CN118076432A - Microwave-assisted silica-based composite desiccant dehumidification method and system - Google Patents

Abstract

The composite adsorbent (100) for water absorption includes a silica cage (110) having a plurality of pores (114) and an internal passage (118) in fluid communication with the plurality of pores (114), at least one internal chamber (120) having an average diameter greater than the average diameter of the plurality of pores (114), wherein the at least one internal chamber (120) is a result of collapse of at least one of the plurality of pores (114) and one of the internal passages (118), and a salt (116) disposed within the plurality of pores (114), the internal passage (118), and the at least one internal chamber (120).

Description

Microwave-assisted silica-based composite desiccant dehumidification method and system

Cross Reference to Related Applications

The present application claims priority from U.S. provisional patent application No. 63/235195 entitled "high performance desiccant System for efficient dehumidification in air conditioner" filed 8/20 of 2021 and U.S. provisional patent application No. 63/235197 entitled "innovative microwave-assisted desiccant dehumidification method and System" filed 8/20 of 2021, the disclosures of which are incorporated herein by reference in their entirety.

Background

Technical Field

Embodiments of the subject matter disclosed herein relate generally to systems and methods for dehumidifying an air stream of an air conditioning system, and more particularly, to generating a highly efficient desiccant material and regenerating the desiccant material in an air conditioning system using microwaves.

Background discussion

Steam is a component of concern in many industrial applications, such as flue gas dehydration, natural gas dehydration, compressed air drying, fruit and vegetable storage, protective clothing, and dehumidification processes that improve indoor air quality. The presence of water vapor in a process stream (e.g., an air stream) or an enclosed space (e.g., a home or office) is not always satisfactory and needs to be controlled. For example, the presence of water vapor in natural gas can create significant problems such as hydrate formation, slugging, corrosion and erosion of pipelines and processing equipment. Removing water from the flue gas will avoid reheating after treatment by the gas desulfurization unit, reduce energy requirements, and increase overall efficiency of the power plant. Another rapidly growing application of water removal is air dehumidification, which is a fundamental function of air conditioning systems, aviation and space flight to provide human comfort humidity control.

The energy usage of HVAC (heating, ventilation and air conditioning) systems has grown excessively, with a significant portion of the total amount of primary energy consumption being used in the air dehumidification process of HVAC systems. In the united states, almost half of the building energy is consumed by cooling systems, which account for about 20% of the total energy consumption. This is considered one of the largest energy end uses, not only in the residential sector, but also in the industrial sector.

Furthermore, the continuing goal of energy consumption makes new building codes a critical priority for energy policies. A prominent example is the european building energy efficiency directive (EPBD), which sets forth an energy efficient standard for ventilation and air conditioning systems. Due to the changing climate conditions, the energy demand of 21 st century air conditioners is expected to increase rapidly, which will reduce global heating demand and increase refrigeration demand significantly. According to model predictions, energy demand is expected to increase from 300TWh (tera hour) in 2000 to about 4000TWh in 2050, and beyond 10000TWh in 2100. Thus, world demand for HVAC equipment and related energy consumption is increasing. According to recent predictive reports on HVAC equipment, the annual growth of HVAC equipment has increased from 4.4 billion dollars (2008-2013) to 1200 billion dollars during 2013-2018, with an annual growth rate of 6%. This means that the energy usage is expected to increase correspondingly.

To alleviate this problem, it is possible for membrane or desiccant based dehumidification systems to reduce energy consumption to a certain level [1,2]. Although the membrane is a compact system, its use in the refrigeration industry is not yet mature. Therefore, an adsorbent or a coating thereof is preferable. When the humidity level exceeds an undesirable range, the ideal adsorbent material should rapidly adsorb water vapor. Such materials, if available, will pave the way for alleviating various existing burdens imposed by currently employed technologies in terms of design capacity, energy efficiency, and overall cost.

One prerequisite for the use of adsorbent materials is high water absorption, i.e. the materials need to be able to adsorb large amounts of water, for which reason various materials are currently being investigated, including membranes, adsorbents such as metal-organic frameworks (MOFs) and Covalent Organic Frameworks (COFs), however, they lack mass production processes and the high cost limits their use in practical industrial applications. Silicon-based materials have been used as adsorbents for many years. More recently, they have gained more attention and their performance improvement options have been utilized. For these purposes, researchers have used various preparation techniques, such as polymer grafting.

However, finding good adsorbent materials is only one aspect of efficient air conditioning systems. Another aspect is how the adsorbent material can be regenerated after it has been saturated with water so that the adsorbent material can be reused. In this regard, current air conditioning systems achieve dehumidification by dew point condensation of water vapor in an air stream using a dual function AC chiller that has reached its progressive performance limit of 0.85kW/Rton (equivalent to a coefficient of performance (COP) of 4 to 4.5). One solution to improve the performance of air conditioning units is to separate dehumidification from isotonic cooling, allowing new dehumidification methods to be employed.

Microwave dehumidification is an emerging process in which water molecules are adsorbed on the pore surfaces of a solid desiccant to dehumidify air, and then the adsorbed water is removed by microwave radiation. The former process is called adsorption and the latter process is called desorption. From the prior art, [2] shows the first microwave dehumidification process using a single mode waveguide. The authors suggested a relationship between desiccant temperature and electric field strength. Furthermore, they propose models to represent the fast kinetics of microwave desorption. Most of the research in the last decades has focused on developing microwave-assisted desorption methods in small volumes [3-9]. Notably, research into desiccant materials has been extended to different adsorbents (activated alumina, zeolite, silica gel) [5].

Microwave desorption shows many advantages, such as more efficient transfer of energy than convective energy transfer, and desorption at low temperatures due to direct energy transfer. However, critical parameters such as coefficient of performance (COP) are often ignored in the literature. Furthermore, no electric power value is provided; in contrast, microwave power is demonstrated. Thus, a microwave coefficient of performance (MCOP) was introduced, which can serve as a platform for comparing different microwave dehumidification systems. MCOP can be calculated using the microwave power, duration of microwave exposure, and amount of desorbed water. The MCOP calculated values for the different authors were very low (below 0.2). The performance of the system depends on the uniform propagation of the electric field strength, the geometry of the microwave chamber, the microwave irradiation time, the irradiation pattern and the amount of reflected power. A multi-mode chamber system similar to a household oven may improve its performance; however, MCOP is around 0.15. In addition, the fixed zeolite coated desiccant rotor was regenerated using microwave and temperature swing desorption methods, but with lower performance MCOP of about 0.18[8,9]. In addition to the low COP and MCOP, the systems discussed in [4-9] are also concerned with small systems, such as systems having a volume of less than 1 liter. Such small systems behave differently than the full-size systems because the electric field strength corresponding to microwaves is not uniform in a larger volume.

