EP4673700A1 - Evaporative coolers with water management features - Google Patents

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 cooling unit can have a rounded square or diamond-shaped cross-sectional shape. The cooling unit can include water management features for increasing efficiency, decreasing fouling, or for other purposes.

Description

EVAPORATIVE COOLERS WITH WATER MANAGEMENT FEATURES 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. In one embodiment, the unit has a rounded square cross-sectional shape. In another embodiment, the unit has a diamond-shaped cross-sectional shape. The unit can include water management features for increasing efficiency, decreasing fouling, or for other purposes. BRIEF DESCRIPTION OF THE DRAWINGS FIG.1A is a front sectional view of a rounded square shape evaporative cooling unit. FIG.1B 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. FIGS 3A-3D are graphs of a pressure drop and cooling effectiveness of an isolation cylindrical evaporative cooler based upon modeling data. FIGS.4A-4B are diagrams of in-line and staggered arrangement of square panels. FIG.4C is a diagram of an arrangement of triangular panels in a hexagonal lattice. FIG.4D is a diagram illustrating flow channeling effect in an array of panels. FIG.4E is a diagram of an annular frustum design to mitigate flow channeling. FIG.4F is a diagram of panels arranged in series. FIGS 5A-5D are graphs of a pressure drop and cooling effectiveness of an in-line arrangement of cylindrical evaporative coolers based upon modeling data. FIG.6A is a front sectional view of a diamond-shaped evaporative cooling unit. FIG.6B is a side sectional view of the diamond-shaped evaporative cooling unit. FIG.6C is a perspective view of the diamond-shaped evaporative cooling unit. FIG.7 is a diagram illustrating air flow through multiple stacked diamond-shaped evaporative cooling units. FIG.8A is a front view of an evaporative cooling unit with bifurcated water flow. FIG.8B is a side view of an evaporative cooling unit with bifurcated water flow. FIG.8C is a rear view of an evaporative cooling unit with bifurcated water flow. FIG.9 is a graph of the water pressure from modelling of the embodiment in FIGS.8A-8C. FIG.10A is a side sectional view of a design of an air duct for the Examples. FIG.10B is a perspective view of the design of the air duct for the Examples. FIG.11A is a graph showing the effect of fiber layer spacing on air pressure drop. FIG.11B illustrates spacing between fiber layers in a hollow fiber membrane. FIG.12A illustrates layers of fibers for different liquids in a first configuration. FIG.12B illustrates layers of fibers for different liquids in a second configuration. FIG.12C illustrates a configuration of distinct flow paths for two different liquids. 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. Rounded Square Shape Cooler FIGS.1A and 1B 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 1B, 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 corner rectangular bar, for example 0.75 inch X 0.25 inch where each corner is radiused with a 0.125 inch radius and set at a 45^o 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 corner 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 constructed of ABS plastic. Alternatively, the posts can be formed from stainless steel, aluminum, or fiberglass. Frames 12 and 20 are preferably constructed 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 (Lf) 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 20-60 fibers per inch and preferred of 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. For the construction shown in FIGS.1A and 1B, the velocity of the incoming air is greatly reduced by the enhancement of the area, and the local air velocity going across the fibers is approximately given by where is the panel frontal area of the construction, is the approximate perimeter of the fiber mat and is the length of the exposed fiber. The frontal area for the panel described herein is , being the length of the side as shown in FIG.1B. The local velocity can be reduced by increasing . The effect of other design variables, such as open area post can be obtained from numerical simulations or experiments. The velocity reduction factor is defined as ratio of the mean local velocity passing through the fiber stack and the air velocity incoming on the frontal face of the panel and is mathematically given by: The value of is the characteristic fixed for a given construction. The local velocity of air passing given by . The effectiveness of the panel (hollow fiber membrane) should increase and the pressure drop decrease with decreasing value of . The cooling effectiveness is given by: where is the inlet air and is the wet bulb at the inlet air The value of quantifies the fraction available evaporative cooling from the cooling device. The flow of air through the panels can also be in the reverse direction to the one shown in FIG.1B. The effect of on the air-side pressure drop is obtained using computational fluid dynamics (CFD) calculations, and its effect on the cooling effectiveness is obtained from a numerical simulation tool. The pressure drop of the panel construction described herein at for different values of and is shown in FIG.3A. The extent of the panel was fixed to and for design. The pressure drop reduces with increasing for a given because of reduction in . Similarly, for a given drop reduces by increasing the The cooling a single panel as a function of and is also shown in FIG.3B. The effectiveness increases with reduced and increased due to the associated reduction in or equivalently reduction in the local air passing the fibers . The pressure-drop is shown as a function of the face velocity in FIG.3C. The pressure drop is a quadratic function of as expected for a porous media formed by a set of cylinders. Therefore, the difference in the pressure drop between the two designs is more pronounced at higher velocities. The effectiveness is also shown for the two designs in FIG.3D which reduces with increasing velocity. The slope ( ) is more gentle for the design with longer since that design has a lower (or lower air velocity flowing across the fibers). The appropriate fiber length can be chosen based on the cooling requirement, the pressure drop constraints and the available space for the panel. In certain scenarios, multiple panels can be used together to handle larger cooling loads. Different panel arrangements are shown in FIGS.4A-4F. FIGS.4A-4B are diagrams of in-line and staggered arrangement of square panels. FIG.4C is a diagram of an arrangement