Patent Publication Number: US-11040123-B2

Title: Air purification system

Description:
FIELD OF INVENTION 
     The invention is related to air purification system. Particularly, a portable or handhold air supply system to provide sterilized air flow to its users. 
     BACKGROUND ART 
     To keep a human being alive, he or she needs take enough energy from food by eating, and also obtain enough oxygen and get rid of carbon dioxide by breathing. A person may keep himself/herself alive life without taking food for a few days but cannot survive more than a few minutes without breathing. Just as eating a heathy food, taking in “heathy” air is extremely important to our life quality. 
     Unfortunately, air can carry quite a lot of pollutants, namely bioaerosols, such as bacteria, mold, viruses, endospores, and even pollen, which can trigger various of infections, allergy and asthma reactions. Some of them can even ultimately lead to complicated short term or long term heath issues. For example, flu is among the top causes of death every year, particularly for the elderly. 
     It has been a long time effort for scientists and engineers to find an affordable solution to provide healthier air to ordinary people. Currently, there are a few air purification methods, each of which will be discussed in the following sections. 
     Physical filtering is one of the simplest method and used on quite some systems on the market. It implements a high-efficiency particulate air (HEPA) filter in the systems to take out particles larger than certain size out of the air flow. However, there are some disadvantageous for such system. Firstly, it has been shown particles with size smaller than 300 nm (or 0.3 um) can pass through the HEPA filter. Unfortunately a lot of pollutants below 0.3 um do exist. Further reducing the size of filter will increase the cost of the filter dramatically and also impeach the smoothness of air flow through the filtration system. Secondly, experiments found that the organic pollutants caught on the filter can even grow on the filter surface and reenter into the air stream. 
     Another air cleaning system is based on ozone oxidation. Ozone generators were once used as an air cleaning method. However, the later studies show clearly that it could do more harm than good to human body particularly to our respiratory system. It has been scientifically proven that breathing ozone is part of root cause of asthma and need to remove totally from the air we take in. 
     Photoelectrochemical oxidication (PECO) is a relatively new commercially available technology used for air cleaning. It uses filters coated with nano particles of titanium dioxide TiO2, which, in the presence of water and under radiation of UVA light (UV light with wavelength 315-400 nm), can produce hydroxyl radicals and super-oxide ions to oxidize the organic contamination into volatile organic compounds (VOCs), and eliminate micro-organisms adsorbed on the catalyst surface. It is claimed that the PECO systems can remove particles as small as 0.1 um. 
     The semiconductor catalyst (TiO2) assisted photoelectrochemical reactions occur as below:
 
TiO2 (with phonon energy  hv )→TiO2( e−+h +)  (1)
 
TiO2( h +)+RX→TiO2+RX+,  (2)
 
TiO2( h +)+H2O→TiO2+HO.+H+  (3)
 
TiO2( h +)+OH—→TiO2+HO.  (4)
 
TiO2( e −)+O2→TiO2+O2−  (5)
 
