Virtual orifice bubble generator to produce custom foam

Abstract

A controlled, high throughput custom foam generator is disclosed which has the ability to generate foam with varying cell characteristics. The generated foam can be two or three dimensional with controlled gas volume ratio, void sizes, placement and distribution in a matrix. Additionally the device can create individual bubbles or bubble strings. The device streams two or more fluids creating one or more virtual orifices that generate uni modal bubbles displaying crystalline behavior. Unlike known prior art, the device embodies simple controls to easily alter and scale the nature of generated foam. The generator can be single, or be part of an array of generators. The ability to easily alter the resulting bubble and cell composition allows the creation of engineered foams of any structure and packing with controlled foam features such as weight, strength, opacity and persistence; thus making it suitable for a wide variety of applications.

Claims

1. A device for creating bubbles comprising: a first fluid gas; a second fluid liquid; a bubble generator having a central channel through which the second fluid flows, and a concentric ring of converging channels arranged circularly around the central channel, the converging channels through which the first fluid flows, and exits from the bubble generator of the central channel and converging channels, the exits in a plane such that the flow of fluid one creates a virtual orifice outside of the bubble generator, the virtual orifice such that bubbles are formed as fluid two flows through the virtual orifice; and wherein the size of the bubbles is
D.sub.bubble=K*((d.sub.bg).sup.3/(4*tan(.sub.bg))).sup.1/3 where D.sub.bubble is a diameter of generated bubbles, K is an empirical constant dependent on fluid characteristics, D.sub.bg is a diameter of the convergent channel ring at the exit plane, and .sub.bg is an angle of convergence of each concentric channel.

2. The device of claim 1, wherein fluid one is air.

3. The device of claim 1, further comprising an air compressor and a metering valve for controlling delivery of the first fluid to the bubble generator.

4. The device of claim 1, further comprising a metering valve controlling delivery of the first fluid to the bubble generator, and wherein the first fluid is a compressed gas.

5. The device of claim 1, further comprising a portable pump connected to deliver the first fluid to the bubble generator.

6. The device of claim 5, wherein the pump is a piston pump.

7. The device of claim 5, further comprising a a flexible reservoir connected between the pump and the converging channels of the bubble generator.

8. The device of claim 1, wherein the second fluid is a solution, suspension, emulsion, or mixture thereof containing a surface active ingredient.

9. The device of claim 1, further comprising a liquid flow controlled pump connected to deliver the second fluid to the bubble generator.

10. The device of claim 9, wherein the pump is a syringe pump or a peristaltic pump.

11. The device of claim 1, further comprising on/off switches connected between each fluid and the bubble generator.

12. The device of claim 1, further comprising: one or more additional bubble generators, wherein all bubble generators are configured in an array; a first distribution channel delivering the first fluid to all bubble generators; a second distribution channel delivering the second fluid to all bubble generators; and wherein exits of all bubble generators are in a planar arrangement such the the array produces bubbles or foam.

13. The device of claim 12, wherein the bubble generators are arranged linearly in the array.

14. The device of claim 12, wherein the bubble generators are arranged in a grid in the array.

15. The device of claim 12, wherein the bubble generators are positioned to create interfering first fluid streams, producing multiple bubble sizes from the array.

16. The device of claim 12, further comprising a first pump and/or a first flow rate regulator on the first distribution channel and a second pump and/or a second flow rate regulator on the second distribution channel, wherein flow control through the pumps and/or flow rate regulators alters output bubble and foam properties including time of persistence and wetness.

17. The device of claim 12, wherein the geometry of the exit channels is different between at least two bubble channels of the array, resulting in output of multiple bubble sizes.

18. The device of claim 17, wherein the bubble generator differences are arranged such that produced bubble output exhibits preferred crystalline packing arrangements.

19. The device of claim 17, wherein the bubble generator geometry differences are arranged such that 80% of the bubble generators produce a unimodal larger bubble, and 20% of the bubble generators produce a unimodal smaller bubble.

20. The device of claim 1, further comprising: one or more additional bubble generators, wherein all bubble generators are configured in an array; a first distribution channel delivering the first fluid to all bubble generators; a second distribution channel delivering the second fluid to one or more of the bubble generators; one or more additional fluids liquid; one or more additional distribution channels delivering additional fluids to one or more of the bubble generators; wherein each bubble generator is delivered one fluid from the second fluid and the one or more additional fluids; and wherein exits of all bubble generators are in a planar arrangement such the the array produces bubbles or foam.