Thus, there is a need for new adsorbent materials and large scale microwave-based dehumidification systems that are capable of adsorbing large amounts of water and also capable of effectively regenerating the adsorbent materials.

Disclosure of Invention

According to an embodiment, a composite adsorbent for adsorbing water is provided and includes a silica cage having a plurality of pores and an internal passage in fluid communication with the plurality of pores, at least one internal chamber having an average diameter greater than the average diameter of the plurality of pores, wherein the at least one internal chamber is a result of collapse of at least one of the plurality of pores and one of the internal passages, and a salt disposed within the plurality of pores, the internal passage, and the at least one internal chamber.

According to another embodiment, an air dehumidification system for removing water vapor from an air stream is provided. The air dehumidifying system includes: a first faraday cage configured to confine microwaves; a desiccant wheel located within the first faraday cage and configured to rotate relative to a longitudinal axis X of the first faraday cage, wherein the desiccant wheel is coated with a desiccant material; a metal plane extending through the diameter DD of the desiccant wheel and dividing the desiccant wheel into a first portion and a second portion; and a magnetron system configured to generate microwaves and direct the microwaves into the desiccant wheel to evaporate water adsorbed by the desiccant material. The metal plane is configured to uniformly distribute microwaves into the first portion of the desiccant wheel at a given moment and to prevent microwaves from entering the second portion.

According to yet another embodiment, there is provided a method of manufacturing a composite adsorbent for absorbing water, the method comprising: providing a silica cage having a plurality of pores and an internal passageway in fluid communication with the plurality of pores; preparing an aqueous salt comprising a salt; placing a silica cage in an aqueous salt to form at least one internal chamber that is the result of collapse of at least one of the plurality of pores and one of the internal channels; removing the salt-loaded silica cage from the aqueous salt; and drying the salt-loaded silica cages.

Drawings

For a more complete understanding of the present invention, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which:

FIGS. 1A and 1B are schematic views of a silica cage having a plurality of holes and channels, FIG. 1C is a cross-sectional view of a silica cage having at least one interior chamber formed when walls of at least one hole and one channel collapse and filled with salt;

FIG. 2 is a flow chart of a method of making a composite adsorbent based on the silica cages and salts shown in FIGS. 1A through 1C;

FIG. 3 shows the water uptake of various silicon-based materials including composite adsorbents made by the method of FIG. 2;

FIG. 4 shows the change in the water uptake of the composite adsorbent as the relative humidity increases and decreases;

FIG. 5 is a schematic diagram of an air conditioning system including an air dehumidification system and an air cooling device;

FIG. 6 illustrates a desiccant wheel used by the air dehumidification system of FIG. 5;

FIG. 7 shows a honeycomb structure of the desiccant wheel of FIG. 6;

FIG. 8 is a table showing various properties and features of the desiccant wheel of FIG. 6;

FIG. 9A shows adsorption isotherms for a combined desiccant wheel, adsorbent, and binder, while FIG. 9B shows dielectric properties of composite desiccant materials with different adsorption amounts;

FIG. 10 shows the microwave distribution in a desiccant wheel when a metal plane is placed in the desiccant wheel;

FIG. 11A shows a temperature and humidity ratio curve at the inlet and outlet of the dehumidification system without the heat recovery device on, while FIG. 11B shows a temperature and humidity ratio curve when the heat recovery device is present and on;

FIG. 12 schematically illustrates how COP and MCOP of the air dehumidification system are calculated;

FIG. 13A shows the COP of the prior art air dehumidification system and the system of FIG. 5, while FIG. 13B shows MCOP of the prior art system and the system of FIG. 5;

FIG. 14A schematically illustrates an air conditioning system including the air dehumidification system of FIG. 5 and an air cooling device co-operating to cool indoor air; fig. 14B-14D show a variation of the air conditioning system of fig. 14A, wherein fig. 14B shows a system with two desiccant wheels, each having a respective microwave generator, fig. 14C shows a system with three desiccant wheels, each having a respective microwave generator, and fig. 14D shows a system with two desiccant wheels sharing a single microwave generator;

FIG. 15 schematically illustrates another air conditioning system that uses a microwave-assisted air dehumidification system and an air cooling device to cool air within a room;

FIG. 16 schematically illustrates how an incoming humid air stream is dehumidified using a desiccant material; and

Fig. 17 shows how the desiccant material is regenerated using microwave radiation.

Detailed Description

The following description of the embodiments refers to the accompanying drawings. The same reference numbers in different drawings identify the same or similar elements. The following detailed description does not limit the invention. Rather, the scope of the invention is defined by the appended claims. For simplicity, the following embodiments are discussed in relation to an adsorbent material comprising a silica cage filled with a hydrophilic salt, and which is used in an air conditioning system to remove moisture from an incoming air stream prior to cooling the air stream. However, the embodiments to be discussed next are not limited to such systems nor to the particular adsorbent materials discussed herein.

Reference throughout this specification to "one embodiment" or "an embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment disclosed. Thus, the appearances of the phrase "in one embodiment" or "in an embodiment" appearing in various places throughout the specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more embodiments.

According to an embodiment, a silica cage based composite adsorbent is produced such that after impregnation with salt, the internal structure of the cage remains largely intact (except for some holes and channel collapse forming large internal chambers), retains its mechanical stability, and is capable of adsorbing up to 530% of the water relative to its dry mass. Such a composite adsorbent or another desiccant material may be used to coat a rotor that includes a rotating reflector for uniformly distributing an electric field associated with microwave radiation. These features are now discussed in more detail with reference to the accompanying drawings.

Fig. 1A to 1C show a single silica cage 110, also referred to as silica particles. Fig. 1A and 1B show the outer surface 102 of the silica cage 110, while fig. 1C shows a cross section of the silica cage 110, i.e., the inner surface 104 of the silica cage. The silica cage 110 has a porous body 112 made of silica. The porous body 112 has a plurality of pores 114 (exterior and interior) that communicate with the environment of the silica cage as shown in fig. 1A and 1B. Hydrophilic salt 116 is added to the silica cage 110 such that a portion of the interior pores 114 are filled with salt. The silica cages 110 together with the hydrophilic salts 116 form the composite adsorbent 100. Fig. 1C shows that some of the apertures 114 and associated internal passages 118 have collapsed and formed a large internal chamber 120 as a result of this process (discussed in more detail below). The term "large" is used herein to mean that the average diameter of the interior chamber 120 is greater than the average diameter of the aperture 114. When at least one of the internal apertures 114 and one of the passages 118 connected to the internal apertures 114 collapse, a large internal chamber 120 is formed.

