The present disclosure relates generally to cooling towers, and more specifically, to evaporative or wet cooling towers.
Cooling towers of the evaporative type are used to cool water to levels that approach ambient air temperatures. Because the water discharged from cooling towers may be recycled back to the cooling tower from processes that apply the water for cooling purpose, cooling towers are most generally used for the purpose of conserving water resources. Common applications for the cooling water produced in cooling towers include removing heat from critical components or controlling the operating temperature of engines, electrical generators, refrigeration compressors (e.g., air conditioning) and a broad range of industrial processes across a broad spectrum of industries. Natural draft and mechanical draft cooling towers are the two types of cooling towers that are most commonly used in commercial service.
As evaporative coolers, natural draft and mechanical draft cooling towers rely on the transfer of both sensible at latent heat between water and air to cool water by rejecting heat to air. Sensible heat is transferred primarily by conduction as heat flows from the warmer water to the cooler air, and latent heat is transferred through evaporation of a portion of the water into the air. The evaporative effect provides the preponderance of heat transfer in evaporative cooling processes, typically about 80%. Theoretically, heat exchange between the water and air within the cooling tower could continue until the air becomes saturated with moisture (i.e., reaches 100% relative humidity) at the adiabatic saturation temperature of the cooling system. Thus, the lowest theoretical temperature that the water can be cooled to is limited by the inlet temperatures of the air and water and the moisture content (humidity) of the inlet air. In practice, the outlet water temperature from a cooling tower may generally be brought to within approximately 10 degrees Fahrenheit of the wet bulb temperature of the incoming air stream.
Because cooling towers rely on heat and mass transfer between water and air and both conductive heat transfer and evaporation proceed fastest when the two phases are in direct contact, the efficiency of a cooling tower is critically dependent on bringing the air and water into intimate contact over a large area of interfacial surface between the two phases. Likewise, given that intimate contact over a finite interfacial surface area exists, increasing the degree of mixing or turbulence within the water and air phases increases both the rate of conductive heat transfer and evaporation (mass transfer). However, the particular method used to create interfacial surface area and the means by which the air is forced to flow over the surface area affect the size of the cooling tower and compact designs are generally more desirable considering: the value of space within industrial facilities; the fact that many cooling towers are installed on rooftops; and the negative aesthetic impact of larger units.
Natural draft cooling towers are used almost exclusively to cool large power generating plants due in part to the tremendous size of such towers and the high circulating rates of the cooling water required to justify the costs of building the towers, usually in range of 100,000 to 200,000 gal/min. Natural draft cooling towers use very large concrete chimneys to introduce air into the system and may be 400 feet or more in height for large applications such as providing cooling water for nuclear power plants. Packing or fill located within the chimney of a natural draft cooling tower is typically used to create a large amount of extended surface area for contacting the water and air phases within the chimney. A water distribution system, usually spray nozzles or a weir system, is normally used to uniformly distribute the incoming warm water over the top of the packing or fill. Thus distributed, the water flows downward over the extended surface area within the chimney of the natural draft cooling tower as a thin film under the force of gravity. Air within the chimney that is contact with the surface of the warm water picks up both heat and moisture from the water causing the density (i.e., weight per unit volume) of the air to decrease. This decrease in density creates a buoyancy effect that causes the air to rise upward through and out of the top of the chimney while higher density ambient air is drawn into openings located at the bottom of the chimney. This flow (natural draft) through the chimney of the natural draft cooling tower continues for as long at the driving forces of differential temperature between warm water and cooler air and the ability of the air to absorb moisture persist within the chimney.
Mechanical draft cooling towers, on the other hand, generally use fans to force air over circulated water as the water flows downward under the force of gravity over the same types of packing or fill as used in natural draft cooling towers. Mechanical draft cooling towers are scalable and generally range in height from approximately 10 feet to more than 40 feet, and from a few gallons of cooling fluid per minute to hundreds or thousands of gallons of cooling fluid per minute depending on the particular cooling requirements. Because mechanical draft cooling towers rely on fans to force air to flow over the film of water distributed over the extended surface area of the packing or fill, the rates of heat and mass transfer per unit of surface area can be increased based on the ability of the fans to directly induce greater turbulence to the air stream and thereby indirectly induce greater turbulence to the water through disturbance of the surface of the water film by the air flowing over it. Thus, at the cost of using higher pressure or higher volume fans, mechanical draft cooling towers can achieve higher efficiency per unit of interfacial contact area than that of natural draft cooling towers. Due to improved efficiency, mechanical draft cooling towers are generally more compact than natural draft cooling towers per unit of cooling, but more expensive to purchase, operate and maintain per unit of cooling.
