Abstract:
A method and apparatus are disclosed for determining fluid flow in a flow path of a vortex amplifier. The method comprises the steps of preventing flow of control fluid in a direction substantially opposite to a primary direction of purge fluid flow in a purge flow path of a vortex amplifier.

Description:
FIELD OF INVENTION 
       [0001]    The present invention relates to an apparatus and a method for controlling the flow of fluid in a vortex amplifier. More particularly, but not exclusively, the present invention relates to an apparatus and a method for controlling the flow of a control fluid in a vortex amplifier so as to help minimise leakage of the control fluid. 
       BACKGROUND 
       [0002]    Extraction systems are well known and commonly used to extract and filter fluids from certain environments. 
         [0003]    In certain extraction systems vortex amplifiers (VXAs) are conventionally used to modulate or control the amount of suction extracted by the extraction system. Vortex amplifiers have a number of advantages. Vortex amplifiers have no moving parts and so they are virtually maintenance free. Also, vortex amplifiers are able to react almost instantaneously to changes in the suction line and regulate the amount of suction as required. 
         [0004]    Extraction systems which use vortex amplifiers are suitable for use with a containment where the atmosphere within the containment must be kept isolated from the outside environment and the atmosphere must be maintained at a predetermined pressure below atmospheric pressure (commonly known as the containment depression). The extraction systems are used to extract and filter the atmosphere from within the containment and optionally any waste and/or contaminants produced by operations within the containment. 
         [0005]    The vortex amplifier of such an extraction system controls the amount of suction extracted from the containment. Under normal operating conditions, the vortex amplifier controls the suction of the extraction system such that the amount of suction extracted from the containment is low and it also helps to maintain the predetermined pressure in the containment. In the case of a small leak, operational characteristics of the vortex amplifier change to increase the amount of suction such that the containment is substantially maintained, although at a slightly smaller depression. Under emergency conditions, when there is a breach in the containment the vortex amplifier significantly increases the amount of suction to help prevent any leaking of the atmosphere etc. from the containment. 
         [0006]    A conventional vortex amplifier includes a cover plate, a vortex plate and a diffuser plate. The plates are configured in a spaced apart relationship such that the region between the cover plate and vortex plate defines a vortex chamber and the region between the vortex plate and diffuser plate constitutes a radial diffuser. 
         [0007]    The vortex plate includes a central aperture such that fluid can flow from the vortex chamber into the radial diffuser. The vortex amplifier comprises an outlet arranged at the rear of the radial diffuser. The outlet is often arranged in fluid communication with a filtering means of the extraction system, which in turn is arranged in fluid communication with a suction means and an outlet duct of the extraction system 
         [0008]    The fluid extracted from a certain environment and filtered by an extraction system is conventionally known as a purge fluid (PF). When the extraction system is used with a containment such as a glove box, the purge fluid includes the atmosphere extracted from within the containment and any waste and/or contaminants produced by operations within the containment. The purge fluid may include components of a gas, liquid, plasma and/or solid material. For example, the purge fluid may comprise a solid entrained in a gas. Additionally or alternatively, the purge fluid may comprise a liquid suspended in a gas. As indicated above, the purge fluid is extracted by the extraction system using suction. The purge fluid is sucked into the vortex chamber of the extraction system via one or more purge fluid ports. 
         [0009]    A conventional vortex amplifier further includes one or more control fluid ports to direct a control fluid (CF) from a control fluid source into the vortex chamber. The control fluid is usually, though not always, derived from the atmosphere outside the purge fluid source, e.g. a containment, and so the control fluid is normally a flow of air. 
         [0010]    The vortex amplifier is able to control the suction of the purge fluid—in other words, the vortex amplifier is able to regulate the amount of purge fluid extracted by the extraction system. The vortex amplifier regulates the flow rate of the purge fluid by manipulating the length of the flow path of the outgoing purge fluid within the vortex chamber. The length of the flow path of the purge fluid within the vortex chamber is dependent on whether or not the purge fluid is deflected and consequently throttled or resisted by the control fluid. If the purge fluid is deflected by the control fluid then the purge fluid follows a long spiral flow path around the vortex chamber and so the flow rate (and thus amount of suction) of purge fluid through the vortex chamber is low. If the purge fluid is not deflected by a control fluid then the purge fluid follows a shorter direct path through the vortex chamber and the rate of purge fluid flowing through the vortex amplifier (and thus amount of suction) is thereby relatively higher. 
