CA1116163A - Rotor for regenerative heat and/or moisture exchanger - Google Patents
Rotor for regenerative heat and/or moisture exchangerInfo
- Publication number
- CA1116163A CA1116163A CA282,637A CA282637A CA1116163A CA 1116163 A CA1116163 A CA 1116163A CA 282637 A CA282637 A CA 282637A CA 1116163 A CA1116163 A CA 1116163A
- Authority
- CA
- Canada
- Prior art keywords
- rotor
- solution
- aluminate
- gas streams
- layers
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F28—HEAT EXCHANGE IN GENERAL
- F28D—HEAT-EXCHANGE APPARATUS, NOT PROVIDED FOR IN ANOTHER SUBCLASS, IN WHICH THE HEAT-EXCHANGE MEDIA DO NOT COME INTO DIRECT CONTACT
- F28D19/00—Regenerative heat-exchange apparatus in which the intermediate heat-transfer medium or body is moved successively into contact with each heat-exchange medium
- F28D19/04—Regenerative heat-exchange apparatus in which the intermediate heat-transfer medium or body is moved successively into contact with each heat-exchange medium using rigid bodies, e.g. mounted on a movable carrier
- F28D19/041—Regenerative heat-exchange apparatus in which the intermediate heat-transfer medium or body is moved successively into contact with each heat-exchange medium using rigid bodies, e.g. mounted on a movable carrier with axial flow through the intermediate heat-transfer medium
- F28D19/042—Rotors; Assemblies of heat absorbing masses
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
- B01D53/26—Drying gases or vapours
-
- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C22/00—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
- C23C22/05—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions
- C23C22/60—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions using alkaline aqueous solutions with pH greater than 8
- C23C22/66—Treatment of aluminium or alloys based thereon
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F24—HEATING; RANGES; VENTILATING
- F24F—AIR-CONDITIONING; AIR-HUMIDIFICATION; VENTILATION; USE OF AIR CURRENTS FOR SCREENING
- F24F13/00—Details common to, or for air-conditioning, air-humidification, ventilation or use of air currents for screening
- F24F13/30—Arrangement or mounting of heat-exchangers
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F24—HEATING; RANGES; VENTILATING
- F24F—AIR-CONDITIONING; AIR-HUMIDIFICATION; VENTILATION; USE OF AIR CURRENTS FOR SCREENING
- F24F3/00—Air-conditioning systems in which conditioned primary air is supplied from one or more central stations to distributing units in the rooms or spaces where it may receive secondary treatment; Apparatus specially designed for such systems
- F24F3/12—Air-conditioning systems in which conditioned primary air is supplied from one or more central stations to distributing units in the rooms or spaces where it may receive secondary treatment; Apparatus specially designed for such systems characterised by the treatment of the air otherwise than by heating and cooling
- F24F3/14—Air-conditioning systems in which conditioned primary air is supplied from one or more central stations to distributing units in the rooms or spaces where it may receive secondary treatment; Apparatus specially designed for such systems characterised by the treatment of the air otherwise than by heating and cooling by humidification; by dehumidification
- F24F3/1411—Air-conditioning systems in which conditioned primary air is supplied from one or more central stations to distributing units in the rooms or spaces where it may receive secondary treatment; Apparatus specially designed for such systems characterised by the treatment of the air otherwise than by heating and cooling by humidification; by dehumidification by absorbing or adsorbing water, e.g. using an hygroscopic desiccant
- F24F3/1423—Air-conditioning systems in which conditioned primary air is supplied from one or more central stations to distributing units in the rooms or spaces where it may receive secondary treatment; Apparatus specially designed for such systems characterised by the treatment of the air otherwise than by heating and cooling by humidification; by dehumidification by absorbing or adsorbing water, e.g. using an hygroscopic desiccant with a moving bed of solid desiccants, e.g. a rotary wheel supporting solid desiccants
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F24—HEATING; RANGES; VENTILATING