In one embodiment, the volume of the interior chamber 120 is greater than the sum of the volume of one aperture 114 and the volume of one channel 118. Note that the silica cage 110 is defined as a network with channels 118 interconnecting the pores 114, and some of the channels are interconnected. Thus, the pores 114 and channels 118 provide the silica cage with a porous structure, i.e., a large volume of internal chamber. For those channels 118 that do not collapse, they retain their original diameter inside. Both the original channel 118 and the newly formed interior chamber 120 may be partially or even completely filled with salt 116. Fig. 1C shows only some of the channels 118 filled with salt 116, but any number of these channels may be filled with salt. This open porous structure of the composite adsorbent 100 allows the salt 116 to impregnate the cage 110 to a maximum extent and also has mechanical stability that prevents further collapse of the remaining channels 118 of the cage 110. This is a known problem with existing adsorbent materials, namely that the internal structure of the cage collapses and the material deposited within the cage leaks.

In one application, salt 116 is selected to be LiCl. However, the salt 116 may also be based on other cations, such as Na, K, mg, ca and Sr. In one application, the salt may be based on other anions, such as Br. The size D of the individual cages/particles 110 (see size D of fig. 1C, which corresponds to the outer diameter of the particles 110) is 5 μm to 75 μm, preferably 6 μm to 15 μm. The loading of salt 116 in silica cage 110 is 30% to 65%, with a preferred loading of 60% to 65%. In one embodiment, the loading is about 62%, and the term "about" means a deviation of plus or minus 10%. The term "loading" refers to the volume of the salt-filled spaces (i.e., pores, channels, and internal chambers).

The method of loading the silica cage 110 with the salt 116 to obtain the composite adsorbent 100 will now be discussed with reference to fig. 2. A silica cage 110 is provided in step 200. Note that the silica cage 110 differs from conventional silica particles in that conventional silica particles do not have the pores 114 and channels 118 and corresponding porous structure shown in fig. 1C. Lithium chloride (LiCl) salts are prepared in step 202. The salt is dissolved in a given amount of water such that the salt is aqueous. In step 204, the silica cages 110 are placed in an aqueous salt, which enters the plurality of channels 118 through the respective apertures 114. Thus, in this step, the silica cage 110 is loaded with salt 116. The amount of supported salt depends on the time the silica cage is maintained in the aqueous salt. The longer the time, the greater the load factor. In step 206, a given time is calculated such that the silica cage is loaded with approximately 62% salt. In step 208, the loaded silica cage, i.e., composite adsorbent 100, is removed from the aqueous salt, and in step 210, the composite adsorbent is dried, for example, with hot dry air having a temperature of about 60 ℃ to 70 ℃. In optional step 212, the composite adsorbent 100 is placed in a sealed container and exposed to vacuum to promote deposition of salts in the channels and interior chambers of the silica cage. Depending on the size (x) and the loading percentage (y) of the silica cage, the composite adsorbent is hereinafter referred to as SCx-y. For the process discussed herein, the resulting composite adsorbent is referred to as SC6-62, since the average size D of the silica cage is about 6 μm. Other y values studied herein were 37% and 50%, and other cage sizes studied herein were 20 μm and 75 μm. Any other digital combination of x and y may be used. Note that the outer surface 102 of the silica cage 110 is free of salt 116. Note also that water 130 (see again fig. 1C) from the environment is absorbed into the channels 118 and the larger interior chamber 120 through the silica body 112 and/or the salt 116.

As now discussed, the properties of the novel composite adsorbent 100 have been investigated. The water vapor adsorption/desorption isotherms of the original (i.e., conventional) silica cage and the composite adsorbent 100 described above were determined at 25 ℃. The water vapor adsorption isotherms for the various porous silica cages are shown in figure 3. Notably, the porous cage has a maximum water absorption of 40% at 25 ℃, as shown at 310. The inset of FIG. 3 shows commercially available silica particles (SIL 54, SIL RD) having a water vapor absorption rate similar to that of silica cages SC6-0 and SC 30-0. Note that the commercially available silica particles SIL 54 and SIL RD shown in fig. 3 have no holes, channels and internal chambers. As shown in fig. 3, the water absorption increased with increasing LiCl loading. All samples exhibited type II isotherms, indicating that they had highly hydrophilic properties and that the water uptake increased with increasing relative humidity. In sharp contrast, the novel SC6-37 and SC30-37 composite adsorbents 100 exhibit similar water vapor absorption over the entire humidity range.

The inventors further analyzed that the water absorption of the composite adsorbent 100 increased with relative humidity and the adsorption curve increased monotonically above rh=20% with a silica cage having an external diameter of about 6 μm, indicating that an aqueous solution of salt 116 was formed and that a maximum water absorption of 530% (mass of dry composite adsorbent) was reached at a LiCl loading of about 62% (see fig. 3, curve 320). Note that the water uptake was calculated by measuring the ratio between the mass of the adsorbed water and the mass of the dry composite adsorbent, while the LiCl loading was calculated as the ratio between (1) the volume occupied by LiCl within the silica cage and (2) the total volume of the internal chamber 120, pores 114 and channels 118 in the silica cage 110. The high water absorption of the composite adsorbent 100 is due to the strong affinity of water vapor for salts and silica. The water absorption capacity of the composite adsorbent is very high compared to the porous materials [4-7], the composite adsorbents [8,9] and various polymers of the prior art.

When RH is not less than 60%, the water vapor absorption amount of the fully activated composite adsorbent 100 is very high. As previously mentioned, the addition of LiCl is expected to play a key role in increasing the water uptake. However, similar systems have the disadvantage of LiCl leakage due to collapse of the host matrix. The unique structure of the silica cage of the composite adsorbent 100 prevents such leakage. To further investigate this advantage of the adsorbent 100, adsorption-desorption analysis was performed with the highest loading of LiCl (SC 6-62). The results shown in fig. 4 demonstrate that at relative humidities exceeding 80%, there is a minimum hysteresis loop due to strong hydrogen bonding interactions under high humidity conditions. Water adsorption may occur in the following steps: the anhydrous LiCl confined in the silica cage absorbs water and converts to crystalline complexes, then the structure absorbs more water, and finally LiCl is completely dissolved, filling the voids/pores 118/120 of the cage 112. The inventors also performed multiple water adsorption-desorption cycles by alternately exposing SC6-37 throughout the humidity range above 40% RH. Unexpectedly, the maximum water absorption remained unchanged throughout the relative humidity range, confirming the stability of this composite adsorbent to the water adsorption/desorption process.

