Evaporative cooler using hollow fibers to produce cooling water and having performance factors

Abstract

A unit for evaporative cooling includes a first frame with a cover and an open second frame opposite the first frame. A post is located between and coupled to the first and second frames. A porous hollow fiber membrane extends around the post between the first frame and the second frame and is coupled to the first frame and the second frame to form an internal volume. The first frame and the second frame are configured for flowing water between the first frame and the second frame via the membrane. The membrane is configured to deliver water between the first frame and the second frame and to allow airflow from the interior volume through the membrane for evaporative cooling. The cooling unit may generate cooling water. Cooling unit performance factors can be controlled through water flow, air flow, water temperature and pressure. The unit can control air humidification.

Description

Background Technology

[0001] Evaporation is a low-cost and energy-efficient cooling method used to regulate temperatures in data centers, food processing plants, or office buildings. Currently, cellulose pads are used for large-scale evaporative cooling in applications such as data centers. Hot, dry air is cooled by evaporating water flowing through the cellulose pad, resulting in cool, humid air at the output. This type of cooling requires large quantities of water, and the medium must be kept either dry or humid to prevent degradation due to scaling or crystallization. The humidity level of the air discharged into the data center can be controlled using louvers or dampers that guide the incoming air through only a portion of the medium or completely around the medium in a bypass duct. Therefore, there is a need for improved evaporative cooling systems.

[0002] Data centers are exploring options for cooling using evaporative cooling. In evaporative cooling, two fluids are present: air and water. As the water evaporates, more moisture accumulates in the air. Evaporative cooling can be done directly or indirectly. Evaporative cooling can be used to cool air. This air is used directly to cool the data center lobby. This is one definition of direct evaporative cooling in the HVAC industry. For indirect evaporation used to cool building air, one definition is the presence of two physically separate air sources, and the entire system typically includes an evaporative cooler and a heat exchanger. The heat exchanger can be air-to-air or air-to-liquid. The cooling fluid (air or water) from the evaporative cooler is used in the heat exchanger to cool the building air. Summary of the Invention

[0003] A unit for evaporative cooling includes a covered first frame and an open second frame opposite to the first frame. A plurality of mechanical supports are located between and connected to the first and second frames. A porous hollow fiber membrane extends around the supports between and connected to the first and second frames to form an internal volume. The first and second frames are configured to allow water to flow between them via the membrane. The membrane is configured to transport water between the first and second frames and to allow airflow through it for evaporative cooling.

[0004] In one embodiment, the unit generates cooling water through an evaporative cooling process. In another embodiment, the unit's performance factor can be controlled by water flow rate, air flow rate, water temperature, and pressure. In yet another embodiment, the unit can control air humidification. Attached Figure Description

[0005] Figure 1A This is a front sectional view of a rounded square evaporative cooling unit.

[0006] Figure 1B This is a side sectional view of a rounded square evaporative cooling unit.

[0007] Figure 2 This is a diagram of the water path through the evaporative cooling unit.

[0008] Figure 3 This is a side view of the air handling unit.

[0009] Figure 4 This is a diagram of a water recirculation system used in a flat panel evaporative cooling unit. Detailed Implementation

[0010] Implementation schemes include evaporative coolers using membranes with hollow fibers having porous walls, which provide enhanced evaporative cooling and reduced pressure drop. This construction includes an array of braided fibers wound into annular cylinders, rounded squares, or other shapes and sealed at both ends to allow liquid water to flow through the fibers. One end of the annular cylinder is open to allow air to pass through, and the other end is capped, forcing air to flow through the fiber array to cool the incoming air. This construction offers ease of manufacture compared to folded designs. This construction also improves panel performance by systematically increasing the length of the panel. Additionally, adding folds in the fiber array surrounding the cylinder also improves performance due to the increased surface area. This construction with hollow fibers without porous walls can also be used as a heat exchanger. When the air is very humid, porous-walled fibers can also be used as a heat exchanger.

[0011] An example of an evaporative cooling unit is disclosed in PCT application publication No. WO 2023 / 037287, which is incorporated herein by reference in its entirety.