- F24F—AIR-CONDITIONING; AIR-HUMIDIFICATION; VENTILATION; USE OF AIR CURRENTS FOR SCREENING
- F24F2203/00—Devices or apparatus used for air treatment
- F24F2203/10—Rotary wheel
- F24F2203/1032—Desiccant wheel
- F24F2203/1036—Details
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F24—HEATING; RANGES; VENTILATING
- F24F—AIR-CONDITIONING; AIR-HUMIDIFICATION; VENTILATION; USE OF AIR CURRENTS FOR SCREENING
- F24F2203/00—Devices or apparatus used for air treatment
- F24F2203/10—Rotary wheel
- F24F2203/104—Heat exchanger wheel
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F24—HEATING; RANGES; VENTILATING
- F24F—AIR-CONDITIONING; AIR-HUMIDIFICATION; VENTILATION; USE OF AIR CURRENTS FOR SCREENING
- F24F2203/00—Devices or apparatus used for air treatment
- F24F2203/10—Rotary wheel
- F24F2203/1048—Geometric details
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F24—HEATING; RANGES; VENTILATING
- F24F—AIR-CONDITIONING; AIR-HUMIDIFICATION; VENTILATION; USE OF AIR CURRENTS FOR SCREENING
- F24F2203/00—Devices or apparatus used for air treatment
- F24F2203/10—Rotary wheel
- F24F2203/1068—Rotary wheel comprising one rotor
Landscapes
- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Mechanical Engineering (AREA)
- General Engineering & Computer Science (AREA)
- Combustion & Propulsion (AREA)
- General Chemical & Material Sciences (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Physics & Mathematics (AREA)
- Organic Chemistry (AREA)
- Materials Engineering (AREA)
- Thermal Sciences (AREA)
- Analytical Chemistry (AREA)
- Oil, Petroleum & Natural Gas (AREA)
- Metallurgy (AREA)
- Drying Of Gases (AREA)
- Solid-Sorbent Or Filter-Aiding Compositions (AREA)
- Central Air Conditioning (AREA)
- Laminated Bodies (AREA)
- Heat-Exchange Devices With Radiators And Conduit Assemblies (AREA)
- Manufacture Of Motors, Generators (AREA)
- Insulation, Fastening Of Motor, Generator Windings (AREA)
- Soft Magnetic Materials (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
The present invention provides a rotor for a regenerative exchanger for the transfer of moisture and/or heat, between two gas streams, the rotor comprising layers of aluminium foil which are alternately flat and corrugated to form a plurality of con-tinuous channels through the rotor for said gas streams, the surface of the foils having a porous hygroscopic coating of aluminium hydroxide obtained by precipitation from a solution of an alkali aluminate applied to the surfaces.
The present invention provides a rotor for a regenerative exchanger for the transfer of moisture and/or heat, between two gas streams, the rotor comprising layers of aluminium foil which are alternately flat and corrugated to form a plurality of con-tinuous channels through the rotor for said gas streams, the surface of the foils having a porous hygroscopic coating of aluminium hydroxide obtained by precipitation from a solution of an alkali aluminate applied to the surfaces.
Description
6~
This invention relates to a rotor for a regenerative exchanger for the transfer of moisture and preferably also heat between two gas streams, particularly air streams.
An ~mportant area of application for a regenerative ex-changer is in supplying fresh alr to premises,; the incoming fresh air and the outgoing exhaust air exchanging moisture and heat in a rotor, so that, for example, in the winter the outgoing exhaust air provides the incoming fresh air with heat and moisture. Each stream of air ;s provided with its own individual inlet and outlet which is separated from the other stream of air so that the res-pective streams of air are directed to individual zones of the rotor. The rotor preferably consists of a plurality of sheets which are alternately flat and corrugated and which form a net-work of continuous, parallel channels for both streams of air.
The corrugated sheets support the flat sheets along the ridges of the corrugations which results in the channels being separated laterally. The rotor is normally cylindrical, the channels run-ning parallel with the axis of rotation.
Previously such rotors were manufactured of foils or ;20 sheets of fibrous, incombustible material, such as asbestos paper, or material made highly porous in another way, such as earthen-ware. Sheets of this type of material then act as carriexs for a hygroscopic substance, preferably a hygroscopic salt solution, lithium chloride being the most usual substance used.
