ELECTROHYDRODYNAMIC ATOMIZATION NOZZLE EMITTING A LIQUID SHEET
Embodiments for producing un-agglomerated, monodisperse droplets using a liquid sheet are provided. Nozzles with exit slit openings shape a spray liquid into a thin liquid sheet as the spray liquid exits from the slit opening. Stable multi-jet operation is achieved by including notches along the edge of the slit. The notches separate the liquid sheet into multiple jets to provide anchoring and stable multi-jet operation. In some embodiments, the liquid sheet electrospray techniques and nozzles described herein provide high mass throughput and versatile multiplexing spray systems while reducing the engineering effort and high manufacturing cost
Electrohydrodynamic atomization, often called electrospray (ES), has recently attracted great attention for potential and practical particle applications in fine powder production, food processing, medicine, pharmaceutics, biology, and chemistry. The technique enables the production of un-agglomerated, monodisperse particles of various materials with sizes ranging from micro-meter to nano-meter. In known ES systems, a liquid meniscus at the exit of a capillary nozzle is subjected to an electrical stress, resulting from a divergent electrical field established between a spray head and a reference electrode. Due to the geometry of capillary nozzles, however, known ES systems have low mass throughput, which makes the feasibility of large scale implementation difficult.
Several recent electrohydrodynamic atomization techniques reportedly increase the mass throughput. For example, in a single-capillary ES nozzle, a multi-jet mode can be generated when the applied voltage exceeds a voltage range for a cone-jet mode. However, multiple liquid jets initiated from a single-capillary head are unstable. Arranging a number of individual capillaries in a one-dimensional linear array also increases the total spray liquid flowrate. However, although the one-dimensional arrangement of individual capillaries is easy to construct for laboratory investigation, it is not practical for industrial scale applications. Further each individual capillary uses a separate feeding and/or distribution channel.
SUMMARYIn a first aspect, a nozzle for electrohydrodynamic atomization is provided. The nozzle includes an inner rod, an outer tube concentrically aligned with the inner rod, an annular channel defined between the inner rod and the outer tube, the annular channel forming a circular slit at a spray end of the nozzle, and at least one electrically chargeable notch located on at least one of the inner rod and the outer tube proximate the circular slit.
In another aspect, a system for electrohydrodynamic atomization is provided. The system includes a nozzle including a source end, a spray end, a first component including a first surface, a second component including a second surface, a fluid channel defined between the first surface and the second surface, the fluid channel forming an exit slit at the spray end of the nozzle (e.g., a circular exit slit, a planar or linear exit slit, etc.), and at least one electrically chargeable notch located on at least one of the first component and the second component proximate the exit slit. The system may further include a voltage source electrically coupled to the nozzle and configured to supply a voltage to the at least one electrically chargeable notch, and a syringe pump in flow communication with the source end of the nozzle, the syringe pump configured to propel a spray liquid through the nozzle.
In yet another aspect, a method for electrohydrodynamic atomization is provided that may use one or more of the nozzle configurations described herein. For example, in one aspect the method may include providing a nozzle including an inner rod, an outer tube concentrically aligned with the inner rod, an annular channel defined between the inner rod and the outer tube, the annular channel forming a circular slit at a spray end of the nozzle, and a plurality of notches located on at least one of the inner rod and the outer tube proximate the circular slit. The method further may include supplying a voltage to the plurality of notches, and pumping a spray liquid through the annular channel of the nozzle.
The embodiments described herein may be better understood by referring to the following description in conjunction with the accompanying drawings.
Embodiments provide electrohydrodynamic atomization using a liquid sheet to produce un-agglomerated, monodisperse droplets. In contrast to the capillaries/tubes used in known electrospray (ES) systems, nozzles with exit slit openings shape a spray liquid into a thin liquid sheet as the spray liquid exits from the slit opening. Stable multi-jet operation is achieved by including notches along the edge of the slit. The notches separate the liquid sheet into multiple jets to provide anchoring and stable multi-jet operation. That is, each notch anchors a corresponding jet by preventing the corresponding jet from migrating around the nozzle, substantially fixing the position of the corresponding jet. In some embodiments, the liquid sheet electrospray techniques and nozzles described herein provide high mass throughput and versatile multiplexing spray systems while reducing the engineering effort and high manufacturing cost.