of triangular panels in a hexagonal lattice. FIG.4D is a diagram illustrating air flow channeling effect in an array of panels. FIG.4E is a diagram of an annular frustum design to mitigate flow channeling. FIG.4F is a diagram of panels arranged in series. The modular arrangements shown in FIGS.4A-4F can provide for operations leading to water savings. In the square panel construction, the panel performance is demonstrated in a collection of panels using the in-line panel arrangement shown in FIG.4A. Such a panel arrangement can be used in large evaporative coolers or in air-handler units which typically have a duct with rectangular cross section. The fluid flow of a collection of panels changes slightly from the isolated panel construction as shown in FIG.4D. The fluid travels through the annular region between the adjacent panels on the outlet side of the set-of-panels. This flow-channeling effect has an additional pressure drop which is absent in the isolated panel construction. Panels can also be arranged in series to obtain higher evaporative cooling in the outlet air. The pressure drop for the collection of panels as a function of is shown in FIG.5A ( symbols) for the same panel design discussed with respect to 3D. In FIGS.5A-5D, square symbols are a case with no-channeling and are ones with channeling effect. FIG.5A also has the corresponding pressure-drop values for an isolated panel (x symbol). The square symbols are isolated panel results. The flow channeling is responsible for the larger pressure drop numbers compared to the isolated panel result. The pressure drop reduces with increasing for small values of until for this design as expected from the isolated panel result. However, the increasing with further increasing because of the flow channeling effect. The pressure drop changes with is small near value of about wherein the channeling effect is small is also sufficiently small. The 4.2” value is only for the construction described herein where W = 12”. The simulation results show that the effectiveness is not significantly affected by the channeling effect and should remain comparable to the isolated panel values. This effectiveness should also hold in practice as evaporation process is a local process that happens near the walls of individual fibers. The local fluid flow should affect the overall evaporation efficiency. The possibility of back flow into the array of fibers due to turbulence in the flow-channeling zone is in general small. FIGS.5A and 5B show, respectively, the pressure drop and cooling effectiveness of an in- line arrangement of cylindrical evaporative coolers as a function of the at (filled o symbols), and pressure drop and cooling effectiveness of an in-line of cylindrical evaporative coolers as a function of with (o symbols). The corresponding values of pressure drop and effectiveness for an isolated panel are also shown (x symbols). In all designs . FIGS.5C and 5D also show the pressure drop and effectiveness, respectively, as a function of (o symbols). The pressure drop for the isolated panel is also shown in the FIG.5C for comparison. The flow channeling effect leads to the higher numbers for the in-line arrangement of panels compared to the isolated panel. The slight reduction in the effectiveness is due to small changes in the flow field that will occur near the ends of the fiber. The flow channeling effects can be mitigated through an annular frustum type construction as shown in FIG.4E, where the mean gap of the channel is increased. Alternatively, a structure (e.g., a cone) can be located within the interior volume, such as against the capped end with the cone extending into the interior volume, in order to disrupt or otherwise change the air flow. Diamond-Shaped Cooler FIGS.6A, 6B, and 6C are, respectively, front sectional, side sectional, and perspective views of a diamond-shaped evaporative cooling unit 50 which includes a knitted fiber array. As shown in FIGS.6A-6C, unit 50 includes an open frame 54, mechanical supports such as posts 56, a porous hollow fiber membrane 62, and a capped frame 52. As an optional alternative, unit 50 can include another membrane wrapped around another set of mechanical supports inside of membrane 62 and spaced apart from it. Unit 50 can be portable unit or non-portable. The frames can have a groove, such as groove 55 shown in FIG.6C, for holding an edge of membrane 62. FIG.6C is shown without membrane 62 for illustrative purposes. As shown in FIG.6A, unit 50 has a diamond-shaped or rhombus-like cross-sectional shape. This exemplary diamond shape has a first pair of sides substantially parallel with one another and a second pair of sides substantially parallel with one another. The first pair of sides are substantially non-parallel with the second pair of sides. In particular, the cross-sectional shape includes an acute angle between two sides (e.g., angle at post 56) of 20^o or 30^o or greater and less than 90^o. The opposing acute angles are typically the same but could be different and still within the recited range of 20^o up to but less than 90^o. The sides can have equal lengths, as represented in FIG.6A, or one or more of the sides can have unequal lengths. If at least some of the sides have different lengths, then the opposing acute angles may be different. Unit 50 can have ports 58 and 60 for recirculation of water or other liquid through membrane 62. In the water recirculation system of FIG.2, for example, port 58 can be coupled to intake line 32 and port 60 can be coupled to return line 42 for circulation of water or other liquid through membrane 62. Alternatively, one of the frames can have both ports for circulation of the water or other liquid through the membrane and opposite frame. The following are exemplary dimensions for unit 50: a length between the frames of 195/8 inches; a width between opposing posts of 17 inches; and a height between opposing posts of 6.25 inches. A liquid such as water flows (64) between frame 54 and frame 52. An air stream or air flow is forced through membrane 62, as described below, to cool the air. Unit 50 preferably has no core, such that the interior volume formed by membrane 62 is open between the frames, for more effective air flow through the interior volume. Posts 56 extend between and are coupled to frames 54 and 52, either directly or through other mechanical structures. Posts 56 can have optional perforations such as perforation 15 shown in FIG.1A. The perforations can provide for air flow through the posts. Posts 56 can be connected to one another to provide more support, for example using a cross