WO2025083488A1

WO2025083488A1 - Evaporative coolers using hollow fibers having protective layers

Info

Publication number: WO2025083488A1
Application number: PCT/IB2024/059245
Authority: WO
Inventors: Anne N. De Rovere; Joseph A. DUNBAR; Todd P. ORME; Carol P. CRUMB
Original assignee: 3M Innovative Properties Co
Current assignee: 3M Innovative Properties Co
Priority date: 2023-10-17
Filing date: 2024-09-23
Publication date: 2025-04-24
Anticipated expiration: 2026-04-17

Abstract

A unit for use in evaporative cooling includes a first capped frame and a second open frame opposite the first frame. Posts are located between and coupled to the first and second frames. A porous hollow fiber membrane extends around the posts between and coupled to the first and second frames to form an interior volume. The first and second frames are configured for flow of water between them via the membrane. The membrane is configured to transport the water between the first and second frames and to provide for air flow from the interior volume through the membrane for evaporative cooling. The unit has a protective layer or layers to minimize or prevent leakage of water from the hollow fiber membrane.

Description

EVAPORATIVE COOLERS USING HOLLOW FIBERS HAVING PROTECTIVE LAYERS

BACKGROUND

Evaporation is a cost and energy efficient way of cooling and is used for regulating temperatures in data centers, food processing plants, or office buildings. Currently, cellulosic pads are used to perform evaporative cooling on a large scale such as in a data center. Hot dry air is cooled by evaporating water flowing over the cellulosic pads yielding cool, humid air on the output. Large amounts of water are required for this type of cooling, and the media must be maintained either in a dry state or wet state to prevent degradation due to fouling or crystalline salt deposition. The humidity level of the air discharged into the data center can be controlled using louvers or dampers which direct the input air through only a portion of the media or completely around the media in a bypass duct. Accordingly, a need exists for an improved evaporative cooling system.

SUMMARY

A unit for use in evaporative cooling includes a first capped frame and a second open frame opposite the first frame. A plurality of mechanical supports are located between and coupled to the first and second frames. A porous hollow fiber membrane extends around the supports between and coupled to the first and second frames to form an interior volume. The first and second frames are configured for flow of a liquid between them via the membrane. The membrane is configured to transport the liquid between the first and second frames and to provide for air flow through the membrane for evaporative cooling.

The unit has a protective layer or layers to minimize or prevent leakage of water from the hollow fiber membrane in the unit.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a front sectional view of a rounded square shape evaporative cooling unit.

FIG. IB is a side sectional view of the rounded square shape evaporative cooling unit.

FIG. 2 is a diagram of a water recirculation system for an evaporative cooling unit.

FIG. 3A is a front view of an evaporative cooling unit with bifurcated water flow.

FIG. 3B is a side view of an evaporative cooling unit with bifurcated water flow.

FIG. 3C is a rear view of an evaporative cooling unit with bifurcated water flow.

FIG. 4A is a cross-sectional view of outer wrap(s) of protective layers of fibers.

FIG. 4B is a cross-sectional view of outer and inner wrap(s) of protective layers of fibers.

FIG. 4C is a cross-sectional view of an outer protective layer or wrap.

FIG. 4D is a cross-sectional view of outer protective layer(s) of fibers.

FIG. 4E is a cross-sectional view of outer and inner protective layer(s) of fibers. DETAILED DESCRIPTION

Embodiments include an evaporative cooler using a membrane having hollow fibers with porous walls, which provides enhanced evaporative cooling and reduced pressure drop. This construction includes an array of knitted fibers rolled into an annular circular cylinder, rounded square, or other shapes and potted at both ends to allow flow of liquid water through the fibers. One end of this annular cylinder is open for the passage of air and the other end is capped, which forces the air to flow through the fiber array to cool the incoming air. This construction could provide for ease of manufacturability compared to a folded design. This construction also provides for improvement of the panel performance by systematically increasing the length of the panel. Additionally, adding folds in the fiber array around the cylinder can also improve the performance due to increase in the surface area. This construction with hollow fibers with non-porous walls could also work as a heat exchanger. Using porous walled fibers can also work as a heat exchanger when the air is very humid.