21. The device of claim 20, wherein the bubble generators are positioned to create interfering first fluid streams, producing multiple bubble sizes from the array.

22. The device of claim 20, further comprising a first pump and/or a first flow rate regulator on the first distribution channel, a second pump and/or a second flow rate regulator on the second distribution channel, and one or more additional pumps and/or one or more additional flow rate regulators on the one or more additional distribution channels, wherein flow control through the pumps and/or flow rate regulators alters output bubble and foam properties including time of persistence and wetness.

23. The device of claim 20, wherein the geometry of the exit channels is different between at least two bubble channels of the array, resulting in output of multiple bubble sizes.

24. The device of claim 23, wherein the bubble generator alignment and geometry differences are arranged such that produced bubble output exhibits preferred crystalline packing arrangements.

25. The device of claim 23, wherein the bubble generator geometry differences are arranged such that 80% of the bubble generators produce a unimodal larger bubble, and 20% of the bubble generators produce a unimodal smaller bubble (80/20 packing) or similarly optimized ratio.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) In the drawings, closely related figures and items have the same number but different alphabetic suffixes. Processes, states, statuses, and databases are named for their respective functions.

(2) FIG. 1 is a diagram of a micro-fluidic bubble generator device with two separate, precisely metered, immiscible fluid inputs.

(3) FIG. 2 shows a vertical cross section of the bubble generator device.

(4) FIG. 3 shows an enlarged view of the cross section of the bubble generator of FIG. 2.

(5) FIG. 4 shows a horizontal cross section depicting the circular distribution ring feeding the converging micro channels for fluid one and the central fluid two channel.

(6) FIG. 5 shows a bottom view of the bubble generator.

(7) FIG. 6 shows a virtual orifice external to the bubble generator.

(8) FIG. 7 shows the unimodal bubble generator with fluid pressure and flow controls included.

(9) FIG. 8 shows an array of three bubble generators all creating unimodal bubbles.

(10) FIG. 9 shows fluid two delivery to each bubble generator.

(11) FIG. 10 shows a three dimensional foam generator.

DETAILED DESCRIPTION, INCLUDING THE PREFERRED EMBODIMENT

(12) In the following detailed description, reference is made to the accompanying drawings which form a part hereof, and in which are shown, by way of illustration, specific embodiments which may be practiced. It is to be understood that other embodiments may be used, and structural changes may be made without departing from the scope of the present disclosure.

Terminology

(13) The terminology and definitions of the prior art are not necessarily consistent with the terminology and definitions of the current disclosure. Where there is a conflict, the following definitions apply.

(14) Bubble generatora physical apparatus with one designed set of channels and reservoirs, including a central fluid two channel with exit in plane with exits of a conical arrangement of fluid one channels, but excluding peripheral tubing, pumps and fluid sources.

(15) Devicea system comprising one bubble generator or an array of bubble generators, the necessary fluid feed containers, the ancillary equipment required to power and pump the fluids, and the virtual orifices dynamically created by the channel designs of the generators and the flow of fluid one.

(16) Inputdescribes any area of the system including pumps, reservoirs, channels that are upstream of the device exit.

(17) Channelthe physical grooves or pipes that carry fluid one and fluid two to the exit of the bubble generator.

(18) Reservoira place where fluid collects.

(19) Virtual Orificean area, existing outside the physical bubble generator, not due solely to the physical generator construction, through which both fluid one and fluid two must pass when co-axially delivered from a bubble generator to form bubbles; acts as an exit opening dynamically created by the flow of fluid one through the device, and due to carefully designed parameters for channel sizes and orientations (.sub.bg, D.sub.bg, and D.sub.f2), and fluid one composition and input conditions.

(20) .sub.bgspecifies the angle off center used to deliver fluid one to create the virtual orifice.

(21) D.sub.bgspecifies the diameter of the circular arrangement of fluid one exit channels around the fluid two exit channel.

(22) D.sub.f2specifies the fluid two exit channel diameter.

(23) Arraya purposely designed arrangement of individual parallel bubble generators, configured to deliver bulk quantities of individual bubbles, or two or three dimensional foams as required for desired performance in an application.