     The PECO system shows a number of pathways for the production of oxidative species that facilitate the oxidation of the organic species, RX, in addition to its direct oxidation by the excited TiO2 itself. To enable the air cleaning, the organic species RX need to contact the surface of the TiO2 to engage to either itself or any oxidative species to make things work, which is not a very efficient way for a consistently running air flow. It is also quite clear that water molecule in the air play a crucial part in these reactions. For air with low humidity, such as air in airplane (usually humidity less than 20%), the reactions described above are much less efficient. Moreover, to make things work, it still need the physical filter. Virus (size as small as −20 nm) below 0.1 um can pass through and escape from the PECO air cleaning system. 
     Germicidal UV-C (UVC, also named as far UV or deep UV light with wavelength 180-280 nm) and UV-B (or UVB with wavelength 280-315 nm) can be used for air cleaning. The UVC and low wavelength UVB can make damage on protein in virus and prohibit its reproduction activity. UVC and UVB light can even efficiently inactivate organic bioaerosols such as multi-drug-resistant bacteria, differing strains of viruses. The basic theory behind this application is that the UVC and low wavelength UVB can deactivate pathogenic bacteria, viruses and other microorganisms via formation of thymine dimers in deoxyribonucleic acid (DNA), which prevents further replication of the DNA strain. It is worth to note that the maximum absorption wavelength of DNA or RNA is approximately 260 nm, therefore UVC is much more efficient than UVB. 
     The widespread use of germicidal ultraviolet light in public settings has been very limited because UV light, particularly UVB, UVA and high wavelength UVC light, are a human health hazard, being both carcinogenic and cataractogenic. Secondly, the conventional UVC sources, which are the most efficient one for germicidal purpose, are Low- or medium-pressure mercury vapor lamps with a high operating voltage on the order of 1-10 kV, and a high-power UV radiation (on the order of 10 W) at a wavelength of 254 nm-close to 260 nm, which are not for the portable, particularly for handhold devices. There are many drawbacks to using mercury vapor lamps; for example, the lamps contain highly toxic mercury sealed in a fragile quartz glass tubes, which is easy to break and contaminate the environment. The lamps have a long warmup times of approximately 10 min. 
     Deep-ultraviolet, i.e. UVC, light-emitting diodes (DUV-LEDs, UVC LEDs), a solid light source based on carrier injection into multiquantum well (MQW) semiconductor layer, has numerous advantages and may provide solutions to the above drawbacks of UV mercury lamps for portable and handhold air cleaning devices. Two materials systems provides most promising working devices—AlGaN, and InGaN. Despite of a lot of progress for AlGaN DUV LED systems, such as achieving a narrow emission spectrum which is tunable between 210 nm (AlN) to 365 nm (GaN), a low operating voltage of the order of DC 10 V, and instantaneous operation, most commercially available DUV LED is still based on InGaN with wavelength at the high boundary of DUV (ie. 265-285 nm). Another issue of existing DUV LED is its really low external quantum efficiency (only a few % for the time being), which means that, to achieve high output power, a significant input power needed with majority of power turning into heat. This demands a solution for quick heat dissipation. On the other hand, UVC LED is much more suitable for handhold air cleaning devices. 
     It is not easy to make a UVC LED working on a handhold air purification device. One one hand, considering UVC LED&#39;s low output efficiency and challenge on heat dissipation for keeping the device alive, only UVC LED with output power of a few mW can be used on the portable or handhold system. On the other hand, to make air cleaning work, the bioaerosols need to expose under enough UVC dosage or enough accumulated light energy to trigger the dimmer formation. This puts forward a great challenges on system designers to answer the question—how to use the lower output UVC LED to provide enough energy exposure to terminate the DNA&#39;s reproduction in the incoming bioaerosols within the air stream. 