[0012] Rounded square cooler

[0013] Figure 1A and Figure 1B These are front and side sectional views of the panel structure of the evaporative cooling unit 10. As an example, the structure includes an array of woven fibers in a rounded square shape. Figure 2 The image shows a perspective view of unit 10. (Example) Figure 1A and Figure 1BAs shown, this panel configuration is also applicable to any other cross-sectional shape. Unit 10 includes a front open frame 12, mechanical supports such as pillars 14, a porous hollow fiber membrane 16, and a covered rear frame 20. Frame 12 is open because it has openings to allow air to pass through or flow into unit 10. Frame 20 is covered, at least partially and preferably completely blocking the passage or flow of air within unit 10. As an alternative, unit 10 may include another membrane that wraps around and is spaced apart from another set of mechanical supports inside membrane 16. Unit 10 may be a portable or non-portable unit.

[0014] A liquid, such as water, flows between the front frame 12 and the rear frame 20 (22). An airflow or airflow (24) from the front frame 12 is forced by the rear frame 20 through the fibers of the membrane 16 to cool the air. Alternatively, air may flow in another direction from the outside of the unit 10 to the internal volume. The unit 10 preferably does not have a core, such that the internal volume is open between the frames to allow airflow through the internal volume more efficiently. Air may be induced into a radial flow through the fibers of the membrane 16. The frame 12 may be mounted horizontally in an air duct and has mechanical structures for attachment to the air duct, wherein a fan draws air from the outside through the membrane 16.

[0015] Multiple units (each configured as or similar to unit 10) can be connected in series via internal volumes as a way to increase the membrane surface area without significantly altering the module design.

[0016] Column 14 extends directly between and connects to frames 12 and 20, either directly or via other mechanical structures. Column 14 may have optional perforations, such as perforations 15. For illustrative purposes, only a single perforation 15 is shown; columns may have multiple perforations while maintaining mechanical stability. The perforations allow airflow through the column. Columns 14 may be connected to each other to provide additional support. For example, columns 14 may include optional crossbeams 18 located between frames 12 and 20 (such as at the midpoint between the frames or elsewhere). Crossbeams 18, or other mechanical connections between columns 14, can deflect airflow through the internal volume of unit 10. One of the supported columns may optionally be used as a conduit to facilitate unit maintenance and installation.

[0017] Although the module is shown as having four columns 14, the module may alternatively include more or fewer columns configured to provide different cross-sectional shapes. For example, the module may have only two columns to provide a substantially flat panel of membrane 16, or it may have multiple columns arranged along the same plane and configured to provide a substantially flat panel of membrane 16.

[0018] Column 14 may have a circular cross-sectional shape as shown, or other shapes such as the following alternatives and options. The column may be a rounded rectangular strip, for example, 0.75 inches × 0.25 inches, wherein each corner is rounded with a radius of 0.125 inches and is set at a 45-degree angle to the circumference of the square. o Angle. A column can be a folding column, in which a 1.5-inch × 0.125-inch sheet of material is folded so that the cross-section becomes 0.75-inch × 0.25-inch. A column can be a corner column, which is a 0.5-inch × 0.5-inch × 0.125-inch angle iron “L” shape. For example, one or more columns can be hollow tubes to facilitate all water connections at one end (frame).

[0019] Column 14 is preferably made of ABS plastic. Alternatively, the column may be formed of stainless steel, aluminum, or fiberglass. Frames 12 and 20 are preferably made of ABS plastic. Alternatively, the frames may be formed of PVC, styrene, polycarbonate, or metal. The material of unit 10 may optionally have a flame retardant (FR) rating.