A schematic diagram of an exemplary electrospray system 100 is shown in
High-voltage source 106 is coupled to nozzle 104 such that high-voltage source 106 enables a voltage to be applied to a spray end 108 of nozzle 104. In an exemplary embodiment, high-voltage source 106 provides a voltage ranging from 13 kV to 16 kV to spray end 108. Alternatively, high-voltage source may apply any voltage to nozzle 104 that enables system 100 to function as described herein.
System 100 also includes a monitoring system 110. Monitoring system 110 includes a microscopic lens 112, a digital camera 114, a monitor 116, and a computer 118, which enable monitoring system 110 to monitor the spray produced by nozzle 104.
System 100 also includes a current system 120. Current system 120 includes a multimeter 122 electrically coupled to a ground 124 and electrically coupled to ring 126 across a resistor 128. By measuring the voltage across resistor 128, current system 120 can measure the current of the spray produced by nozzle 104. Through multimeter 122, ring 126 is also electrically coupled to ground 124.
In operation, syringe pump 102 applies a pressure to a spray liquid, such that the spray liquid is pushed towards nozzle 200 and received at source end 202 of nozzle 200. The spray liquid is then evenly distributed into annular flow channel 212 and emitted from circular slit 218 as a thin liquid sheet. In the exemplary embodiment shown in
Nozzle 200 further includes one or more notches 230 proximate to circular slit 218. As used herein, a “notch” refers to a protruding element that extends from a spray end of a nozzle, such as notches 230 extending from spray end 204 of nozzle 200. For example, such notches may extend or protrude further in the direction of the spray jet than other regions of the spray end separating such notches. In an exemplary embodiment, notches 230 are located on both inner rod 206 and outer tube 208. Alternatively, notches 230 may be located only on inner rod 206 or outer tube 208. When high-voltage source 106 applies a voltage to spray end 204 of nozzle 200, the shape and configuration of notches 230 facilitate local enhancement of an electric field at notches 230. When the spray liquid reaches the circular slit 218, it exits nozzle 200 as a thin liquid sheet due to the shape of annular flow channel 212. With a sufficiently high voltage applied to spray end 204 of nozzle 200, the thin liquid sheet is separated into multiple jets. Each jet is located at one of notches 230 due to the locally intensified electric field at each notch 230. Further, with a high enough voltage applied to spray end 204, stable multi-jet operation may be achieved. In some embodiments, “stable multi-jet operation” means that a jet of spray liquid is emitted from each notch 230 on nozzle 200.
Each nozzle 300 in
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Multiple experiments were executed utilizing the nozzles described herein. In the following examples, Isopropanol was selected as the spray liquid, and nitric acid was used as an ion additive to vary the electrical conductivity of the spray liquid from 0.0079 μS/cm (pure isopropanol) to 1,044 μS/cm. The electrical conductivity of the spray liquid was measured by a conductivity meter (Orion 162A, Thermo Electron Corporation), and the electrical resistance of pure isopropanol was measured by a lab-made liquid cell. Alternatively, those of ordinary skill in the art will understand that any spray liquid may be utilized which allows system 100 to function as described herein.
In one example, to study the evolution in the formation of multiple jets, the spray current was measured, and the number of jets was counted as the applied voltage was continuously increased and then decreased.
In another example, to determine the mass throughput of the nozzles, spray liquids with various electrical conductivities were used to find the maximum liquid flowrate (Q max) for nozzle operation.
Notably, the value of Q max for a liquid sheet nozzle with twenty notches is much higher than the sum of the total liquid flowrates for twenty single-capillary nozzles. This same phenomenon was also observed using liquid sheet nozzles with six and twelve notches. This indicates that, as compared to existing one-dimensional and two-dimensional arrays of single-capillary nozzles, liquid sheet nozzles have potential to drastically increase the mass throughput for spray liquids having a wide range of electrical conductivity.
