1. Field of the Invention
The present invention relates to a filter cartridge typically used in a gravity filtration system, where the filter media is enclosed in a filter housing where water flow is directed opposite the flow normally realized in the prior art. Specifically, the flow of the ingress water is directed towards and into the filter media central bore or annulus, while the flow of the egress, filtered water is directed radially outwards from the central bore through the filter media sidewalls. More specifically, the present invention provides a filter media and filter housing design that minimizes or eliminates the affect that accumulated air bubbles have on a filter media exposed to a reverse directional flow.
2. Description of Related Art
Disposable filter cartridges having pleated, granular, or carbon block filtration media, to name a few, are well known in the art. In this regard, the filter media is conventionally provided within a filter housing that directs fluid flow through the filter. For cylindrically shaped filters, which are dominant in the art for gravity-fed water filtration, especially for point-of-use configurations such as pitchers and countertop dispensers, the direction of fluid flow in the prior art lends itself to gravity-fed designs.
The unfiltered fluid propagates through circumferentially located and spaced apart flow channels formed in an outer flange of the filter housing top and/or side, and then into the lower portions of the interior chamber of the sump or body of the filter housing. The unfiltered fluid is essentially directed inwards, radially propagating inwards through the cylindrical filter media, such as a carbon block element or pleated filter media, and into the central bore (axial cavity) of the filter media cylinder. After travelling through the axial cavity of the filter media, the now-filtered fluid exits the filter media in gravity-fed applications at the lower or bottom end of the axial cavity through a filter media bottom end cap, and out the lower portion of the filter housing
The filter housing cover and body are designed with openings, apertures, and the like so as to allow fluid to flow normally longitudinally or axially downwards, and in a radial direction through the cylindrical walls of the filter media into the axial cavity. When the filtered fluid is discharged axially from the filter cartridge through a coaxially disposed discharge opening in one of the filter cartridge's end caps, it typically enters a reservoir for later dispensing.
In some industrial environments, it may be desirable to reverse the normal flow of the fluid through the filter cartridge so as to dislodge and remove accumulated particulates on the surface of a pleated filter media so that the filter cartridge substantially (if not completely) regains its initial filtration capabilities and/or so that fresh particulates may be pre-coated onto the filter media's surface. This is a back-flushing technique that is performed more often for certain types of filter applications, such as for pool system water filters, and filters that are difficult to access, such as underdrain filters in a nuclear power plant. In some industries (e.g., the power generation industry), filtration cartridges having filter media pre-coated with ion exchange particles are sometimes used. Thus, it would be desirable if exhausted ion exchange particles could be removed from the filter media via back-flushing so that fresh ion exchange particles could then be recoated onto the filter media's surface. This reverse flow backwashing of the filter media is of course under pressure to overcome the gravitational forces, and opposite the directional flow of filtration. Consequently, no “filtration” is performed during the reverse backwashing.
One reason for the prior art preferred directional flow of filtration (radially inwards through the filter media sidewalls to the annular cavity) is that gravity-fed systems induce air bubbles within the filter housing that can substantially reduce flow and/or airlock the filter cartridge from any filtration. If the directional flow of filtration was reversed (as is proposed in the present invention)—first through the annular cavity, then radially outwards through the filter media cylindrical sidewalls—air bubbles formed within the lower portion of the annular cavity would deter or block efficient filtrate flow. The present invention resolves this problem by forming a filter media with dimension limitations to reduce or eliminate blocking air bubbles in the annular cavity when ingress fluid is traversing into the annular cavity.
Bearing in mind the problems and deficiencies of the prior art, it is therefore an object of the present invention to provide a reverse flow filter cartridge capable of efficient filtration when ingress fluid enters the annular cavity and is filtered as it traverses radially outwards through the filter media sidewalls.
