WO2001030718A1

WO2001030718A1 - Media for evaporative cooler

Info

Publication number: WO2001030718A1
Application number: PCT/US2000/028512
Authority: WO
Inventors: Ronald J. Yaeger
Original assignee: Air and Refrigeration Corp
Current assignee: Air and Refrigeration Corp
Priority date: 1999-10-22
Filing date: 2000-10-13
Publication date: 2001-05-03
Anticipated expiration: 2002-04-22
Also published as: AU8023800A

Abstract

Gas-liquid contacting media treated with an aqueous-based cationic or non-anionic resin prevents scale build-up from forming on the surface of the media. The contact media is constructed from a fibrous web of materials, for example glass, impregnated with an aqueous-based cationic or non-anionic resin, preferably a polyamide-imide resin.

Description

MEDIA FOR EVAPORATIVE COOLER

TECHNICAL FIELD OF THE INVENTION

The invention relates to gas-liquid contact media.

BACKGROUND OF THE INVENTION

The adiabatic saturation process conducted by evaporative coolers is an energy-efficient method for cooling and humidifying in HVAC (heating/venting/air conditioning) systems. However, the formation of water- borne scale on the gas-liquid contacting apparatus, commonly called media (hereinafter referred to as media) , presents a persistent problem to users of such systems. In fact, a major limitation to increased use of evaporative cooling is the high costs of coping with scale build-up.

Water contains dissolved salts such as carbonates, sulfates, and nitrates of Ca⁺⁺ and Mg⁺⁺ which, upon precipitation, form scale. As water evaporates in an evaporative cooling system, the concentration of these scale-forming salts in the water increases until precipitates form. Deposits of these precipitates routinely form onto the surfaces of the gas-liquid contact media utilized in the evaporative cooling system. As the deposits build up, the water and air passages in the media become blocked or partially blocked, reducing the cooling efficiency of the system. Moreover, the added weight from the scale deposits can cause deterioration or collapse of insufficiently supported media.

Several methods for operating evaporative coolers are currently known which address the problem of scale build-up on the evaporative media: (1) use of once- through water or a high rate of bleed water in recirculated water to reduce the concentration and hence, the precipitation of scale-forming salts; (2) addition of chemicals to recirculated water to inhibit the deposition of scale; and (3) use of untreated, recirculated water and periodic replacement the evaporative media. All of these methods can result in high operating or maintenance costs; however, the third method becomes more economically attractive if the gas-liquid contact media is durable enough to withstand prolonged use between replacement .

Gas-liquid contact media used in evaporative cooling systems are routinely made of layered cellulose, asbestos, or fiberglass sheets which contain folds, channels, or passageways through which the air and water pass. The media can be configured in stacked arrays or formed into drip pads, sprayed pads, packed cells, rotating wheels, or other types of such contact media.

It is known to impregnate such evaporative cooler media with selected materials in order to increase its strength (especially when wet) , and thereby increase its durability and resistance to deformation caused by scale build-up. For example, U.S. Patent No. 3,262,682 issued to Bredberg and U.S. Patent No. 3,792,841 issued to Munters disclose gas-liquid contact bodies consisting of layered facially-opposed corrugated sheets disposed such that an alternating pattern of parallel channels are formed. In these designs, water introduced along the top edge of contact body flows through parallel channels having openings along the top edge, and air flows through channels having openings along a side edge of the contact body. Bredberg and Munters disclose impregnating cellulose or asbestos sheets used to make these contact bodies with a phenolic aldehyde resin or phenolic resin, respectively, to increase wet strength. Munters further discloses use of a water glass, or silicic acid, treatment for increasing moisture adsorptivity and structural strength of the cellulose or asbestos sheets (U.S. Patent No. 3,307,617 to Munters).

Along with water glass and phenolic resins, other stiffening resins for increasing wet strength have been used in the treatment of contact media including urea formaldehyde, melamine, and melamine formaldehyde. These resins are readily hydrolyzed and removed from the contact media on exposure to strong acidic or alkaline conditions .

In U.S. Patent No. 3,798,057 and U.S. Patent No. 3,862,280, Polovina discloses a gas-liquid contact apparatus made with an acid-, alkali-, and water- resistant fibrous web impregnated with a mixture of a chlorinated polymeric C₃ and C₅ hydrocarbon, a plasticizer of chlorinated terphenyl or chlorinated paraffin, and a polyglycidyl ether of a polyhydric phenol such as bisphenol A or bisphenol F. According to Polovina, this treatment provided increased durability under conditions such as pH and temperature extremes which normally cause rapid disintegration of contact bodies.