A rotor of the type described above incorporating highly porous foils or sheets can possess exceptional characteristics, e.g. incombustibility, a high capacity for moisture transfer and good mechanical strength. However, a large number of operations are re~uired to provide a rotor with these properties, and this re-sults in the rotor being relatively expensive and time-comsuming to manufacture. The material from which the sheets are constructed has to be impregnated with several substances in order to give the - 1 - ~
.~, mechanical strength re~uired, particularly when wet, and this impregna-tion has to be perforrmed after -the shee-ting has been cor~
rugated and fashioned into the form of a rotor. Moreover tne ro-tor's peripheral surfaces have to be finished once these manu-facturing stages have been completed; grinding and milling being required to achieve the requisite flatness and accuracy.
If the sheets are made of aluminium foil manufacturi.ng costs can be reduced considerably, particu]~lrly if -the manufacturing technique described in our copending ~anadian applica-tion No.
278,159 is used. Such a rotor can be givcn fireproof propcr-ti.es and rnechan;.cal strength that are complete]y acceptable bu-t it lacks one property that is important in a moisture exchanger -hygroscopicity.
An object of this invention is to produce a ro-tor which is totally or partially made of a]uminium foil and which possesses exce]lent hygroscopic properties while keepi.ng the rnanufacturing process simple and the costs of material low.
According to -the prese11t inverlt:i.on l.here :is provi(1ed a rotor for a regene:rati.ve exchc.,l~(Je:r for l.h(- Ir.lnsfer of mois-ture and/or heat, between two gas streams, the ro~or comprising layers of aluminium foil, which are preferably alternately ~lat and cor-rugated to fo.rm a p:lura:Lity of continuous channels extending through sai.d rotor for said gas s-treams, the sur:Eace of the foils having a porous hygroscopic coating oE alurninium hydroxide obtained by precipitation from a solu-tion of an alkal.i aluminate applied to the surfaces.
The invention also includes a me-thod of manufacturing a roLor for a reyel-1era-tive exchanger for -the tral1sfer of moisture, and/or heat between two gas streams composed of layers of alumi-nium foil, which are preferably alternately flat and corrugatedto form a plurality of continuous channels extending through said rotor for said gas streams the method comprising treating the foils with an aluminate solution so that the surfaces thereof are given a porous hygroscopic structure.
~ referably the rotor is manufactured using a method in which two strips of aluminium foil, which can be 0.03 - 0.1 mm thick, are used. One strip is provided with corrugations of a height of 1 - 3 mm and is attached to the other strip, which is flat, using a simple adhesive, e.g. the one described in detail in the copending patent application ~entioned above, the strips then being formed into a cylindrical rotor of the required size by winding.
The aluminium foils are treated with an aqueous solution of an al~ali aluminate which may be potassium, sodium or lithium aluminate or a mixture of these. Preferably the treatment with the alkali aluminate solution consists, either of immersing the completed rotor into a bath of 15 - 20% aluminate solution, or such a solution is applied to the rotor in a sufficiently large quantity to effect the treatment e.g. by pouring the solution over the rotor.
The concentration is preferably 16 - 17% aluminate in the solution and, when effected in a bath, the bath i5 suitably at room temperature or somewhat lower such as 18 and the treat-ment time is relatively short e.g. 3 minutes. In this way the channels of the rotor are at least partially filled by the alumi-nate solution so that the surfaces of the foils are being etched so that a hygroscopic coating later can adhere to it.
This hygroscopic coating is created in subsequent treat-ment step as follows.
The rotor is lifted from the impregnation bath or the supply of solution stopped so that substantially all the solu-tion leaves the channels except for a film or a skin of the solu-tion which remains on the surfaces of the rotor. This film is more easily retained by turning the rotor immediately after empty-L$~
ing of the solution so that the channels are brought to a horlzon-tal position. The liquid in the channels is then converted gen-erating heat and subjecting the foils of the rotor to a substantial rise in temperature so that aluminium, being a part of the re-tained treatmentliquid, will be deposited on the surfaces and adheres as a hygroscopic coating consisting mainly of hydroxides and at the same time hydrogen gas will escape. This subsequent step continues for longer than the immersion step, preferably as long as water remains in the channels. When the reaction has ceased the rotor is washed to remove unwanted water soluble residuals.