         [0011]    Conventionally the control fluid ports of a vortex amplifier are configured (shaped and arranged with respect to an adjacent purge fluid port) such that control fluid emerges from the outlet of the control fluid port and flows in a direction within the vortex chamber such that it deflects and mixes with the flow of the purge fluid. Ideally, all the control fluid drawn into the vortex chamber would be directed to deflect and mix with the purge fluid and subsequently flow through the vortex amplifier to the filtration means etc. of the extraction system. However, it has been found that this does not happen in practice and that control fluid can leak from the vortex amplifier into the containment via the purge fluid ports. 
         [0012]    The leaking of control fluid via the purge fluid ports of the vortex amplifier has a detrimental effect on the operation of the extraction system. More specifically, the leakage of control fluid impairs the regulation of the suction of the purge fluid by the vortex amplifier. When the vortex amplifier is part of an extraction system for a containment the leaking of control fluid into the containment is problematic. This problem is particularly serious when the containment is intended to operate in an inert atmosphere mode (i.e. in an atmosphere excluding oxygen) and the control fluid is air drawn from the outside atmosphere. 
         [0013]    To date, the problem of leaking control fluid has been overcome by increasing the flow of an inert gas into the containment. However, the costs associated with sufficiently increasing the flow of inert gas are substantial. As an example from the nuclear industry, it is estimated that the cost of sufficiently increasing the flow of nitrogen gas into the containment of a MOX processing plant to counteract the leaking of air from the associated vortex amplifier is approximately £1 million per annum. The increased flow of nitrogen is to maintain the safe level of oxygen to prevent combustion. 
         [0014]    In addition to costliness this solution is often unsuitable because the pressure inside the containment will no longer be maintained at a predetermined pressure below atmospheric pressure and so the vortex amplifier will no longer operate under normal operating conditions. The increase in the pressure of the inert gas will change the pressure difference between supply pressure and the control pressure of the vortex amplifier. The change in the pressure difference will reduce the amount of control fluid drawn into the vortex amplifier and lead to an increase in the flow of inert gas through the vortex amplifier, which ultimately leads to an increase in the operating costs of the containment. 
         [0015]    It is an aim of the present invention to at least partly mitigate the above-referenced problems. 
         [0016]    It is an aim of certain embodiments of the present invention to address or overcome the problem of control fluid leaking from the vortex chamber into the containment. More specifically, it is an aim of these embodiments to control the flow of control fluid and thereby at least reduce or minimise the leaking of control fluid from the vortex amplifier. 
         [0017]    It is an aim of certain embodiments of the present invention to seek to counteract the problem of leaking control fluid without impeding the overall performance of vortex amplifier and extraction system. These embodiments seek to control the flow of control fluid and thereby at least reduce the leakage of control fluid from the vortex amplifier without requiring an increase in the flow of purge fluid into the vortex chamber. 
       BRIEF SUMMARY OF THE DISCLOSURE 
       [0018]    According to a first aspect of the present disclosure there is provided a method for determining fluid flow in a flow path of a vortex amplifier, comprising the steps of:
       preventing flow of control fluid in a direction substantially opposite to a primary direction of purge fluid flow in a purge flow path of a vortex amplifier.       
 
         [0020]    According to a second aspect of the present invention there is provided apparatus for determining fluid flow in a flow path of a vortex amplifier, comprising:
       a purge flow path along which purge fluid is flowable in a primary direction of purge fluid flow; and   a control flow path along which control fluid is flowable in a further direction of control fluid flow; wherein   the purge flow path and control flow path are arranged to prevent the flow of control fluid in a direction substantially opposite to said primary direction.       