brace such as optional cross brace 18 shown in FIG.1A. One of the standoff posts can optionally be used as a pipe to facilitate the servicing and installation of the unit. Posts 56 can have the exemplary shapes and dimensions as described above with respect to the embodiment shown in FIGS.1A and 1B. Posts 56 and frames 54 and 52 can be constructed of the exemplary materials as described above with respect to the embodiment shown in FIGS.1A and 1B. Membrane 62 (e.g., a knitted fiber mat) extends around the four posts 56 (e.g., wrapped around) to form an interior volume and can be mechanically held in place between posts 56 and the frames, as illustrated in FIG.6A, or between an inner and outer frame assembly. Membrane 62 preferably forms a continuous loop around posts 56, as shown in FIG.6A, to create the interior volume; alternatively, membrane 62 can form a discontinuous loop around the posts. The hollow fibers in membrane 62 are potted at the two ends of the frame in groove 55 or in other ways. For example, the fibers of membrane 62 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 62 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 50 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 62 can include multiple layers, for example 27-33 layers wrapped around posts 56. Alternatively, a length of membrane 62 can be increased to reduce the number of layers. The membrane is hydrophobic (at least on the inside) for water. Air flows 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 20-60 fibers per inch and preferred of 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.7 is a diagram illustrating air flow through multiple stacked diamond-shaped evaporative cooling units. This example includes three diamond-shaped cooling units: a unit 66 having posts 68; a unit 70 having posts 72; and a unit 74 having posts 76. The cooling units 66, 70, and 74 can be held within a frame 80. Two of the posts between units 66 and 70, and between units 70 and 74, can be coupled to one another as shown. One of the posts in unit 66 and one in unit 74 can be coupled to frame 80 as shown. The cooling units 66, 70, and 74 can be constructed as described above with respect to cooling unit 50. The air flow is illustrated by lines 82 for the air flow through unit 66, lines 84 for the air flow through unit 70, and lines 86 for the air flow through unit 74. As shown, the air flows from outside of the cooling units through the membrane and the interior volume and then back outside the cooling units. The multiple stacked diamond-shaped evaporative cooling units can optionally have a filler material in the “dead space” region at the outlet air side. This filler material would help prevent eddies from developing in the flow field and allow for more of the humidified air to reach data servers, for example, improving efficiency of this cross-flow design. The filler material could be located between post 68 and frame 80, between post 76 and frame 80, between the posts coupled together between units 66 and 70, and between the posts coupled together between units 70 and 74. Bifurcated Water Flow FIGS.8A, 8B, and 8C 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 corners 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 1B 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 diamond-shaped evaporative cooling unit 50 shown in FIGS.6A-6C. 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 1B at the same gallons per minute flow rate. This change results from the water travelling twice as far through half as many fiber openings. FIG.9 is a graph of the water pressure from the modelling of this embodiment. Water Management Features The following describes various water management features for the coolers described herein and other such coolers. Additional water management features are described in the Examples. The water management features are used to control one or more aspects of the water or liquid used in the coolers. Some water management features can include the following: use of an anti-scalant in the system, particularly the water tank; biofilm prevention to limit mineral scaling and fouling; and a standard way to characterize the evaporative cooling versus cycles of concentration definition based on water concentration and not conductivity. “Cycles of concentration” (COC) measures the degree to which the solid impurities in the make-up water are concentrated in the recirculating water of an evaporative system. The higher this ratio, the more the impurities in the make-up water are being concentrated in the system water. It can be estimated by dividing the conductivity of the system water by the conductivity of the make- up, or by dividing the chloride of the system water by the chloride of the make-up. In this document, cycles of concentrations were calculated as the ratio of the concentration of a non-precipitating tracer in water relative to the concentration of dissolved solids in the make-up water (or the concentration of water at the onset of the evaporation process). The tracer could be total-dissolved solids or any other species that does not precipitate. Cycles of concentration value is preferably greater than 2, and generally less than 20. Cycles of concentration is calculated as follow: reading = Time = Concentration relative to make-up water concentration ( = Volume of water in the system at time (includes a variable tank volume and a constant that is present in the panel and the piping) = Water evaporated between time and = Bleed-off volume = maximum concentration the system (chosen for a given COC) = lower tank concentration during cycling. (concentration cycles between and for calculating COC Initially, , , = initial tank volume. The rest of the concentration is obtained through the following 2 equations: 1. If 2. If , water is bled-off by a volume , and the appropriate amount of make-up water the tank level to . The concentration at time is given by In the above equation, the terms on the left (C*(V_k – V_e,k – V_b)) represent the salts present in the water after bleed-off and the terms on the right (Ctap – (Vk – Ve,k – Vb))) represent the salts added from the make-up water. is the concentration relative to the first value, and is the direct COC value at time . For cycling the system, the bleed off volumes and make up water volumes are chosen such that and . Ensuring can be critical to the operation of the evaporative cooling system. Partially filled or empty fibers could result in precipitation of minerals from the water into the fibers. This precipitation then results in either blocking the hollow fiber and therefore not