WO2000058014A1

WO2000058014A1 - Liquid sprayer using atomising gas mixed with the liquid in a swirl chamber

Info

Publication number: WO2000058014A1
Application number: PCT/IL2000/000182
Authority: WO
Inventors: Michael Levitzky
Original assignee: Rasys-Refined Atomization Systems Ltd.
Priority date: 1999-03-29
Filing date: 2000-03-24
Publication date: 2000-10-05
Also published as: EP1183106A1; CA2366370A1; AU3451500A; IL129235A0

Abstract

A two-phase sprayer for spraying a liquid using an atomizing gas that comprises an annular swirl chamber (50) having a downstream end comprising a substantially annular throat region (52) having an inner diameter and an outer diameter; a gas feed tube (20) adapted for the supply of the atomizing gas where the gas feed tube has a downstream gas feed end (22) comprising a lateral gas port (25) in fluid communication with the swirl chamber (50). The lateral gas port (25) adapted to impart a tangential velocity component to gas fed from gas feed pipe (20) to the swirl chamber (50) within the throat region (52); and a liquid feed tube (30) adapted for the supply of the liquid to be sprayed and having a downstream liquid feed tube end (32) comprising a lateral liquid port (35) in fluid communication with the swirl chamber (50). The liquid port (35) is in fluid communication with the annular throat region (52).

Description

LIQUID SPRAYER USING ATOMISING GAS MIXED WITH THE LIQUID IN A

SWIRL CHAMBER

Field of the Invention

The present invention relates to a two-phase sprayer for spraying a liquid using an atomising gas, in particular to such a sprayer in which the atomising gas is mixed with the liquid in a swirl chamber.

Background of the Invention

The atomisation of a liquid by an atomising gas is a process that has diverse applications in many fields of technology. Examples of such applications include the atomisation of liquid fuel in combustion processes for power plants, internal combustion engines and gas turbines; in chemical and pharmaceutical industries; in agriculture (spraying of water and pesticides, for example); sprayers of paint or other liquid coating in various industries; to name but a few.

The two-phase fluid produced by such atomising processes essentially comprises a suspension of liquid particles or droplets in the atomising gas. One of the basic characteristics required of liquid atomisers, also referred to herein as sprayers, is that the size of the liquid particles, obtained by the dispersion process inherent in the atomisation, be within preset parameters. For example, in the context of liquid hydrocarbon fuels, small liquid particle size, say about 40-60 μm, for the dispersed liquid ensures substantially complete combustion of the fuel, leading to high fuel efficiency as well as low levels of emissions including pollutants. _

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One type of two-phase sprayer known in the art consists of an inner tube for the liquid, and an outer tube concentric with the inner tube, in which the annular space between the tubes is used for the gas. An axial annular outlet for the gas flow is concentric with an inner axial outlet for the liquid flow, and these outlets may be coplanar or axially displaced from one another. As gas and liquid are discharged from their respective outlets, the shear pressure induced by the gas flow at the gas-liquid interface induces an unstable gas-liquid interaction leading on the liquid flow shears the liquid and leads to dispersal of the fluid flow into small fluid particles. In US 4,171,091 an improvement to this type of sprayer is disclosed in which the outer tube extends substantially beyond the liquid outlet and further comprises an annular inner wall at an angle of between 70° and 90° to the sprayer axis downstream of the liquid outlet. As the liquid is discharged axially from the liquid outlet, it is dispersed by the annular airflow, which comprises a radial velocity component arising from the change in flow direction induced by the annular inner wall. However, such devices have poor atomisation characteristics, and very large gas flows are required to atomise a relatively small amount of liquid. Furthermore, such sprayers only provide an axially-directed spray, and cannot provide 2-phase fluid spray at angles to the sprayer axis, necessary for applications such as mixing injectors in burners, combustion chambers and the like.

In US 3,963,178, a number of vanes are arranged so as to produce a spirally converging flow of air, which becomes a vortex surrounding the axial liquid outlet end, shearing the liquid and spreading the sheared liquid on the vanes, such that the liquid is further sheared into smaller particles. While providing high liquid dispersion at relatively low airflow rates, this arrangement does not enable a high gas exit velocity to be achieved. Since the liquid is essentially discharged into the part of the sprayer comprising the vanes, the air flowing therethrough immediately merges with the liquid transferring to it part of its angular momentum. Thus, the amount of angular momentum available in the airflow for dispersing the liquid is reduced, thereby reducing the extent of dispersion hitherto potentially available. Furthermore, the tangential velocity component imparted to the airflow by the vanes does not enable predetermined spray angles to be obtained, particularly for viscous liquids. Rather, only a limited range of angles is possible, related to the relative magnitudes of the tangential and axial velocity components of the airflow and 2-phase flow, respectively, the value of achievable tangential velocity in such a system being relatively low, as explained above.

It is therefore an aim of the present invention to provide a sprayer device that overcomes the limitations of prior art two-phase sprayers.

It is another aim of the present invention to provide a sprayer that may be adapted for widely ranging uses.

It is another aim of the present invention to provide such a sprayer that may be adapted to be used with liquids of different viscosities.

It is another aim of the present invention to provide such a sprayer that is relatively simple mechanically and thus economic to produce as well as to maintain.