Examples of evaporative cooling units are disclosed in PCT Application Publication No. WO 2023/037287, which is incorporated herein by reference as if fully set forth.

Evaporative Cooling Unit

FIGS. 1A and IB are front and side sectional views of an evaporative cooling unit 10 panel construction which includes a knitted fiber array using a rounded square shape, as an example. A perspective view of unit 10 is illustrated in FIG. 2. As shown in FIGS. 1A and IB, this panel construction also works for any other cross-sectional shape as well. Unit 10 includes a front open frame 12, mechanical supports such as posts 14, a porous hollow fiber membrane 16, and a capped rear frame 20. Frame 12 is open in that frame 12 has an opening to allow for the passage or flow of air into unit 10. Frame 20 is capped in that frame 20 at least partially, and preferably completely, blocks the passage or flow of air in unit 10. As an optional alternative, unit 10 can include another membrane wrapped around another set of mechanical supports inside of membrane 16 and spaced apart from it. Unit 10 can be portable unit or non-portable.

A liquid such as water flows (22) between front frame 12 and rear frame 20. An air stream or air flow (24) from front frame 12 is forced by rear frame 20 through the fibers of membrane 16 to cool the air. Alternatively, air can flow in the other direction from outside unit 10 to the interior volume. Unit 10 preferably has no core, such that the interior volume is open between the frames, for more effective air flow through the interior volume. The air can be induced into a radial flow through the fibers of membrane 16. Frame 12 can be mounted in a horizontal direction in an air duct, and have mechanical structures for attachment to the air duct, with a fan to pull air from outside through membrane 16. Posts 14 extend between and are coupled to frames 12 and 20, either directly or through other mechanical structures. Posts 14 can have optional perforations such as perforation 15. Only a single perforation 15 is shown for illustrative purposes; the posts have multiple perforations while still maintaining the mechanical stability of the posts. The perforations can provide for air flow through the posts. Posts 14 can be connected to one another to provide more support. For example, posts 14 can include an optional cross brace 18 located between frames 12 and 20, such as at a midpoint between the frames or other location. Cross brace 18, or other mechanical connection between posts 14, can divert the air flow through the interior volume of unit 10. One of the standoff posts can optionally be used as a pipe to facilitate the servicing and installation of the unit.

Posts 14 can have a circular cross-sectional shape, as shown, or other shapes such as the following alternatives and options. The posts can be a round comer rectangular bar, for example 0.75 inch X 0.25 inch where each comer is radiused with a 0. 125 inch radius and set at a 45° angle to the circumference for a square. The posts can be a folded post, where a 1.5 inch X 0.125 inch piece of material is folded such that the cross section becomes 0.75 inch X 0.25 inch. A post can be a comer post that is a 0.5 inch X 0.5 inch X 0. 125 inch angle iron “L” shaped piece. One or more of the posts can be a hollow pipe to facilitate all of the water connections on one end (frame), for example.

Posts 14 are preferably constmcted of ABS plastic. Alternatively, the posts can be formed from stainless steel, aluminum, or fiberglass. Frames 12 and 20 are preferably constmcted of ABS plastic. Alternatively, the frames can be formed from PVC, styrene, polycarbonate, or metal(s). Materials of unit 10 can optionally have a Flame Retardant (FR) rating.

Membrane 16 (e.g., a knitted fiber mat) extends around the four posts 14 (e.g., wrapped around) to form an interior volume and can be mechanically held in place between posts 14 and the frames, as illustrated in FIG. 1A, or between an inner and outer frame assembly. Membrane 16 preferably forms a continuous loop around posts 14, as shown in FIG. 1A, to create the interior volume; alternatively, membrane 16 can form a discontinuous loop around the posts. The hollow fibers in membrane 16 are potted at the two ends of the frame. For example, the fibers of membrane 16 can be held in an epoxy in the frame with open ends of the hollow fibers to receive water or other liquid. As another example, the ends of the fibers in membrane 16 can be held by an adhesive, the adhesive can then be cut to open the ends of the fibers, and an end plate can be fixed over the open ends of the fibers. Alternatively, unit 10 can have a frame construction where the framework supports the open end of the hollow fibers, which are then attached to an air handler unit in a system that has water channels for use in circulating the water through the hollow fiber membrane.

Membrane 16 can include multiple layers, for example 27-33 layers wrapped around posts 14. Alternatively, a length of membrane 16 (Lj) can be increased to reduce the number of layers. The membrane is hydrophobic (at least on the inside) for water. Air flows from the front of the panel and through the fibers where evaporation cools the air. The air flow velocity through the fibers is reduced due to enhanced surface area. The following are exemplary parameters for the hollow fiber membrane: a pore size of 0.01-0.2 microns and preferred of 0.03-0.04 microns; a porosity of 25%-80%; a wall thickness (single layer) of 15-75 microns and preferred of 25-50 microns; and a knitting density of 15-65 fibers per inch, or 20-60 fibers per inch, or 35-53 fibers per inch. An example of a hollow fiber membrane is disclosed in U.S. Patent No. 9,541,302. Examples of hollow fiber membranes are also included in the following products: the LIQUI-CEL MM Series Membrane Contactor from 3M Company (product ID B5005009013) and the LIQUI-CEL SP Series Membrane Contactor Cartridge from 3M Company (product ID B5005009016).

FIG. 2 is a diagram of a water recirculation system for evaporative cooling unit 10. A water tank 30 provides water on an intake line 32 to a pump 34, which circulates the water through a water filter 36 to an inlet 38 in frame 12. An outlet 40 on frame 20 provides the water to a water return line 42 back to water tank 30. Alternatively, the water can flow in the other direction with frame 20 receiving the water. Optionally, one frame can include both the inlet and the outlet. The water can have a particular type of quality. The water recirculation system can optionally include an anode/cathode feature to control mineral buildup within the water loop.

Bifurcated Water Flow

FIGS. 3A, 3B, and 3C are front, side, and rear views, respectively, of an evaporative cooling unit 90 with bifurcated water flow. Unit 90 includes a front frame 92 having a channel 94 and flow separation elements 96 that divide channel 94 into two channels and prevent flow of water between the two channels. A rear frame 102 for unit 90 includes a continuous channel 104. Channels 94 and 104 can be formed by machining the frames to create a groove, and flow separation elements 96 can be formed by not machining the comers such that those portions of the frames block water flow. A porous hollow fiber membrane 106 with hollow fibers is located between front frame 92 and rear frame 102. In use, front frame 92 includes a water inlet 98 for water flow in (108) through the hollow fibers in membrane 106 to rear frame 102. The water is forced under pressure through channel 104 in rear frame 102 for water flow out (110) to a water outlet 100 in front frame 92.

In this embodiment, the water inlet and water outlet are thus located on the same side of unit 90 in frame 92. This feature bifurcates the water channel and sends the water down two contiguous faces of the unit and back through the other two contiguous faces. In unit 90, the water flows to the right in the top two surfaces and returns to the left in the bottom two surfaces. Alternatively, unit 90 can include water inlets and outlets on both frames 92 and 102 to bifurcate the water flow on both ends. This feature can provide advantages for the end-use customer including ease of assembly and lower air pressure drop during operation. Also, in this embodiment there is no need to use a pipe as one of the posts to transport water between the ends (frames) of the unit.

Unit 90 can have a similar configuration, features, and materials as unit 10 shown in FIGS. 1A and IB aside from the bifurcated water flow feature. In particular, frame 92 can be an open frame, and frame 102 can be a capped frame. Alternatively, frame 102 can include the inlet, outlet, and flow separation elements with frame 92 having the continuous channel. Frame 92 can be coupled to frame 102 with mechanical supports, such as posts, with membrane 106 wrapped around the posts. Membrane 106 can be held in the frames with an adhesive and with open ends of the fibers in membrane 106 being in fluid communication the channels in the frames. Membrane 106 can have the properties as described above for unit 10. In use, inlet 98 can be coupled to intake line 32 (see FIG. 2), and outlet 100 can be coupled to return line 42.

The bifurcated water flow feature can also be incorporated into evaporative cooling units having other shapes.

Modeling has shown that this bifurcated water flow design does not negatively affect cooling efficiency or air pressure drop during operation. The only noticeable change in the modeling was that the water pressure through the fibers should be upwards of four times as high as the design shown in FIGS. 1A and IB at the same gallons per minute flow rate. This change results from the water travelling twice as far through half as many fiber openings.