     The invention proposed here provides a solution for this dilemma for portable or handhold air cleaning device based on UVC and/or UVB LED. 
     SUMMARY OF THE INVENTION 
     In this invention, we proposed a design for a portable or handhold air cleaning device based on the UVC and/or UVB LED. 
     The concept of this invention is to use the high UVC and/or UVB reflection (&gt;75%) and low UVC and/or UVB absorption material at least on the internal surface of air supply pipeline, whose internal surface acts also as a UV light waveguide. By doing so, it provides enough UVC and/or UVB light exposure to deactivate all the incoming bioaerosols in the supplied air, therefore offers a cleaned air stream to its user. 
     The design principle of the proposed system is to allow everything in the air flow through the system, from the air inlet to the air outlet, to experience maximum UV exposure. As such, we add UV photon entanglement block(s) within the air flow pipeline (also UV waveguide) to locally further boost the UV area density (dosage) as well as reduce the air flow speed to provide more UV exposure for everything in the incoming air flow. In one design, several UV reflector, also acting as air flow speed buffer, are built in the air flow pipeline using the highly reflective material to provide either a further enhancement for the UV exposure time or reflect the UV light back to the system for the safety of the its user. In another design, porous highly UV reflective materials is chosen to act as UV entanglement block and air flow speed buffer. 
     Moreover, a new plamonic feature or several features with electrical isolated metal nano-particles (NP) on top of the high UV reflective substrate, are added inside the air flow pipeline to further enhance the cleaning functionality. The incoming UV light will induce plasmonic resonance in the metal nano particles, to either generate the plasmon induced heating or re-emit enhanced UV light around the NP at the interface between the NP and air. Several materials, such as Al, Ga, Rh will be used for such purpose. The plasmonic feature is also used at the air outlet of the system to provide UV absorption as well as air heating before the air supplied to its user(s). 
     In another design, device with TiO2 or ZnO nano particles on a either solid or porous highly UV reflective materials is introduced to provide further air cleaning based on either photocatalytic reactions or PECO when there is enough moisture in the incoming air. This also help to absorb the UV light at the middle point of air flow path. 
     The plasmonic feature(s) and UV photon entanglement blocks will be placed around the middle point of the air flow path so that UV light, injected from both the air inlet side and the air outlet side can interact with them. 
     Considering the UV light interacting with oxygen in the air could potentially generate some small amount of ozone, the system also implements an activated carbon filter near the air outlet inside the air flow pipeline purely for the purpose of removing the small amount of ozone from air supply to its user. 
     To provide cooling to the UVC and/or UVB LED, we implement a thermal electrical cooler (TEC) with a heat sink, whose higher temperature end is placed near the air outlet outside the air flow pipeline to warm up the output air above the ambient temperature, which provides an expelling force to the ambient air. This helps to create an air supply system to ensure the air reaching to its user is the purified air from the system rather from the surrounding environment. 
     Our portable and/or handhold air cleaning system is very useful for travelers in the closed environment such as in an airplane, or on a train. It can also use in office during flu season particularity for the elderly as well as provide cleaned air for users against the hay-fever. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  a schematic embodiment of the portable or handhold system proposed in this invention to use UVC or UVB LED for air purification. 
         FIG. 2  one of the embodiment of UV photons entanglement structure also acting as an air flow buffer. 
         FIG. 3  an embodiment of another design with air flow path reduction, UV entanglement structure and plasmonic feature in the system. 
     