To further determine the unique water adsorption performance associated with the composite adsorbent 100 and evaluate the effect of temperature on SC6-37 water absorption, additional water adsorption studies were conducted at temperatures approaching the humidity control operating range (i.e., 35 ℃ and 45 ℃). The results showed that all these samples behaved similarly to the 25 ℃ samples. The kinetics of water vapor adsorption under different conditions for the four composite adsorbents were studied and compared to the adsorbents based on technical silica. The change in the moisture absorption rate with time shows a stable relationship. It was found that the water absorption rate of commercial desiccants (RD type silica and 54 type silica) was highest at lower relative humidity, decreasing with increasing relative humidity. The maximum water absorption rate of these desiccants was 0.12%/min. However, the silica cage shows the opposite kinetic pattern, which increases with increasing relative humidity. This results from the hydrophilic nature of the silica cage and achieves a maximum water absorption rate of 0.37%/min.

All these results demonstrate that a continuous rapid process for making composite adsorbent 100 is possible using the scalable process shown in fig. 2, which is capable of synthesizing and forming silica cages while limiting salts. The resulting composite exhibits unique water vapor adsorption properties compared to commercial silica adsorbents. Specifically, the SC6-62 composite adsorbent has an ultra-high adsorption rate exceeding 500%, making it unique in dehumidifying applications. The change in the moisture absorption rate with time shows a stable relationship. In addition, composite adsorbent 100 maintains its structural integrity and unique properties over multiple moisture adsorption cycles. In addition, SC6-62 can adsorb and desorb large amounts of water within the desired operating range. Based on these findings, the composite adsorbent 100 is an ideal candidate material for an air conditioning system.

Such an air conditioning system 500 is discussed next. As shown in fig. 5, the air conditioning system 500 includes an air dehumidification system 502 and an air cooling device 560. The air dehumidification system 502 is configured to remove water vapor from an incoming air flow AF1 prior to being cooled by the air cooling device 560. To this end, the air dehumidification system 502 includes a desiccant wheel 510 disposed within a first faraday cage 512, among other elements. In this embodiment, the desiccant wheel 510 is circular in shape such that the desiccant wheel can rotate about the longitudinal axis X. In effect, the desiccant wheel 510 has a shaft 514 extending along an axis X and is connected to a motor 516. The local controller 520 is programmed to control the speed of the motor 516. The motor 516 may be an AC or DC motor, or any special motor, such as a stepper motor, brushless motor, servo motor, universal motor, etc. Local controller 520 may be any logic control or processor based system. As shown in fig. 6, the desiccant wheel 510 is made as a cellulose-based honeycomb wheel in this embodiment. The cellulose-based material 610 is arranged to form a number of holes or channels 612, as more particularly shown in fig. 7. The cellulose-based material 610 is then coated with a desiccant 614, which desiccant 614 may be the composite adsorbent 100 discussed above.

As shown in fig. 5, the desiccant wheel 510 has a metal plate 518 that extends across the entire diameter DD of the desiccant wheel. The metal plate 518 essentially divides the wheel in half. The metal plate 518 is configured to reflect incident microwave radiation 524 generated by a magnetron system 526. The metal plate 518 may be solid or perforated as long as it is capable of reflecting incident radiation 524 back through the desiccant wheel 510. For the desiccant wheel position shown in fig. 5, incident radiation 524 enters the upper half 510A of the wheel 510, is reflected at the metal plate 518, and the reflected wave 524' passes through the upper half 510A of the wheel 510A second time. In this way, microwaves uniformly propagate through the upper half 510A of the wheel 510 for a first period of time, and then the same process is repeated for the lower half 510B of the wheel as the rotation of the wheel reverses the position of the upper and lower halves of the wheel for a second period of time. Thus, by controlling the speed of the motor 516, the duration of the first and second time periods is controlled. Notably, for small scale experiments conducted in this field, the microwave radiation is generally uniform through the desiccant material. However, as the size of the structure 510 supporting the desiccant material increases (e.g., by several tens of centimeters in this case), the microwave radiation becomes non-uniform. If this is the case, regeneration of the desiccant material is affected as the water evaporated from the desiccant material decreases. This problem was not observed by others, as all previous groups dealt with only very small desiccant material support structures. For the embodiments discussed herein, the features of the desiccant wheel 510 are shown in the table shown in fig. 8, and it is noted that the desiccant wheel is quite large, i.e., the cylinder has a radius of about 23cm and a height of about 40 cm. By controlling the microwave power, stub tuner, fan speed, motor speed and rotation of the magnetron system 526 (discussed below), the generated microwave radiation is uniform. Larger sizes may be used.

Returning to fig. 5, the air dehumidification system 502 also includes a second faraday cage 530 comprising a first faraday cage 512, a magnetron system 526, a controller 520, and a motor 516. In one embodiment, a temperature sensor 532 may be placed beside or inside the first faraday cage 512 for measuring the temperature of the vapor. The distance L from the desiccant wheel 510 to the porous metal mesh 534 closing the top and bottom ends of the first faraday cage 512 may be about 2mm. The second faraday cage 530 can also house a water container 536 for storing water 538, the water 538 being condensed from water vapor as the desiccant material regenerates.

The air dehumidification system 502 also includes a first air inlet 540, the first air inlet 540 being in fluid communication with the first air damper AD1 and the second air damper AD2. The air damper is essentially an air valve that is in a closed position when no air is passing therethrough and in an open position when air is passing therethrough. The air damper may be electronically controlled, for example, by controller 520 to close or open or in any open position between closed and fully open. The air dampers AD1 and AD2 may be connected to the controller 520 in a wired or wireless manner so that the controller can control the opening and closing of the air dampers. The air flow conduits from air damper AD1 and air damper AD2 merge along common conduit 542-1 and are fed to axial fan 544. The speed of the axial fan 544 is also controlled by the controller 520 via a wired or wireless connection. The air flow through conduit 542-1 may enter a flow measurement device 546, which flow measurement device 546 is coupled to a differential pressure sensor 548 for measuring the velocity of the air flow. The signal measured by the differential pressure sensor 548 is provided to the local controller 520.