It is another aim of the present invention to provide such a device that incorporates means for providing a predetermined spray angle relative to the sprayer axis. It is another aim of the present invention to provide such a device in which the required liquid pressure is not much greater than ambient pressure.

It is another aim of the present invention to provide such a device in which cavitation and erosion in the ducts for the liquid flow are substantially reduced or altogether eliminated.

It is another aim of the present invention to provide such a device having a longer service life than corresponding prior art devices.

It is another aim of the present invention to provide such a device requiring lower gas flow rates for liquid atomisation than corresponding prior art devices.

It is another aim of the present invention to provide such a device for fuel atomisation applications providing improved ecological characteristics of combustion products.

The present invention achieves these and other aims by providing a two-phase sprayer device comprising a liquid feed tube and a gas feed tube. Each of these tubes is blanked off at its downstream end and provides the corresponding fluid, liquid and air, respectively, to a swirl chamber, via corresponding lateral fluid outlets between each respective tube end and the swirl chamber. The lateral air outlets are located upstream of the liquid outlets, and are configured to provide a swirl motion to the airflow entering the swirl chamber. The swirl chamber is configured to maintain the swirl motion of the gas and comprises a downstream annular throat region into which liquid is laterally injected via the liquid outlets. The radial extent of the swirl chamber is generally greater than that of the annular throat region. Thus, as the airflow progresses axially downstream in the swirl chamber to WO 00/58014 _ PCT/ILOO/00182

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the annular throat region, the angular velocity of the airflow increases to conserve angular momentum, and thus the static pressure of the airflow decreases. At an optimum radius r (typically for the throat region), the static pressure of the air flowing in the swirl chamber becomes equal to that of the ambient fluid (e.g. air, for applications in which the sprayer discharges to the atmosphere) into which the liquid is to be dispersed, while the tangential or angular velocity reaches a maximum value. As a result, the liquid static pressure required to enable liquid to be inject into the swirl chamber becomes a minimum under these conditions, and thus the liquid outlets to the swirl chamber are optimally positioned in the throat region. Furthermore, as the airflow angular velocity reaches its maximum value, airflow turbulence is at maximum thereby enabling high atomisation quality or fineness to be achieved for the liquid. In a further improvement of the sprayer, the liquid outlets to the throat region are adapted to provide a swirl motion to the liquid in the same direction as the swirling air, thereby reducing losses in airflow angular velocity in the area of interaction with the liquid, thereby improving the rate of atomisation. The provision of a suitable angled diffuser downstream of the annular throat region enables predetermined spray angles for the two-phase fluid to be attained.

The present invention also overcomes specific problems hitherto present in prior-art centrifugal atomisers used for liquids of high viscosity, such as for example high viscosity fuels. In such prior art atomisers, high velocities for the liquid flow were difficult to attain because of angular momentum losses in the vortex chamber due to considerable friction forces between the liquid and the chamber's walls. In the present invention, fine liquid dispersion is achieved not by imparting high velocities to the liquid, but by making use of the interaction between a high velocity air jet and the low velocity liquid WO 00/58014 „ PCT/ILOO/00182

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flow. Therefore, viscosity has little influence on dispersion quality, and thus the present invention may be used for a range of liquids, particularly fuels, having widely varying viscosities.

Summary of Invention

The present invention relates to a two-phase sprayer for spraying a liquid using an atomising gas, comprising: - an annular swirl chamber having a downstream end comprising a substantially annular throat region, the throat region having an inner diameter and an outer diameter; a gas feed tube adapted for the supply of said atomising gas, said gas feed tube having a downstream gas feed tube end comprising at least one lateral gas port in fluid communication with said swirl chamber, said at least one lateral gas port adapted to impart a tangential velocity component to gas fed from said gas feed pipe to said swirl chamber at least within said throat region; a liquid feed tube adapted for the supply of said liquid to be sprayed and having a downstream liquid feed tube end comprising at least one lateral liquid port in fluid communication with said swirl chamber, said at least one liquid port being in fluid communication with said annular throat region.

The present invention further comprises a method for producing a spray of liquid, which comprises the following steps: feeding a stream of gas; imparting to said stream of gas a swirling motion; concurrently advancing said swirling stream of gas in an axial direction, said swirling stream of gas having a first annular cross-sectional area perpendicular to said direction; constraining said stream of gas to a second annular cross-sectional area smaller than said first area, whereby to accelerate said swirling stream of gas both axially and tangentially; and injecting a stream of said liquid tangentially into said accelerated swirling gas stream, whereby to generate the spray of liquid.

Preferably, the stream of liquid is injected into the swirling gas stream immediately after the gas stream has been constrained to said second cross-sectional area and therefore has been accelerated.

Brief Description of the Drawings

Figure 1 shows, in side elevational cross-sectional view, a first embodiment of the present invention;

Figure 2 shows, in cross-sectional view, the embodiment of Figure 1 along A-A;

Figures 3(a) and 3(b) show, in cross-sectional view, two alternative configurations for the liquid ports of embodiment of Figure 1 along B-B; - o -

Figure 4 shows, in cross-sectional view, the embodiment of Figure 1 along C-C;

Figure 5 shows the embodiment of Figure 1 comprising an alternative configuration of the liquid ports;

Figure 6 shows the embodiment of Figure 1 comprising an alternative configuration of the liquid ports comprising a liquid swirl chamber;

Figure 7 shows, in cross-sectional view, the embodiment of Figure 6 along E-E;

Figure 8 shows, in side elevation cross-sectional view, a second embodiment of the present invention incorporating a diffuser;

Figures 9(a) and 9(b) shows, in side elevation cross-sectional view and in end view, respectively, the embodiment of Figure 8 incorporating baffles;

Figures 10(a) and 10(b) shows, in side elevation cross-sectional view and in end view, respectively, an alternative embodiment of the present invention incorporating a diffuser and baffles; and

Figure 11 shows, in side elevation cross-sectional view, an alternative embodiment of the present invention, comprising axial alignment adjustment means.