    
    
     DETAILED DESCRIPTION 
     The following numerous specific detail descriptions are set forth to provide a thorough understanding of various embodiments of the present disclosure. It will be apparent to one skilled in the art, however, these specific details need not be employed to practice various embodiments of the present disclosure. In other instances, well known components or methods have not been described. 
       FIG. 1  shows a schematic embodiment of the proposed handhold system in this invention. As mentioned previously, the design principle of the proposed system is to allow everything in the air flow to experience maximum UV exposure from the air inlet to air outlet by using the air flow pipeline as a UVC/B light waveguide based on the reflection from the internal surface of the air pipeline made of UVC/B highly reflective and low absorption material(s). For the purpose of simplicity, in  FIG. 1 , only the internal surface of the air pipeline is shown and represented here. Having said that, the highly UVC/B reflective material for internal surface of the air flow pipeline and the body of the air flow pipeline can certainly be the same materials such as Polytetrafluoroethylene (PTFE). As shown, the whole air pipeline at least the internal surface made of highly UVC/B reflective material has a sealed end indicated here as  101 . Ambient air  102  shown here as a arrow is taken into the system from the air inlet with an air filter  103  either from an air pump or a blow-in fan. The air filter built in the air inlet is just a low grade filter to prevent dust in the air into the system. The air flow inside the system shown here as  104 , represented by the broken lines, goes through the whole air flow pipeline and reach to the air outlet  105  indicated by another arrow  106 . The whole air flow pipeline presented here as a U shape with the dotline  107  indicating that the whole pipeline can be much longer than what is being shown here. 
     The light injection into the system is from two UVC/B LEDs  108 . For the simplicity of drawing, two UVC/B LEDs are shown here. Nevertheless, a single LED can certainly be used in the system with proper design of the reflection from the internal surface of the waveguide for splitting the beam (batch of light) from one LED into two similar paths as indicated here in  FIG. 1 . In fact, using one UV LED saves power and make the heat dissipation relatively easier, which is particularly important for handhold device. Nevertheless, with main power outlet available on modern airplanes and trains, even for personal handhold air purification device, power may not be a limited factor here. The UVC/B (much more preferable UVC due to the main DNA absorption peaking at 260 nm) LED(s)  108  sits on its own package mostly with a heat sink  109 . A thermoelectric cooler TEC  110  is used and mounted over the LEDs&#39;s own heat sink  109  to assist the heat dissipation of the LED  108 . The TEC is also thermally connected to its own heat sink  111 , which also links to a heat spreader/radiator  112  surrounding and being out the air flow pipeline. The heat spreader/radiator  112  helps to warm up the air  106  out from the air outlet  105 , which helps to provide warmer air than that of ambient air to the user. The warmer air also has a higher pressure than that of the ambient air therefore provide an expel force pushing the colder ambient air away from the user and makes the post-purified air from the system become the solo air source for the user(s). 
     The UVC/B light  113  emitting from the LED  108  is also surrounded by UVC/B waveguide  114  made of UVC/B highly reflective materials with low light absorption, and is guided and split into the air inlet branch and air outlet branch to purify the air flow  104  at both branches. The batch of arrows  115  indicated the UVC/B, at the air inlet branch, bounced by the internal reflection of the waveguide  114  and the internal surface of air flow pipeline  101  while the branch of arrows  116  indicated those at the air outlet branch experience similar reflection. It is worth to note the two branch of arrows or UV light will eventually meet around the middle point of the air flow path  117 . Near the middle point of the air flow path  117 , there are some special structures and or functional features to further enhance the air purification and cleaning, which will be discussed in the following sections. 
     As shown in  FIG. 1 , near the air outlet  105 , there are also a couple of functional features:  119  is a plasmonic device made of UVC/B highly reflective material, on which there is specially fabricated electrically isolated metal nano particles being able to generate plasmonic resonance at the UVC and low UVB wavelength; near the air outlet  105 ,  120  is an activated carbon filter, whose function is to remove any trace of ozone, which could be produced or already existing in the incoming air flow. It also help to remove any odor, if there is any, from the incoming air flow and it is the last safeguard before the purified air reaching its user(s). 
     There are quite a few choice of materials for UVC/B with high reflection and low absorption. They are general PTFE film or tube (eg. those from Gore); or ePTFE (expanded PTFE) film or tube; or porous PTFE film or tube; film of Nitrocellulose; or even Nitrocellulose pain with special components (without those for high UVC/B absorption); Teflon® tape/film and tube; Aluminum foil or tube; Tetratex® film or tube from Tetratec Corp (with its main composition as ePTFE); 3M™&#39;s enhanced spec reflector (ESR) film/sheet (made of multi-layer polymer); Dupont™&#39;s Tyvek® paper (made of high density polyethylene fibers) or Melinex® film/sheet (polyester); or Toray&#39;s Lumirror™ sheet (polyester). 