allowing recirculation of the water or blocking of the channels which allow for cooling. Both the previously stated conditions result in decreased performance of the module. Foreign debris which can either partially block or completely block the hollow fiber will also lead to restricted flow or loss of flow through the hollow fiber. Placement of an appropriate filter upstream of the cooling module can be important to prevent blockage of the fibers which will result in reduced performance of the media. Flow restrictions caused by occlusions from manufacturing imperfections which lead to reduced flow and thus increased retention time of the water in the hollow fiber can also lead to the formation of precipitates. Therefore, it can be important to ensure the ends of the fibers are adequately cut so no left over material, such as flaps or crushing of the fiber occurs, all of which restrict the flow through the fibers. A minimum flow rate should be maintained to ensure all of the hollow fibers will have a minimum water so none dry out. This flow rate changes as the evaporation rate of the media changes. For example, assuming a nominal evaporation rate of 1.5 gal/hr the flow rate must be greater than 0.05 gal/min, otherwise 100% of the water will evaporate in some of the layers before exiting the module. In general, minimum water flow rate should be at least the same as the evaporation rate. Tank placement can also be critical to ensure the hollow fibers remain filled. Placing the tank below the module, coupled with low flow rates (e.g., less than 0.25 gpm), under the experimental setup and conditions, results in the upper most layers either being partially filled or empty. This will result in precipitation of those fibers which will ultimately cause fouling of the system. One potential solution to tank placement is restricting the outlet to generate enough back pressure to fill the entire module. The pressure needed is depended on the flow rate and tubing selection. Water tank dimensions and shape can also be used as a water management feature. As demonstrated herein, recirculating small volumes of water have been seen to lead to less fouling at high COC, and generally water tank size should be minimized as much as possible, going as low as the volume of water contained inside the module and water pipes, tubing, and pump. Water tank design and shape should also be adjusted to minimize interface area between water and air, such as a small bladder. Another consideration of the media for operation of the cooler includes the layers gap arrangement (e.g., model, warp yarn, adhesive, different size fibers, and other such factors). Another feature involves controlling the spacing between fiber layers in an evaporative cooling module. One construction allows the fibers to “nest” into each other which cuts off or reduces airflow and, conversely, a spacing between fiber layers increases airflow with the theory that increasing the gap between layers will cause a sizable decrease in air pressure drop through the media. This theory was supported by modeling showing a noticeable decrease in air pressure drop as center-to-center spacing between fiber layers is increased. FIG.11A is a chart showing this effect, with the y axis showing inches of water of air pressure drop, the x axis showing air speed, and the legend showing different levels of center-to-center spacing between fiber layers. FIG.11B illustrates center-to-center spacing between fiber layers in a hollow fiber membrane, as represented by line 116 illustrating a spacing between fiber layers 112 and 114. Increased spacing can also possibly allow more efficient use of the fibers, which could lower the amount of fiber required in a module. Methods to do this could include: using a thicker warp yard during the knitting process, preventing the hollow fibers from laying as close to each other; laying down a spacer or several spacers in the machine direction during winding, including additional beads of hot melt at a desired thickness, yarn or string, a thin strip of tape (pinstriping tape, double sided, or others); and lowering the tension during winding to leave loft and spacing in the wind. Preferably, spacing between layers of fibers could be up to 10 times the diameter of an individual fiber. Some cooler designs described herein mostly have two fluid flow paths: one for water (flowing inside the hollow fibers), and one for air (flowing outside the hollow fibers). Optional fluid/liquid inlets could be integrated to the module to be able to connect the module to more than one water tank (if fouling occurs in one tank or array of hollow fibers for example), or to connect to a different fluid/liquid (not water) and bring new functionality. For example, a first liquid inlet could be used to introduce water through a first array of porous hollow fibers to provide air cooling performance, and a second liquid inlet could be used to introduce a liquid desiccant through another, independent second array of porous hollow fibers which lumen does not communicate with the lumen of the first array of hollow fibers. For example, the module could be constructed by alternating layers of a first array of hollow fibers and a second array of hollow fibers, so that the air could be chilled by the first array of hollow fibers and humidity could be controlled by the second array of hollow fibers. Layers of first and second arrays of hollow fibers could also be arranged by blocks of a first fiber array next to a block of a second fiber array. The number of layers for each array could be identical or different. The flow rate in each array could also be the same or different, depending on performance expected from the module. Optionally, additional inlet of fluids could be connected to additional layers/arrays of hollow fibers. FIGS.12A and 12B illustrate layers of fibers for different liquids. FIG.12A shows layers 120 for a first liquid interspersed with layers 122 for a second liquid different from the first liquid. FIG.12B shows a stack of layers 124 for a first liquid and a separate layer 126 for a second liquid different from the first liquid. FIG.12C illustrates a configuration of distinct flow paths for two different liquids. A first flow path for a first liquid has ports 128 and 130 for circulating the first liquid through the first flow path, and a second flow path for a second liquid has ports 132 and 134 for circulating the second liquid through the second flow path. The first liquid is different from the second liquid, and the two flow paths are distinct in that they are not in fluid communication with one