[0020] A membrane 16 (e.g., a woven fiber mat) extends (e.g., wraps) around four posts 14 to form an internal volume, and can be positioned between the posts 14 and the frame (e.g. Figure 1A (As illustrated) or mechanically held in place between the inner frame assembly and the outer frame assembly. The membrane 16 preferably forms a continuous ring around the pillar 14, as shown. Figure 1A As shown, this creates an internal volume; alternatively, membrane 16 may form a discontinuous ring around a column. Hollow fibers in membrane 16 are encapsulated at both ends of a frame. For example, the fibers of membrane 16 may be held in epoxy resin within the frame, with the open ends of the hollow fibers receiving water or other liquids. As another example, the ends of the fibers in membrane 16 may be held by an adhesive, which can then be cut to open the fiber ends, and end plates can be fixed to the open ends of the fibers. Alternatively, unit 10 may have a frame configuration in which the frame supports the open ends of the hollow fibers, which are then attached to an air handling unit in the system having water channels for circulating water through the hollow fiber membrane.

[0021] The membrane 16 may comprise multiple layers, such as 27 to 33 layers surrounding the pillar 14. Alternatively, the length (L) of the membrane 16 may be increased. fTo reduce the number of layers, the membrane (at least internally) is hydrophobic. Air flows from the front of the panel through the fibers, evaporating and cooling the air at the fibers. The airflow through the fibers is reduced due to the increased surface area. Exemplary parameters for hollow fiber membranes are as follows: pore size from 0.01 micrometers to 0.2 micrometers, preferably from 0.03 micrometers to 0.04 micrometers; porosity from 25% to 80%; wall thickness (single layer) from 15 micrometers to 75 micrometers, preferably from 25 micrometers to 50 micrometers; and weaving density from 15 to 65 fibers per inch, or from 20 to 60 fibers per inch, or from 35 to 53 fibers per inch. Examples of hollow fiber membranes are disclosed in U.S. Patent No. 9,541,302. Examples of hollow fiber membranes also include the following products: LIQUI-CEL MM series membrane contactors (product ID: B5005009013) from 3M Company and LIQUI-CEL SP series membrane contactor boxes (product ID: B5005009016) from 3M Company.

[0022] Figure 2 This is a diagram of a water recirculation system for an evaporative cooling unit 10. A water tank 30 supplies water to a pump 34 via an inlet line 32, which circulates the water through a water filter 36 to an inlet 38 in a frame 12. An outlet 40 on the frame 20 supplies water to a water return line 42 returning to the water tank 30. Alternatively, water may flow in the opposite direction while the frame 20 receives water. Optionally, a frame may include both an inlet and an outlet. The water may have a specific type of quality. The water recirculation system may optionally include an anode / cathode feature to control mineral buildup within the water loop.

[0023] for Figure 1A and Figure 1B The structure shown indicates the speed at which air enters. The velocity decreases significantly due to the increase in area, and the local air velocity through the fiber is approximately given by the following formula.

[0024]

[0025] in, It is the front area of ​​the constructed panel. It is the approximate perimeter of the fiber mat, and This refers to the length of the exposed fibers. The front area of ​​the panel described in this article is... , For example Figure 1B The length of the edge shown. Local velocity. By increasing The velocity reduction is systematically reduced. The effects of other design variables (such as opening area and column size) can be obtained from numerical simulations or experiments. The velocity reduction factor λ is defined as the ratio of the average local velocity through the fiber stack to the air velocity entering the front of the panel, and is mathematically given by the following formula:

[0026]

[0027] The value of λ is a characteristic feature of the design and is fixed for a given construction. The local velocity of air through the fiber is approximated by... Given that as the λ value decreases, the efficiency of the panel (hollow fiber membrane) should increase and the pressure drop should decrease. Air cooling efficiency. It is given by the following formula:

[0028]

[0029] in It is the inlet air temperature. It is the outlet air temperature, and It is the wet-bulb temperature under the conditions of inlet air temperature and relative humidity. The value is quantified from the maximum available evaporative cooling fraction of the cooling unit. The airflow through the panel can also be... Figure 1B The opposite direction shown.

[0030] Example

[0031] These embodiments are for illustrative purposes only and are not intended to limit the scope of the appended claims.