Next, depending on the circulation of the desiccant wheel 510, an air stream is provided to the desiccant wheel 510 at the inner end 550 of the second faraday cage 530 for being dehumidified or for regenerating the desiccant material. The dehumidified air stream AF2 is then extracted from the second faraday cage 530 at port 552 and provided to a third air damper AD3 or a fourth air damper AD4, respectively, also controlled by the controller 520. The air dampers AD3 and AD4 may have structures similar to those of the air dampers AD1 and AD 2. The air flow received by the third air damper AD3 is discharged to the air cooling device 560 at the first air outlet 554. The air cooling device 560 may be any known air cooler that cools or heats an air stream, such as a refrigeration system having an evaporator 560-1, a compressor 560-2, a condenser 560-3, and an expansion valve 560-4. Other types of air cooling devices may be used, such as the system described in PCT patent application PCT/IB2022/054621 (case No. 0338-640-wo) filed at month 5 of 2022, which is assigned to the assignee of the present invention, the entire disclosure of which is incorporated herein by reference. Details of the air cooling device 560 are omitted herein because they are described in the above PCT patent application.

The air flow from the fourth air damper AD4 passes through the heat recovery device 556 to exchange heat with the incoming air flow AF3 flowing through conduit 542-2. Examples of heat recovery devices are described in the above PCT patent application, and therefore their structure is omitted here. Conduit 542-2 is in fluid communication with a second inlet 558, which second inlet 558 may receive air from the environment or a chamber or air cooling device 560 to be cooled or heated. The air flow from the fourth air damper AD4 exits at the second air outlet 562 after exiting the heat recovery device 556. The second air outlet 562 may be in fluid communication with an ambient, a chamber to be cooled or heated, or an air cooling device 560. Various air flow and temperature sensors 564 and 566 may be provided along various conduits carrying air, respectively, to measure air flow velocity and temperature. All of this data may be fed to either the local controller 520 or the external global controller 570, or both. The external global controller 570 may be a global controller of the air dehumidification system 502 and the air cooling device 560. Both controllers 520 and 570 include at least a processor and associated memory.

The principle of operation of microwave dehumidification is based on the hygroscopic properties of a desiccant (silica gel or composite adsorbent) that captures water vapor from the air, and then desorbs the water from the desiccant by microwave radiation. Microwaves facilitate this process by being characterized by the fact that they can cause water molecules to wave and desorb from the adsorbent surface (e.g., silica gel). The air dehumidification system 502 takes into account two situations: without heat recovery (i.e., without heat recovery system 556) and with heat recovery from the outlet air. The local controller 520 and/or global controller 570 continuously record temperature and differential pressure readings. The speed and rotation pattern of the desiccant wheel spin motor 516 is controlled by the controller 520 and it operates only during the desorption phase, i.e., when it is desired to remove water vapor from the desiccant material.

For the case where the heat recovery device 556 is not used, the controller 520 turns on the first and third air dampers AD1 and AD3, turns off the second and fourth air dampers AD2 and AD4, and lets air bypass the heat recovery device 556. The honeycomb desiccant wheel 510 is then moisture saturated at a prescribed airflow rate at a constant relative humidity and temperature until the inlet and outlet temperatures are the same. Note that adsorption may be performed at different relative humidities and temperatures until full saturation. In this regard, the same temperature and humidity show equilibrium conditions. Thus, the magnetron system 526 is turned on and the microwaves 524 are generated according to the preset time and preset power configured in the local controller 520. The desorption process ends when the humidity ratio of the outlet 554 becomes lower than the humidity ratio of the inlet 540. However, the desorption process step may be completed after stopping the microwave irradiation.

The heat recovery device 556 functions similarly to the case without heat recovery, i.e., when the temperatures of the inlet 540 and the outlet 554 become the same, the first air damper AD1 and the third air damper AD3 are closed, and the second air damper AD2 and the fourth air damper AD4 are opened to recover heat from the outlet air.

For both cases, the thickness of the desiccant coating was measured by SEM images and the average value was 209 μm. The coating thickness may be less than or greater than this value. From the SEM images, cracking of the desiccant coating surface was found. These cracks enhance the mass transfer and flow of water vapor. As shown in fig. 9A, adsorption isotherms of the desiccant wheel, i.e., the honeycomb cellulose, adsorbent, and binder, were measured. The results in this figure show that the desiccant wheel 510 can absorb water vapor and its mass can reach 30% of the full dry mass of the desiccant at higher humidity. Fig. 9B shows the dielectric properties (effective complex permittivity) of the composite desiccant material as a function of the adsorption absorption value. The results in fig. 9B show that microwaves can reach the center of the wheel 510. As the amount of adsorbed water decreases, the penetration depth of the electric field increases, which indicates that a larger size desiccant wheel can be regenerated.

A metal plate 518 is added to the desiccant wheel 510 to extend within a plane that includes the wheel diameter DD so that the microwave power is more evenly distributed in half of the wheel and so that reflected microwave power is minimized, thus minimizing unheated areas for a given cage. Various cages have been studied, and a cylindrical faraday cage 512 has been found to be the most effective cage. In this regard, fig. 10 shows streamlines of microwave hill-print vectors in the cross section of a cylindrical cage 512 for a desiccant wheel 510 having a metal plane 518. Note that the microwaves 524 are distributed as uniformly as possible in the upper half 510A of the wheel 510 above the metal plane 518 and that there are no microwaves in the lower half 510B of the wheel.

Tests performed on the air dehumidification system 502 without and with heat recovery will now be discussed. Fig. 11A shows temperature and humidity ratio curves at the inlet 540 and outlet 554 of the system 502 when the heat recovery device 556 is closed. The microwave irradiation time was set to 17 minutes. In addition, the microwave irradiation time may be longer or shorter than the above-described set time. However, due to the residual energy (thermal mass of the desiccant wheel), the desorption time is longer than the irradiation time. The desorption time may be the same as or longer than the microwave irradiation time. During the adsorption and desorption cycles, the inlet air temperature remained stable, equal to 24 ℃. But the inlet air temperature may vary during operation. The humidity ratio (ω) of the inlet air remained stable throughout the test, equal to 10.3g/kg. As shown in fig. 11A, the temperature 1110 of the desiccant wheel 510 increases at the beginning of the microwave radiation. During microwave radiation, the temperature of the outlet air 1112 increases, but is lower than the temperature of the wheel. This indicates that microwave energy is directly transferred to the adsorbed water. Thus, the amount of desorbed water increases, as can be seen from the outflow value of the humidity ratio (43 g _{Water and its preparation method} /kg _{Air-conditioner} ). The value of the outlet humidity ratio may vary depending on the control parameters. The air flow rate during desorption was controlled to a value equal to 185m ³/h. The air flow velocity value may be lower or higher depending on the system capacity and other conditions.