another. The configuration shown in FIG.12C can be replicated to have more than two distinct flow paths. EXAMPLES These examples are merely for illustrative purposes only and are not meant to be limiting on the scope of the appended claims. Table 1. Material Abbreviation Description HFPM Hollow fiber porous membrane, 3M MEMBRANA Oxygenation Membrane Series X30-230 on a bobbin, ~30 micron wall thickness and an internal diameter of 230 microns, available from 3M Company, St. Paul, MN. Table 2. Air Handling Unit and Equipment Abbreviation Description Air blower Terrabloom 10 inch Inline Duct Fan available from Amazon Air temp/humidity Digital Hygrometer/Thermometer model 4085, 03313-66, NIST Traceable, sensor TRACEABLE Products, Webster, TX. Water pump High-head enclosed motor PP centrifugal pump; 11.4 GPM/43.2 ft, 115V, from Cole-Parmer HF-35 water filter 3M water filter, HF351.67 GPM flow rate, 1 micron nominal, from 3M company, St Paul, MN Air pressure meter Airdata multimeter ADM-880C, Shortridge Instruments, Inc, Scottsdale, AZ Air velocity VelociCalc, from TSI incorporated sensor Water tank and Plastic easy-drain tank, 10 gallon and stand, McMaster-Carr Supply stand Company Water flow meter Model A1Q9GMN025NA1 GPI water flow meter, from Great Plains Industries, Inc., Wichita, KS Water pressure 0 to 300 psi digital pressure gauge, SSI Technologies, Inc. gauge Water temperature Thermometer, Omega HH802U with K type thermocouple, Newark, sensor Chicago, IL Hot air gun 110V/14.5A Varitemp heat gun, model VT-750C, Master Appliance Corp, Racine, WI EXAMPLE 1 Construction of evaporative cooling unit Figure 1A and 1B show the evaporative cooling unit. This was constructed by assembling 4 posts (15.5 inch long, ¾ inch diameter – ABS from International Plastics) into bottom and top end frames (7.5 inch inner opening – ABS). An 18.5 inch-wide array of knitted HFPM was wound around the support posts and held in place with a bead of adhesive at the top and bottom edge. The evaporative cooling unit was built with 33 wraps of knitted HFPM. Next, an outer frame (ABS) was attached around both top and bottom fames and potted in place with adhesive. After the adhesive was set, an end cap was attached to each end of the inner/outer frame assembly to form a ¼ inch water channel that communicated with the HFPM. Tapped ports (1/4 inch NPT) were made on the top and bottom of the end caps to facilitate water flow to and from the evaporative cooling unit. A 1/8 inch aluminum cap was attached to the downstream side frame of the evaporative cooling unit closing off this end of the unit. Testing Equipment To characterize the performance of evaporative cooling unit, an air handling unit consisting of an air duct with enclosure, closed loop water recirculation system, and measurement equipment was assembled. Air duct, enclosure, and mounting backplane The design for the air duct is shown in FIGS.10A and 10B in side sectional and perspective views, respectively. A plexiglass enclosure with a backplane for mounting the evaporative cooling unit was built to attach to the inlet side of the air duct. The evaporative cooling unit was attached with the open side aligned to a cut-out hole of the backplane to allow for airflow into the unit. Air circulation/heating equipment and air measurement devices To enable air movement, two air blowers were attached to the outlet side of the end of the air duct. To provide heated air, a hot air gun was inserted into the inlet side of the air duct. The gun was operated on the high setting. Air temperature and humidity sensors were installed at the inlet and outlet of the air duct. An air pressure meter was also installed to measure the pressure drop across the evaporative cooling unit. Closed loop water recirculation system – FIG.2 A water recirculation system was installed to cycle water through the evaporative cooling unit. A 10-gallon plastic water tank with stand (30) was used to hold the water. The gravity feed under the tank was plumbed with plastic tubing to deliver water to the water pump (34). The pump sent the water through the inlet water flow meter, water filter (36), water pressure gauge, and finally into the water inlet of the evaporative cooling unit (10). Water travelled through the HFPM to the outlet side of the evaporative cooling unit. Plastic tubing was attached and connected to an outlet water pressure gauge, outlet water flow meter, and finally connected to the side of the water tank. This formed a closed system to recirculate water through the system. A water temperature sensor with K-type thermocouple was used to monitor the temperature of water in the tank. Testing Conditions and Results Water was recirculated through the 33 layer evaporative cooling unit at 1 gallon/minute. Inlet water pressure was 8.5 psi and outlet water pressure 3 psi. The water temperature in the tank was 74.9 deg F. The blowers were turned on to setting 6. The air velocity was measured and a volumetric flow of 715 ft³/min was calculated. An air pressure of 0.78 inches of water was measured. The inlet and outlet air temperatures and % relative humidity values were measured as shown in Table 3. The wet bulb temperature was determined to be 68 deg F. The cooling effectiveness was calculated according to equation 3, expressed as a percentage. Table 3. Results - Measured Air Properties Inlet Air Temp Inlet Air Outlet Air Outlet Air % Cooling (deg F) %RH Temp %RH Effectiveness (deg F) 84 42.4 72.5 80.9 71.9 Water Management Features EXAMPLE 2 This feature demonstrates an active control of cooling effectiveness by regulating the water flow rate in an evaporative cooler, for example within the flow path shown in FIG.2. Such active control is aimed at handling aggressive loads for short periods of time or changes in the ambient conditions (temperature and relative humidity) without compensating the cooling performance of the system. This technique would be most useful either when the water tank can be maintained at a nearly constant cold temperature (e.g., an underground tank) or if the tank capacity is much larger than the total amount of water used for cooling. This feature uses the design of the evaporative coolers described herein. However, this feature could be used for any evaporative cooler, and the degree of tunability will vary depending on the specific design of the cooling solution. Actively controlling the effectiveness of an evaporative cooler is useful to adjust to changing ambient air conditions. The need of the evaporative cooler is to retain the outlet air temperature near a set value. Given the water tank temperature retained