REIJMER, Chris (K-3A-12, Solaris 2 Jalan Solari, Mount Kiara Kuala Lumpur, 50480, MY)
BULDER, John (No 29 Jalan TR9/1, Tropicana, Petaling Java, 47410, MY)
REIJMER, Chris (K-3A-12, Solaris 2 Jalan Solari, Mount Kiara Kuala Lumpur, 50480, MY)
| CLAIMS 1. A rotor assembly (1 ) for a rotary atomizer comprising: a rotor (2); and at least one nozzle insert (3) that acts as an atomizing nozzle of rotor assembly (1); characterized in that the nozzle insert (3) is preferably a porous plastic insert (3). 2. A rotor assembly (1) according to claim 1 , wherein the rotor (2) is disc shaped. 3. A rotor assembly (1 ) according to claim 1 , wherein the at least one porous plastic insert (3) has the shape of a centrally apertured disc. 4. A rotor assembly (1) according to claim 1 , wherein the at least one porous plastic insert (3) is positioned along the perimeter of rotor (2). 5. A rotor assembly (1 ) according to claim 1 , additionally comprising a rotor back plate (4) to further secure the at least one porous plastic insert (3). 6. A rotor assembly (1 ) according to claim 1 , wherein the rotor (2) has a plurality of insert holders (5) whereby the insert holders (5) secure the position of the porous plastic inserts (3). 7. A rotor assembly (1 ) according to claim 6, wherein the insert holders (5) are positioned along the perimeter of rotor (2). 8. A rotor assembly (1 ) according to claim 6, wherein the insert holders (5) have uniform sizes and are spaced apart uniformly. 9. A rotor assembly (1 ) according to claim 6, wherein the porous plastic inserts (3) have uniform sizes and are spaced apart uniformly. 10. A rotor assembly (1 ) according to claim 6, wherein the porous plastic insert (3) is preferably of a shape that fits between consecutive insert holders (5). 11. A rotor assembly (1 ) according to claim 6, wherein a radial cross sectional area (6) of porous plastic insert (3) is larger than a radial cross sectional area (7) of porous plastic insert (3), said cross sectional area (7) being further away from the center of rotor (2) than cross sectional area (6). 12. A rotor assembly (1 ) according to claim 1 , wherein the at least one porous plastic insert (3) is made of sintered porous thermoplastic resin. 13. A rotor assembly (1 ) according to claim 12, wherein the thermoplastic resin is Ultrahigh Molecular Weight Polyethylene (UHMWPE). 14. A rotor assembly (1 ) according to claim 1 , wherein the average pore size of the at least one porous plastic insert (3) is smaller than 500 micron. 15. A rotor assembly (1 ) according to claim 1 , wherein the void volume of the at least one porous plastic insert (3) is between 30 and 80 percent. 16. A rotor assembly (1 ) according to any of the proceeding claims, wherein the rotary atomizer is used to atomize water. 17. A rotor assembly (1 ) according to any of the proceeding claims, wherein the rotary atomizer is used for evaporative cooling purposes. |
The present invention relates to a rotor assembly for a rotary atomizer used to atomize liquids, and more specifically to a rotor assembly for a rotary atomizer with nozzle inserts.
BACKGROUND
A rotary atomizer is a device to atomize liquids such as water, insecticide, fertilizer, resin or paint into a cloud of droplets. The average droplet size is important, and depends on the type of liquid to be atomized, required flow rate, nozzle insert pore size and dimensions, and rotor diameter and speed.
Typical rotary atomizers have the liquid to be atomized fed near the axis of an atomizer rotor. The rotor has a plurality of holes which act as nozzles. As the liquid's inertia forces the liquid through the rotating nozzles and rotor, the liquid is dispersed in a cloud of droplets in a radial direction. The atomizer rotor can be driven by a propeller, a turbine, a belt or an electrical motor. International application WO 2010/030156 A1, by the same inventors of the present invention, discloses a rotary atomizer for dispersing liquids, which uses a rotor with metal foam inserts as the atomizing nozzle, whereby the metal foam inserts are installed along the perimeter of the rotor supported by insert holders. Metal foam makes a suitable nozzle because it is rigid and highly porous.