However, before the washing it is advantageous to slowly cool the rotor in order to prevent separation of the coating and from the foil carriers as a result of thermal stresses. The coating may be further strengthened by allowing the foils of the rotor time to age in a moist atmosphere e.g.during a time oftwo days (48hours). In this way an increase ofthe grain size in the coating adheringto the foils is obtained and the risk-of aecomposition is further mini-mized.
As stated above, in the first treatment step in etching of the surface of the foil is accomplished to give the same a possibility to form a secure seat for the porous hygroscopic coating of aluminium hydroxide. However, whilst the effect on the thickness of aluminium foil itself is insignificant in the first step, the second treatment step provides the addition of a porous hygroscopic coating of about lO - 20 ~m on each side of the foil.
The increase of weight on a foil with a thickness of e.g. 50 ~m may be about 10%. The main components of the coating are alumi-nium hydroxides which are taken from the impregnation solution and not by any conversion of the aluminium foil itself.
The treatment of the invention should preferably be car-ried out after the rotor has been formed. This method has proved to have an effect that is of value for the strength of the rotor.
d, It appears that sorne type of brid~ing takes place between the porous coatings at the con-tact surfaces between adj~cent foil layers arld thi:s ~esults in a strengthenin~ oE the joints between the corrugated sheets.
The hygroscopic coating can be concentrated by repeated immersion in the aluminate solu-tion in the first -t:reatment step.
In addition a crushed or pulverised solid adsorption medium, e.g.
silic gel, can he in-troduced into the aluminate solution a-t some stage of the immersion process. Such a powder attaches itself surprisinyly well to -the surface of -the foil without reducing its sorpt;on propert;.es -to any greclt extell-t.
'I'he hygroscopic properties obtained usiny -the me-thod described above are based on adsorption and have proved to re-sult in moisture transfer properti.es comparable wi-th -those ob-ta;.ned in ro-tors manufactured using hi.ghly porous foil made of asbestos or earthenware with :Lithium chloride as the hygro-scopic substance, as menti.oned in the opening section.
In many cases, where -the rotor is used in velltilal-:i.on appardtus there is a :ri.sk th~lt pol.ln.ltion ;rl thc e.;l~ st air, e.y.
fats or oils, can cover the surfaces wi.th a thin film which can restrict the diffusion of the moisture to and from the hygro-scopic coating, if this consists of a soli.d adsorption medium.
It i.s easy for its fine pores and capillaries, in which the mois-ture condenses, to become blocked and put out of action. If, on the other hand, the hygroscopic suhstallce consists of a salt solu-tion, the entire wet surface becomes dc-tive whi.le the liquid tends -to seep in and break through the film of con-tclmination.
In si.milar operating sol.utions a hygroscopic capacity provided by a salt solution is preferableO
3~ Howeyer, untreated aluminium foil does no-t have the capa-bility of retaining a sufficient quantity of the salt solution on its surface. It has now been shown that the porous coating ob-1: 116~3 tained by the treatment of aluminium fo~l with alkali aluminate is capable of retain~ng a greater quantity of salt solution than an untreated surface. Moreover, treatment with aluminate provides a base onto which other coats that will further increase the porosity can be bonded. ~ description has already been given of such a coating where the addition of powder to, for example so-dium aluminate, during the immersion process provided an addition-al coating. The water absorbency capability of foil suxfaces can be considerably increased by this method of treatment. The rotor, once treated with aluminate, can also be immersed in water-glass and then exposed to carbon dioxide. This gives an addition-al coating of chemically precipitated silicon dioxide which also increases porosity.
One vital question when using a salt solution as the hygroscopic substance is the degree of corrosion that can occur.
Extensive tests have shown that lithium chloride cannot be used;
corrosion attacks far too rapidly. However lithium chloride can be used in solution with an inhibitor such as lithium hydroxide which makes the salt solution less corrosive.
Another lithium salt, lithium nitrate, has proved to result in, practically speaking, no corrosion of aluminium foil treated with aluminate. At the same time lithium nitrate gives the foil extremely good hygroscopic properties within the relative moisture range for the simultaneous moisture and temperature exchange in question here, i.e. a relative moisture in excess of 10 - 10$. Calcium bromide and sodium chloride have also proved to be considerably less corrosive than lithium chloride on surfaces treated with aluminate, although they are not so benign as lithium nitrate, Calciumbxomide has shown itself to be hygroscopically part~cularly suitable.