[0032]

[0033]

[0034]

[0035] equipment

[0036] Construction of a rounded square evaporative cooling module

[0037] Figure 1A and Figure 1BThe evaporative cooling unit is shown. It is constructed by assembling four posts (15.5 inches long, ¾-inch diameter (ABS, from International Plastics)) into a bottom frame and a top frame (7.5-inch inner opening (ABS)). An 18.5-inch wide array of woven HFPM is wound around the support posts and held in place with adhesive droplets at the top and bottom edges. The evaporative cooling unit consists of 33 turns of woven HFPM. Next, the outer frame (ABS) is attached around the top and bottom frames and sealed in place with adhesive. After the adhesive has cured, end caps are attached to each end of the inner / outer frame assembly to form a ¼-inch water channel communicating with the HFPM. Threaded ports (1 / 4-inch NPT) are formed at the top and bottom of the end caps to allow water to flow in and out of the evaporative cooling unit. A 1 / 8-inch aluminum cap is attached to the downstream side frame of the evaporative cooling unit, sealing that end of the unit.

[0038] Construction of a planar evaporative cooling panel

[0039] A flat panel module measuring approximately 4 inches × 17 inches × 0.5 inches is constructed using 30 layers of knitted HFPM to fit a small AHU. The open fiber area is 16 inches × 3.5 inches. The frame is 19.5 inches × 4.5 inches.

[0040] Air handling unit setting 1

[0041] In another implementation scheme, such as Figure 3 As shown, an air handling unit (AHU) is assembled to test the performance of a rounded square evaporative cooler. The AHU includes a first housing 50 mechanically coupled to a second housing 52, with the evaporative cooler 54 located between the housings. A fan 56 is coupled to an end of housing 50, and a heat source 58 is coupled to an end of housing 52. The evaporative cooler 54 is constructed as described in the rounded square evaporative cooling module section above. Table 2 lists the component descriptions.

[0042] The duct system begins with a 5-inch diameter circle and expands to a square casing of approximately 18 inches by 18 inches. A second section is 18 inches by 18 inches, approximately 7 inches in diameter, then narrows back to a 5-inch diameter circle. A plate with cutout holes is installed in the central square section inside the duct. The evaporative cooling unit (module 54) is mounted on this plate. A blower (fan 56) is attached to the outlet side of the air duct. A hot air gun (heat source 58) is located on the inlet side of the air duct to supply hot air. Air and humidity sensors are located upstream and downstream of the evaporative cooler. The hot air gun operates at its highest setting. Air temperature and humidity sensors are installed at the inlet and outlet of the air duct. Air velocity is measured using a hot-wire anemometer from TSI, and the air velocity is converted into volumetric airflow based on the duct cross-sectional area.

[0043] Figure 2 This is a diagram of the water path through the evaporative cooling unit, except that in this embodiment the water is not recirculated and no filter is used. A 10-gallon plastic tank with a support (30) is used to hold the inlet water. Below this tank, gravity feed is routed through plastic tubing (32) to deliver the water to the pump (34). The pump pumps the water through an inlet flow meter into the water inlet of the evaporative cooler (38). The water moves to the outlet side of the evaporative cooler (40) via an HFPM. Plastic tubing connects the outlet of the evaporative cooler to a 5-gallon plastic container (outlet tank). Temperature sensors are used to measure the temperatures of the inlet and outlet tanks, each containing two type-K thermocouples. The average of the two readings is used.

[0044] Before the experiment, hot water is preheated using a temperature control unit (TCU) and a shell-and-tube heat exchanger. Water in the inlet tank is recirculated through the heat exchanger until the desired experimental temperature is reached. The piping is then disconnected from the heat exchanger and connected to the module's inlet, exiting the module. The piping at the module's outlet is then connected to the outlet tank.

[0045] Air handling unit setting 2

[0046] Assemble a small air handling test unit to test the performance of a flat panel evaporative cooler made by HFPM (see [link]). Figure 4 The diagram shows an air duct with a flat-panel evaporative cooler module mounted at the center. A blower is attached to the inlet of the air duct. A heating element with a temperature controller is located on the inlet side of the air duct to supply hot air. Air and humidity sensors are located upstream and downstream of the evaporative cooler, respectively. Table 3 summarizes the components used in this setup.