Detailed Description of Preferred Embodiments

The present invention is defined by the claims, the contents of which are to be read as included within the disclosure of the specification, and will now be described by way of example with reference to the accompanying Figures. - y -

The present invention relates to a sprayer device for spraying a two-phase fluid, typically produced as a result of atomising processes, the two-phase fluid essentially comprising a suspension of the desired liquid in particle or droplet form in the atomising gas.

As will be described hereinbelow, the present invention essentially comprises an annular swirl chamber having at least one upstream lateral gas port providing fluid communication between the swirl chamber and the downstream end of a gas feed tube, and at least one lateral liquid port providing fluid communication between the downstream end of a liquid supply tube and the swirl chamber. The gas port is adapted such that gas entering the swirl chamber is swirled around the chamber, eventually meeting liquid introduced into the swirl chamber radially, or preferably tangentially in the same direction as the swirling gas, shearing the liquid and atomising it.

The relative positional term "upstream" and "downstream" respectively refer to axial directions along and away from the direction of flow of gas or liquid within the sprayer. The terms "upstream" and "downstream" are respectively designated (U) and (D) in the figures.

Referring to the figures, Figures 1 to 6 illustrate a first embodiment of the present invention. The sprayer device, also referred to herein as the sprayer, designated by the numeral (10), comprises a gas feed tube (20), a liquid feed tube (30) and a swirl chamber (50).

The liquid feed tube (30) is adapted for the supply of the desired liquid to be sprayed from any suitable source. The liquid feed tube (30) has a downstream liquid feed tube end (32) comprising at least one lateral liquid port (35) in fluid communication with said swirl chamber (50). In the first embodiment, the said downstream liquid feed tube end (32) is substantially coaxial with said swirl chamber (50), though in other embodiments the said downstream liquid feed tube end (32) may be in any suitable configuration, requiring simply that it comprises at least one lateral liquid port providing communication with the swirl chamber. Thus, in other embodiments, the said downstream liquid feed tube end (32) may comprise, for example, a tube end having an axis parallel to and radially displaced from the axis of the swirl chamber (50), having at least one lateral liquid port (35) in fluid communication with said swirl chamber (50).

The term "lateral" in relation to said at least one lateral liquid port (35) and to the at least one lateral gas port (25), described hereinbelow, relates to the direction of the axes thereof being non-aligned with respect to the axis (100) of the swirl chamber (50).

Thus, in the first embodiment, the downstream liquid feed tube end (32) typically comprises a substantially cylindrical wall (34) having an outer surface (36) and is blanked off at the downstream end thereof (38).

The swirl chamber (50) has an upstream end (51), axially bounded by annular wall (58), having a relatively large axial cross-sectional flow area, and a downstream open end comprising a substantially annular throat region (52) having a smaller axial cross-sectional flow area. The throat region (52) terminates in a downstream annular opening, (54), and the throat region (52) is defined by an inner diameter d_b and an outer diameter d_c.

The swirl chamber (50) in the first embodiment is radially bounded by at least a portion of the outer surface (36) of said downstream liquid feed tube end (32) and by the inner surface (56) of an outer substantially cylindrical swirl chamber wall (55) that is substantially concentric with respect to said downstream liquid feed tube end (32).

The swirl chamber wall (55) typically comprises a downstream portion (53) corresponding to said annular throat region (52) and having a diameter corresponding to said outer diameter for said annular throat region. The said swirl chamber (50) further comprises an upstream portion having a diameter greater than said outer diameter of said annular throat region (52).

The said gas feed tube (20) is adapted for the supply of the atomising gas from any suitable source. The gas feed tube (20) has a downstream gas feed tube end (22) and comprises at least one lateral gas port (25) in fluid communication with said swirl chamber (50). In the first embodiment, the said downstream gas feed tube end (22) is substantially coaxial with said swirl chamber (50), though in other embodiments the said downstream gas feed tube end (22) may be in any suitable configuration, requiring simply that it comprises at least one lateral gas port providing communication with the swirl chamber (50). Thus, in other embodiments, the said downstream gas feed tube end (22) may comprise, for example, a tube end having an axis parallel to and radially displaced from the axis of the swirl chamber (50), having at least one lateral gas port (25) in fluid communication with said swirl chamber (50).