at a fairly constant temperature, the water flow rate can be adjusted to provide cooling for variations in the inlet operating conditions which are the inlet air velocity, temperature, and relative humidity. The air velocity might need to increase during peak hours, the relative humidity could increase suddenly during an operating cycle, or the ambient temperature could significantly increase. In all these cases, an evaporative cooler could be used to provide additional (or reduced) cooling by changing the flow rate of water going through the cooler. Controlling the cooling through water flow control can also satisfy cooling needs in regions where high temperature and high humidity conditions are only present for a short duration of time without the need to have additional cooling systems or change the overall pumping system. The evaporative cooler described herein is used to describe the active cooling effectiveness control technology. For the purpose of demonstrating this feature, the velocity of the incoming air was restricted below 5 m/s, the inlet air temperature and relative humidity were set at 80^o F and 30% respectively, and the inlet water temperature was set at the wet bulb temperature at these inlet conditions. An evaporative cooler described herein uses cold water flowing through a set of porous fibers which allows both convective and evaporative cooling to take place at the water-air interface. This exchange of heat between air and water changes the local temperatures of air and water in a non-trivial manner and requires the simultaneous solution of the fluid, heat and mass transfer equations. In this analysis the inlet water temperature ( ) is assumed to be constant and equal to the wet bulb temperature based on the inlet air temperature and relative humidity. The overall heat flux, q ([W/m²]), at any point inside the cooler is given by where is the local air temperature, is the local water temperature, is the heat transfer coefficient that quantifies the convective (or sensible) is the latent heat of evaporation and is the evaporative flux that depends on , humidity of air and the surface of the membrane. Both and can be obtained from experiments, computational fluid dynamics computations (CFD) calculations or existing correlations. The water heats (or cools) depending on the value of and the rise in temperature across each fiber is which is approximately given by where is the dimension along the fiber length, is the outer radius of the fiber, is the water flow rate and is the specific heat of water. Equation (2) suggests that the temperature drop across the fiber is inversely proportional to the water flow rate . Thus, increasing the water flow rate will control the temperature gradient across the fiber length and also control the average water temperature in the fibers. The average water temperature the value of the heat flux , as per equation (1), and thus allows for control of the cooling capacity of the evaporative cooler. EXAMPLE 3 Hollow fiber membrane systems used for evaporative cooling with water are prone to fouling which can compromise performance. Fouled membranes will have lower cooling effectiveness (i.e., the ability to humidify and cool air streams), potentially higher water pressures which can burden equipment, and in extreme cases can become non-functional. Examples of fouling includes fiber clogging due to particles, biological growth on the surfaces, and nucleation and growth of minerals onto the surfaces of the fiber. Several examples of minerals in water which can foul fibers are calcite (CaCO3), MgCO3, gypsum (hydrate of CaSO4), iron oxides, and copper oxides. Because of the relatively low solubility of calcite in water, and its inverse solubility with temperature, this material is a primary concern for fouling in fibers. There are existing approaches to mitigating calcite formation, for example ion exchange resin systems and scale inhibitors are frequently used to remove or isolate calcium from the water. However, ion exchange resins can require large amounts of salts to regenerate the ion exchange bed, which can be significant added cost. Scale inhibitors or other added chemicals may not be allowed if they are not compatible with the water permits required to discharge wastewater from the facility. Unexpectedly, a filtration solution that was believed to only address particle filtration and removal of chlorine was found to also inhibit fouling in a hollow fiber evaporative cooling system. This filter may be removed and replaced from the system with minimal waste generated. A carbon-based water filter with no added chemicals to mitigate scale enabled long term operation of a hollow fiber media panel. The experiment was run on a cooler described herein for 62 days (approximately 8 hours/day) without loss in performance. During that time, the levels of salts in the water increased significantly, as indicated by ICP MS analysis. Calcium and magnesium levels were also highly elevated, as shown by titrations to determine total hardness. The filter was removed on the 63^rd day of operation. Quickly, the inlet water pressure increased from 7.6 to 9.1 psi and the cooling effectiveness dropped. An attempt was made to recover the panel by reverse-flow flushing water through the panel, however this was unsuccessful. Analysis of the fibers from the fouled panel revealed the presence of CaCO3. The experiment showed that the filter prevented fouling. Analysis of the filter media showed the presence of calcium and magnesium. However, analysis of water samples taken from the tank during the experiment also revealed significant amounts of calcium and magnesium. The filter may have served to capture nucleating particles, which prevented the ability of calcite to form. This may be another unexpected benefit – the filter capacity may be much larger since a significant amount of the calcium and magnesium need not be removed from the water to prevent fouling. The filter is preferably located before the water inlet to the module, for example before inlet 38 to unit 10 as shown in FIG.2. However, the filter could be located elsewhere in the water path between the tank and unit (or module). Also, the filter can be used in addition to or in place of filter 36, for example. Exemplary types of filters for this feature include the following: carbon-based, polypropylene, fiberglass, nonwoven, depth, and pleated. Filter porosity is preferably from 1 micron to less than 200 micron. Also, an anti-scalant can be added into the make-up water stream. EXAMPLE 4 An experiment was performed on an air handling unit (AHU) having a cooler as described herein with the capability of heating the air to a temperature of 90^o – 95°F at 700 cfm. A 14 gallon tank supplied the water to the cooler at a flow rate from 0.25 gal/min to 2+ gal/min. Conductivity and water temperature were measured in line at 1 min intervals. The pH and flow rate were measured at 30 – 60 min intervals. The pH was measured at the tank. Inlet and outlet humidity and air temperature were measured every 5 min. Air pressure across the cooler was also monitored. Several water chemistries were identified and tested on AHU system. The SI and LSI values were calculated along with their associated precipitation times. Values less than -0.3 indicated a low precipitation potential and values greater than 0.3 indicated a greater precipitation potential. The calculated aragonite formation potential was in agreement with the observed aragonite formation as indicated by hour to turbidity. Aragonite has been identified as the major type of precipitation associated with the cooler operation. To maximize the life cycle of any given type of water, several operational conditions have been identified which can affect the rate of precipitation formation in the system. Evaporation rate has been identified as a potential primary source of aragonite formation. At low fan speeds and all else equal, approximately 273 cfm and an evaporation rate of approx.0.7 gal/hr, one type of water, was operated for 300+ hours without cooler efficiency degradation. At 700 cfm and approx.1.4 gal/hr, the same water reached around 10 hours of operation before aragonite formation occurs. While aragonite formation does not have an immediate, measurable, effect on efficiency, a noticeable build in water inlet pressure from 6 psi to greater than 15 psi was observed within several hour after precipitation occurs. Secondary to evaporation rate, both flow rate and water pressure were investigated to determine their effect on precipitation rate. The following were identified as the effect of water inlet pressure and flow rate on fouling. A 2 gal/min flow rate resulted in the least amount of cycles, while a 0.5 gal/min flow rate resulted in the greatest cycles achieved. Keeping the pressure constant while varying the flow rate had little effect on the cycle of concentration achieved before fouling occurred. Holding the flow rate constant while increasing the water inlet pressure, resulted in a decrease in number of cycles achieved before fouling. This data suggested that pressure versus flow rate, effects the number of cycles that can be achieved before fouling occurs. At flow rates lower than 0.35 gal/min there was insufficient pressure to keep the entire cooler filled with water. This allowed air from the outside to flow through the fibers, causing significant air bubbles inside the water lines. In order to run at flow rates less than 0.35 gal/min, the water level had to be raised above the cooler. Moving the water level higher, allows the cooler to be completely filled with water during operation. EXAMPLE 5 Examples of fouling in hollow fiber membranes includes clogging due to particles, biological growth on the surfacers, and nucleation and growth of minerals onto the surfaces of the fiber. Several examples of minerals in water which can foul fibers are calcite (CaCO3), MgCO3, gypsum (hydrate of CaSO4), iron oxides, and copper oxides. During use, water is cycled through the hollow fiber panel and the water tank. As water evaporates, concentration of salts and minerals dissolved in water increases, until they reach their precipitation points. Salt precipitation can happen in tank, tubing, panel channels or hollow fibers, and can lead to fouling of the hollow fiber system, as precipitated solids can plug hollow fiber, or line/channels leading to hollow fibers. To limit precipitation risks, there are known methods such as softening, dilution with RO water, filtration, or additives (such as anti-scalants). Most of these methods have undesirable impact on the environment and cost. Evaporative cooling customers are interested in identifying better solutions to increase the number of concentration cycles, and lower the frequency of fouling event and cleaning/flushing cycles. These features cover several characteristics of the water tank design, for example tank 30 shown in FIG.2, that were identified for their beneficial impact on time between salt precipitation occurrences: (a) Unexpectedly, the size of the water tank was found to have a significant impact on the time it takes for the system to foul: when operating at low water flow (0.25-0.3 gpm), the use of a smaller water tank has led to a significant increase in the time it takes for CaCO3/Mg to precipitate, even though the use of a smaller water tank leads to higher rate of mineral concentration. (b) The position of the input and outlet ports to the water can be optimized to contain precipitated minerals (CaCO3, MgCO3, etc.) on the bottom of the tanks and prevent them from being circulated to the narrower tubing, channels and hollow fibers. Positioning the water inlet port above the outlet port is also a helpful practice. (c) Minimizing the tank water surface exposure to atmospheric air (especially CO2) is also a helpful practice to limit CaCo3 and MgCO3 precipitation as much as possible. This could be done by tank shape (e.g., small top opening, small diameter tank), preventing contact between water surface and atmospheric air by the use of a film, floating bubbles, or other techniques. In order to study the water parameters effect on fouling, tank size, geometry, and water flow rate were investigated. To test the impact of tank volume on fouling, initial water tank volumes from 14 gallon to 1.5 gallons were tested. It was observed that a decrease in initial volume resulted in a decreased time to observed fouling, until 1.5 gallons was tested. Unexpectedly, at an initial tank volume of 1.5 gallons, the system was able to be upcycled to 5.5 cycles of concentration and operated for 15 hours before precipitation was observed. The tank geometries effect on time to fouling was also investigated. Initially, the water inlet (water pulled from the tank to the module) was placed at the lowest point in the tank, and the water outlet (water returning from the module to the tank) was placed at the highest point in the tank. Having the water outlet elevated above the waterline resulted in a turbulent environment in the tank. This resulted in a time to precipitate of approximately 11 hrs with a start volume of 14 gallons. Once precipitation did occur, it quickly coated all surfaces in contact with water.