Of course, typical cooling towers have inefficiencies. Some entrained droplets of water escape with the air as it rises through the cooling tower. This phenomenon is known as drift or windage. To mitigate this problem, known systems employ drift eliminators, typically in the form of a series of baffle-like devices to collect the entrained droplets and return them to the water phase. Additionally, the evaporation of water causes dissolved solids within the cooling fluid to become more concentrated. Eventually, without corrective action, the solids will begin to precipitate out of the cooling fluid and join with additional particles of solids that are brought into the cooling tower with the air causing fouling of the system.
Each of these problems requires mitigation in the form of periodic cleaning and replacement of the concentrated water with fresh water in order to maintain dissolved solids at acceptable levels. Normally, In order to maintain the level of concentration within the cooling tower at acceptable levels, a portion of the cooling water is continuously withdrawn as waste (blow down) and an equal portion of fresh water is continuously added to the cooling tower.
Submerged gas evaporators, also known as submerged gas reactors and/or combination submerged gas evaporator/reactor systems in which gas is dispersed within the liquid phase are used to concentrate wastewater streams by evaporation prior to disposing of any unwanted compounds within the wastewater. Such submerged gas evaporators may be useful as cooling towers as well. U.S. Pat. No. 5,342,482, which is hereby incorporated by reference, discloses a common type of submerged combustion gas evaporator, in which gas is delivered though an inlet pipe to a dispersal unit submerged within the liquid to be evaporated. The dispersal unit includes a number of spaced-apart gas delivery pipes extending radially outward from the inlet pipe, each of the gas delivery pipes having small holes spaced apart at various locations on the surface of the gas delivery pipe to disperse the combustion gas as small bubbles as uniformly as practical across the cross-sectional area of the liquid held within the processing vessel. According to current understanding within the prior art, this design provides desirable intimate contact between the liquid and the combustion gas over a large interfacial surface area while also promoting thorough agitation of the liquid within the evaporation vessel.
Because submerged gas evaporators disperse gas into a continuous liquid phase, for a given ratio of gas to liquid at a particular pressure the volume of the required space within the equipment that is used to bring the two phases into contact is the minimum possible and generally a much smaller volume than that required in gas-liquid contacting devices used in conventional cooling towers where the gas is the continuous phase and the liquid is dispersed into the gas stream either as droplets or thin moving films flowing over the extended surfaces of packing or fill.
However, during the evaporation process dissolved solids within the liquid phase become more concentrated often leading to the formation of precipitates that are difficult to handle. In certain cases precipitation of solids can lead to the formation of large crystals or agglomerates that can block passages within processing equipment, such as the gas exit holes in the system described in U.S. Pat. No. 5,342,482. Generally speaking, liquid streams that cause deposits to form on surfaces and create blockages within process equipment are called fouling fluids
Unlike conventional cooling towers where heat and mass are transferred from the liquid phase as it flows over the extended surface of fill or packing, heat and mass transfer within submerged gas evaporators takes place at the dynamic renewable interfacial surface area of a discontinuous gas phase dispersed within a continuous liquid phase and there are no solid surfaces upon which deposits can accumulate.
Submerged gas evaporators also tend to mitigate the formation of large crystals because dispersing the gas beneath the liquid surface promotes vigorous agitation within the evaporation zone, which is a less desirable environment for crystal growth than a more quiescent zone. Further, active mixing within the evaporation vessel tends to maintain precipitated solids in suspension and thereby mitigates the formation of potential blockages that are related to settling and/or agglomeration of suspended solids.
However, mitigation of crystal growth and settlement is dependent on the degree of mixing achieved within a particular submerged gas evaporator, and not all submerged gas evaporator designs provide adequate mixing to prevent large crystal growth and related blockages. Therefore, while the dynamic renewable heat transfer surface area feature of submerged gas evaporators eliminates the potential for fouling fluids and/or precipitates to coat extended surfaces, conventional submerged gas evaporators are still subject to potential blockages and carryover of entrained liquid within the exhaust gas flowing away from the evaporation zone.