The stiffening resins described above are all categorized as anionic, forming negatively charged sites along the polymer chain of the resin which attract positively charged particles or ions such as calcium (Ca⁺²) , magnesium (Mg⁺²) , potassium (K⁺) , and sodium (Na⁺) ions. Consequently, these resins contribute to the attraction of scale-forming materials onto the surface of contact media, exacerbating the problem of scale buildup.

A need, therefore, exists for a gas-liquid contact media which has good durability and also which resists, repels, and/or minimizes the deposit of scale on its surface . SUMMARY OF THE INVENTION

In one aspect, the present invention is a gas-liquid contact media having a web of fibrous material impregnated with an aqueous-based resin which maintains a positive charge on the surface of the web when exposed to water. In one embodiment, the fibrous material comprises glass. In a preferred embodiment, the fibrous material comprises borosilicate glass. In another embodiment, the resin comprises an aqueous-based polyamide-imide having a pH within the range of about 2.0 to about 6.5 which cross-links at a temperature range of about 275° to about 400°F. Another preferred embodiment comprises an aqueous-based polyamide-imide having a pH within the range of about 6.0 to about 6.5 which cross-links at an temperature of about 275° to about 400°F. In yet another embodiment, the resin content is within the range from about 5% to about 25% by dry weight of the treated contact media. In yet another preferred embodiment, the resin content is within the range from about 10% to about 15% by dry weight of the treated contact media.

In a further preferred embodiment, the web is an array of a plurality of facially opposed corrugated sheets with the corrugations in adjacent sheets being disposed at an angle to each other and the corrugations in alternate sheets being disposed parallel to each other to form a plurality of criss-crossing channels. A most preferred embodiment is a gas-liquid contact media comprising an array of corrugated sheets comprising a fibrous web of borosilicate glass impregnated with an aqueous-based polyamide-imide resin having a pH within the range from about 6.0 to about 6.5 which cross-links at a temperature of about 275° to about 400°F. and maintains a positive charge on the surface of the fibrous web when exposed to water, wherein the final resin content of the contact media is within the range from about 10% to about 15% dry weight of the contact media, and wherein the array of corrugated sheets is a plurality of facially opposed corrugated sheets with the corrugations in adjacent sheets being disposed at an angle to each other and the corrugations in alternate sheets being disposed parallel to each other such that the corrugated sheets form a plurality of criss-crossing channels.

In another aspect, the present invention is a web of fibrous material impregnated with an aqueous-based resin which maintains a positive charge on the surface of said fibrous web when exposed to water. In one embodiment, the fibrous material comprises glass. In a preferred embodiment the fibrous material comprises borosilicate glass. In one embodiment, the resin comprises an aqueous-based polyamide-imide having a pH within the range of about 2.0 to about 6.5 which cross-links at a temperature of about 275° to about 400°F. A preferred embodiment comprises an aqueous-based polyamide-imide having a pH within the range of about 6.0 to about 6.5 which cross-links at a temperature of about 275° to about 400°F. In one embodiment, the resin content is from about 5% to about 25% by dry weight of the treated fibrous material. In a preferred embodiment, the resin content is from about 10% to about 15% by dry weight of the treated fibrous material.

In yet another aspect, the present invention is a method of cooling air by evaporation wherein water and air are passed through a gas-liquid contact media having a web of fibrous material impregnated with an aqueous- based resin which maintains a positive charge on the surface of the web when exposed to water, whereby the water evaporates adiabatically into to air and thereby cools the air. In one preferred method, the fibrous material comprises glass. In a more preferred method, the fibrous material comprises borosilicate glass. In another preferred method, the resin comprises an aqueous- based polyamide-imide having a pH within the range of about 2.0 to about 6.5 which cross-links at a temperature of about 275° to about 400°F. In another more preferred method the resin comprises an aqueous-based polyamide- imide having a pH within the range of about 6.0 to about 6.5 which cross-links at a temperature of about 275° to about 400°F. In yet another preferred method, the resin content is from about 5% to about 25% by dry weight of the treated contact media. In yet another more preferred method, the resin content is from about 10% to about 15% by dry weight of the treated contact media.

In a further preferred method, the web is an array of a plurality of facially opposed corrugated sheets with the corrugations in adjacent sheets being disposed at an angle to each other and the corrugations in alternate sheets being disposed parallel to each other to form a plurality of criss-crossing channels. In a most preferred method, water and air are passed through a gas- liquid contact media comprising an array of corrugated sheets comprising a fibrous web of borosilicate glass impregnated with an aqueous-based polyamide-imide resin having a pH within the range from about 6.0 to about 6.5 which cross-links at a temperature of about 275° to about 400°F. and maintains a positive charge on the surface of the fibrous web when exposed to water, wherein the final resin content of the contact media is from about 10% to about 15% dry weight of the contact media, and wherein the array of corrugated sheets is a plurality of facially opposed corrugated sheets with the corrugations in adjacent sheets being disposed at an angle to each other and the corrugations in alternate sheets being disposed parallel to each other such that the corrugated sheets form a plurality of criss-crossing channels.