In the first embodiment, said downstream gas feed tube end (22) is radially bounded by at least a portion of the outer surface (57) of said swirl chamber wall (55) and by at least a portion of the inner surface (26) of a substantially cylindrical outer gas feed tube wall (24) substantially concentric with respect to said swirl chamber wall. The said at least one lateral gas port (25) is characterized in being adapted to impart a tangential velocity component to gas fed from said gas feed pipe (20) to said swirl chamber (50) at least within said throat region (52). Referring to Figure 2, this is typically accomplished by arranging the said at least one lateral gas port (25) as a tangential aperture into the swirl chamber (50), i.e., the axis of the lateral gas port (25) being substantially perpendicular both to the axis of the swirl chamber and to a radial line taken form this axis. Alternatively, the said at least one gas port (25) could take the form of corresponding spaces between suitable radially spaced vanes mounted in a circumferential slot on said swirl chamber wall (55) (not shown). Furthermore, the said at least one gas port (25) is located upstream of said annular throat region (52). Thus, gas entering the swirl chamber (50) comprises a tangential velocity component due to the said geometrical configuration of the inlet thereto, i.e., the lateral gas port (25), as well as an axial velocity component due to the general flow direction of the gas along the axis (100). Both these velocity components together provide a swirling gas flow in the swirl chamber (50), which is maintained at least until exit thereof, and therefore through the said annular throat region (52), due to the annular geometry of the swirl chamber. To further enhance the gas swirl in the swirl chamber (50), the said gas feed tube end (22) comprises a plurality of said lateral gas ports (25) in fluid communication with said swirl chamber (50). Optionally, and preferably, the said plurality of gas ports (25) is arranged in at least two axially spaced groups. Further optionally, each of these groups comprises an equal number of said gas ports (25), for example 4 ports, substantially uniformly distributed circumferentially. Each of these gas ports of one row may be substantially aligned axially, or alternatively angularly displaced, with corresponding gas ports of an adjacent group of gas ports, as for example described hereinbelow with reference to the said liquid ports (35), mutatis mutandis. Typically, the number of lateral gas ports (25), in particular the number of axially spaced groups, and the number of gas ports (25) per group, as well as the dimensions of each gas port (25) of the sprayer (10) may be chosen advantageously taking into consideration factors such as the flow rate characteristics of the device as well as the available total pressure head.

In the first embodiment, the said at least one liquid port (35) may be axially aligned with said annular throat region (52) as illustrated in Figures 1 to 6.

Optionally, and referring in particular to Figures 3(a) and 4, said at least one lateral liquid port (35) is adapted to impart a radial velocity component to liquid fed from said liquid feed pipe (30) to said swirl chamber (50) at least within said throat region (52), and thus the liquid port (35) is in the form of a radial aperture into the swirl chamber (50).

Alternatively, and referring in particular to Figure 5, the at least one liquid port (32) may optionally be angled to the axis (100) of the swirl chamber (50) so as to reduce flow losses. In other words, said at least one lateral liquid port (35) is adapted to impart a radial velocity component and an axial velocity component to liquid fed from said liquid feed pipe (30) to said swirl chamber (50) at least within said throat region (52).

Alternatively, and preferably, said at least one lateral liquid port (35) is adapted to impart a tangential velocity component to liquid fed from said liquid feed pipe (30) to said swirl chamber (50) at least within said throat region (52), as illustrated in Figure 3(b), said tangential velocity being in the same direction as the tangential velocity component of the swirling gas within the swirl chamber (50). In the first embodiment, the latter option is adopted, and a tangential velocity component is imparted to the liquid flow on entering the swirl chamber by arranging the said at least one lateral liquid port (35) as a tangential aperture into the swirl chamber (50), i.e., the axis of the lateral liquid port (35) being substantially perpendicular both to the axis of the swirl chamber and to a radial line taken form this axis.

Optionally, and referring in particular to Figures 6 and 7, the said device (10) comprising tangential liquid ports (35) may further comprise a substantially cylindrical sleeve (70) radially displaced from said liquid feed end (32), i.e., intermediate said outer surface (36) of said downstream liquid feed tube end (32) and the inner surface (56) of said swirl chamber wall (55). The annular space (76) between the said outer surface (36) and the sleeve (70) acts as a swirl chamber for the liquid exiting the tangential liquid ports (35) of the liquid feed tube end (32). In this situation, angular momentum losses of the gas flow are reduced, providing larger values of the tangential velocity of the two-phase medium at exit from the sprayer, thereby improving atomisation quality on account of the stronger centrifugal forces acting to fragment liquid drops. The minimum clearance δ_mi_n between the sleeve (70) and the said outer surface (36) is related to the diameter d of the at least one liquid port (35) by the expression :-

The said sleeve (70) extends axially downstream from the said swirl chamber wall (58) and may extend into the throat region (52), with the said liquid ports (35) axially aligned with the throat region (52), as illustrated in Figure 6, or alternatively situated at any suitable location upstream thereof. Optionally, the inner and outer diameters of the throat region (52), d_b and d_c, respectively, may be adjusted to compensate for the presence of the sleeve (70) within the throat region (52). Alternatively, the sleeve (70) only extends as far as the entry to the throat region (52), and the said liquid ports (35) are axially disposed upstream with respect to the throat region (52), in which case, liquid communication between the said liquid ports (35) and the throat region (42) is still maintained via said annular space (76) provided by the sleeve (70).