Regardless of the type of submerged gas evaporator, in order for the process to continuously perform effectively, reliably and efficiently, the design of the submerged gas evaporator must include provisions for efficient heat and mass transfer between gas and liquid phases, control of entrained liquid droplets within the exhaust gas, mitigating the formation of large crystals or agglomerates of particles and maintaining the mixture of solids and liquids within the submerged gas evaporation vessel in a homogeneous state to prevent settling and agglomeration of suspended particles.
A cooling tower includes an evaporator vessel and one or more tubes partially disposed within the evaporator vessel, which are adapted to transport a gas (e.g., air) into the interior of the evaporator vessel. The evaporator vessel has an inlet that transports warm liquid to be cooled into the vessel at a rate that maintains the liquid level inside the evaporator vessel at a predetermined level. The evaporator vessel may include an open top or an exhaust stack to allow gas to flow away from the vessel. In addition, the cooling tower includes one or more weirs that at least partially surround the tube or tubes and are submerged in the liquid to create a liquid circulation path formed by the space between each weir or each weir and the interior wall surface of the evaporation vessel and each tube. In one embodiment, each weir is open at both ends and forms a lower circulation gap between a first one of the weir ends and a bottom wall of the evaporator vessel and an upper circulation gap between a second one of the weir ends and the normal operating level of the surface of the liquid within the evaporation vessel
During operation, gas introduced through each tube mixes with the liquid in a first confined volume formed by a weir, or a weir and the interior wall surface of the evaporation vessel and the tube, and the mixture of gas and liquid flows at high volume with a high degree of turbulence along the circulation path defined around the weir, thereby imposing a high degree of mixing action between the gas and the liquid and any suspended particles within the liquid. Shear forces within this two-phase or three-phase turbulent flow region that result from the high density liquid phase overrunning the low density gas phase create extensive interfacial surface area between the gas and the liquid that favors minimum residence time for mass and heat transfer between the liquid and gas phases to come to equilibrium compared to conventional gas dispersion techniques. Still further, vigorous mixing created by the turbulent flow hinders the formation of large crystals of precipitates within the liquid and, because the system does not use small openings to introduce the gas into the liquid, clogging and fouling are significantly reduced or entirely eliminated. Still further, the predominantly horizontal flow direction of the liquid and gas mixture over the top of the weir and along the surface of the liquid within the evaporator vessel enables the gas phase to disengage from the liquid with minimal entrainment of liquid droplets due to the significantly greater momentum of the much higher density liquid that is directed primarily horizontally compared to the low density gas with a relatively weak but constant vertical momentum component due to buoyancy. The cooled liquid may be pumped through an outlet port to any number of heat exchange systems for the purpose of cooling equipment, the heated liquid may then be returned to the cooling tower for additional cooling.
In addition, a method of cooling a liquid using a submerged gas evaporator includes providing the warm liquid to be cooled to a vessel at a rate sufficient to maintain the surface of the liquid at a predetermined level within the vessel, supplying a gas to the vessel, and mixing the gas and cooling fluid within the vessel by causing the gas and liquid to flow around a weir or multiple weirs, within the cooling tower to thereby transfer heat and mass between the gas and liquid.
Advantages of cooling towers according to the disclosure may be realized by substituting such cooling towers for conventional cooling towers in most cooling applications. Wherever cooling towers according to the disclosure are employed, conventional means may be employed to control the flow of the gas and the flow of cooling fluid through the cooling tower and, if required, to post-treat the cooling liquid and/or gas. Likewise, most other conventional means of controlling cooling tower systems to meet the requirements of a particular application may be employed. Also, multiple cooling towers according to the disclosure may be connected in series or parallel configurations to meet the cooling demand of a particular application.
Referring to
In the cooling tower of
As illustrated in
During operation, a pressurized mixture of gas from the line 51 is forced to flow under pressure into and through the gas inlet tube 22 before reaching the sparge or exit ports 24. The gas exits the gas inlet tube 22 through the sparge ports 24 into the confined volume 70 enclosed by the weir 40, the gas inlet tube 22 and the side wall of the evaporation vessel 30, causing the gas to be dispersed into the liquid 35 within the evaporator vessel 30. Generally speaking, gas exiting from the sparge ports 24 mixes with the liquid 35 within the confined volume 70 and causes a high volume flow pattern to develop around the weir 40. The velocity of the flow pattern and hence the turbulence associated with the flow pattern is highest within the confined volume 70 and at the locations where the liquid flows through the upper gap 37 and the lower gap 36 of the weir 40. The turbulence within the confined volumes 70 and 71 significantly enhances the dispersion of the gas into the liquid 35 which, in turn, provides for efficient heat and mass transfer between the gas and the liquid 35. In particular, after exiting the sparge ports 24, the gas is dispersed as a discontinuous phase into a continuous liquid phase of the liquid 35 forming a gas/liquid mixture within the confined volume 70. The mass per unit volume of the gas/liquid mixture at any point within the confined volume 70 is significantly less than the average mass per unit volume of the mixture of gas and the liquid 35 in the volume 71 due to the large difference in mass per unit volume of the liquid compared to the gas, typically on the order of approximately 1000 to 1. This difference in mass per unit volume creates a difference in static hydraulic pressure between the gas/liquid mixture in the confined volume 70 and the liquid phase in the volume 71 at all elevations within the vertical extent of the weir. This imbalance in static hydraulic pressure forces the liquid 35 to flow from the higher pressure region, i.e., the volume 71, to the lower pressure region, i.e., the confined volume 70, at a rate that overcomes the impressed static hydraulic pressure imbalance and creates flow upward through the confined volume 70.
Put another way, the dispersion of gas into the liquid 35 within the confined volume 70 at the sparge ports 24 develops a continuous flow pattern that draws liquid 35 under the bottom edge 41 of the weir 40 through the lower circulation gap 36, and causes the mixture of gas and liquid 35 to move through the confined volume 70 and toward the surface 80 of the liquid 35. Near the surface 80, the gas/liquid mixture reaches a point at which the imbalance of static hydraulic pressure is eliminated. Generally speaking, this point is at or near the upper circulation gap 37 formed between the second end 42 of the weir 40 and the surface 80. At the balance point, the force of gravity, which becomes the primary outside force acting on the gas/fluid mixture, gradually reduces the vertical momentum of the gas/liquid mixture to near zero. This reduced vertical momentum, in turn, causes the gas/liquid mixture to flow in a predominantly horizontal direction over the second end 42 of the weir 40 (through the circulation gap 37 defined at or near the surface 80 of the liquid 35) and into the liquid 35 within the volume 71.
This flow pattern around and over the weir 40 affects the dispersion of the gas into the liquid 35 and, in particular, thoroughly agitates the continuous liquid 35 within the evaporator vessel 30 while creating a substantially horizontal flow pattern of the gas/liquid mixture at and near the surface 80 of the continuous liquid phase of the liquid 35. This horizontal flow pattern significantly mitigates the potential for entrained liquid droplets to be carried vertically upward along with the dispersed gas phase as the dispersed gas phase rises through the liquid phase due to buoyancy and finally disengages from the continuous liquid phase of the liquid at the surface 80 of the liquid 35.
Also, the mixing action created by the induced flow of liquid and liquid/gas mixtures within both the confined volume 70 and the volume 71 hinders the formation of large crystals of precipitates, which generally requires a quiescent environment. By selectively favoring the production of small incipient particles of precipitates, the mixing action within evaporator vessel 30 helps to ensure that suspended particles formed in the evaporation process may be maintained in suspension within the liquid phase circulating around the weir 40, which effectively mitigates the formation of blockages and fouling within the cooling tower. Likewise, because relatively small particles that are readily maintained in suspension are formed through precipitation, the efficiency of the evaporator is improved over conventional evaporation systems in terms of freedom from clogging and fouling and the degree to which the cooling liquid may be concentrated.
In addition, as the circulating liquid 35 within volume 71 approaches the bottom wall 31 of the evaporator vessel 30, the liquid 35 is forced to flow in a predominantly horizontal direction and through the lower gap 36 into the confined volume 70. This predominantly horizontal flow pattern near the bottom wall 31 of the evaporator vessel 30 creates a scouring action at and above the interior surface of the bottom wall 31 which maintains particles of solids including precipitates in suspension within the circulating liquid while the cooling tower is operating. The scouring action at and near the bottom wall 31 of the evaporator vessel 30 also provides means to re-suspend settled particles of solids whenever the cooling tower is re-started after having been shutdown for a period of time sufficient to allow suspended particles to settle on or near the bottom wall 31.
Cooling towers generally employ a process that affects evaporation by contacting a gas with a liquid or liquid mixture, which may be a compound, a solution or slurry. Within an evaporation process that uses a submerged gas evaporator, heat and mass transfer operations occur simultaneously at the interface formed by the dynamic boundaries of the discontinuous gas and continuous liquid phases. Thus, all submerged gas evaporators include some method to disperse gas within a continuous liquid phase. The system shown in
As will be understood, the weirs 40 and 140 of
As illustrated in
As will be understood, the gas exits the gas inlet tube 222 through the sparge ports 224 into a confined volume 270 formed between the gas inlet tube 222 and a tubular shaped weir 240. In this case, the weir 240 has a circular cross-sectional shape and encircles the lower end of the gas inlet tube 222. Additionally, the weir 240 is located at an elevation which creates a lower circulation gap 236 of approximately 4 inches between a first end 241 of the weir 240 and a bottom dished surface 231 of the evaporator vessel 230. The second end 242 of the weir 240 is located at an elevation below a normal or at rest operating level of the liquid within the evaporator vessel 230. Further, a baffle or shield 238 is disposed within the vessel 230 approximately 8 inches above the second end 242 of the weir 240. The baffle 238 is circular in shape and extends radially outwardly from the gas inlet tube 222. Additionally, the baffle 238 is illustrated as having an outer diameter somewhat greater than the outer diameter of the weir 240 which, in this case, is approximately 46 inches. However, the baffle 238 may have the same, a greater or smaller diameter than the diameter of the weir 240 if desired. Several support brackets 233 are mounted to the bottom surface 231 of the evaporator vessel 230 and are attached to the weir 240 near the first end 241 of the weir 240. Additionally, a gas inlet tube stabilizer ring 235 is attached to the support brackets 233 and substantially surrounds the bottom end 226 of the gas inlet tube 222 to stabilize the gas inlet tube 222 during operation.
During operation of the cooling tower 210, gas is ejected through the sparge ports 224 into the confined volume 270 between the outer wall of the gas inlet tube 222 and the inside wall of the weir 242 creating a mixture of gas and liquid within the confined volume 270 that is significantly reduced in bulk density compared to the average bulk density of the fluid located in the volume 271 outside of the wall of the weir 240. This reduction in bulk density of the gas/liquid mixture within confined volume 270 creates an imbalance in head pressure at all elevations between the surface 280 within evaporator vessel 230 and the first end 241 of the weir 240 when comparing the head pressure within the confined volume 270 and head pressure within the volume 271 outside of the wall of the weir 240 at equal elevations. The reduced head pressure within the confined volume 270 induces a flow pattern of liquid from the higher head pressure regions of volume 271 through the circulation gap 236 and into the confined volume 270. Once established, this induced flow pattern provides vigorous mixing action both within the confined volume 270 and throughout the volume 271 as liquid from the surface 280 and all locations within the volume 271 is drawn through the circulation gap 236 and upward through the confined volume 270 where the gas/liquid mixture flows outward over the second end 242 of the weir 240 and over the surface 280 confined within the evaporator vessel 230.
Within confined volume 270, the induced flow pattern and resultant vigorous mixing action creates significant shearing forces that are primarily based on the gross difference in specific gravity and hence momentum vectors between the liquid and gas phases at all points on the interfacial surface area of the liquid and gas phases. The shearing forces driven by the significant difference in specific gravity between the liquid and gas phases, which is, generally speaking, of a magnitude of 1000:1 liquid to gas, cause the interfacial surface area between the gas and liquid phases to increase significantly as the average volume of each discrete gas region within the mixture becomes smaller and smaller due to the shearing force of the flowing liquid phase. Thus, as a result of the induced flow pattern and the associated vigorous mixing within the confined area 270, the total interfacial surface area increases as the gas/liquid mixture flows upward within confined volume 270. This increase in interfacial surface area or total contact area between the gas and liquid phases favors increased rates of heat and mass transfer between constituents of the gas and liquid phases as the gas/liquid mixture flows upward within confined volume 270 and outward over the second end 242 of the weir 240.