The outlet humidity ratio increases after the start of microwave irradiation, which is slowly increased initially due to the thermal mass of the adsorbed water. However, the increase in the outlet humidity ratio cannot last for a long time, so it starts to decrease. In the present case, 2kg of water is desorbed during the desorption cycle, which indicates that a large amount of water vapor can be captured and converted into potable water or used to operate an indirect evaporative cooling system. The amount of desorbed water depends on the capacity, and may be higher or lower than 2kg. The COP of the system in the present case was 0.55 and the mcop was 0.83. The temperature of the desiccant wheel is not too high, which demonstrates the good distribution of microwave and electric field intensities obtained due to the metal plate 518. No degradation of system performance, unheated areas or hot spots were observed due to the controlled rotation of the metal plate (stirrer) 518 in the center of the desiccant wheel, which rotation made the system safe and sustainable. In addition, the temperature of the desiccant material does not exceed 80 ℃. However, when the outlet temperature reached 51 ℃, it was observed that a portion of the transmitted microwave energy was unnecessarily converted into heat. This heat may be recovered by using heat recovery device 556. In this way, heat from the hot outlet air at the air damper AD4 can be used to heat the inlet air stream at the second air inlet 558, which is then provided through the second air damper AD2 to regenerate the desiccant material. In this regard, various arrows shown in fig. 5 indicate the flow directions of various air streams.

Fig. 11B shows a temperature and humidity ratio curve for microwave desorption when the heat recovery device 556 is turned on. The microwave irradiation time is equal to 12 minutes and 20 seconds, and the air flow rate is controlled to be 140m ³/h. The temperature of the inlet air increases due to heat exchange with the hot outlet air flow from the fourth air damper AD 4. Furthermore, the temperature of the outlet air reaches 51 ℃ after a shorter time than in the former case. Due to the heat recovery, the system has the highest COP, which is equal to 0.58 and MCOP is equal to 0.87. Furthermore, this high COP can be explained from the humidity ratio curve that increases before the microwave irradiation is stopped. This example uses energy more efficiently than the non-heat recovery case shown in fig. 11A, and therefore the system performance is highest. 1.54kg of water vapor is desorbed from the desiccant wheel, and depending on the capacity, the amount of desorbed water vapor may be higher or lower.

The system 502 was further tested to evaluate the amount of desorbed water for the different microwave irradiation times (3.5 minutes to 17 minutes) in both cases. Depending on the capacity of the system, the time of desorption may be different. The amount of desorbed water was found to be almost linear with time. The results show that COP increases with the microwave irradiation time without heat recovery due to the thermal mass of the saturated composite desiccant. At the beginning of the microwave irradiation, a portion of the energy is used to rapidly heat the saturated desiccant wheel from 24 ℃ to 48 ℃ (see fig. 11A), so the COP is initially low. The microwave operation time is prolonged, the influence of thermal quality can be reduced, and the COP of the system can be improved. However, the microwave irradiation does not exceed 17 minutes, since after this time most of the water is desorbed (adsorption amount of 0.03).

The highest COP (0.58) in the case of heat recovery corresponds to the time at which the humidity ratio reaches the highest value. The recovered heat may improve the performance of the system, but the heat recovery is less effective for short or long periods of time. At the same time, the amount of desorbed water in the case of heat recovery is higher than in the case of non-heat recovery.

The microwave desorption performance of system 502 was also evaluated based on COP and MCOP using the following equation:

And

Where Δm is the mass of desorbed water, h _fg is the amount of heat generated by evaporation, E _mw is the microwave energy emitted by the magnetron system, and P _elec is the electrical energy consumed. Therefore, the conversion efficiency η was found to be 0.7. Fig. 12 schematically illustrates the difference in calculation method for MCOP and COP, MCOP only taking into account the microwave energy and the energy of the useful product (i.e. desorbed/absorbed water), while COP also takes into account the electrical energy used by the system to generate microwaves.

Fig. 13A shows a COP comparison of different systems using microwave desorption. It can be seen that the current system shown in fig. 5 (point 1310) has the highest COP. A MCOP comparison shown in fig. 13B shows that current MCOP is 0.87, five times higher than other systems. These results demonstrate that the novel features disclosed in the system 502 of fig. 5 improve the efficiency of the dehumidification process and make the system 502 desirable to be implemented in any air conditioning system that separates the dehumidification process from the cooling/heating process.

The air conditioning system 500 is configured to operate as follows. Depending on the inputs received at the local controller 520 and/or the global controller 570, either a "no heat recovery" mode (also referred to as a "cool" mode) or a "heat recovery" mode (also referred to as a "regeneration" mode) is selected. For the no heat recovery mode, the controller 520 and/or 570 instructs the first air damper AD1 and the third air damper AD3 to open, and the second air damper AD2 and the fourth air damper AD4 to close. In this way, the heat recovery device 556 is bypassed by the moving air flow. More specifically, if the incoming air flow AF1 needs to be dehumidified before being provided to the air cooling device 560, then the no heat recovery mode is selected. For this case, the incoming air flow AF1 enters the first air inlet 540, passes through the first air damper AD1 and reaches the axial flow fan 544 (see fig. 5 and 14). Note that no air passes through the second air damper AD2, since this air damper is closed. The fan 544 pushes the air flow through the port 550 into the second faraday cage 530 and into the desiccant wheel 510. At this time, the incoming air flow AF1 is dehumidified as the desiccant material 614 deposited on the honeycomb structure of the impeller 510 absorbs water vapor. The magnetron system 526 is not activated at this time. The dehumidified air flow AF2 exits the second faraday cage 530 at port 552 and is directed to the air cooling device 560 through the open third air damper AD3 to be cooled (or heated). Fig. 14A schematically illustrates various components of an air dehumidification system 502 located in a housing 504. FIG. 14A also shows that the air cooling device 560 is in fluid communication with the air dehumidification system 502 at a port 554. Because the fourth air damper AD4 is closed, the entire dehumidified air flow AF2 enters the air cooling device 560, is cooled in the air cooling device 560, and is then released into the chamber 1410 that is desired to be cooled.