(24) Dropletthe output of the bubble generator when the gas fraction is approaching zero, i.e. the bubble is substantially liquid.

(25) Dispersitya measure of the heterogeneity of the bubble sizes.

(26) Mono dispersedthe condition where the device has created droplets having uniform enough size to exhibit crystalline behavior such as self assembly of mono layers with specific packing.

(27) Uni, bi or multi modal bubbleshaving one, two, or more designed and controlled bubble sizes.

(28) Emulsiona fine dispersion of minute beads of one liquid which are not soluble or miscible with the surrounding continuous phase.

(29) Operation

(30) Referring to FIG. 1, co-axial, flow focusing, bubble generator 100 has two separate, precisely metered immiscible fluid inputs. Fluid one 110 is a gas, preferably air, and fluid two 120 is an engineered, foamable liquid or emulsion containing a surface active component.

(31) Referring also to FIG. 2, viewing a vertical cross section of bubble generator 100 at its midpoint shows that fluid one 110 and fluid two 220 never contact within the physical device.

(32) Referring also to FIGS. 3-5, operation of bubble generator 100 involves feeding fluid one 110 at a constant pressure through a concentric ring of converging channels 330. The fluid one input stream fills a number of microchannels 330 arranged around, and converging towards the coaxial and central fluid two channel 340. The converging channels of fluid one are all fed from circular reservoir 430, and are configured similarly to the sheath gas nozzles used in aerosol jet printing. Simultaneously, a constant flow of fluid two 120 (e.g. surfactant in water) is maintained through centrally located channel 340. Fluids one and two exit the bubble generator planarly in close proximity to create a flow focused virtual orifice that generates uniform bubbles of controllable size and characteristics.

(33) The size of the generated uni-modal bubbles is determined by the dimensions, angles and geometry of the immiscible fluid channels, and specific input conditions and characteristics of the fluids. The size of the bubbles is given by:
D.sub.bubble=K*((d.sub.bg).sup.3/(4*tan(.sub.bg))).sup.1/3

(34) where

(35) D.sub.bubble is the diameter of the generated bubbles,

(36) K is an empirical constant dependent on fluid characteristics, such as viscosity,

(37) D.sub.bg is the diameter of the convergent channel ring at the exit plane, and

(38) .sub.bg is the angle of convergence of each concentric channel.

(39) This means that by altering the geometry of the device and/or the characteristics or delivery of fluid one and/or fluid two, one can manufacture bubble generators that create specific diameter, unimodal bubbles. Diameter 550 of the convergent channel ring in the generator exit plane, D.sub.bg, and/or angle of convergence 350 of each concentric channel, .sub.bg, are altered to control bubble size. A typical gas angle .sub.bg of the current invention is 8 degrees. Diameter 560 of the fluid two exit channel, D.sub.f2, along with the flow rate of fluid two and the pressure of fluid one are used to control the gas ratio of the resulting bubbles.

(40) The polydispersity of the bubbles is so low that the created bubbles exhibit preferred packing and crystalline behavior. The device produces significant and useful quantities of uni-modal bubbles with precise control over bubble size and gas volume fraction, from wet to very dry.

(41) The device allows the control of wetness independent of the drop or bubble size by altering flow rates. For example, in generating foam, the generated bubble size is D.sub.bubble. By feeding more liquid, D.sub.bubble stays the same while the wall thickness increases, thereby producing a wetter foam. In the extreme, the foam bubble becomes a drop.

(42) Referring also to FIG. 6, the the flow of fluid one exiting the bubble generator from the microchannels dynamically creates a narrowing cone or virtual orifice 660. This virtual orifice is located externally to bubble generator 100, with geometric similarities to micro fluidic flow focusing devices. The narrowing cone of fluid one encapsulates a volume into which fluid two is precisely metered to form each bubble. The utilization of the virtual orifice decouples the interaction of the fluid streams while also decoupling the pressure and regulation of each fluid, and results in very stable bubble generation. This decoupling eliminates the known issues, associated with conventional micro-fluidic flow focusing devices, that typically occur at the interface where fluid one and fluid two meet.