Preferably, the said liquid feed tube end (32) comprises a plurality of said lateral liquid ports (35) in fluid communication with said swirl chamber (50). In particular, the plurality of lateral liquid ports (35) are advantageously arranged in at least two axially spaced groups. Further optionally, each of these groups comprises an equal number of said liquid ports (35), for example 4 ports, substantially uniformly distributed circumferentially. Each port on one row may be substantially aligned axially with corresponding liquid ports (35) of an adjacent group of liquid ports (35), though preferably, the liquid ports (35) on one row are angularly displaced with respect to the liquid ports (35) of an adjacent row, as illustrated in Figure 4. In the latter case, the precise angular displacement between adjacent rows may be advantageously chosen such as to maximize homogenous introduction of liquid into the swirl chamber (50). Thus, for example, if there are two rows of four liquid ports (35), the liquid ports (35) in one row could be displaced by 45° with respect to the liquid ports (35) of the adjacent row. If there were three such rows, the liquid ports could be angularly displaced by 30° rather than 45°. Typically, the number of lateral liquid ports (35), in particular the number of axially spaced groups, and the number of liquid ports (35) per group, as well as the dimensions of each liquid port (35) of the sprayer (10) may be chosen advantageously taking into consideration factors such as the flow rate characteristics of the device as well as the viscosity of the liquid.

It is seen that in the embodiment described gas is fed through tube (20) and is imparted a swirling motion by feeding it into the swirl chamber (50) through ports (25) that are lateral (as this term is defined hereinbefore), viz. have axes that do not intersect the axis (100) of the swirl chamber. Axis (100) is also the general axis of the device and the swirling gas stream generally, or in the average, progresses in the direction of said axis, while not being directed along it at any point. Lateral ports (25) are tangential, in the sense that their axes are tangential to circles concentric with the inner cylindrical surface of the swirl chamber. While this is the simplest way of imparting to the stream of gas a swirling motion, different means could be used for imparting said motion without departing from the invention as claimed. Concurrently with its swirling motion, therefore, the gas stream is advanced in the direction defined by the axis (100) of the swirl chamber and of the device as a whole. The cross-sectional area of the swirling gas stream perpendicular to said axial direction is initially that of the swirling „ „

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chamber (50), but as the stream progresses, it is constrained within the throat region (52), and its cross-sectional area is decreased. Due to the conservation of angular momentum, this causes the intensification of the rotational gas motion and the reduction in gas pressure due to acceleration in both the axial and the tangential velocity components of the gas. The gas is thus brought to a high rotational velocity and low pressure, which pressure is preferably close to that prevailing downstream of the sprayer outlet. The stream of liquid is then injected into the gas stream, preferably in the throat region and tangentially to it. The liquid injection ports (35) are lateral, and preferably tangential, in the sense that their axes are tangential to circles concentric with the inner cylindrical surface of the throat region. It is seen, in the embodiment described, that ports (35) positioned shortly after the beginning of the throat region, viz. the stream of liquid is injected tangentially into the swirling gas stream immediately after said stream has been constrained to the second cross-sectional area and has therefore been accelerated. This is desirable because, on the one hand, the changes in rotational velocity of the gas stream and in pressure have already occurred before the injection of the liquid, and on the other hand the liquid will participate in the swirling motion of the gas stream and its atomizing effects before issuing from the throat through the sprayer outlet. The injection requires low feed pressure, because of the low pressure prevailing in the throat region. The gas mass and flow rate required for atomization of the liquid are smaller than in other atomizing devices because of said low pressure and of the high gas velocity at the points of liquid injection. Preferred, but not limiting, dimensional relationship are set forth hereinafter.

At an inner diameter d_b of the throat, given by the expression:

d_b=d_cV(l-φ)

(the terms d_c and φ being defined below) the static pressure of the gas flow in the swirl duct (50) becomes substantially equal to that of the medium into which the two-phase liquid is dispersed downstream of the sprayer outlet, while the tangential velocity of the airflow in the swirl chamber (50) reaches a maximum. Thus, under these conditions, the required liquid pressure differential with respect to the swirl chamber static pressure for injecting liquid into the swirl chamber (50) is a minimum, while the shear forces on the liquid (due to the tangential velocity component of the swirling gas) is at a maximum leading to high atomisation quality for relatively low gas flow rates and low liquid pressure values. By providing tangential liquid ports (35), as illustrated in Figure 3(b) for the first embodiment, the liquid is injected into the swirl chamber with a tangential velocity in the same direction as the swirling air, thereby reducing air rotation losses in the area of interaction with the liquid, thereby improving further the atomisation characteristics of the sprayer (10).

Thus, in the first embodiment, the optimal relative magnitudes of said inner diameter and said outer diameter of said annular throat region are substantially related by the expression:

wherein : d_b is said inner diameter d_c is said outer diameter φ is a parameter linked to the throat flow rate coefficient μ by the expression:

The throat flow rate coefficient μ is a measure of the effective flow area Fx relative to the actual flow area Fc.

For the swirled gas stream outflow, the flow rate coefficient μ at the throat (52) may be determined by the characteristic "A" of the swirl chamber (50). The characteristic "A" is a complex of geometrical dimensions determining the intensity of the gas stream swirling, and is a similarity criterion in which theoretically different dimensional representations of vortex chambers characterized by the same value of "A" feature the same value of flow rate coefficient μ. "A" may be determined from the relationship: -

A = πrcRmin/FG

wherein: -

r_c is the outer radius of the throat region (52).

R_mi_n is the minimum distance between the axis (200) of each gas port (32) and the axis (100) of the swirl chamber (50) (see

Figure 2).

F_G is the total geometrical area of the said gas ports (25). The "A" characteristic is related to the parameter φ by the expression:-

A=[(l-φ)V2]/[ φ φ ]

Thus, the flow rate coefficient μ may be determined given the "A" characteristic of the swirl chamber (50).

The following hydrodynamic considerations are offered to provide background information and facilitate the understanding of phenomena that may have some relationship to the process and device of the invention, but they are only approximate and in any case not relevant and not binding in the definition of the invention.

At precritical gas flow regimes, i.e., where the Mach number of the gas flow at the throat region is less than unity, the gas mass flow rate "m" may be determined from the following relationship:-

At a critical flow regime, i.e., with sonic flow conditions at the throat region (52), the gas mass flow rate may be determined from the relationship:-

wherein

P_in is the total gas pressure at inlet to the swirl chamber (50). Ti_n is the total gas temperature at inlet to the swirl chamber (50). P_out is the total pressure of the medium into which the two-phase flow is being discharged. F_c is the geometric area of the throat (52). k is the adiabatic index of the gas, which for air is typically about

1.4. R is the Universal Gas Constant.

The total area F_L of the liquid ports (35) may be determined from the following relationship :-

wherein:-

m_L is the liquid flow rate. μ_L is the flow rate coefficient of the liquid ports (35), typically about 0.5 to about 0.6. g is the acceleration due to gravity constant. γ is the specific weight of the liquid. ΔP is the difference between the total pressure of the liquid and the total pressure of the gas at entry to the swirl chamber (50).

A second embodiment of the invention will now be described.

Typically, the two-phase flow flows axially from the annular exit (54) of the swirl chamber (50). In some applications, it is important for the two-phase flow to flow at an angle to the axis of the sprayer (10). Thus, turning to Figure 8, this figure illustrates a second embodiment of the present invention incorporating a diffuser (90) downstream of and in fluid communication with said annular throat region (52). The diffuser (90) is adapted to impart a radial velocity component to two phase fluid flowing from said downstream opening of said swirl chamber. The said radial velocity component may be chosen to be such as to provide a predetermined spray angle for said two phase fluid exiting said diffuser (90). In this embodiment, said diffuser (90) comprises an outer substantially frustoconical diverging wall (92) which is at an angle αl to the axis (100) of the diffuser (and thus to the axis of the sprayer (10)) at planes through this axis. The diffuser (90) also comprises a substantially coaxial inner substantially frustoconical diverging plug (94) which is at an angle α2 to the axis (100) of the diffuser (and thus to the axis of the sprayer (10)) at planes through this axis. The diverging plug (94) and the diverging wall (92) define therebetween an axially diverging conical channel (96) having an average cone angle or apex angle α, defined as the average value of the angles {twice αl} and {twice al}. Said angles αl and α2 may be equal, in which case the said conical channel (96) is parallel but of increasing area in the downstream direction. Said average apex angle α is typically between about 70° and about 120°, i.e., about 35° and about 60° to the axis (100).

Structurally, and with reference to Figure 8, the said diverging plug (94) may be optionally integrally connected to the downstream end (38) of said liquid feed tube end (32), and the said diverging wall (92) may be optionally integrally connected to the said outer gas feed tube wall (24) of said gas feed end (22). WO 00/58014 _{n n} PCT/ILOO/00182

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In high temperature applications such as in fuel atomisation for combustion processes, the high velocity two-phase fluid flow through the diffuser (90) provides cooling thereof, leading to longer service life of the sprayer (10).

Another requirement that must usually be met for sprayers used as fuel atomisers is that of enabling a range of velocities to be provided for the two-phase flow. The axial flow velocity within the diffuser is reduced as a result of the diffusion therein. The degree of flareout or diffusion, DK, may be determined from the relationship :-

DK= F_d0 /F_c

wherein:-

F_c is the geometric area of the throat (52).

F _o is the geometric area of the conical channel (96) at the downstream end of the diffuser (90).

The value of DK may be advantageously chosen to be between 2 and 5 for many applications, and depends on many factors including gas pressure, properties of the liquid, and so on. Typically, reducing DK increases the value of the outflow velocity, which may worsen the index of combustion completeness in such applications. On the other hand, excessive diffusion lowers the dispersion quality and increases the size of the dispersed liquid particles.

Optionally, the said sprayer (10) comprises at least one baffle (80) for separating two-phase fluid flow exiting said sprayer (10) into at least two streams and for enhancing mixing thereof with ambient fluid external to the said sprayer (10). In particular, if the said sprayer (10) incorporates a diffuser (90), the said at least one baffle (80) is comprised at the downstream end of the diffuser, as illustrated in Figure 9. Preferably, a plurality (e.g. 4) of circumferentially equi-spaced baffles (80) are comprised at the downstream end of the sprayer (10) or said conical channel (96), as appropriate. The baffles (80) separate the annular or conical flow exiting the sprayer (10) or diffuser (90), respectively, into a number of adjacent streams, promoting mixing with the ambient fluid. In combustion applications, where the sprayer (10) (with or without the said diffuser (90)) is used for atomising fuel, thorough mixing of the atomized fuel with ambient oxidizer gas (typically compresses air or oxygen) enables the fuel to be more fully combusted, resulting in a more efficient combustion process and in lower emissions, particularly pollutants.