At the point where gas/liquid mixture flowing upward within confined volume 270 reaches the elevation of the surface 280 and having passed beyond the second edge 242 of the weir 240, the difference in head pressure between the gas/liquid mixture within the confined volume 270 and the liquid within volume 271 fluid is eliminated. Absent the driving force of differential head pressure and having the confining effect of the wall of the weir 240, gravity and the resultant buoyancy of the gas phase within the liquid phase become the primary forces affecting the continuing flow patterns of the gas/liquid mixture exiting the confined space 270. The combination of the force of gravity and the impenetrable barrier created by the baffle 238 in the vertical direction eliminates the vertical velocity and momentum components of the flowing gas/liquid mixture at or below the elevation of the bottom of the baffle 238 and causes the velocity and momentum vectors of the flowing gas/liquid mixture to be directed outward through the gap 239 created by the second end 242 of the weir 240 and the bottom surface of the baffle 238 and downwards near the surface 280 within the evaporator vessel 230 causing the continuing flow pattern of the gas/liquid mixture to assume a predominantly horizontal direction. As the gas/liquid mixture flows outwards in a predominantly horizontal direction, the horizontal velocity component continually decreases causing a continual reduction in momentum and a reduction of the resultant shearing forces acting at the interfacial area within the gas/liquid mixture. The reduction in momentum and resultant shearing forces allows the force of buoyancy to become the primary driving force directing the movement of the discontinuous gas regions within the gas/liquid mixture, which causes discrete and discontinuous regions of gas to coalesce and ascend vertically within the continuous liquid phase. As the ascending gas regions within the gas/liquid mixture reach the surface 280 within the evaporator vessel 230, buoyancy causes the discontinuous gas phase to break through the surface 280 and to coalesce into a continuous gas phase that is directed upward within the confines of the evaporator vessel 230 and into the vapor exhaust duct 260 under the influence of the differential pressure created by the blower or blowers supplying gas to the cooling tower 210.
Some design factors relating to the design of the cooling tower 210 illustrated in
The embodiment of a cooling tower shown in
The embodiment of a cooling tower shown in
Turning now to
In the example of
Generally speaking a series of smaller cooling towers (such as the cooling towers illustrated in
The cooling system of
Generally speaking, in any of the disclosed cooling towers, the liquid has a temperature that is greater than a temperature of the gas flowing through the gas inlet tube. The gas inlet tube may be connected to a source of cool gas and the fluid inlet may be connected to a source of warm liquid. The temperature of the liquid at the fluid inlet may be greater than the temperature of the gas entering the gas inlet tube. In some embodiments the temperature of the liquid may be between about 1° F. and about 60° F. greater than the temperature of the gas. In other embodiments, the temperature difference may be between about 5° F. and about 40° F., and more specifically between about 10° F. and about 30° F.
It will be understood that, because the weir and gas dispersion configurations within the cooling towers illustrated in the embodiments of
While several different types cooling towers having different weir configurations are illustrated herein, it will be understood that the shapes and configurations of the components, including the weirs, baffles and gas entry ports, used in these devices could be varied or altered as desired. Thus, for example, while the gas inlet tubes are illustrated as being circular in cross section, these tubes could be of any desired cross sectional shape including, for example, square, rectangular, oval, etc. Additionally, while the weirs illustrated herein have been shown as flat plates or as tubular members having a circular cross-sectional shape, weirs of other shapes or configurations could be used as well, including weirs having a square, rectangular, oval, or other cross sectional shape disposed around a gas inlet tube, weirs being curved, arcuate, or multi-faceted in shape or having one or more walls disposed partially around a gas inlet tube, etc. Also, the gas entry ports shown as rectangular may assume most any shape including trapezoidal, triangular, circular, oval, or triangular. Furthermore, the weirs need not be solid surfaces and may be perforated or latticed if desired. Further, virtually any liquid may be used in the cooling towers disclosed herein (e.g., anti-freeze solutions).
Additionally, various elements illustrated in the individual embodiments illustrated in
While certain representative embodiments and details have been shown for purposes of illustrating the invention, it will be apparent to those skilled in the art that various changes in the methods and apparatus disclosed herein may be made without departing from the scope of the invention, which is defined in the appended claims.
This application is a continuation-in-part of U.S. patent application Ser. No. 11/625,022, filed on Jan. 19, 2007, the entire specification of U.S. patent application Ser. No. 11/625,022 is hereby incorporated by reference herein.
Number | Date | Country | |
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Parent | 11625022 | Jan 2007 | US |
Child | 13423941 | US |