(43) The decoupling eliminates the need to match fluid pressures at a mechanical orifice. This in turn eliminates the continuous pressure build up experience in existing devices and the increasing shear load on fluid two during extended operation. It minimizes the power required to operate the device over extended periods of use. The decoupling also increases the range of useful fluid two compositions or mixtures to include more shear sensitive materials (e.g. emulsions). Furthermore, mechanical orifice wear is not an issue in generators of the current design and no additional carrier fluid(s) are required for the generated bubbles.

(44) Referring also to FIG. 7, a very useful consequence of the decoupling of the fluid streams is that it is now operationally simple to turn bubble generator 100 on and off as required. On/off switches 710 and 720 may be included in line with both fluid one 110 and fluid two 120 streams. Pressure regulators and/or flow rate regulators may also be included on either or both fluid streams, either separately or integrated as part of the on/off switches.

(45) The decoupled generators do not have fluid one/fluid two interfaces where fluid one can backfill into fluid two channels or vice versa. This eliminates issues related to surface wetting characteristics of channel walls. Also, when the bubble generator is turned on using known fluid settings for flow and pressure, the conditions to create the necessary bubble stability regime are consistently initiated, thus creating, uni-modal bubbles on demand in the desired quantity.

(46) In preferred examples, the liquid fluid two is delivered in concentrated form from a pre-filled container using standard lab Clearflex 60 Premium PVC tubing. The flow rate is controlled with a laboratory Aladdin AL-1000 Programmable Syringe Pump. Fluid one enters the bubble generator, which was created using 3D printing to create the fluid channels in plastic. Fluid two then fills the centrally located channel. Ambient air is delivered at the necessary volume by using a Powermate electric air compressor and air tank in conjunction with a Fairchild 72010 NKR model pressure regulator. The fluid two stream may be turned on and off by the controls on the syringe pump. The fluid one stream may be turned on and off by using the pressure regulator, or alternately by means of a laboratory stopcock inserted inline in the flexible tubing.

(47) The device input channel dimension D.sub.bg 550 and angle .sub.bg 350 for fluid one is determined based on the parameters needed for the end use application. One preferred embodiment, for instance, uses fluid one input channel dimensions .sub.bg of eight degrees, with D.sub.bg of 1.45 millimeters and fluid two exit channel diameter D.sub.f2 560 of 0.54 millimeters.

(48) For functional use of controlled bubbles in high throughput applications it is desirable to create integrated systems of bubble generators (an array) as opposed to having many individual generators. Given the robust operating characteristics of the single decoupled fluid bubble generator described above, it is readily scalable to an array of generators. Decoupling the fluid streams has eliminated the known issue of crosstalk and instability between conventional generators when combined in an array. Crosstalk creates transient pressure variations across individual generators, degrading bubble size control in arrays of conventional flow focusing.

(49) Referring also to FIG. 8, array 800 may be fabricated joining multiple bubble generators 100 (three shown in the figure for illustration purposes). The channels for the fluid one 110 and fluid two 120 have equivalent design parameters D.sub.f2, .sub.bg, and D.sub.bg, such that the output from the entire array is uni-modal in size and crystalline in behavior.

(50) The co-axial, flow focusing, bubble generator can be effectively combined into large arrays provided sufficient feeder channels and reservoirs to ensure each bubble generator receives an equivalent flow of fluid two and pressure of fluid one. Since each bubble is formed in the dynamically created orifice and not at an interface where fluid one meets fluid two within the physical array, regulation of the incoming fluid streams is decoupled from each other and there is no interference between the bubble created at one generator from those created at the other two generators. This creates very stable, precise bubble generation across the array.

(51) In preferred examples of the decoupled array, liquid fluid two is delivered from a source of concentrated form using standard lab Clearflex 60 Premium PVC tubing and a Kamoer LLS Plus laboratory peristaltic pump, but any style liquid pump can be used. Referring also to FIG. 9, the liquid enters distribution channel 900 with dimensions on the order of 0.25 diameter in a 3D plastic printed array of bubble generators. Distribution channel 900 directly feeds a smaller diameter, constricted channel 910. The fluid two constriction is built inline to dampen the flow rate variation of fluid two. Fluid two then enters circular reservoir 920, which feeds the central channels 340 of the individual bubble generators.