Optionally, said at least one baffle (80) is in the form of a vane-like member (82) radially extending the width of said conical channel at the downstream end thereof, and having a substantially blunt trailing edge. The said vane-like member (82) may be optionally integrally connected to said conical plug (94). Alternatively, the vane-like member (82) may be optionally integrally connected to said diverging wall (92).

Alternatively, and with reference to Figure 10, said at least one baffle (80) may be integrally connected at an inner radial end thereof to said inner plug (94), said inner plug comprising a free upstream end (97) comprising a diameter substantially equal to the said inner diameter of said throat region d_b) said upstream end (97) being optionally abuttable against the downstream end of said swirl chamber (50), i.e. of said blank (38). The said at least one baffle (80) may also be integrally connected at the outer radial end thereof to a suitable annular ring (98) having an inner diameter substantially equal to the diameter d₀ of the downstream end of said diverging wall (92). Said annular ring (98) is integrally connected to a downstream end portion of said outer gas feed tube wall (24). This configuration for the diffuser and baffles is particularly advantageous with respect to the manufacture of these components.

Referring to Figure 11, the sprayer (10) comprises suitable adjustment means for enabling said downstream liquid feed end (32) to be axially movable with respect to said throat region (52). Such adjustment means may be necessary for compensating for manufacturing errors which may otherwise bring into misalignment the said liquid ports (35) with respect to the said annular throat region (52).Preferably, said suitable adjustment means comprises mutually engaging complementary screwthread surfaces (72), (74) respectively comprised on the said outer surface (36) of an upstream portion of said inner liquid feed tube wall (34), and on a lower radial portion (59) of said swirl chamber wall (58), which swirl chamber wall (58) may further comprise an axial extension (59) in the upstream direction, as illustrated in Figure 11. The said adjustment means may advantageously comprise a locking nut (60) to lock the said liquid feed end (32) in any particular axial alignment with respect to said swirl chamber (50). While the said adjustment means has been illustrated and described with respect to the embodiment of Figure 11, it may also be comprised in each of the other embodiments of the present invention described herein, and with reference to Figures 1 to 10, mutatis mutandis.

While in the foregoing description describes in detail only a few specific embodiments of the invention, it will be understood by those skilled in the art that the invention is not limited thereto and that other variations in form and details may be possible without departing from the scope and spirit of the invention herein disclosed.

Claims

1. A two-phase sprayer for spraying a liquid using an atomising gas, comprising :- an annular swirl chamber having a downstream end comprising a substantially annular throat region, said throat region having an inner diameter and an outer diameter; a gas feed tube adapted for the supply of said atomising gas, said gas feed tube having a downstream gas feed tube end comprising at least one lateral gas port in fluid communication with said swirl chamber, said at least one lateral gas port adapted to impart a tangential velocity component to gas fed from said gas feed pipe to said swirl chamber at least within said throat region; a liquid feed tube adapted for the supply of said liquid to be sprayed and having a downstream liquid feed tube end comprising at least one lateral liquid port in fluid communication with said swirl chamber, said at least one liquid port being in fluid communication with said annular throat region.

2. A sprayer as claimed in claim 1, wherein the relative magnitudes of said inner diameter and said outer diameter of said annular throat region are substantially related by the expression: d_b≤d_cV(l-φ) wherein : d_b is said inner diameter d_c is said outer diameter φ is a parameter linked to the throat flow rate coefficient μ by the expression: μ = V[φ³/(2-φ)]

3. A sprayer as claimed in any preceding claim, wherein said downstream liquid feed tube end is substantially coaxial with said swirl chamber and comprises a substantially cylindrical wall blanked off at the downstream end thereof and having an outer surface.

4. A sprayer as claimed in claim 3, wherein said swirl chamber is radially bounded by at least a portion of the outer surface of said downstream liquid feed tube end and by the inner surface of an outer substantially cylindrical swirl chamber wall substantially concentric with respect to said downstream liquid feed tube end.

5. A sprayer as claimed in claim 4, wherein said swirl chamber wall comprises a downstream portion corresponding to said annular throat region and having a diameter corresponding to said outer diameter for said annular throat region, and wherein said swirl chamber further comprises an upstream portion having a diameter greater than said outer diameter of said annular throat region.

6. A sprayer as claimed in any one of claims 4 or 5, wherein said downstream gas feed tube end is substantially coaxial with said swirl chamber, and said downstream gas feed tube end is radially bounded by at least a portion of the outer surface of said swirl chamber wall and by at least a portion of the inner surface of a substantially cylindrical outer gas feed tube wall substantially concentric with respect to said swirl chamber wall.

7. A sprayer as claimed in any preceding claim, wherein said at least one gas port is located upstream of said annular throat region.

8. A sprayer as claimed in any preceding claim, wherein said gas feed tube end comprises a plurality of said lateral gas ports in fluid communication with said swirl chamber.

9. A sprayer as claimed in claim 8, wherein said plurality of lateral gas ports are arranged in at least two axially spaced groups.

10. A sprayer as claimed in claim 9, wherein each said group comprises an equal number of said gas ports substantially uniformly distributed circumferentially and substantially aligned axially with corresponding said gas ports of an adjacent said group.

11. A sprayer as claimed in any preceding claim, wherein said at least one lateral liquid port is adapted to impart a radial velocity component to liquid fed from said liquid feed pipe to said swirl chamber at least within said throat region.