 
         [0024]    Embodiments of the present invention reduce back flow of control fluid into a zone of a containment by ensuring that control fluid ejected from a control port does not experience the Coanda effect as it impacts against a side wall of a purge flow port. Certain embodiments of the present invention achieve this by ensuring that a flow of control fluid exiting a control fluid port is directed in such a direction that fluid flow therefrom wholly avoids impact or is baffled to avoid impact with an outlet of a purge fluid flow path. 
         [0025]    Certain embodiments of the present invention provide the advantage that fluid flowing backwards down a purge flow path via the Coanda effect is stripped away from the walls of the fluid flow path. This may be achieved by increasing pressure at a desired region of the outlet. 
         [0026]    Certain embodiments of the present invention provide the advantage that fluid flowing backwards down a purge flow path via the Coanda effect has a flow path increased either by providing recesses or protrusions in the side wall of the fluid flow path. As a result the fluid flow path of the control fluid follows a labyrinthine route which reduces overall backwards motion of the control fluid. 
         [0027]    Certain embodiments of the present invention reduce or eradicate backward flow of control fluid by a combination of the techniques noted above for reducing control fluid flow. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0028]    For a better understanding of the present disclosure and to show how it may be carried into effect, reference shall now be made, by way of example only, to the accompanying drawings in which: 
           [0029]      FIG. 1  illustrates part of a vortex amplifier; 
           [0030]      FIG. 2  illustrates the generation of a vortex; 
           [0031]      FIG. 3  illustrates vortex amplifier under emergency conditions; 
           [0032]      FIG. 4  illustrates how back flow of control fluid in a purge flow path may be avoided; 
           [0033]      FIG. 5  illustrates how back flow of control fluid in a purge flow path may be avoided; and 
           [0034]      FIG. 6  illustrates how back flow of control fluid in a purge flow path may be avoided. 
       
    
    
     DETAILED DESCRIPTION 
       [0035]    Reference will be made hereinafter to the Coanda effect. It is to be noted that the Coanda effect refers to the tendency of fluid in a fluid jet to remain attached to a surface against which a part or a whole of the fluid jet contacts. As a result of the Coanda effect fluid is entrained or caused to “stick” to the contacted surface. Such fluid can flow along the contacted surface against a primary flow direction defined by another fluid flowing along a path defined by the surface. 
         [0036]      FIG. 1  illustrates a vortex amplifier  10 . The vortex amplifier (VXA) is a non-moving part fluidic device that uses the variable resistance offered by a vortex to effect flow changes in an extract line. The VXA is thus a fluidic device that does not have any moving parts and uses differing flow path lengths to bring about a change in resistance offered. This offered resistance is able to modulate fluid flow through it. 
         [0037]    A containment  11  which might be a glove box or chemical clean chamber or other such environment is defined by a housing which encompasses a zone  12 . Access to the zone  12  may be provided by sealed gloves (for example where the containment is a glove box) or other manipulators as will be appreciated by those skilled in the art. A cover plate  13  has a first surface facing the internal chamber of the containment and a reverse surface  14  which defines a wall of a vortex chamber  15 . Another wall of the vortex chamber  15  is defined by an inner surface  16  of a vortex plate  17 . The vortex chamber  15  is generally circular and has a central outlet  18  and radial and tangential inlets (described in further detail below). A radial diffuser  19  is provided by a baffling plate to diffuse the radial flow of fluid exiting the vortex chamber. An exit port  20  is used to extract fluid which may then be filtered and is drawn through the vortex chamber from the containment via a power source (not shown) such as an extractor fan. 
         [0038]    A supply flow of purge fluid enters the vortex chamber  15  from the containment  12  generally directed and in the absence of a vortex can pass relatively easily through the VXA. A control fluid enters the vortex chamber  15  through control fluid ports along control fluid communication paths  21 . The flow of control fluid enters tangentially into the vortex chamber and generates a vortex which causes high resistance to the flow of purge fluid from the containment to the exit port  20 . The vortex generated can produce such a high resistance that flow of purge fluid can be substantially reduced or even stopped. A small control flow can thus reduce to zero a supply flow some 10 to 20 times greater. The VXA therefore provides flow amplification and this is often quantified as a “turn down ratio”. 