[0047] exist Figure 4The diagram shows a water recirculation loop with a glass container (70), a copper coil connected to the TCU (62), and a pump (72) connected to the evaporative cooling module (66). An air duct (68) has an air inlet, a heater section (64) for supplying heated, dry air to the module (66), and an outlet section (60) for supplying cooled, humid air. The copper coil connected to the TCU is immersed in water within the glass container. The glass container is insulated. The water in the container is heated to the desired temperature using the TCU. Two type-K thermocouples connected to sensors are placed in the glass container to measure the water temperature. Plastic tubing from the glass container is connected to the water pump. The pump pumps water through an inlet flow meter, through a tee containing a type-K thermocouple (inlet water temperature), and then to the inlet of the evaporative cooler unit. The water moves to the outlet side of the evaporative cooler via the HFPM. Plastic tubing connects the outlet of the evaporative cooler unit to a tee containing a type-K thermocouple (outlet water temperature) and connects the tubing to the water container. This creates a closed system that allows water to be recycled while also maintaining the water in the container at the desired temperature.

[0048] Example 1 :

[0049] This embodiment, using a single stream of water through a rounded square module, employs an air handling unit set to 1. The experiment lasted 10 minutes. The average of the last 4 minutes was reported, with the first 6 minutes considered the transition to steady state. Preheated DI water was pumped through the evaporative cooler at a rate of 0.3 gallons / minute. The blower was turned on to gear 3. Air velocity was measured, and the calculated volumetric flow rate was 362 ft. 3 / min. The hot air gun is operated at the high setting. Table 4 shows the water temperature, water temperature variation, inlet air temperature, outlet air temperature, and relative humidity values ​​for the inlet and outlet chambers.

[0050]

[0051] This indicates that by evaporating warm water through the rounded square hollow fiber membrane module, the inlet water can be cooled to a lower temperature. Additionally, the outlet air is cooled and humidified due to evaporation. The surface area of ​​the HFPM within the module can be optimized to meet the specific capacity requirements of the cooler. For example, to increase the length of the internal volume, two rounded square modules can be connected in series if the end cap of the first module is modified or removed.

[0052] Example 2 :

[0053] In this embodiment, where water is recirculated through the flat panel module, an air processor unit (Set 2) was used and operated for approximately 1 hour. Representative average values ​​for air and water conditions are reported in Table 5. The TCU setpoint was set to 128.6 degrees Fahrenheit, and the temperature of the DI water in the tank was measured at 102.6 degrees Fahrenheit. Heated water was pumped through the evaporative cooler at a rate of 300 mL / min (0.08 gallons / min). The water temperatures at the module's inlet and outlet are shown in Table 5. The blower was turned to gear 1, and the autotransformer was set to 38. Air velocity was measured, and the calculated volumetric flow rate was 31 ft. 3 / min. The heater setpoint is 98 degrees Fahrenheit. The inlet and outlet air temperatures, relative humidity, and water temperature are measured and shown in Table 5.

[0054]

[0055] This indicates that by evaporating warm water through a flat hollow fiber membrane module, the inlet water can be cooled to a lower outlet water temperature.

[0056] Example 3 :

[0057] A set of operating conditions has been developed that allow for controlled air humidification via evaporative cooling through porous hollow fibers.

[0058] Modules and panels of various shapes, sizes, and properties (square modules, flat panels, various hollow fiber membrane surface areas, etc.) can be used to generate and release humid air. Operating conditions can be optimized based on multiple factors, such as inlet air characteristics, hollow fiber membrane surface area, and target conditioning air characteristics. Other factors, such as air and water pressure drops, can also be considered.

[0059] For this embodiment, air handling unit setting 2 is used. A TCU is not used to heat the water, and the water is recirculated. The air flow rate is set to 70 CFM. The inlet air temperature is controlled at approximately 90 to 95 degrees Fahrenheit. For all samples, the water flow rate is set to 0.025 gpm.