Thé substances and techniques described above which are intended to provide the rotor with adsorbing and absorbing proper-, - 6 -6~
ties are inexpensiVe and of such a nature that the principles of the manufacturin~ method described in the copending Canadian patent ~pplication 278,159 can be retained. Together these re-sult in manufacturing costs which considerably undercut the costs which were necessary to manufacture high-efficiency transfer ro-tors in the past.
In this specification the term "aluminium foil" is to be construed broadly asincluding sheets consisting of a carrier of non-metallic material such as fibers of glass or cellulose or plastic foils which are provided with a layer or coating of alumi-nium.
This invention relates to a rotor for a regenerative exchanger for the transfer of moisture and preferably also heat between two gas streams, particularly air streams.
An ~mportant area of application for a regenerative ex-changer is in supplying fresh alr to premises,; the incoming fresh air and the outgoing exhaust air exchanging moisture and heat in a rotor, so that, for example, in the winter the outgoing exhaust air provides the incoming fresh air with heat and moisture. Each stream of air ;s provided with its own individual inlet and outlet which is separated from the other stream of air so that the res-pective streams of air are directed to individual zones of the rotor. The rotor preferably consists of a plurality of sheets which are alternately flat and corrugated and which form a net-work of continuous, parallel channels for both streams of air.
The corrugated sheets support the flat sheets along the ridges of the corrugations which results in the channels being separated laterally. The rotor is normally cylindrical, the channels run-ning parallel with the axis of rotation.
Previously such rotors were manufactured of foils or ;20 sheets of fibrous, incombustible material, such as asbestos paper, or material made highly porous in another way, such as earthen-ware. Sheets of this type of material then act as carriexs for a hygroscopic substance, preferably a hygroscopic salt solution, lithium chloride being the most usual substance used.
A rotor of the type described above incorporating highly porous foils or sheets can possess exceptional characteristics, e.g. incombustibility, a high capacity for moisture transfer and good mechanical strength. However, a large number of operations are re~uired to provide a rotor with these properties, and this re-sults in the rotor being relatively expensive and time-comsuming to manufacture. The material from which the sheets are constructed has to be impregnated with several substances in order to give the - 1 - ~
.~, mechanical strength re~uired, particularly when wet, and this impregna-tion has to be perforrmed after -the shee-ting has been cor~
rugated and fashioned into the form of a rotor. Moreover tne ro-tor's peripheral surfaces have to be finished once these manu-facturing stages have been completed; grinding and milling being required to achieve the requisite flatness and accuracy.
If the sheets are made of aluminium foil manufacturi.ng costs can be reduced considerably, particu]~lrly if -the manufacturing technique described in our copending ~anadian applica-tion No.
278,159 is used. Such a rotor can be givcn fireproof propcr-ti.es and rnechan;.cal strength that are complete]y acceptable bu-t it lacks one property that is important in a moisture exchanger -hygroscopicity.
An object of this invention is to produce a ro-tor which is totally or partially made of a]uminium foil and which possesses exce]lent hygroscopic properties while keepi.ng the rnanufacturing process simple and the costs of material low.
According to -the prese11t inverlt:i.on l.here :is provi(1ed a rotor for a regene:rati.ve exchc.,l~(Je:r for l.h(- Ir.lnsfer of mois-ture and/or heat, between two gas streams, the ro~or comprising layers of aluminium foil, which are preferably alternately ~lat and cor-rugated to fo.rm a p:lura:Lity of continuous channels extending through sai.d rotor for said gas s-treams, the sur:Eace of the foils having a porous hygroscopic coating oE alurninium hydroxide obtained by precipitation from a solu-tion of an alkal.i aluminate applied to the surfaces.
The invention also includes a me-thod of manufacturing a roLor for a reyel-1era-tive exchanger for -the tral1sfer of moisture, and/or heat between two gas streams composed of layers of alumi-nium foil, which are preferably alternately flat and corrugatedto form a plurality of continuous channels extending through said rotor for said gas streams the method comprising treating the foils with an aluminate solution so that the surfaces thereof are given a porous hygroscopic structure.
~ referably the rotor is manufactured using a method in which two strips of aluminium foil, which can be 0.03 - 0.1 mm thick, are used. One strip is provided with corrugations of a height of 1 - 3 mm and is attached to the other strip, which is flat, using a simple adhesive, e.g. the one described in detail in the copending patent application ~entioned above, the strips then being formed into a cylindrical rotor of the required size by winding.
The aluminium foils are treated with an aqueous solution of an al~ali aluminate which may be potassium, sodium or lithium aluminate or a mixture of these. Preferably the treatment with the alkali aluminate solution consists, either of immersing the completed rotor into a bath of 15 - 20% aluminate solution, or such a solution is applied to the rotor in a sufficiently large quantity to effect the treatment e.g. by pouring the solution over the rotor.
The concentration is preferably 16 - 17% aluminate in the solution and, when effected in a bath, the bath i5 suitably at room temperature or somewhat lower such as 18 and the treat-ment time is relatively short e.g. 3 minutes. In this way the channels of the rotor are at least partially filled by the alumi-nate solution so that the surfaces of the foils are being etched so that a hygroscopic coating later can adhere to it.
This hygroscopic coating is created in subsequent treat-ment step as follows.
The rotor is lifted from the impregnation bath or the supply of solution stopped so that substantially all the solu-tion leaves the channels except for a film or a skin of the solu-tion which remains on the surfaces of the rotor. This film is more easily retained by turning the rotor immediately after empty-L$~
ing of the solution so that the channels are brought to a horlzon-tal position. The liquid in the channels is then converted gen-erating heat and subjecting the foils of the rotor to a substantial rise in temperature so that aluminium, being a part of the re-tained treatmentliquid, will be deposited on the surfaces and adheres as a hygroscopic coating consisting mainly of hydroxides and at the same time hydrogen gas will escape. This subsequent step continues for longer than the immersion step, preferably as long as water remains in the channels. When the reaction has ceased the rotor is washed to remove unwanted water soluble residuals.
However, before the washing it is advantageous to slowly cool the rotor in order to prevent separation of the coating and from the foil carriers as a result of thermal stresses. The coating may be further strengthened by allowing the foils of the rotor time to age in a moist atmosphere e.g.during a time oftwo days (48hours). In this way an increase ofthe grain size in the coating adheringto the foils is obtained and the risk-of aecomposition is further mini-mized.
As stated above, in the first treatment step in etching of the surface of the foil is accomplished to give the same a possibility to form a secure seat for the porous hygroscopic coating of aluminium hydroxide. However, whilst the effect on the thickness of aluminium foil itself is insignificant in the first step, the second treatment step provides the addition of a porous hygroscopic coating of about lO - 20 ~m on each side of the foil.
The increase of weight on a foil with a thickness of e.g. 50 ~m may be about 10%. The main components of the coating are alumi-nium hydroxides which are taken from the impregnation solution and not by any conversion of the aluminium foil itself.
The treatment of the invention should preferably be car-ried out after the rotor has been formed. This method has proved to have an effect that is of value for the strength of the rotor.
d, It appears that sorne type of brid~ing takes place between the porous coatings at the con-tact surfaces between adj~cent foil layers arld thi:s ~esults in a strengthenin~ oE the joints between the corrugated sheets.
The hygroscopic coating can be concentrated by repeated immersion in the aluminate solu-tion in the first -t:reatment step.
In addition a crushed or pulverised solid adsorption medium, e.g.
silic gel, can he in-troduced into the aluminate solution a-t some stage of the immersion process. Such a powder attaches itself surprisinyly well to -the surface of -the foil without reducing its sorpt;on propert;.es -to any greclt extell-t.
'I'he hygroscopic properties obtained usiny -the me-thod described above are based on adsorption and have proved to re-sult in moisture transfer properti.es comparable wi-th -those ob-ta;.ned in ro-tors manufactured using hi.ghly porous foil made of asbestos or earthenware with :Lithium chloride as the hygro-scopic substance, as menti.oned in the opening section.
In many cases, where -the rotor is used in velltilal-:i.on appardtus there is a :ri.sk th~lt pol.ln.ltion ;rl thc e.;l~ st air, e.y.
fats or oils, can cover the surfaces wi.th a thin film which can restrict the diffusion of the moisture to and from the hygro-scopic coating, if this consists of a soli.d adsorption medium.