BRIEF DESCRIPTION OF THE DRAWINGS

A better and more complete understanding of the present invention and the advantages thereof will be gained from the following detailed description, claims and accompanying drawing in which:

Fig. 1 is a perspective view of a block of corrugated media according to the preferred embodiment of the present invention, with portions broken away to better illustrate the structure.

DETAILED DESCRIPTION

Contact media for evaporative coolers have now been developed which are treated with aqueous-based resins that are cationic or non-anionic. This treatment provides improved chemical resistance and structural strength by preventing scale build-up.

The media, or gas-liquid contact apparatus, of the present invention can be constructed from corrugated sheets of fibrous web material, for example glass fibers. Preferably, borosilicate glass is used. While glass fibers are the preferred composition, any material capable of providing a suitable gas-liquid contact means which is (1) unreactive to the aqueous-based cationic or non-anionic resins of the present invention and (2) maintains a positive charge on the surface of the material when impregnated with an aqueous-based resin and exposed to water, would fall within the scope of this invention.

Sheets of fibrous webs are impregnated with an aqueous-based cationic or non-anionic resin. Preferred resins are polyamide-imide resins or polyamide-imide resins blended with other compatible polymer resins such as epoxies, acryides, etc. All resins are water dispersible in an acidic media without the use of emulsifying surfactants. The resins/resin blends, after evaporation of water, provide water insoluble films by their inherent thermoplastic or thermosetting characteristics or attain such properties through cross- linking due to heat and/or reaction with functional groups which are compatible with the acidic media used. Preferably, the resin is a polyamide-imide having a pH within the range of about 2.0 to about 6.5, and preferably having a pH within the range of about 6.0 to about 6.5 which cross-links when cured at a temperature of about 275° to about 400°F., more preferably, of about 300° to about 350°F.

After application of the resin to the sheets, the sheets are forced into a mold having a desired shape, e.g., corrugated mold, and carried through an oven at temperatures appropriate for drying and curing. An elevated temperature is required in the curing of the resin and also increases the rate of cross-linking in the resin, i.e., the higher the temperature range the faster the rate of cross-linking. The required elevated temperature range varies for different types of resins, and would be within the skill of one in the art to determine the appropriate temperature range. For the preferred polyamide-imide resins/blends, the preferred temperature range is from about 275° to about 400°F., and more preferably, from about 300° to about 350°F.

The final resin content of the cured sheets is in the range of about 5% to about 25% by dry weight of the sheets, and preferably in the range of about 10% to about 15% by dry weight.

The cross-linked resins of the present invention normally exhibit chemical resistance to pH variances in water. This durability under extreme acid or base conditions provides distinct advantages over other treatment methods .

Additives may be added to the resins of the present invention which provide improved physical and chemical strength to the resin. Such additives cannot interfere with the cationic or non-anionic properties of the resin. Starches which are cationic are examples of one type of additive useful in the present invention.

Now referrring to Fig. 1, a preferred embodiment of the current invention is described. Shown in Fig. 1 is a block 10 of media, formed from corrugated sheets 12 impregnated with aqueous based cationic or non-anionic resin as described above. The sheets 12 are formed into the relatively homogeneous block 10 of media by the following process. A water resistant adhesive is applied to the corrugations 14 or ridges of the sheets 12, and an appropriate number of sheets are stacked facially opposed such that the corrugations in adjacent sheets (i.e., sheets attached to each other in the array) are disposed at an angle to each other and the corrugations in alternating sheets (i.e., every other sheet in the array) are parallel. This arrangement of the corrugated sheets 12 forms a plurality of crisscrossing channels (indicated by arrows 16) , the channels in every other sheet running parallel to each other, and with the channels in adjacent sheets running at a fixed angle to each other. If desired, upon curing the water resistant adhesive, the block 10 of corrugated sheets 12 comprising the media can be cut into a size and shape preferable for the gas- liquid contact media.