[0060] The relative humidity of the air was measured and captured over several hours. Data points were collected every 1 to 5 minutes. Table 6 lists the experimental conditions and measurements.

[0061]

Claims

1. A unit for evaporative cooling, the unit comprising: The first frame with a lid; An open second frame, which is relative to the first frame; Multiple mechanical support members are located between the first frame and the second frame and are connected to the first frame and the second frame; and A porous hollow fiber membrane, the membrane extending around the mechanical support between the first frame and the second frame to form an internal volume, and connected to the first frame and the second frame. The first frame and the second frame are configured to allow water to flow between the first frame and the second frame via the membrane, and the membrane is configured to transport water between the first frame and the second frame and to allow airflow through the membrane for evaporative cooling. The unit is configured to produce cooling water during the evaporative cooling process, wherein the cooling water output from the unit has a lower temperature than the water input into the unit.

2. A unit for evaporative cooling, the unit comprising: The first frame with a lid; An open second frame, which is opposite to the first frame; Multiple mechanical support members are located between the first frame and the second frame and are connected to the first frame and the second frame; and A porous hollow fiber membrane, the membrane extending around the mechanical support between the first frame and the second frame to form an internal volume, and connected to the first frame and the second frame. The first frame and the second frame are configured to allow water to flow between the first frame and the second frame via the membrane, and the membrane is configured to transport water between the first frame and the second frame and to allow airflow through the membrane for evaporative cooling. The control unit performance can be controlled by at least one of the following during the evaporative cooling: water flow rate (air or water), temperature, and pressure.

3. A unit for evaporative cooling, the unit comprising: The first frame with a lid; An open second frame, which is opposite to the first frame; Multiple mechanical support members are located between the first frame and the second frame and are connected to the first frame and the second frame; and A porous hollow fiber membrane, the membrane extending around the mechanical support between the first frame and the second frame to form an internal volume, and connected to the first frame and the second frame. The first frame and the second frame are configured to allow water to flow between the first frame and the second frame via the membrane, and the membrane is configured to transport water between the first frame and the second frame and to allow airflow through the membrane for evaporative cooling. The unit is configured to control at least some air humidification during the evaporative cooling process.

4. The unit according to any one of claims 1 to 3, wherein the mechanical support is configured to provide a substantially flat panel for the membrane.

5. The unit according to any one of claims 1 to 3, wherein the unit further comprises a plurality of said units connected in series via the internal volume.

6. The unit according to any one of claims 1 to 3, wherein the plurality of mechanical supports comprises columns.

7. The unit according to claim 6, wherein one of the columns comprises a pipe for conveying water.

8. The unit according to any one of claims 1 to 3, wherein the membrane has a plurality of layers.

9. The unit according to any one of claims 1 to 3, the unit further comprising a pump connected to the first frame and the second frame for circulating water through the membrane.

10. The unit according to any one of claims 1 to 3, wherein the unit is configured to circulate air from the internal volume through the membrane.

11. The unit according to any one of claims 1 to 3, wherein the second frame includes an inlet and the first frame includes an outlet.

12. The unit according to any one of claims 1 to 3, wherein the first frame or the second frame includes an inlet, an outlet, a first channel for the inlet, a second channel for the outlet, and a flow separation element located between the first channel and the second channel.

13. The unit of claim 12, wherein the first frame or the second frame comprises a continuous channel.

14. The unit according to any one of claims 1 to 3, wherein the membrane has a pore size of 0.01 micrometers to 0.2 micrometers.

15. The unit according to any one of claims 1 to 3, wherein the membrane has a porosity of 25% to 80%.

16. The unit according to any one of claims 1 to 3, wherein the membrane has a wall thickness of 15 micrometers to 75 micrometers.

17. The unit according to any one of claims 1 to 3, wherein the membrane has a weave density of 35 to 53 fibers per inch.

18. The unit according to any one of claims 1 to 3, wherein the membrane has a weave density of 15 to 65 fibers per inch.

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