After a given time, depending on the size of the desiccant wheel 510, the type of desiccant material 614, the speed of the air flow, and the power of the microwave radiation (or even based on the readings of the temperature sensor 532), the local controller 520 and/or global controller 570 determine that the desiccant wheel 510 is no longer active (i.e., its desiccant material is saturated with water) and needs to be regenerated (i.e., water is removed from the desiccant material). At this time, the controller 520 turns off the first and third air dampers AD1 and AD3, and turns on the second and fourth air dampers AD2 and AD4. This means that no air flow from the air dehumidification system 502 is provided to the air cooling device 560. However, as shown in fig. 14A, a second air dehumidifying system 502' having the same structure as the first air dehumidifying system 502 may be used during regeneration of the desiccant wheel 510 to dehumidify air supplied to the air-cooling device 560, so that the air-cooling device operates without interruption. The second dehumidifier system 502' can be controlled by the same local controller 520 and the same global controller 570. This also means that the first dehumidifier system 502 has entered the heat recovery mode, while the second dehumidifier system 502' is in the no heat recovery mode. It can be seen that the two dehumidifier systems 502 and 502' are used in concert, i.e., when one is in the no heat recovery mode, the other is in the heat recovery mode, and vice versa.

For the heat recovery mode, the first dehumidifier system 502 activates the magnetron system 526 to evaporate water stored in the desiccant material 614. Thus, the incoming air flow AF3 received at port 558 and provided to the fan 544 and the cage 530 via the second air damper AD2 removes evaporated water vapor from the desiccant wheel 510. The water vapor then condenses on the walls or other interior walls of the second faraday cage 530 and accumulates as condensed water 538 in the container 536 shown in fig. 5 and 14. The humid air flow AF4 is then directed by the fourth air damper AD4 into the heat recovery device 556 and heats the incoming air flow AF3 before it is released into the environment at port 562. In this way, water from the desiccant wheel 510 is removed, and the desiccant material is regenerated.

Variations of the system 500 shown in fig. 14A may be implemented as follows. Fig. 14B shows a portion of a system 500 having two desiccant wheels 510-1 and 510-2 and associated hardware for removing moisture from an incoming air stream and producing a dry air stream DA. When the desiccant wheels saturate, they enter a regeneration mode in which hot air is circulated through them to remove air, which results in a flow of humid air HA. Additional air dampers AD 5-AD 5 and corresponding ducts as shown may be used to direct the dry and wet air streams to the first and second air outlets 554, 562. Note that each of the desiccant wheels 510-1, 510-2 has its own magnetron system 526-1, 526-2, respectively, for generating microwaves. In yet another embodiment, as shown in FIG. 14C, three desiccant wheels 510-1 through 510-3 and associated hardware are used, each with a corresponding individual magnetron system 526-1 through 526-3. The air dampers AD1 to AD10 serve to guide the dry air flow DA, the first wet air flow HA1, and the second wet air flow HA2. Fig. 14D shows another variation of the system 500 shown in fig. 14B. In this embodiment, there are two desiccant wheels 510-1 and 510-2 sharing a single magnetron system 526. Waveguide switch 1426 may be used to couple microwaves from magnetron system 526 to each of desiccant wheels 510-1 and 510-2. A person skilled in the art may implement a variant of the embodiment shown in fig. 14B to 14D, for example, the input air flow provided to each desiccant wheel 510 may be different, i.e. one desiccant wheel receives a wet air flow for dehumidification and the other desiccant wheel receives a dry hot air flow for regeneration, so that the desiccant wheels work in concert. Other variations will occur to those skilled in the art having the benefit of this disclosure.

The composite adsorbent 100 may be used with microwave technology in different air dehumidification systems, as now discussed with respect to fig. 15-17. Fig. 15 shows an air conditioning system 1500 that includes an air dehumidification system 1502 and an air cooling device 1504 (similar to air cooling device 560). Both systems may be housed in a common housing 1506. The air dehumidification system 1502 may include multiple levels or stages, each level being supplied with a flow of humid air 1510. Water vapor from the wet air stream 1510 is removed and a dry air stream 1512 is provided at the output port of the air dehumidification system 1502. The air cooling device 1504 receives a stream of dry air 1512, cools it, and then supplies cool air to the housing 1514. The air dehumidification system 1502 also includes a cooling system 1520 located opposite the microwave generator 1522 for maintaining a temperature gradient along the system. Energy is supplied along energy supply line 1530 to microwave generator 1522 and cooling system 1520.

Fig. 16 shows the internal structure of a multi-level air dehumidification system 1502 in more detail. Each layer includes a microwave transparent material 1610 having a high surface area configured to receive microwave radiation generated by a microwave generator 1522. One side of each microwave transparent material 1610 is coated with a solid desiccant, such as the composite adsorbent 100 discussed previously. Other desiccant materials (e.g., non-composite materials) may be used. The microwave transparent material 1610 is positioned to form an air channel 1610 through which the incoming wet air flow 1510 moves. As the wet air flow 1510 moves through the desiccant material 100, moisture in the air is absorbed, which creates a dry air flow 1512. Note that during this phase, the microwave generator 1522 is turned off. The channel 1610 is provided at both ends with respective valves 1620 and 1622 for controlling the flow of air through the channel. Microwave radiation passing through the channels 1612 of the first layer may enter the microwave transparent material 1610 of the second layer, and the process discussed above with respect to the first layer is repeated in the second layer. In this way, moisture from the incoming air stream 1510 is adsorbed by the desiccant material of each stage.

As shown in fig. 17, when the desiccant material 100 is saturated with water, the valves 1620 and 1622 are closed and the microwave generator 1522 is turned on, causing microwaves 1710 to form and pass through the stages. The microwave radiation evaporates the water in the desiccant material 100 to form water vapor 1712. A metal mesh layer 1714 may be placed in the air channel 1612 of the first stage to prevent microwave radiation from reaching the second or subsequent stages. If this is the case, the heated water vapor 1712 from the first stage moves through the metal mesh layer 1714 and heats the microwave transparent material 1610 to heat the desiccant material in the second stage and evaporate water therefrom. For this case, material 1610 may be a highly conductive material with a high surface area. As shown in fig. 17, water vapor 1712 from the air channels 1612 condenses on the back of the second layer of material 1610 and forms condensed water 1720, which condensed water 1720 is collected by the drainage system 1722 and removed from the air dehumidification system 1502. In this manner, the desiccant material 100 is regenerated and ready for a new cycle to remove moisture from the incoming air stream 1510. By closing and opening valves 1620 and 1622, the controller of the system switches between dehumidification and regeneration at different levels. For the regeneration mode, the microwave radiation may be caused to propagate through all layers, or through only the first layer, and the resulting vapor stream is then used to evaporate water from the desiccant material of the other layers.