In an exemplary embodiment, a plurality of notches 514 are located on both first plate 502 and second plate 504, and staggered with respect to one another. Alternatively, notches 514 may only be located on one of first plate 502 and second plate 504. With a voltage applied to notches 514, notches 514 facilitate separating the thin liquid sheet into a plurality of jets, substantially similar to notches 230 of nozzle 200.
The nozzles illustrated in
In addition to the cylindrical and planar nozzles specifically described herein, those of ordinary skill in the art will understand that any nozzle shape and/or configuration may be utilized which allows system 100 to function as described herein.
Embodiments described herein enable electrohydrodynamic atomization, or electrospray (ES), using nozzles that produce a thin liquid sheet. The methods and systems described herein increase the mass throughput of ES systems while decreasing the design and manufacturing costs as compared to known ES systems utilizing multiple single-capillary nozzles. The nozzles described herein include annular and/or planar slits designed emit a thin liquid sheet of spray liquid. To separate the thin liquid sheet into multiple jets and to anchor the jets for stable operation, a plurality of notches are included at the annular and/or planar slits. That is, each notch anchors a corresponding jet by preventing the corresponding jet from migrating around the nozzle, substantially fixing the position of the corresponding jet. When a voltage is applied to the nozzles described herein, these notches enable local enhancement of an electric field. Further, stable multi-jet operation of the nozzles described herein can be established for a wide range of spray liquids having various electrical conductivities.
Moreover, as compared to known ES systems utilizing arrays of single-capillary nozzles, multiple liquid flow feeding and/or distribution channels are no longer necessary for the nozzles described herein. As such, the design concept and fabrication of the nozzles described herein is simpler than known nozzles, enabling flexibility in the design and/or geometry of the nozzles.
Through experimentation utilizing the nozzles described herein, it was demonstrated that the applied voltage for establishing stable multi-jet operation increased as both the number of jets and the liquid flowrate increased. Further, the maximum operational flowrate through the nozzles described herein was a function of the electrical conductivity of the spray liquid. Moreover, the maximum flowrate for liquid sheet nozzles with various numbers of notches was consistently greater than the total flowrate sum of an array of an equivalent number of single-capillary nozzles. Accordingly, the liquid sheet nozzles described herein enable superior ES techniques. Further, the liquid sheet shape of the spray liquid, as opposed to the cone jet emitted from known single-capillary nozzles, enables the nozzle design to have various geometries, including, but not limited to annular and/or planar slits.
The order of execution or performance of the operations in the embodiments of the disclosure illustrated and described herein is not essential, unless otherwise specified. That is, the operations may be performed in any order, unless otherwise specified, and embodiments of the disclosure may include additional or fewer operations than those disclosed herein. For example, it is contemplated that executing or performing a particular operation before, contemporaneously with, or after another operation is within the scope of aspects of the disclosure.
When introducing elements of aspects of the disclosure or embodiments thereof, the articles “a,” “an,” “the,” and “said” are intended to mean that there are one or more of the elements. The terms “comprising,” including,” and “having” are intended to be inclusive and mean that there may be additional elements other than the listed elements.
This written description uses examples to disclose the disclosure, including the best mode, and also to enable any person skilled in the art to practice the disclosure, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the disclosure is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal language of the claims.
Claims
1. A nozzle for electrohydrodynamic atomization, said nozzle comprising:
- an inner rod;
- an outer tube concentrically aligned with said inner rod;
- an annular channel defined between said inner rod and said outer tube, said annular channel forming a circular slit at a spray end of said nozzle; and
- at least one electrically chargeable notch located on at least one of said inner rod and said outer tube proximate said circular slit.
2. A nozzle in accordance with claim 1, wherein said inner rod comprises a central flow channel defined therethrough.
3. A nozzle in accordance with claim 2, wherein said central flow channel is configured to facilitate flow of at least one of a stabilizing gas and a stabilizing liquid therethrough.
4. A nozzle in accordance with claim 1 further comprising an outermost tube concentrically aligned with said inner rod and said outer tube such that an outer flow channel is defined between said outer tube and said outermost tube.
5. A nozzle in accordance with claim 4, further comprising at least one electrically chargeable notch located on said outermost tube.
6. A nozzle in accordance with claim 1, wherein said at least one electrically chargeable notch is located on only one of said inner rod and said outer tube.
7. A nozzle in accordance with claim 1, wherein said inner rod comprises a center piece at the spray end of said nozzle and said outer tube comprises an end portion at the spray end of said nozzle, said center piece recessed with respect to said end portion.
8. A nozzle in accordance with claim 1, wherein said inner rod comprises a center piece at the spray end of said nozzle and said outer tube comprises an end portion at the spray end of said nozzle, said center piece extended with respect to said end portion.
9. A nozzle in accordance with claim 1, wherein said at least one electrically chargeable notch comprises a plurality of notches, said plurality of notches spaced a distance apart from one another such that when said plurality of notches are electrically charged, an electric field produced by one notch of said plurality of notches does not interfere with an electric field produced by an adjacent notch of said plurality of notches.
10. A system for electrohydrodynamic atomization, said system comprising:
- a nozzle comprising: a source end; a spray end; a first component comprising a first surface; a second component comprising a second surface; a fluid channel defined between said first surface and said second surface, said fluid channel forming an exit slit at said spray end of said nozzle; and at least one electrically chargeable notch located on at least one of said first component and said second component proximate said exit slit; a voltage source electrically coupled to said nozzle and configured to supply a voltage to said at least one electrically chargeable notch; and a syringe pump in flow communication with said source end of said nozzle, said syringe pump configured to propel a spray liquid through said nozzle.
11. A system according to claim 10, wherein said first component comprises a first plate and said second component comprises a second plate, such that said fluid channel is substantially planar.
12. A system according to claim 10, further comprising a nozzle means for emitting a liquid sheet.
13. A system in accordance with claim 10, further comprising notch means for separating a liquid sheet emitted from said nozzle into multiple jets.
14. A system in accordance with claim 10, further comprising means for maintaining a shape of a liquid sheet emitted from said nozzle.
15. A system in accordance with claim 10, wherein said at least one electrically chargeable notch comprises a first notch and a second notch, said first and second notches spaced a distance apart from one another such that when a voltage is supplied to said first and second notches, an electric field produced by said first notch does not interfere with an electric field produced by said second notch.
16. A method for electrohydrodynamic atomization, said method comprising:
- providing a nozzle comprising an inner rod, an outer tube concentrically aligned with the inner rod, an annular channel defined between the inner rod and the outer tube, the annular channel forming a circular slit at a spray end of the nozzle, and a plurality of notches located on at least one of the inner rod and the outer tube proximate the circular slit; supplying a voltage to the plurality of notches; and pumping a spray liquid through the annular channel of the nozzle.
17. A method in accordance with claim 16, wherein the inner rod includes a central flow channel defined therethrough, said method further comprising pumping a stabilizing gas through the central flow channel.
18. A method in accordance with claim 16, wherein the inner rod includes a central flow channel defined therethrough, said method further comprising pumping a stabilizing liquid through the central flow channel.
19. A method in accordance with claim 16, further comprising:
- providing an outermost tube concentrically aligned with the inner rod and the outer tube, such that a outer flow channel is formed between the outer tube and the outermost tube; and
- pumping a sheath liquid through the outer flow channel.
20. A method in accordance with claim 16, wherein supplying a voltage comprises supplying a voltage such that a jet of spray liquid is formed at each of the plurality of notches.
Type: Application
Filed: Feb 13, 2020
Publication Date: Jun 11, 2020
Inventors: Daren Chen (St. Louis, MO), Jingjie Zhang (St. Louis, MO)
Application Number: 16/789,865