         [0039]    As illustrated in  FIG. 1  a flow of purge fluid accesses the vortex chamber  15  around a peripheral edge of the cover plate  13  between the cover plate  13  and the containment housing  11 . Control blocks  22  are secured to the downstream surface  14  of the cover plate or maybe integrally formed therewith. Alternatively the control blocks  22  may be secured to an upstream surface  16  of the vortex plate  60  or be integrally formed therewith. 
         [0040]      FIG. 2  illustrates a downstream surface  14  of the cover plate  13  and downstream surface of the control blocks  22 . As illustrated the cover block in the exemplary embodiment is provided by four sub-plates secured via bolting, adhesive, screwing or any other fastening mechanism to the downstream surface  14  of the cover plate. It will be understood that references to upstream and downstream refer to the flow of fluid from the containment (upstream) to the exit port  20  (downstream). In this sense  FIG. 2  shows a view of the downstream surface of the cover plate and control blocks looking towards the glove box from the vortex plate. Fluid flow is shown spiraling in a clockwise vortex and will flow out of the purge away from the reverse of the cover plate through the central outlet  18  in the vortex plate. 
         [0041]    As illustrated in  FIG. 2  four purge flow inlets  25  1-4 are provided. The purge flow inlets are defined by sidewalls  26  of the raised circumferentially extending parts  27  of the vortex plate. Purge fluid flows from the containment around the periphery of the cover plate between the spaces between the sub-plates  27 . 
         [0042]    Four control ports  28  are located proximate to an outlet region of each purge flow port. Each control port  28  includes a passageway  21  with an exit passageway  29   1-4  formed in the control blocks  22  which is orientated so that control fluid flows from passageway  21  in a direction out of the paper shown in  FIG. 2  and then substantially at right angles to flow across the flow of purge fluid at the respective purge flow outlet. Control fluid thus flows tangentially with respect to a flow of purge fluid flow and causes the purge fluid to be entrained in a generally circulating path within the vortex chamber  15 . By controlling the flow of control fluid the vortex can be developed or cancelled to produce a respective effect on the flow of purge fluid. As illustrated in  FIG. 2 , when a generally swirling motion is developed within the vortex chamber a relatively high resistance is offered to purge fluid flow into the vortex chamber. This is typical of a situation when the containment is operating normally. 
         [0043]      FIG. 3  illustrates a scenario when the containment is breached. Under these conditions control fluid flow is reduced so that a swirling vortex is not developed within the vortex chamber. As a result little resistance is offered to the flow of purge fluid outwards from the containment. This is illustrated in  FIG. 3  by the larger, darker arrows  30  illustrating a major flow of fluid through the purge fluid outlets into the centre of the vortex chamber where they are extracted through a central opening  18  via the one or more extraction fans. As illustrated in  FIG. 3  under such circumstances the relative flow of control fluid is weak in comparison to the flow of purge fluid flow. This is illustrated by thin arrows  31 . Such a scenario occurs when a breach in the containment occurs in which circumstances a large quantity of purge fluid is continually sucked from an inlet  32  illustrated in  FIG. 1  through the inner zone  12  of the housing  11  through openings in the control port cover plate and through the vortex chamber and central opening in the vortex plate. 
         [0044]    As noted above, it has now been appreciated that a flow of control fluid must be avoided against the normal flow of purge fluid incoming through the purge fluid inlets  25 . It has now been appreciated that with conventional vortex amplifiers the spray of control fluid exiting conventional control fluid outlets has at least partially impacted against an opposite surface  26  defining the purge fluid flow inlet. As a result of the Coanda effect control fluid impacting in this way has been entrained against the surface and has flowed along that surface against the primary flow direction defined by the flow of purge fluid. In this way with conventional vortex amplifiers control fluid has found its way into the zone  12  of the containment. 