Reticulated metal foam basically can be manufactured with an average pore size of 300 micron, up to an average pore size of 1000 micron. Atomizers with metal foam inserts generally atomize a liquid into a cloud of droplets with an average droplet size of 20 micron up to an average droplet size of 200 micron, depending on the liquid to be atomized, the required flow rate, rotor diameter and speed, and pore size used.
However, there are many applications where a smaller average droplet size, ranging from an average droplet size of 0.5 micron to an average droplet size of 20 micron, has a significant advantage. It is difficult to achieve said droplet size range with a rotary atomizer assembled with metal foam inserts. In the case of atomizing water for the purpose of humidification or evaporative cooling, an average droplet size below 20 micron has an advantage. Another requirement for atomizers used for humidifying or evaporative cooling applications is the fact that these devices should be robust enough to withstand 8 to 16 hours of use a day over a prolonged period of time.
SUMMARY OF INVENTION
The invention is conceived by the need to provide a rotary atomizer that is effective in terms of droplet size distribution and flow rate, and strong enough to withstand 8 to 16 hours of use a day over a prolonged period of time, with a target mean droplet size smaller than 20 micron. Disclosed is an atomizer in which one or more preformed porous plastic inserts are placed along the perimeter of the atomizer rotor and act as nozzles. The at least one porous plastic insert is securely held in position in the disclosed rotor assembly. The rotor assembly of the rotary atomizer can be designed to meet the output requirements regarding the liquid to be atomized, flow rate and droplet size in terms of nozzle insert pore size and dimensions, and rotor diameter and speed. The porous plastic insert can be manufactured with an average pore size as small as 0.1 micron, which means that the desired droplet size can be reached at lower rotor speed and input power levels compared to currently available rotary atomizers.
BRIEF DESCRIPTION OF DRAWINGS
The invention will now be described in greater detail, by way of an example, with reference to the accompanying drawings, in which:
Fig. 1 illustrates an axial cross section of a rotor assembly for a rotary atomizer in accordance with an embodiment of the present invention;
Fig. 2 illustrates a perspective view of a rotor with porous plastic inserts in accordance with another embodiment of the present invention; Fig. 3 illustrates a perspective view of an axial cross section of a porous plastic insert of the rotor assembly in Fig. 1 ; Fig. 4 illustrates a perspective view of a porous plastic insert of the rotor assembly in Fig. 2;
Fig. 5 illustrates an axial cross section of a porous plastic insert in accordance with yet another embodiment of the present invention.
DESCRIPTION OF EMBODIMENTS
Fig. 1 shows an axial cross section of a rotor assembly (1 ) for a rotary atomizer in accordance with an embodiment of the present invention. The rotor assembly (1) includes a rotor (2), at least one nozzle insert (3) and a rotor back plate (4). Rotor (2) is disc shaped. The nozzle insert (3) which acts as an atomizing nozzle of rotor assembly is characterized as a porous plastic insert (3). In the figure, porous plastic insert (3) has the shape of a centrally apertured disc. The porous plastic insert (3) is positioned along the perimeter of rotor (2), and ultrasonically welded between rotor (2) and rotor back plate (4). The liquid to be atomized is axially fed into rotor (1 ) through the gap between rotor (2) and rotor back plate (4). As the liquid's inertia forces the liquid through the rotating porous plastic insert (3) and rotor (2), the liquid exits porous plastic insert (3) in a cloud of droplets in a radial direction. Fig. 2 illustrates a perspective view of a rotor (2) with ten insert holders (5), whereby the insert holders (5) secure the position of the porous plastic inserts (3). In the figure only five porous plastic inserts (3) are shown for the purpose of illustrating the concept. Insert holders (5) are positioned along the perimeter of rotor (2). The insert holders (5) have uniform sizes and are spaced apart uniformly.