(52) Channel size should not be overly constricted at any point so that the shear load on fluid two does not increase. This minimum size limitation depends on the chemical composition of fluid two. For example, large, solvent soluble molecules, charged systems or other molecules that have a driving force to self assemble into larger aggregates or micelles, emulsions (which may be electronically or sterically stabilized such that true particle size and the actual size when swollen in the continuous phase of fluid two maybe quite different), etc. all have a different minimum channel dimension in order to flow without a build in shear load.

(53) For an array of bubble generators, fluid one may be delivered with an air compressor and pressure regulator as described above, or more portable pressure controlled systems may be utilized. For example, this can be accomplished with a compressed gas tank and bleed approach. For applications where fluid one is air, a motor driven piston pump has been used. A flexible reservoir such as a rubber balloon may be inserted inline between the pump and the bubble generator array to dampen pressure fluctuations. Flexible PVC tubing may carry air to a 3D printed bubble generator array and fill a distribution channel having a 0.25 diameter. This fluid one distribution channel then fills each circular reservoir feeding concentrically arranged fluid one exit channels of each individual bubble generator.

(54) The array of bubble generators can easily be scaled. One example is to scale sets of three generators in parallel. Referring also to FIG. 10, one example is array 1000 of twenty-four (24) individual bubble generators, constructed as eight sets of three bubble generators 800 in parallel. In this example, fluid one 110 goes through a 0.25 distribution channel 1040 and feeds all twenty-four sets of converging fluid one channels, by first filling a circular reservoir (as illustrated in FIG. 4) leading to each individual bubble generator. Fluid two 120 passes through 0.25 distribution channel 1050 to simultaneously feed eight constricted flow channels, which branch off perpendicularly to the feeder liquid channel. As illustrated in FIG. 9, each of the eight constricted channels feeds a circular reservoir, with each circular reservoir in turn feeding three individual bubble generators.

(55) This array can create large quantities of individual bubbles. Alternately, a three dimensional foam with uni-modal void sizes is created if the sets of three generators are spaced more closely together with separation distances on the order of D.sub.bubble. If the individual bubble generators are packed even closer still, with separation distances on the order of <D.sub.bubble, fluid one streams of adjacent bubble generators interfere with each other. This creates a second, smaller bubble size mode, such that the resulting foam has two void sizes. This bimodal size distribution is robust and repeatable.

(56) Orientations of individual bubble generators other than eight sets of three can be manufactured to create custom foams with controlled void sizes and placement. Criteria that need to be maintained for successful array bubble generators include the decoupled fluid stream virtual orifices, feeder and distribution channels that maintain consistent flow of fluid two to each bubble generator, and consistent pressure of fluid one to each bubble generator. The positioning of bubble generators in the array determines whether the array creates bubbles or foam, however individual unimodal bubbles delivered to a flat surface demonstrate crystalline behavior and will self assemble into ordered foams.

(57) Variations of scaled arrays of bubble generators with decoupled orifices may be manufactured using 3D printing techniques. Conventional micro droplet and bubble generators (e.g. flow focusing Y or T junction, etc.) may similarly be designed and manufactured with decoupled orifice designs to produce similarly improved bubbles and foams. The minimum design feature sizes, and therefore the generated bubble sizes, are also dependent upon the fabrication techniques and construction materials used. Alternative to 3D printing, standard or other device fabrication techniques (for instance in creating a PDMS type flow focusing device) may be used to create decoupled orifice generators.

(58) Controlling exit placement or varying geometry at select exits, during printing or manufacturing, allows consistent production of bimodal foams to improve properties. For example, in emulsion chemistry the number of unimodal large droplets might be set at four times the number of unimodal small droplets (an 80/20 packing) in a batch with a typical size regime ranging from 50 nm to 450 nm. This 80/20 packing with two distinct size modes greatly enhances final properties, for example surface characteristics (i.e. packing at the surface upon film formation), even though the placement of large and small droplets from the bulk liquid in the film formed state is somewhat random. Such 80/20 packing, with ordered structuring of precise and constant bubble and foam sizes, will also allow improvement of current known ratios and resulting properties.

(59) Air and carbon dioxide are preferred gasses for use as fluid one. The bubble generator will also function with other compressed gas compositions delivered from tanks, reservoirs or pumps. Fluid one pressure ranges are preferably within 0.1 to 20 PSI. With high viscosity fluid two compositions, higher pressures may be required to create bubbles.