The disclosed embodiments provide an air dehumidifying system and an air conditioning system that dehumidify air more effectively using microwave radiation. It should be understood that this description is not intended to limit the invention. On the contrary, the embodiments are intended to cover alternatives, modifications and equivalents, which may be included within the spirit and scope of the invention as defined by the appended claims. Furthermore, in the detailed description of the embodiments, numerous specific details are set forth in order to provide a thorough understanding of the claimed invention. However, it will be understood by those skilled in the art that the various embodiments may be practiced without these specific details.

Although the features and elements of the present embodiments are described in the embodiments in particular combinations, each feature or element can be used alone without the other features and elements of the embodiments or in various combinations with or without other features and elements disclosed herein.

This written description uses examples of the subject matter disclosed to enable any person skilled in the art to practice the subject matter, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the subject matter is defined by the claims, and may include other embodiments that occur to those skilled in the art. Such other embodiments are intended to be within the scope of the claims.

Reference to the literature

The entire contents of all publications listed herein are incorporated by reference into this patent application.

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[4]G.Roussy,A.Zoulalian,M.Charreyre,J.M.Thiebaut,How microwaves dehydrate zeolites,J.Phys.Chem.88(1984)5702-5708.https://doi.org/10.1021/j150667a049.

[5]I.Polaert,L.Estel,R.Huyghe,M.Thomas,Adsorbents regeneration under microwave irradiation for dehydration and volatile organic compounds gas treatment,Chem.Eng.J.162(2010)941-948.https://doi.org/10.1016/J.CEJ.2010.06.047.

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Claims (20)

1. A composite adsorbent (100) for absorbing water, the composite adsorbent (100) comprising:

a silica cage (110) having a plurality of apertures (114) and an internal passage (118) in fluid communication with the plurality of apertures (114);

at least one internal chamber (120) having an average diameter greater than an average diameter of the plurality of pores (114), wherein the at least one internal chamber (120) is a result of collapse of at least one of the plurality of pores (114) and one of the internal passages (118); and

A salt (116) disposed within the plurality of apertures (114), the internal passage (118), and the at least one internal chamber (120).

2. The composite adsorbent of claim 1, wherein the salt comprises LiCl.

3. The composite adsorbent of claim 1, wherein the silica cage is spherical and has an average outer diameter of about 6 μιη.

4. The composite adsorbent of claim 3, wherein the silica cage has a salt loading of about 62%, wherein the loading is defined as a ratio between (1) a volume of salt and (2) a total volume of the plurality of pores, the internal channels, and the at least one internal chamber.

5. An air dehumidification system (502) for removing water vapor from an air stream, the air dehumidification system (502) comprising:

a first faraday cage (512) configured to confine microwaves (524);

A desiccant wheel (510) located within the first faraday cage (512) and configured to rotate relative to a longitudinal axis X of the first faraday cage (512), wherein the desiccant wheel (510) is coated with a desiccant material (614);

a metal plane (518) extending through the diameter DD of the desiccant wheel (510) and dividing the desiccant wheel (510) into a first half (510A) and a second half (510 b); and

A magnetron system (526) configured to generate microwaves (524) and direct them into the desiccant wheel (510) to evaporate water adsorbed by the desiccant material (614),

Wherein the metal plane (518) is configured to uniformly distribute microwaves (524) into the first half (510A) of the desiccant wheel (510) at a given moment and to prevent microwaves (524) from entering the second half (510B).

6. The system of claim 5, further comprising:

a motor configured to rotate the desiccant wheel relative to the generated microwaves; and

A local controller configured to control the motor and the magnetron system.

7. The system of claim 6, further comprising:

A housing containing the first faraday cage, the motor, and the magnetron system, wherein the housing acts as the second faraday cage.

8. The system of claim 7, further comprising:

A fan configured to move air through the system; and

The first to fourth air dampers are configured to control air flow to the fan.

9. The system of claim 8, wherein the first and second air dampers control the flow of incoming air to the desiccant wheel, the third air damper controls the flow of dehumidified air after passing through the desiccant wheel to the air cooling device, and the fourth air damper controls the flow of humid air to the heat recovery device.

10. The system of claim 9, wherein the controller is configured to open the first air damper and the third air damper and close the second air damper and the fourth air damper during the no heat recovery mode.

11. The system of claim 10, wherein the controller is further configured to close the first air damper and the third air damper and open the second air damper and the fourth air damper during the heat recovery mode.

12. The system of claim 11, further comprising:

a heat recovery device configured to receive the flow of wet air from the fourth air damper and transfer heat from the flow of wet air to the flow of incoming air provided to the second air damper during a heat recovery mode.

13. The system of claim 8, further comprising:

an air cooling device (560) is in fluid communication with the third air damper for receiving a flow of dry air.

14. The system of claim 5, wherein the desiccant wheel is cylindrically shaped, is made of cellulose, and has a honeycomb structure.

15. The system of claim 5, wherein the desiccant material comprises:

a silica cage (110) having a plurality of apertures (114) and an internal passage (118) in fluid communication with the plurality of apertures (114);

At least one internal chamber (118) having an average diameter greater than an average diameter of the plurality of pores (114), wherein the at least one internal chamber (118) is a result of collapse of at least one of the plurality of pores (114) and one of the internal passages (118); and

A salt (116) disposed within the plurality of apertures (114), the internal passage (118), and the at least one internal chamber (118).

16. The system of claim 15, wherein the salt comprises LiCl, the silica cage is spherical and has an average outer diameter of about 6 μm.

17. The system of claim 16, wherein the silica cage has a salt loading of about 62%, wherein the loading is defined as a ratio between (1) a volume of salt and (2) a total volume of the plurality of pores, the internal channels, and the at least one internal chamber.

18. A method of manufacturing a composite adsorbent (100) for absorbing water, the method comprising:

providing (200) a silica cage (110) having a plurality of apertures (114) and an internal passage (118) in fluid communication with the plurality of apertures (114);

preparing (202) an aqueous salt comprising salt (116);

placing (204) a silica cage (110) in an aqueous salt to form at least one internal chamber (120), the at least one internal chamber (120) being a result of collapse of at least one of the plurality of pores (114) and one of the internal channels (118);

removing (208) the silica cage (110) loaded with salt (116) from the aqueous salt; and

The silica cage (110) loaded with salt (116) is dried (210).

19. The method of claim 18, wherein the salt comprises LiCl and the silica cage is spherical and has an average outer diameter of about 6 μιη.

20. The method of claim 18, further comprising:

The silica cage with salt is exposed to a vacuum to increase the salt loading to about 62%, where the loading is defined as the ratio between (1) the volume of salt and (2) the total volume of the plurality of pores, the internal channels, and the at least one internal chamber.