     For material used for the plasmonic device, nano particles in the size range from 5 nm-100 nm from Aluminium (Al) with AlOx, Ga, even more expensive Rh, or their combinations as an alloy system or an composite system for plasmonic resonance within UVC/B wavelength. 
       FIG. 2  shows one of the embodiment of cross-section view for the UV photons entanglement structure also acting as air flow buffer shown as  118  near the middle point of the air flow path  117  in  FIG. 1 . In this specially designed structure in the pipeline  200 , just as shown in  FIG. 1 , the internal surface of the air pipeline  201  is made of highly UVC/B reflective and low UVC light (and/or UVB light) absorption materials, the structures  202  are planes also made of highly reflective and low UVC light (and/or UVB light) absorption materials, which is inserted into the air flow pipeline. The arrangement of the planes  202  still allows the air flow  203  to pass from left to right in this particular illustration but it will slow down the air flow speed to allow more dwell time of the air flow in this area. The incoming bounced UV light from left  204  and from right  205  all will be reflected multiple times, as represented by the solid arrows, by these planes at various locations while they try to find a way proceed. The dot lines of  207  indicates that the reflection will continue till all the light energy is fully absorbed by the materials during the propagation of UVC/B light in the air flow pipeline or absorbed by any pollutant or bioaerosols in the air flow. The whole structure  200  allows air flow and tangled UVC/B photons interact more thoroughly therefore effectively increase the opportunity of UVC/B exposure for any pollutant in the air flow. For any pollutant in the air flow, the overall UVC/UVB dosage which it exposes is the total UVC/B light it experiences after it gets into the system at air inlet before it gets out at the outlet. The longer it stays within the air pipeline, the higher the local UVC/B light intensity is, the higher the dosage it will see for any pollutant in the air stream. The structure  200  literally acts as a local UV light enhancement features via light entanglement (also with air flow) due to the reflection as well as extend the time for any pollutant exposed under the UV light. 
       FIG. 3  shows an embodiment of another design with cross section reduction of the air flow path, UV entanglement structure, and a plasmonic feature near the middle point of the air flow path  117  in  FIG. 1  in the system. The design  300  has the internal surface of the air pipeline  301  made of highly UVC/B reflective and low UVC (and/or UVB) light absorption materials. As shown, the cross section of the air flow pipeline  301  is larger at the both ends and smaller in the middle of air flow pipeline. As such, the air flow is forced to reduce it cross section dimension while the air flow speed gets increased. The increase of air flow speed helps the flow go smoothly through the feature  302 , which is made of either thin film with pass through channels with predetermined size (eg. certainly larger than 320 nm—upside of the UVC/UVB wavelength) or porous films of the highly reflective materials for UVC/B beams (batch of light) from both left  303  and right  304 . The channels size varies in such a way that the closer to the center, the smaller the size. The ideas is that the air can flow through the the channels with greatly reduced cross section while the UVC/B photons can pass through the channels but get entangled in this areas due to multiple reflection induced light bouncing to provide more interactions with any pollutant in the air flow. Therefore, this provides chance for any pollutant to see more UVC/B dosage when it goes along with the air flow from air inlet to the outlet. The longer the UVC/B LED is on, the higher the intensity of the UC/B light within the feature  302 . As shown in  FIG. 3 , there is another devices  305 , which locates near the middle of the air flow path. It is arranged similar as what has been shown in  FIG. 2 . 
     In one case, the device  305  is made of electrically isolated metal nano particles (NPs), which can generate plasmonic resonance at the wavelength of UVC/B, deposited on highly UVC/B reflective film or substrate. The incoming UVC/B light will generate plasmonic resonance within these NPs, which can either heat up the NPs (plasmonic photothermal effect) or produce enhanced UVC/B light (plasmonic light enhancement effect) at the interface between the metal NPs and air. Metals such as Al, Ga, Rh, or their combination either as an alloys or a composite is capable of doing such tricks. Photothermal effect can raise the local temperature to significant high enough to deactivate some organic materials while the light enhancement effects products much stronger UVC/B light around the edge particularly the sharp corner of metal NPs (as antennas), which can boost local UVC/B dosage dramatically. 
     In another case, photocatalyst NPs, such as Titanium dioxide (TiO2), or Zirconium oxide (ZrO), or Zinc oxide (ZnO), or Magnesium oxide (MgO), or tungsten trioxide (WO3), or the combinations of the above mentioned photocatalyst along with or without small amount of addition of precious metal such as Pt, Au, Ru, Rd, Rh, is deposited on UV highly reflective and low UVC/B absorptive solid film or porous film. The UVC/B induced photocatalyst effect (if the incoming air is dry) or PECO effects (if the incoming air has high moisture) can further assist the air purification for the system. It is worth to note that our proposal here is different from the normal PECO systems in the market, which uses UVA light and also the catalyst particles is deposited on air filter(s). Here, the proposal catalyst is deposited on high UVC/B reflective and low UVC/B absorptive substrate to enhance the interaction between the photons and NPs of photocatalyst. Also the designed system expect to work well for dry air with low humidity based on photocatalyst effect alone.