(60) A wide range of fluid two compositions may be used to create uni-modal bubbles and custom foams for specific end use applications. Solutions, emulsions and suspensions with particle sizes and viscosities ranging over several orders of magnitude are all effective, provided that:

(61) fluid two contains a surface active ingredient to stabilize the resulting bubble;

(62) the liquid readily flows through the device; and

(63) the fluid two liquid is more hydrophilic then fluid one.

(64) Some preferred examples for fluid two include, but are not limited to, aqueous polymer systems with solids ranging from 1.5% to 65%, including natural and synthetic proteins, polysaccharides, and polymers and copolymers of vinyl and acrylic esters. These polymers systems may be either anionically or sterically stabilized.

(65) Other materials which may be incorporated into preferred examples of fluid two include, but are not limited to, optical brighteners, dyes, pesticides, herbicides, disinfectants, and cleaners; as well as biological formulations including bacteria and enzymes. Preferred fluid two flow rates are in the range of 1.0 to 100.0 ml/minute per bubble generator.

(66) Preferred device channel dimensions include .sub.bg ranging from 4 to 12, D.sub.bg from 0.15 to 3.0 mm, and D.sub.f2 from 0.05 mm to 1.0 mm. These preferred range may be limited due to 3D printing resolution, but alternative printers or fabrication techniques with current or future improvement in feature resolution may allow construction of devices with critical dimensions outside of these preferred ranges.

(67) The size of the bubbles generated across these preferred ranges is also dependent on the characteristics and parameters of the various fluid two compositions listed above, as well as fluid one and fluid two input conditions. With the preferred dimensions and fluids, a range of bubble sizes from about 25 microns to 5.0 mm in diameter may be generated. With different geometric dimensions and fluid compositions, the bubble generating device will perform over a larger operational space.

(68) Given the ease of scaling up decoupled bubble generators into arrays, and the range of design parameters and compositions available to the end user, custom foam generation of materials with significant engineered value and characteristics may be created. Furthermore, the delivery of multiple fluid two compositions through separate feeder channels to specific bubble generators within an array can generate foams with blended properties. When these compositions dry, set or cure, the resulting foam has specific controlled void sizes in specific designated locations within the generated foam.

Other Embodiments

(69) Different fluids may be used for different application uses. In one application, fluid one is a gas preferably air, and fluid two is a foaming liquid composition containing a material that needs to be delivered to a substrate such as a cleaning agent or disinfectant. In this case the expansion ratio of the foam can be used to control the concentration of the liquid fluid two, as well as the rheology of the foamed coating. An example of this is a foam that is used to hold the chemical against a surface for instance to clean artificial turf fields or wrestling mats.

(70) The process of forming a foam may include aerating an aqueous foaming composition containing a film forming polymer, for example an emulsion polymer of appropriate glass transition temperature, combined with appropriate surfactants, with or without thickeners, stabilizers, or other additives, which dries, sets, or cures to a closed or open celled foam coating. The film forming polymer may simply dry, or be set or cured by a destabilization mechanism when exposed to air or alternate gas, or by using ionic, thermal, two part chemical or energy curable chemistry. Alternately, the gas chosen for fluid one may contain the acid carbon dioxide to chemically set the fluid in liquid two. An example of this includes fluid two being a solution of sodium or potassium silicate.

(71) In another application, a foamed coating composition is altered to deliver anti or de icing chemicals to roads, parking areas or walkways. In the case of anti-icing chemicals, a hygroscopic solution, for example of magnesium chloride is striped onto the road surface. The salt releases heat when mixed with water. This action, and the freezing point depression allow the road surface to resist icing at lower atmospheric temperatures then regular road salt or sand allows. The coating also functions to make the ice and snow form a weaker bond with the road surface, which allows easier snow removal and less resulting damage to the road surface. Formulations with the physical incorporation of the air as stable foam would weaken the road ice interface, and aid in subsequent ice removal.

(72) Another application may apply a foam blanket for dust and erosion control at construction sites, various agriculture sites, or race tracks without using a large quantity of water, and without making the site muddy, or have runoff issues to surrounding areas.

(73) A further alternate application where fluid one is a gas, preferably air, and fluid two is a foaming liquid composition where the coating is delivered for use as temporary insulation for use in crop protection for example.