The above and other objects, which will be apparent to those skilled in the art, are achieved in the present invention which is directed to a filter cartridge for gravity-fed reverse flow filtering applications comprising: a filter housing having a top, a bottom, and sidewalls having at least one aperture for fluid egress; a filter media insertable within the filter housing, the filter media shaped to have a central bore circumferentially surrounded by filter media sidewalls; a top end cap having an aperture to allow ingress fluid to the central bore, and sealed to prohibit fluid ingress to the filter media sidewalls except through the central bore; a bottom end cap configured to prohibit egress fluid from leaving the filter media; wherein ingress fluid enters the central bore and is directed through the filter media sidewalls, and exits through the at least one aperture of the filter housing sidewall.
The central bore or the top end cap aperture is defined by an area such that the maximum flow rate into the central bore, Fmax, is greater than the flow rate through the filter media, and is determined by head height pressure and central bore cross-sectional area, by the expression:
F
max=(√{square root over (Hr*2*g)})*(Ao)*6*107
where,
The reduction in air bubble production in the central bore of the filter media of the reverse flow filtering applications may be optimized by maintaining a ratio of central bore cross-sectional area to central bore perimeter at a value equal to or greater than approximately 2.25.
The central bore has a cylindrical cross-section, a square or rectangular cross-section, an oval cross-section, or an obround cross-section, such that the ratio remains equal to or greater than approximately 2.25.
The top end cap aperture exhibits greater than 2950 ml/min flow at a maximum head pressure or greater than 4664 ml/min at maximum head pressure.
In a second aspect, the present invention is directed to a filter cartridge for reverse flow filtering applications comprising: a filter housing having at least one aperture for fluid ingress and at least one aperture for fluid egress; a filter media insertable within the filter housing, the filter media shaped to have a central bore in fluid communication with the at least one aperture for fluid ingress, the central bore circumferentially surrounded by filter media sidewalls; a top end cap having an aperture to allow fluid ingress to the central bore, and sealed to prohibit fluid ingress to the filter media sidewalls except through the central bore; a bottom end cap configured to prohibit fluid from leaving the filter media; wherein ingress fluid enters the central bore and is directed through the filter media sidewalls, and exits through the at least one aperture of the filter housing sidewalls; and wherein the central bore or the top end cap aperture is defined by an area such that the maximum flow rate into the central bore, Fmax, is greater than the flow rate through the filter media, and is determined by head height pressure and central bore cross-sectional area, by the expression:
F
max=(√{square root over (Hr*2*g)})*(Ao)*6*107
where,
In a third aspect, the present invention is directed to a method for eliminating airlock in a reverse-flow filter cartridge assembly, where the filter cartridge assembly includes a filter housing, a filter media inside the filter housing having a top end cap, the filter media having a central bore for fluid received from an aperture on the top end cap, said method comprising: defining a top end cap aperture area, Ao, such that the maximum flow rate into said central bore, Fmax, is greater than the flow rate through said filter media, and is determined by head height pressure and top end cap aperture cross-sectional area, by the expression:
Fmax=(√{square root over (Hr*2*g)})*(Ao)*6*107
where,
The features of the invention believed to be novel and the elements characteristic of the invention are set forth with particularity in the appended claims. The figures are for illustration purposes only and are not drawn to scale. The invention itself, however, both as to organization and method of operation, may best be understood by reference to the detailed description which follows taken in conjunction with the accompanying drawings in which:
In describing the preferred embodiment of the present invention, reference will be made herein to
The particular filter media which is employed in the practice of this invention is not critical. Thus, any conventional activated carbon block or pleated non-woven fibrous filter media may be employed having the desired porosity.
As water needing treatment passes through the filter cartridge of a standalone point of use water purification device, such as a carafe filter cartridge, it will contact the filter media, and the quantity of filter media contacted by the water and the water flow rate determine the absorption efficiency.
As the water flows through the filter cartridge, it takes the path of least resistance and makes its own channels through the filter media. For a reverse flow filter cartridge, the water enters the annular cavity or central bore of the filter media and exits radially outwards through the filter media sidewalls.
It is understood that other shaped configurations are easily adaptable for the filter media design of the present invention, such as oval, square, triangular, obround, or the like. Certain shapes may be more inclined to accommodate particular types of filter media and thus the cross-sectional shape of the filter assembly may be something other than circular for receiving a cylindrical housing; rather, for instance, it may be oval, obround, or rectangular, to name a few, provided the geometric configuration allows for a central bore for receiving unfiltered fluid and allows for fluid to exit via the sidewalls. In such designs, the bottom end cap is designed not to allow fluid flow so that fluid has no alternative but to exit the filter media via the filter media side walls.
Fluid flow will generally traverse longitudinally downwards until it reaches bottom end cap 24, which is circumferentially sealed to the filter media lower or bottom end. A back pressure is generated by the fluid, unable to exit the filter media from the bottom. Fluid is then directed radially outwards 26b through filter media sidewalls 20. The filter bottom end cap 24 prohibits fluid from exiting the filter media in any direction except radially outwards in the direction of arrow 26b. That is, contrary to prior art designs, in the preferred embodiment, the bottom end cap does not include a discharge opening coaxially aligned with the interior central passageway or annular cavity 18 of the internal core element of the filter media. Fluid is directed through the filter media sidewalls to circumferential channel 30 located between the filter housing sidewall 28 and filter media outer sidewall surface 20, and then exits apertures located on filter housing sidewall 28. Filter cartridge bottom end cap 24 is sealed to the filter media at least about the portion that connects to the bottom surface of the filter media. In this manner, fluid must exit through filter media sidewalls 20, and then through apertures located on the filter housing sidewall 28 in order to flow into bottom reservoir 16 as depicted by directional flow 26c.
As discussed previously, a significant detriment to establishing filter flow in this “reverse” direction (direction opposite the normal filtration direction of the prior art) is the establishment of an air bubble or pocket 32 in the annular cavity 18 of the filter media.
It has been determined that designing the filter cartridge to particular geometrical considerations will enhance the flow rate of the fluid and substantially decrease the formation of air bubbles or pockets capable of affecting the flow rate. This determination facilitates reverse-flow by analytically accommodating the flow rate.
For a particular head pressure or head height, Hr, and cross-sectional area, Ao, of the top end cap opening that allows for fluid ingress, the top cap will allow for maximum fluid flow, Fmax, as represented by the following equation:
F
max=(√{square root over (Hr*2*g)})*(Ao)*6*107
where,
It is desirable to have Fmax greater than the flow rate of filter media egress, such that head pressure can build to drive the fluid through the filter.
This equation represents the relationship between the maximum flow rate, Fmax on milliliters per minute (ml/min), and the head height, Hr (mm), and cross-sectional area of the top end cap opening, Ao (mm2), for a reverse flow gravity-fed carafe filter cartridge system.
It should be noted that the cross-sectional area of the end cap aperture is a governing factor, and not the particular shape of the aperture. More particularly, as calculated, the ratio of the area of the cavity to the perimeter of the cavity, independent of the cavity shape, e.g., circular, square, oval, etc., determines the suitable criteria for addressing adverse air bubble formation.
As indicated, it has been determined that an optimum ratio of the aperture area to perimeter should be greater than 2.25 to overcome the surface tension presented by air bubble formation, and remove detrimental effects from air bubbles in a reverse carafe filter cartridge system, especially where the top cap orifice exhibited greater than 2950 ml/min flow at the maximum head pressure, or alternatively, where the top cap orifice exhibits greater than 4664 ml/min flow at maximum head pressure.
The present invention further provides for a method of designing a reverse-flow filter cartridge assembly, where the filter cartridge assembly includes a filter housing, a filter media inside the filter housing having an end cap at each end, the filter media having a central bore for fluid ingress received from an aperture on the top end cap, and ensuring that the ratio of the area of either the top end cap aperture or the central bore, to their respective perimeter, is greater than 2.25 to maximize the flow rate based on the above-identified expression.
While the present invention has been particularly described, in conjunction with a specific preferred embodiment, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art in light of the foregoing description. It is therefore contemplated that the appended claims will embrace any such alternatives, modifications and variations as falling within the true scope and spirit of the present invention.
Number | Date | Country | |
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62043861 | Aug 2014 | US |