It i.s easy for its fine pores and capillaries, in which the mois-ture condenses, to become blocked and put out of action. If, on the other hand, the hygroscopic suhstallce consists of a salt solu-tion, the entire wet surface becomes dc-tive whi.le the liquid tends -to seep in and break through the film of con-tclmination.
In si.milar operating sol.utions a hygroscopic capacity provided by a salt solution is preferableO
3~ Howeyer, untreated aluminium foil does no-t have the capa-bility of retaining a sufficient quantity of the salt solution on its surface. It has now been shown that the porous coating ob-1: 116~3 tained by the treatment of aluminium fo~l with alkali aluminate is capable of retain~ng a greater quantity of salt solution than an untreated surface. Moreover, treatment with aluminate provides a base onto which other coats that will further increase the porosity can be bonded. ~ description has already been given of such a coating where the addition of powder to, for example so-dium aluminate, during the immersion process provided an addition-al coating. The water absorbency capability of foil suxfaces can be considerably increased by this method of treatment. The rotor, once treated with aluminate, can also be immersed in water-glass and then exposed to carbon dioxide. This gives an addition-al coating of chemically precipitated silicon dioxide which also increases porosity.
One vital question when using a salt solution as the hygroscopic substance is the degree of corrosion that can occur.
Extensive tests have shown that lithium chloride cannot be used;
corrosion attacks far too rapidly. However lithium chloride can be used in solution with an inhibitor such as lithium hydroxide which makes the salt solution less corrosive.
Another lithium salt, lithium nitrate, has proved to result in, practically speaking, no corrosion of aluminium foil treated with aluminate. At the same time lithium nitrate gives the foil extremely good hygroscopic properties within the relative moisture range for the simultaneous moisture and temperature exchange in question here, i.e. a relative moisture in excess of 10 - 10$. Calcium bromide and sodium chloride have also proved to be considerably less corrosive than lithium chloride on surfaces treated with aluminate, although they are not so benign as lithium nitrate, Calciumbxomide has shown itself to be hygroscopically part~cularly suitable.
Thé substances and techniques described above which are intended to provide the rotor with adsorbing and absorbing proper-, - 6 -6~
ties are inexpensiVe and of such a nature that the principles of the manufacturin~ method described in the copending Canadian patent ~pplication 278,159 can be retained. Together these re-sult in manufacturing costs which considerably undercut the costs which were necessary to manufacture high-efficiency transfer ro-tors in the past.
In this specification the term "aluminium foil" is to be construed broadly asincluding sheets consisting of a carrier of non-metallic material such as fibers of glass or cellulose or plastic foils which are provided with a layer or coating of alumi-nium.
Claims (11)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A rotor for a regenerative exchanger for the transfer of moisture and/or heat, between two gas streams, the rotor comprising layers of aluminium foil which for a plurality of continuous channels extending through said rotor for said gas streams, the surface of the foils having a porous hygroscopic coating of aluminium hydroxide obtained by precipitation from a solution of an alkali aluminate applied to the surfaces.
2. A rotor according to claim 1, wherein the layers of aluminium foil are alternately flat and corrugated.
3. A method of manufacturing a rotor for a regenerative exchanger for the transfer of moisture, and/or heat between two gas streams composed of layers of aluminium foil which form a plurality of continuous channels extending through said rotor for said gas streams, the method comprising forming a film of aluminate solution on the foils and causing said aluminate solution to deposit on the foil surfaces a porous hygroscopic coating by precipitation from the solution.
4. A method according to claim 3, wherein the layers of aluminium foil are alternately flat and corrugated.
5. A method according to claim 3, wherein the aluminate solution is sodium aluminate.
6. A method according to claim 3, wherein the aluminate treatment is effected after the rotor has been formed.
7. A method according to claim 3, wherein an additional coating of an inorganic powder is effected by ad-mixing such a powder to the aluminate solution.
8. A method according to claim 7, wherein the powder consists of a solid adsorption medium, such as silica gel.
9. A method according to claim 3,4 or 5, wherein to the sur-face layer is added a hygroscopic substance which is a solution of lithium nitrate.