(74) In another application, fluid one is ambient air, and fluid two is a chemical or chemical mixture (potentially hazardous) with a specific function. In this case, the bubble size and distribution are controlled to minimize exposure to the operator or environment from chemical drift as well as to optimize concentration of fluid one. This may be used for applications such as the dispensing of agriculture and lawn care chemicals like pesticides or fungicides.

(75) Purposeful foaming may opacify hazardous chemicals, that are diluted and mixed in a closed system, so that they can be visualized in an end use application (as opposed to traditional atomized chemical applications for applications such as pesticides or herbicides for example). This prevents unknown exposure to the operator or other people in the environment by touch or inhalation. Having a visible coating is an easy way for the operator to see where material has already been applied, ensuring uniform coverage.

(76) In another application, performance attributes of the uni-modal bubbles are utilized to add value. For instance the liquid level and poly-dispersity may be controlled such that the bubbles behave to self-assemble into monolayers. A surgical blanket may be created at the incision point to deliver antibiotic. Blood coagulating medicine may be delivered to a wound at the injury site in precisely metered, tiny amounts.

(77) In another application, chemical foam may be applied to function as an insulative blanket for evaporation control that can be rapidly created at the point of use without using a physical cover. For example, This may used for pools, or as a coating over freshly poured concrete or cement. Concrete and cement require moisture to cure to ultimate strength properties which the formulation could both provide and prevent from evaporating. Ultimately the foam disappears.

(78) Improved foam stability also allows the use of alternate ingredients to create the foam, an increase and/or precise control of the amount of air which can be incorporated in the foam over the time of persistence needed in the application, for instance enhancing whipped egg whites, cream or gelatin in food foams, or increasing air content in baked goods.

(79) In another application, fluid one is carbon dioxide and used with larger draft containers of beer to perfectly foam each glass for proper mouth feel, or to extend the lifetime of the keg, if the beer inside should go flat.

(80) In another application, the device is used to deliver one liquid, or to mix two or more liquids at the point of delivery, where the end use application is not dependent upon the incorporation of the fluid one gas. Instead, fluid one is primarily used to deliver the liquid droplet in precisely metered amounts, and incorporation of the gas is not critical to the end use application. This may be accomplished by either creating a core gas fraction that is small or approaching zero, or by tuning the solubility of fluid one and fluid two such that a created bubble rapidly becomes a smaller liquid droplet as the carrier fluid one diffuses and exits the bubble. In both cases, the size control is still excellent enough for the droplets to display crystalline behavior.

(81) In other applications, engineered foams with optimized structure and properties can be industrially applied in traditional continuous web applications such as tapes, gaskets or gap fillers, traditional sheet foam, or the manufacture of smart fabrics. With controlled, precise and accurate void sizes, gas ratios and void distributions and packing in two or three dimensions, foam properties can be optimized for performance. Additionally, by having more than one fluid two delivery system to the foam generator, multiple engineered liquids can be incorporated in the foam; all while maintaining void fraction, size and distribution in the foam. For example, this allows incorporating hard and soft chemicals into the same matrix, or reactive chemical systems of different liquids, and/or reactive with the void gas. The final foam properties such as toughness, flexibility, strength, weight, opacity and insulative properties can be dialed in, thereby adding value.

(82) In another application bubble dryness (gas volume fraction) is controlled to improve foam function. A homogeneous or heterogeneous array of generators in terms of orifice size or placement is configured with fluid streams feeding it such that a layered configuration of foam dryness is created. For example, a foam with increased wetness on the bottom may improve wet out to a substrate. Alternatively, a dryer foam on the bottom may create quick adherence to a substrate, or reduce liquid drainage in the foam, or increase open time on the top surface. Foams with three or more layers may be constructed such as, for example, dryer foam skins sandwiching a more moist foam layer.

(83) In another application, a foamed system can deliver a costly or useful material to surfaces, and have that material more accessible to the end use, and not trapped in the bulk. For example, such materials may enhance the appearance or optical properties of an article, keep adhesion promoters at surfaces, enable drug delivery, disinfect, or preferred position nanoparticles.

(84) It is to be understood that the above description is intended to be illustrative, and not restrictive. Many other embodiments will be apparent to those of skill in the art upon reviewing the above description. The scope should, therefore, be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled.