exchanger after at least one of claims 23 to 35, characterized that as semi-finished molded part a medium-density or high-density and to the desired extent machined or reshaped fiberboard is used. Heat exchanger according to at least one of claims 23 to 36, characterized in that the carbonized or ceramized semi-finished molded part has a density between 600 kg / m ³ and 700 kg / m ³ and 700 kg / m ³ and 900 kg / m ³ . Heat exchanger according to at least one of claims 23 to 37, characterized in that the preferably funnel-shaped end portion ( 44 . 46 ) at the end into a flange plate ( 48 . 50 ), which consists of a cellulose-containing, in particular lignocellulose-containing semi-finished molded part, the kera is mized.

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