Protective Layers for Hollow Fibers in Coolers

A diagram of water flow through an evaporative cooling unit is shown in FIGS. 3A-3C, as described above. One desirable requirement is that no liquid water can bead up or leak from the fibers during operation. Ideally, only water vapor should release from the fibers and enter the air, but water leaks can sometimes occur, as well as small beads of water sometimes referred to as “weeps.”

These water leaks have been shown to be caused by several things. One cause is physical damage to the fibers, which can result from improper handling or accidentally hitting the fibers with a tool or other sharp object. Another cause that has been discovered is fiber surface contamination. Certain contaminants on the surface of the fibers can induce weeping, where water can penetrate through the pores of the fibers and collect on the outer surface due to compromised hydrophobicity of the polymer. These contaminants can include silicone, oils, and other chemicals.

Several solutions have been devised to eliminate both physical damage and surface contamination of the fibers. These solutions, as described below with respect to FIGS. 4A-4E, involve a protective layer of hollow fiber or another material to physically block the water filled fibers from being affected by damage or contaminants. These protective layers would not participate to the evaporative cooling effectiveness of the module, and typically should be configured to minimize cost and air pressure drop.

In the embodiments shown in FIGS. 4A-4E, the cross-sectional views are plan views through the unit between frames 12 and 20 as represented by line A-A shown in FIG. 2.

FIG. 4A is a cross-sectional view of outer wrap(s) 120 of protective layers of fibers around functional layers 122. FIG. 4B is a cross-sectional view of outer wrap(s) 124 and inner wrap(s) 126 of protective layers of fibers around functional layers 128. The functional layers 122 and 128 are hollow fibers with water flow and provide for the evaporative cooling as described above. The protective layers 120, 124, and 126 are fibers without water flow. These fibers without water flow could be implemented, for example, with hollow fibers having no connection to water flow or solid fibers with no inner path for a fluid, or by not opening specific fiber ends of fibers or sealing specific fiber ends. This feature also results in a sacrificial layer of fibers on the module to protect the module from damage. The desired fiber edges or ends to be sealed could be selectively cut, crimped, melted, crushed, sealed, or folded over by a variety of equipment as the fiber mat is wound onto the frame. This would give precise control over how much of the fiber becomes a sacrificial layer with no water flow.

FIG. 4C is a cross-sectional view of an outer protective layer or wrap 130 around functional layers 132. The functional layers 132 are hollow fibers with water flow and provide for the evaporative cooling as described above. The protective material 132 could be implemented with, for example, a mesh, net, nonwoven, or another material that allows air flow to pass through. Alternatively, the protective material can also be used on the inside of the module shown in FIG. 4C. Preferably, the material for the protective layer is flame retardant. The protective layer material could also include an antibacterial coating to limit biological growth.

FIG. 4D is a cross-sectional view of outer protective layer(s) of fibers 134 around functional layers 136. FIG. 4E is a cross-sectional view of outer protective layer(s) of fibers 138 and inner protective layer(s) of fibers 140 around functional layers 142. The functional layers 136 and 142 are hollow fibers with water flow and provide for the evaporative cooling as described above. The protective layers 134, 138, and 140 are hollow fibers without pores, which can be implemented, for example, with porous hollow fibers that were treated to block or plug the pores so that water could not escape through the pores and with no weeping or seeping. This treatment can involve, for example, an additional coating onto the outer layers of fibers to block the pores and not allow water to escape. This treatment could be performed during the winding process or as a secondary coating step after the module is wound around the frame. Testing could be done to ensure air pressure drop and cooling efficiency are not negatively impacted by this additional coating.

The number of protective and functional layers shown in FIGS. 4A-4E are for illustrative purposes. More or fewer protective or functional layers could be used in these or other embodiments depending upon, for example, an optimized or desired design.

Although the embodiments shown in FIGS. 4A-4E each include an outer protective layer, these embodiments could alternatively each include an inner protective layer with an optional outer protective layer. The inner protective layers and optional outer protective layers could be any of the protective layers described with respect to FIGS. 4A-4E. These inner protective layers could be useful, for example, if the inside of the module is touched or handled during an installation process for the module. Furthermore, the embodiments shown in FIGS. 4A-4E can be combined in various ways to implement other types of protective layers. For example, the protective layers of fibers of FIGS. 4A or 4D could be used on the inside of the module shown in FIG. 4C along with the protective outer wrap. As another example, the protective wrap of FIG. 4C could be used on the inside of the modules shown in FIGS. 4A or 4D along with the outer protective layers of fibers. Also, the types of protective layers of fibers shown in FIGS. 4A and 4D can be combined as another type of protective layer.