10. A method according to claim 3, 4 or 5, wherein to the surface is added a hygroscopic substance being a salt solution such as lithium chloride and an inhibitor making the salt solution less corrosive, such as lithium hydroxide.
11. A method according to claim 3, wherein the channels of the rotor are entirely or practically entirely filled with an aluminate solution during a first, short period of time and that the aluminum surface of the rotor thereafter is held in contact with only a film of the solution during a second, longer period of time.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| SE7608329-4 | 1976-07-21 | ||
| SE7608329A SE407455B (en) | 1976-07-21 | 1976-07-21 | ROTOR FOR A REGENERATIVE EXCHANGE OF MOISTURE AND HEAT AND WAY TO PRODUCE SUCH A ROTOR |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1116163A true CA1116163A (en) | 1982-01-12 |
Family
ID=20328527
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA282,637A Expired CA1116163A (en) | 1976-07-21 | 1977-07-13 | Rotor for regenerative heat and/or moisture exchanger |
Country Status (8)
| Country | Link |
|---|---|
| JP (1) | JPS5313252A (en) |
| CA (1) | CA1116163A (en) |
| CS (1) | CS198261B2 (en) |
| DE (1) | DE2732989C2 (en) |
| FR (1) | FR2358913A1 (en) |
| GB (1) | GB1581262A (en) |
| NO (2) | NO143714C (en) |
| SE (1) | SE407455B (en) |
Families Citing this family (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS58124521A (en) * | 1982-01-20 | 1983-07-25 | Mitsubishi Electric Corp | Moisture permeable gas barrier |
| SE8207166D0 (en) * | 1982-12-15 | 1982-12-15 | Svante Thunberg | REGENERATIVE HEAT EXCHANGER WITH MOISTURIZING AND TEMPERATURES |
| JPS613994A (en) * | 1984-06-18 | 1986-01-09 | Baanaa Internatl:Kk | Rotary element for total heat exchanger and/or dehumidifier |
Family Cites Families (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3702156A (en) * | 1970-12-03 | 1972-11-07 | Aero Flow Dynamics Inc | Air-to-air energy exchange wheel and method of fabrication |
| US3733791A (en) * | 1971-08-13 | 1973-05-22 | Wehr Corp | Heat transferer |
| DE2243408A1 (en) * | 1971-09-10 | 1973-03-15 | Luft U Kaeltetechnik Veb K | Treatment of aluminium heat exchanger used for cooling moist - air - with alkaline soln to facilitate removal of condensate |
| FR2152802A1 (en) * | 1971-09-10 | 1973-04-27 | Luft Kaltetechn K |
-
0
- NO NO143714D patent/NO143714L/no unknown
-
1976
- 1976-07-21 SE SE7608329A patent/SE407455B/en unknown
-
1977
- 1977-07-13 CA CA282,637A patent/CA1116163A/en not_active Expired
- 1977-07-14 GB GB29639/77A patent/GB1581262A/en not_active Expired
- 1977-07-20 FR FR7722249A patent/FR2358913A1/en active Granted
- 1977-07-20 NO NO772595A patent/NO143714C/en unknown
- 1977-07-21 JP JP8674377A patent/JPS5313252A/en active Granted
- 1977-07-21 DE DE2732989A patent/DE2732989C2/en not_active Expired
- 1977-07-21 CS CS774871A patent/CS198261B2/en unknown
Also Published As
| Publication number | Publication date |
|---|---|
| NO143714C (en) | 1985-12-03 |
| DE2732989A1 (en) | 1978-01-26 |
| NO772595L (en) | 1978-01-24 |
| FR2358913B1 (en) | 1980-04-04 |
| CS198261B2 (en) | 1980-05-30 |
| DE2732989C2 (en) | 1984-06-28 |
| FR2358913A1 (en) | 1978-02-17 |
| JPS6127680B2 (en) | 1986-06-26 |
| JPS5313252A (en) | 1978-02-06 |
| SE7608329L (en) | 1978-01-22 |
| GB1581262A (en) | 1980-12-10 |
| NO143714L (en) | 1900-01-01 |
| NO143714B (en) | 1980-12-22 |
| SE407455B (en) | 1979-03-26 |
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| MKEX | Expiry |