         [0045]      FIG. 4  illustrates the vortex amplifier of  FIGS. 1 to 3  in more detail according to a first embodiment of the present invention. As illustrated in  FIG. 4  purge fluid flows in a primary direction illustrated by the direction of arrow A through the purge flow inlet port  25  and then on to the vortex amplifier chamber  15 . A control fluid port  28  is used to eject control fluid along a control fluid passageway  29  defined by side walls  40 . The shape and orientation of the side walls  40  are defined during the design of the vortex amplifier so that the spray of control fluid ejected into the vortex amplifier chamber  15  does not impact whatsoever or only to a very limited degree onto the opposite side wall  26 . In this way no control fluid ejected from the control fluid port  28  impacts on the side wall and is thus not entrained against that side wall so as to move in a direction opposite to the direction illustrated by A in  FIG. 4 . The side walls are of course directed in such a way that a vortex can be established in the vortex chamber. 
         [0046]      FIG. 5  illustrates an alternative embodiment of the present invention in which the exit passageway from the control fluid port  28  is arranged in a direction which might result in ejected control fluid spray impacting at least partially into the opposite surface  26  of the purge fluid flow outlet. To avoid such contact a baffle  50  is located in the purge fluid flow path. The baffle  50  presents a narrow cross section to the purge fluid flow path but presents a greater cross sectional surface against the ejected spray of control fluid. It will be appreciated that the position and size of the baffle element  50  is such that the development of a vortex in the vortex chamber  15  by virtue of ejecting control fluid from the control fluid port is not prevented. The baffle may extend outwardly from a surface of the vortex plate or may be held by one or more struts (not shown) extending to the surface  26 . 
         [0047]      FIG. 7  illustrates an alternative embodiment of the present invention in which a shaped deflecting surface is provided at a location on the side wall  26  against which control fluid being ejected from the control fluid port  28  will hit. During use control fluid is sprayed out of the control fluid port  28  in order to set up the swirling vortex in the vortex chamber  15 . It is appreciated that in this embodiment at least a portion of this control fluid will impact against the opposite surface of the purge fluid outlet. In order to prevent such fluid impacting the side wall and being entrained on the side wall the side wall is shaped so as to generally narrow the passageway along which the purge fluid flows in the direction of arrow A. It will be appreciated that the narrowing can be produced by using a tapered surface  70 . The narrowing results in a steadily increasing pressure towards the exit region  71  of the purge fluid flow inlet. This steadily increasing pressure results in any fluid entrained by the Coanda effect being stripped away from the surface  70 . 
         [0048]    As illustrated in  FIG. 7  the tapered surface  70  may optionally include one or more recesses  72 . This also reduces or prevents flow of control fluid in a direction opposite to direction A by substantially increasing the length of flow path for such fluid flow. Effectively a labyrinthine path is produced. Control fluid may be caused to collect in the bottom of the recess. 
         [0049]    Optionally, instead of or in addition to the recess  72 , a prominent protuberance may be included extending outwardly from the surface of the side wall. This also increases pressure in the purge fluid outlet which will ensure the purge fluid flow flowing into the vortex chamber strips away any entrain control fluid. Also a labyrinthine path for control fluid flow is established. 
         [0050]    It will be appreciated that any combination of the tapered inlet, recess, protuberance, baffle and/or angled control fluid port may be used so as to minimise or eradicate backward flow of control fluid into the containment. 
         [0051]    Throughout the description and claims of this specification, the words “comprise” and “contain” and variations of the words, for example “comprising” and “comprises”, means “including but not limited to”, and is not intended to (and does not) exclude other moieties, additives, components, integers or steps. 
         [0052]    Throughout the description and claims of this specification, the singular encompasses the plural unless the context otherwise requires. In particular, where the indefinite article is used, the specification is to be understood as contemplating plurality as well as singularity, unless the context requires otherwise. 
         [0053]    Features, integers, characteristics, compounds, chemical moieties or groups described in conjunction with a particular aspect, embodiment or example of the invention are to be understood to be applicable to any other aspect, embodiment or example described herein unless incompatible therewith.