Claims

The invention claimed is:

1. A unit for use in evaporative cooling, comprising: a first capped frame; a second open frame opposite the first frame; a plurality of mechanical supports between and coupled to the first frame and the second frame; a porous hollow fiber membrane extending around the mechanical supports between the first frame and the second frame to form an interior volume, and coupled to the first frame and the second frame; and a protective layer comprising an outer wrap of protective layers of fibers around the hollow fiber membrane, wherein the first and second frames are configured for flow of a liquid between the first and second frames via the membrane, and the membrane is configured to transport the liquid between the first and second frames and to provide for air flow through the membrane for evaporative cooling.

2. The unit of claim 1, wherein the protective layer further comprises an inner wrap of protective layers of fibers around the hollow fiber membrane.

3. The unit of claims 1 or 2, wherein the outer or inner wrap of protective layers of fibers comprises hollow fibers without liquid flow or solid fibers.

4. A unit for use in evaporative cooling, comprising: a first capped frame; a second open frame opposite the first frame; a plurality of mechanical supports between and coupled to the first frame and the second frame; a porous hollow fiber membrane extending around the mechanical supports between the first frame and the second frame to form an interior volume, and coupled to the first frame and the second frame; and a protective layer comprising an outer protective layer or wrap around the hollow fiber membrane, wherein the first and second frames are configured for flow of a liquid between the first and second frames via the membrane, and the membrane is configured to transport the liquid between the first and second frames and to provide for air flow through the membrane for evaporative cooling.

5. The unit of claim 4, wherein the protective layer further comprises an inner protective layer or wrap around the hollow fiber membrane.

6. The unit of claims 4 or 5, wherein the outer or inner protective layer or wrap comprises a mesh, a net, or a nonwoven.

7. A unit for use in evaporative cooling, comprising: a first capped frame; a second open frame opposite the first frame; a plurality of mechanical supports between and coupled to the first frame and the second frame; a porous hollow fiber membrane extending around the mechanical supports between the first frame and the second frame to form an interior volume, and coupled to the first frame and the second frame; and a protective layer comprising an outer protective layer of fibers around the hollow fiber membrane, wherein the first and second frames are configured for flow of a liquid between the first and second frames via the membrane, and the membrane is configured to transport the liquid between the first and second frames and to provide for air flow through the membrane for evaporative cooling.

8. The unit of claim 7, wherein the protective layer further comprises an inner protective layer of fibers around the hollow fiber membrane.

9. The unit of claims 7 or 8, wherein the outer or inner protective layer of fibers comprises porous hollow fibers treated to block or plug the pores in the fibers.

10. The unit of any of claims 1-9, wherein the plurality of mechanical supports comprises posts, and one of the posts comprises a pipe for transporting the liquid.

11. The unit of any of claims 1-9, wherein the membrane forms a continuous loop around the posts.

12. The unit of any of claims 1-9, wherein ends of fibers in the membrane are held by an adhesive with at least some of the ends being open.

13. The unit of any of claims 1-9, wherein the second frame includes an inlet, and the first frame includes an outlet.

14. The unit of any of claims 1-9, wherein the first or second frame includes an inlet, an outlet, a first channel for the inlet, a second channel for the outlet, and flow separation elements between the first and second channels.

15. The unit of claim 14, wherein the first or second frame includes a continuous channel.

16. The unit of any of claims 1-9, wherein the membrane has a pore size of 0.01-0.2 microns.

17. The unit of any of claims 1-9, wherein the membrane has a porosity of 25%-80%.

18. The unit of any of claims 1-9, wherein the membrane has a wall thickness of 15-75 microns.

19. The unit of any of claims 1-9, wherein the membrane has a knitting density of 35-53 fibers per inch.

20. The unit of any of claims 1-9, wherein the membrane has a knitting density of 15-65 fibers per inch.