The rotor (2) is designed to deliver the internal tensile stress that provides the required centripetal force for circular motion. Another design objective for rotor (2) is to make rotor assembly (1) sufficiently strong to counter liquid pressure buildups along the perimeter of rotor assembly (1 ). In the rotor assembly (1 ) shown in the figure, the porous plastic inserts (3) have uniform sizes and are spaced apart uniformly. Porous plastic insert (3) is preferably of a shape that fits between consecutive insert holders (5). A radial cross sectional area (6) of porous plastic insert (3) is larger than a radial cross sectional area (7) of porous plastic insert (3), said cross sectional area (7) being further away from the center of rotor (2) than cross sectional area (6), and as a result porous plastic insert (3) is supported by and wedged between rotor (2), insert holders (5) and back plate (4). Fig. 3 illustrates a perspective view of an axial cross section of porous plastic insert (3) shaped as an apertured disc, in accordance with an embodiment of the present invention. Preferably the porous plastic insert (3) is ultrasonically welded between rotor (2) and back plate (4). Fig. 4 illustrates a perspective view of a porous plastic insert (3) in accordance with another embodiment of the present invention. Fig. 5 illustrates an axial cross section of a cone shaped porous plastic insert (3) in accordance with yet another embodiment of the present invention. The figure also shows a position of cross sectional area (6), and a position of cross sectional area (7), said cross sectional area (7) being further away from the center of rotor (2) than cross sectional area (6). The radial cross sectional area (6) of porous plastic insert (3) is larger than the radial cross sectional area (7) of porous plastic insert (3).
The porous plastic insert (3) is made of sintered porous thermoplastic resin. Porous plastic insert (3) is a cohesive mass of resin particles fused together in a sintering process. The result of this process is a highly customizable porous thermoplastic medium of particular shape. A wide variety of thermoplastic resins can be sintered to make porous plastic insert (3). Particle size and shape of resin powders are manipulated to optimize physical characteristics for atomizing liquids. These physical characteristics include pore size, void volume, surface texture, and strength. Further customization is possible by introducing active ingredients into the raw materials and by molding unique geometries.
Pore size is determined by controlling the resin particle size and can range from 0.1 to 500 microns. Generally, median pore size is twenty five percent of the resin particle size.
Void volume is controlled independently of pore size and is determined by the resin particle shape. Irregularly shaped particles yield higher void volume. Spherical particles yield lower void volume. Void volumes may also be manipulated by creating aggregate blends of resins. Porous plastic insert (3) void volumes can be targeted between thirty and eighty percent, depending on the application and liquid to be atomized. Surface texture and strength are manipulated by controlling particle size and shape. Smoother textures can be achieved by using smaller more spherical resin particles. Larger, irregular particles yield more coarse or abrasive end products. Strength is manipulated by the degree to which the resin particles melt and adhere to one another during the sintering process. Crosslinking the sintered porous plastic insert (3) is possible with certain thermoplastics, and improves wear resistance and reduces creep. Crosslinking can be achieved chemically (by adding 0.3-0.5% organic peroxides) as well as by beta or gamma irradiation.
Resin selection also allows control of flexibility, hardness, and other physical characteristics. Some resins are extremely flexible and elastic while others are very strong and rigid.
Porous plastic is easily impregnated by a variety of active ingredients to achieve specific performance objectives. These active ingredients include surfactants, activated carbon, ion exchange resins, and self-sealing additives. Porous plastic insert (3) can be manufactured in sheet form with subsequent die cutting to deliver the desired shape, or molded into unique three dimensional geometries.
Porous plastic insert (3) can be suitably made by sintering resins such as Ultra High Molecular Weight Polyethylene (UHMWPE), High Density Polyethylene (HDPE), Low Density Polyethylene (LDPE), Very Low Density Polyethylene (VLDPE), Polypropylene (PP), Ethylene Vinyl Acetate (EVA), Polytetrafluoroethylene (PTFE), Polyvinylidene fluoride (PVDF), Polystyrene (PS), Nylon, Epoxy Glass or Phenol Glass.
Preferably, porous plastic insert (3) is made of sintered porous Ultra High Molecular Weight Polyethylene (UHMWPE), with average pore size smaller than 500 micron and void volume between 30 and 80 percent. Ultra high molecular weight polyethylene (UHMWPE), also known as high-modulus polyethylene (HMPE) or high- performance polyethylene (HPPE) is a linear, low-pressure, Ziegler-type-catalyst, polyethylene resin.
It has extremely long chains, with molecular weight numbering in the millions, usually between 2 and 6 million. The longer chain serves to transfer load more effectively to the polymer backbone by strengthening intermolecular interactions. UHMWPE has very high abrasion resistance and impact strength.
It is highly resistant to corrosive chemicals, with exception of oxidizing acids. It has extremely low moisture absorption, has a low coefficient of friction, is self-lubricating, and is highly resistant to abrasion. Its coefficient of friction is significantly lower than that of nylon, and is comparable to that of Teflon, but UHMWPE has better abrasion resistance than Teflon. It is odorless, tasteless, and nontoxic.
These characteristics make sintered UHMWPE a preferable material for a nozzle insert (3) for a rotary atomizer.
Other sintered porous inserts for a rotary atomizer have been tested, such as sintered porous ceramic inserts or sintered porous metal inserts. These inserts, with their relatively high density, large pressure drop and limited output do not perform adequately in a rotary atomizer. The present invention is suitable for various uses, such as the dispersing of liquids in general - liquid fertilizers, insecticides, scents, disinfectants, water, paint or oil. An important area of application of the invention is evaporative cooling by atomizing water, both indoors and outdoors. Another important area of application of the invention is humidification by atomizing water, both indoors and outdoors. Based upon the liquid to be atomized and the design droplet size and liquid flow rate through the atomizer, pore size and exit surface area of, and pressure differential across the porous plastic insert (3) are determined. Based upon the required pressure differential across the insert, diameter and angular velocity of rotor (2) are determined. The porous plastic insert (3) can be manufactured with an average pore size as small as 0.1 micron, which means that the desired droplet size can be reached efficiently even at relatively high liquid flow rates, compared to currently available rotary atomizers.
When atomizing water, bacterial contamination of the source liquid is a serious concern. Air borne aerosols containing for instance Legionella Pneumophila can lead to lung disease and even death upon inhalation by humans. The majority of water borne bacteria is larger than 0.5 micron. These bacteria are killed as they disintegrate when pushed through the porous plastic insert (3), if it has a pore size smaller than 0.2 micron.
The present invention offers specific advantages over other types of rotor assemblies for rotary atomizers. One advantage of the present invention is that it provides a simple, robust and cost effective construction. Rotor (2) can be produced in volume to close tolerances by injection molding an engineering plastic. The fact that sintered porous plastic insert (3) can be molded to close tolerances with predictable pore size ranges and distributions is another advantage. When using a thermoplastic with a low coefficient of friction for porous plastic insert (3), atomizing noise levels drop significantly as well.
The present invention also allows an increased lifespan of the atomizer. The assembly of rotor (2), insert holders (5), back plate (4) and porous plastic inserts (3) can be designed specifically to bear the load required to get the desired liquid output flow rate and droplet size, and to prevent premature yielding of the porous plastic insert (3) during the atomizer's usable life.
While embodiments of the invention have been illustrated and described, it is not intended that these embodiments illustrate and describe all possible forms of the invention. Rather, the words used in the specifications are words of description rather than limitation and various changes may be made without departing from the scope of the invention.