When placed in an evaporative cooler, water is applied to a top edge of the media such that water travels through the channels having openings along the top edge, and air is applied to a side edge of the contact media such that air travels through the channels having openings along the side edge. As water travels through the media, the aqueous-based cationic or non- anionic resins of the present invention ionize to form positively charged sites along the polymer chain of the resin, and consequently, repulse positively charged particles or ions such as calcium (Ca⁺²) , magnesium (Mg⁺²) , potassium (K⁺) , and sodium (Na⁺) ions which may be present in the water. Consequently, scale-forming ions in the water supplied to the contact media are repulsed and do not precipitate on or bind to the media, preventing scale build-up. By imparting a cationic or non-anionic surface to the media to prevent scale deposits, the durability of the contact media when exposed to untreated water is increased significantly. It is to be understood that the above description is of a preferred exemplary embodiment of the invention and is intended to be illustrative of the invention, but is not to be construed to limit the scope of the invention in any way. Modifications may be made in the structural features of the invention without departing from the scope of the invention. It will be readily apparent to those skilled in the art that alternative materials may also be utilized without departing from the scope of the invention.

In another aspect of the invention, a method of cooling air by adiabatic evaporation of water utilizes a gas-liquid contact media which has been treated with a cationic or non-anionic resin that maintains a positive charge on the surface of the media so as to prevent scale build-up. Water is applied to the surface of the media, and air is moved through the media is such a way that the air comes in contact with the water. As the water on the media adiabatically evaporates into the air, the air is cooled.

Claims

WE CLAIM :

1. A gas-liquid contact media comprising a web of fibrous material impregnated with an aqueous-based resin, wherein said resin maintains a positive charge on the surface of said web when exposed to water.

2. The contact media of Claim 1, wherein said fibrous material comprises glass.

3. The contact media of Claim 2, wherein said glass comprises borosilicate glass.

4. The contact media of Claim 1, wherein said resin comprises a polyamide-imide having a pH within the range of about 2.0 to about 6.5 which cross-links at a temperature of about 275° to about 400°F.

5. The contact media of Claim 4, wherein said polyamide-imide having pH within the range of about 6.0 to about 6.5 which cross-links at a temperature of about 275° to about 400°F.

6. The contact media of Claim 4, wherein said final resin content of said media is within the range from about 5% to about 25% by dry weight.

7. The contact media of Claim 6, wherein said final resin content of said media is within the range from about 10% to about 15% by dry weight.

8. The contact media of Claim 1, wherein said web comprises a plurality of facially opposed sheets, each said sheet having a plurality of generally parallel corrugations formed thereon, the corrugations in adjacent sheets being disposed at an angle to each other and the corrugations in alternate sheets being disposed parallel to each other, so as to form a plurality of crisscrossing channels therebetween.

9. A web of fibrous material impregnated with an aqueous-based resin, wherein said resin maintains a positive charge on the surface of said fibrous web when exposed to water.

10. The web of Claim 9, wherein said fibrous material comprises glass.

11. The web of Claim 10, wherein said glass comprises borosilicate glass.

12. The web of Claim 9, wherein said resin comprises a polyamide-imide having a pH within the range of about 2.0 to about 6.5 which cross-links at a temperature of about 275° to about 400°F.

13. The web of Claim 12, wherein said polyamide- imide having a pH within the range of about 6.0 to about

6.5 which cross-links at a temperature of about 275° to about 400°F.

14. The web of Claim 12, wherein said final resin content of said web is within the range from about 5% to about 25% by dry weight.

15. The web of Claim 14, wherein said final resin content of said web is within the range from about 10% to about 15% by dry weight.

16. A method of cooling air, comprising the steps of: a. providing a gas-liquid contact media comprising a web of fibrous material impregnated with an aqueous- based resin, wherein said resin maintains a positive charge on the surface of said web when exposed to water; b. applying water to the surface of said media; and c. moving air through said media such that it comes in contact with said water; whereby said water evaporates adiabatically into said air, thereby cooling said air.

17. The method of Claim 16, wherein said fibrous material comprises glass.

18. The method of Claim 17, wherein said glass comprises borosilicate glass.

19. The method of Claim 16, wherein said resin comprises a polyamide-imide having a pH within the range of about 2.0 to about 6.5 which cross-links at a temperature of about 275° to about 400°F.

20. The method of Claim 19, wherein said polyamide- imide having a pH within the range of about 6.0 to about 6.5 which cross-links at a temperature of about 275° to about 400°F.

21. The method of Claim 19, wherein said final resin content of said media is within the range from about 5% to about 25% by dry weight.

22. The method of Claim 21, wherein said final resin content of said media is within the from about 10% to about 15% by dry weight.

23. The method of Claim 16, wherein said web further comprises a plurality of facially opposed corrugated sheets with the corrugations in adjacent sheets being disposed at an angle to each other and the corrugations in alternate sheets being disposed parallel to each other, said corrugated sheets forming a plurality of crisscrossing channels.