12. A sprayer as claimed in any preceding claim, wherein said at least one lateral liquid port is adapted to impart a radial velocity component and an axial velocity component to liquid fed from said liquid feed pipe to said swirl chamber at least within said throat region.

13. A sprayer as claimed in any preceding claim, wherein said at least one lateral liquid port is adapted to impart a tangential velocity component to liquid fed from said liquid feed pipe to said swirl chamber at least within said throat region.

14. A sprayer as claimed in claim 13, further comprising an annular sleeve radially displaced from said liquid feed end.

15. A sprayer as claimed in any preceding claim, wherein said liquid feed tube end comprises a plurality of said lateral liquid ports in fluid communication with said swirl chamber. — O —

16. A sprayer as claimed in claim 15, wherein said plurality of lateral liquid ports are arranged in at least two axially spaced groups.

17. A sprayer as claimed in claim 16, wherein each said group comprises an equal number of said liquid ports substantially uniformly arranged circumferentially.

18. A sprayer as claimed in claim 17, wherein said liquid ports of one said group of liquid ports is angularly displaced with respect to said liquid ports of an adjacent said group of liquid ports.

19. A sprayer as claimed in any preceding claim, further comprising a diffuser downstream of and in fluid communication with said annular throat region.

20. A sprayer as claimed in claim 19, wherein said diffuser is adapted to impart a radial velocity component to two phase fluid flowing from said downstream opening of said swirl chamber.

21. A sprayer as claimed in claim 20, wherein said radial velocity component is such as to provide a predetermined spray angle for said two phase fluid exiting said diffuser.

22. A sprayer as claimed in any one of claims 19 to 21, wherein said diffuser comprises an outer substantially frustoconical diverging wall and a substantially coaxial inner substantially frustoconical diverging plug defining therebetween a axially diverging conical channel.

23. A sprayer as claimed in claim 22, wherein said conical channel has an average apex of between about 70° and about 120°.

24. A sprayer as claimed in any one of claims 22 or 23, wherein said diverging plug is integrally connected to the downstream end of said liquid feed tube end.

25. A sprayer as claimed in any one of claims 19 to 24, wherein said diffuser comprises at least one baffle for separating two-phase fluid flow exiting said diffuser and for enhancing mixing thereof with ambient fluid external to the said diffuser.

26. A sprayer as claimed in claim 25, wherein said at least one baffle is in the form of a vane-like member radially extending the width of said conical channel at the downstream end thereof.

27. A sprayer as claimed in any one of claims 25 or 26, wherein said diffuser comprises a plurality of said baffles being angularly disposed substantially uniformly at the downstream end of said conical channel.

28. A sprayer as claimed in any one of claims 25 to 27, wherein said at least one baffle is integral with said inner plug.

29. A sprayer as claimed in any one of claims 25 to 27, wherein said diverging wall is integrally connected to the downstream end of said gas feed tube end.

30. A sprayer as claimed in any one of claims 25 to 27, wherein said at least one baffle is integrally connected at an inner radial end thereof to said inner plug, said inner plug comprising a free upstream end comprising a diameter substantially equal to the said inner diameter of said throat region and optionally abuttable against the downstream end of said swirl chamber, said at least one baffle being integrally connected at the other radial end thereof to a suitable annular ring having an inner diameter substantially equal to the diameter of the downstream end of said diverging wall, said annular ring being integrally connected to a downstream end portion of said outer gas feed tube wall.

31. A sprayer as claimed in any one of claims 19 to 30, wherein the degree of flareout or diffusion, DK, is between about 2 and about 5, wherein DK is determined from the relationship:-

DK= F_d0 /F_c

wherein :-

F_c is the geometric area of the throat (52).

F_do is the geometric area of the conical channel (96) at the downstream end of the diffuser (90).

32. A sprayer as claimed in any preceding claim, further comprising suitable adjustment means for enabling said downstream liquid feed end to be axially movable with respect to said throat region.

33. A sprayer as claimed in claim 32, wherein said suitable adjustment means comprises mutually engaging complementary screwthread surfaces respectively comprised on the said outer surface of an upstream portion of said inner liquid feed tube wall, and on a lower radial portion of said swirl chamber wall.

34. A sprayer as claimed in claim 33, wherein said swirl chamber wall further comprises an axial extension in the upstream direction comprising an inner screwthread surface engageable with said screwthread surface comprised on the said outer surface of an upstream portion of said inner liquid feed tube wall.

35. A sprayer as claimed in claim 33 or claim 34, further comprising a locking nut for locking the said liquid feed end in any particular axial alignment with respect to said swirl chamber.

36. Method for producing a spray of liquid, which comprises the following steps:

feeding a stream of gas; imparting to said stream of gas a swirling motion; concurrently advancing said swirling stream of gas in an axial direction, said swirling stream of gas having a first annular cross-sectional area perpendicular to said direction; constraining said stream of gas to a second annular cross-sectional area smaller than said first area, whereby to accelerate said swirling stream of gas both axially and tangentially; and injecting a stream of said liquid tangentially into said accelerated swirling gas stream, whereby to generate the spray of liquid.

37. Method according to claim 36, comprising discharging the generated spray of liquid."

38. Method according to claim 36, wherein the stream of said liquid is injected tangentially into said accelerated swirling gas stream immediately after constraining the stream of gas to a second cross-sectional area.