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, 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; and a water management feature for use in controlling one or more aspects of the liquid or evaporation, or both liquid and evaporation.

2. The unit of claim 1, wherein the plurality of mechanical supports comprise posts.

3. The unit of claim 2, wherein the plurality of posts form a square shape with rounded corners.

4. The unit of claim 2, wherein the plurality of posts form a polygonal shape.

5. The unit of claim 2, wherein one or more of the posts are perforated.

6. The unit of claim 2, wherein the posts are composed of a plastic material.

7. The unit of claim 2, wherein one of the posts comprises a pipe for transporting the liquid.

8. The unit of claim 1, wherein the membrane forms a continuous loop around the posts.

9. The unit of claim 1, wherein the membrane has a plurality of layers.

10. The unit of claim 1, wherein the liquid is water.

11. The unit of claim 1, wherein the second frame is configured for attachment to an air duct.

12. The unit of claim 1, further comprising a pump coupled to the first frame and the second frame for circulating the liquid through the membrane.

13. The unit of claim 12, further comprising a filter coupled to the pump.

14. The unit of claim 1, wherein the unit is configured to circulate air from the interior volume through the membrane.

15. The unit of claim 1, further comprising a cross brace between and coupled to the mechanical supports.

16. The unit of claim 1, wherein the interior volume is open between the first frame and the second frame.

17. The unit of claim 1, wherein the first and second frames are composed of a plastic material.

18. The unit of claim 1, wherein ends of fibers in the membrane are held by an adhesive with the ends being open.

19. The unit of claim 1, wherein the second frame includes an inlet, and the first frame includes an outlet.

20. The unit of claim 1, 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.

21. The unit of claim 20, wherein the first or second frame includes a continuous channel.

22. The unit of claim 1, wherein the membrane has a pore size of 0.01-0.2 microns.

23. The unit of claim 1, wherein the membrane has a porosity of 25%-80%.

24. The unit of claim 1, wherein the membrane has a wall thickness of 15-75 microns.

25. The unit of claim 1, wherein the membrane has a knitting density of 35-53 fibers per inch.

26. The unit of claim 1, wherein the water management feature comprises filtering the liquid.

27. The unit of claim 1, wherein the water management feature comprises controlling cycles of concentration of the liquid.

28. The unit of claim 1, wherein the water management feature comprises controlling a flow rate of the liquid.

29. The unit of claim 1, wherein the water management feature comprises controlling a size of a tank containing the liquid.

30. The unit of claim 1, wherein the water management feature comprises controlling a geometry of a tank containing the liquid.

31. The unit of claim 1, wherein the water management feature comprises using an anti-scalant in the unit.

32. The unit of claim 1, further comprising a first flow path for the liquid and a second flow path for another liquid different from the liquid, wherein the first flow path is not in fluid communication with the second flow path.

33. The unit of claim 32, wherein the liquid is water and the another liquid is a liquid desiccant.

34. The unit of claim 9, further comprising controlling a spacing between the plurality of layers.

35. A unit for use in evaporative cooling, comprising: a first frame; a second 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, 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, wherein the first and second frames with the mechanical supports form a diamond-shaped cross-sectional shape of the unit; and a water management feature for use in controlling one or more aspects of the liquid or evaporation, or both liquid and evaporation.

36. The unit of claim 35, wherein the plurality of mechanical supports comprise posts.

37. The unit of claim 36, wherein one or more of the posts are perforated.

38. The unit of claim 36, wherein the posts are composed of a plastic material.

39. The unit of claim 36, wherein one of the posts comprises a pipe for transporting the liquid.

40. The unit of claim 35, wherein the membrane forms a continuous loop around the posts.

41. The unit of claim 35, wherein the membrane has a plurality of layers.

42. The unit of claim 35, wherein the liquid is water.

43. The unit of claim 35, further comprising a first port for receiving the liquid from a pump and a second port for returning the liquid.

44. The unit of claim 35, wherein the unit is configured to circulate air from outside of the unit through the membrane and the interior volume and then back outside the unit.

45. The unit of claim 35, wherein the first and second frames are composed of a plastic material.

46. The unit of claim 35, wherein ends of fibers in the membrane are held by an adhesive with the ends being open.

47. The unit of claim 35, wherein the membrane has a pore size of 0.01-0.2 microns.

48. The unit of claim 35, wherein the membrane has a porosity of 25%-80%.

49. The unit of claim 35, wherein the membrane has a wall thickness of 15-75 microns.

50. The unit of claim 35, wherein the membrane has a knitting density of 35-53 fibers per inch.

51. The unit of claim 35, wherein the diamond-shaped cross-sectional shape has a plurality of sides of equal lengths.

52. The unit of claim 35, wherein the diamond-shaped cross-sectional shape has a plurality of sides, and at least two of the sides have different lengths.

53. The unit of claim 35, wherein the water management feature comprises filtering the liquid.

54. The unit of claim 35, wherein the water management feature comprises controlling cycles of concentration of the liquid.

55. The unit of claim 35, wherein the water management feature comprises controlling a flow rate of the liquid.

56. The unit of claim 35, wherein the water management feature comprises controlling a size of a tank containing the liquid.

57. The unit of claim 35, wherein the water management feature comprises controlling a geometry of a tank containing the liquid.

58. The unit of claim 35, wherein the water management feature comprises using an anti-scalant in the unit.

59. The unit of claim 35, further comprising a first flow path for the liquid and a second flow path for another liquid different from the liquid, wherein the first flow path is not in fluid communication with the second flow path.

60. The unit of claim 59, wherein the liquid is water and the another liquid is a liquid desiccant.

61. The unit of claim 41, further comprising controlling a spacing between the plurality of layers.