Apparatus for Seeding a Fluid with Tracing Material

A new seeder for laser-based velocity measurements in gaseous combusting and non-combusting flows is described herein. The performance of the seeder was tested under a variety of flow rate conditions. The testing revealed that control over the concentration of seeding particles, stability of particles supply, extended range of flow rate, and breakup of the agglomerates makes the newly designed seeder advantageous over its counterparts, especially for weak flow rates applications.

DETAILED DESCRIPTION

Design of a New Seeder

Referring initially toFIGS. 4 and 5, there is illustrated a seeding apparatus generally indicated by reference numeral10. The apparatus10is particularly suited for seeding a tracing material, for example micro sized particulate material into a carrier fluid, for example a gas flow.

The apparatus10includes a seeding chamber12which generally cylindrical and elongate in a horizontal direction to extend axially between an inlet end14and an outlet end16. The chamber is bound by an outer cylindrical wall18spanning horizontally in the longitudinal direction of the chamber between end walls20at the inlet and the outlet ends respectively.

An inlet coupling22is mounted in communication with the seeding chamber through the outer wall18at the top side thereof adjacent the inlet end of the chamber. The inlet coupling22is arranged to introduce the flow of carrier fluid into the seeding chamber in operation. When not in operation, the inlet coupling22includes an upper opening selectively enclosed by a threaded cap24which permits the tracing material to be introduced into the seeing chamber therethrough when the cap is removed.

An outlet coupling26communicates with the seeding chamber through the end wall at the outlet end16adjacent the top end thereof. The outlet coupling is arranged to discharge the carrier fluid from the seeding chamber therethrough once the carrier fluid has been seeded with the tracing material within the seeding chamber.

Both the inlet and outlet couplings are located adjacent the top side of the seeding chamber so as to define a flow area28occupying the upper half of the seeding chamber where the carrier fluid is permitted to flow longitudinally from the inlet end to the outlet end primarily within the upper half of the seeding chamber. A sump area30is thus defined below the flow area such that the sump area extends in the longitudinal direction along the bottom half of the chamber between the inlet and outlet ends where the tracing material is arranged to settle. The level of tracing material in the chamber may substantially fully occupy the sump area corresponding to the bottom half of the seeding chamber.

An agitator32is supported within the seeding chamber for operation between the sump area30and the flow area28thereabove to carry the settled tracing material in the sump area upwardly into the flowing carrier fluid in the flow area. The agitator32includes a shaft34concentrically supported in the cylindrical seeding chamber to extend horizontally and longitudinally between the opposing end walls20.

An outlet bearing36supports one end of the shaft34at the inner side of the outlet end wall such that the outlet end of the shaft and the outlet bearing36are fully contained within the boundary of the chamber to be fully pressurized together with the hollow interior of the seeding chamber in operation and therefore prevent any leakage to the exterior at the outlet bearing. An inlet bearing38is mounted in the inlet end wall to receive the shaft extending therethrough so that the shaft is accordingly rotatably supported relative to both of the end walls.

At the exterior of the end wall of the chamber the shaft is connected to an axle40for rotation together relative to the walls of the chamber. The axle40is connected to an electric variable speed motor42for driving rotation of the agitator shaft relative to the chamber. A pressure chamber44surrounds the portion of the shaft protruding outwardly from the seeding chamber at the inlet end wall as well as the axle connected thereto. The pressure chamber44fully surrounds the shaft and is arranged to be connected to a source of air under pressure so that the chamber about the exterior side of the inlet bearing38can be pressurized to a pressure which is equal or greater than the working pressure within the seeding chamber to prevent leakage of the carrier fluid through the inner end wall.

The agitator further comprises a plurality of mixing elements46which are mounted at evenly circumferentially spaced positions about the shaft and so as to be oriented generally in the radial direction relative to the shaft. The mixing elements are supported by two end plates48which are generally circular and fixed at opposing ends of the shaft to extend radially outward within the respective planes oriented perpendicularly to the shaft. In the illustrated embodiment 8 elements46are evenly spaced apart from one another in the circumferential direction.

Each mixing element46comprises a planar paddle which extends longitudinally between opposed ends fixed to the two end plates48respectively. Furthermore, each mixing element spans radially outward from an inner edge spaced outward from the shaft to an outer edge in proximity to the cylindrical outer wall18of the seeding chamber. The radial distance from the shaft to the inner edge of each mixing element as approximately equal to the radial dimension between the inner and outer edges of the element.

Each paddle further includes a plurality of apertures formed therein at spaced positions in the longitudinal direction such that the apertures are evenly distributed along the full length resulting in a perforated mixing element. The planar surface of the mixing element is well suited for lifting considerable amounts of the tracing material settled in the sump area upwardly into the flow area while the perforations enhance the fluid flow about the surfaces of the mixing elements carrying the tracing material thereon from the sump area to the flow area.

The apparatus10further comprises a carrier fluid source which communicates with an inlet tee50which separates the initial flow from the source into a first branch line directed towards the inlet coupling and an opposing second branch line in parallel with the first branch line. A first valve52is coupled in series with the first branch line between the inlet tee50and the inlet coupling22to adjustably control the volume of carrier fluid flow to the inlet coupling and thus through the seeding chamber.

The second branch line comprises a by-pass line54which is arranged to receive the carrier fluid flow therethrough in parallel relation with the seeding chamber. A second valve56is connected in series with the by-pass line to adjustably control the volume of carrier fluid flow through the by-pass line relative to the seeding chamber.

The first and second valves are adjustable such that all of the flow can be directed to the seeding chamber for lower volume flows, or alternatively an adjustable portion of the carrier fluid flow can be redirected through the by-pass line in parallel with the seeding chamber for high speed flows where it is desirable to limit the overall speed of flow through the seeding chamber. An outlet tee58joins the by-pass line54and the outlet of the outlet coupling26so that flows from both connections to the outlet tee can be subsequently directed to a sonic valve60.

The sonic valve generally includes a valve body62having an inlet opening64and an outlet opening66. A generally cylindrical chamber within the body62is coaxial with the outlet opening and a valve seat68defined within the inner body. In particular the valve seat68comprises a generally conical surface which is reduced in diameter towards an orifice which defines a valve opening or nozzle by being reduced in diameter in a direction from the inlet opening towards the outlet opening. The inlet opening64communicates within the inner chamber within the cylindrical body in a radial direction relative to the axis of the cylindrical chamber and outlet opening.

The sonic valve60further includes a shuttle or valve member70which has a generally elongate and cylindrical body received within the chamber of the valve body62such that an outer diameter of the valve member body is much smaller in diameter than the chamber of the valve body while being larger in diameter than the orifice or valve opening defined by the seat68. The valve member extends in the axial direction of the outlet opening from a mounting end72which is mounted in threaded connection through one end of the valve body axially opposite from the outlet opening to an opposing working end74.

The working end portion is generally conical so as to be reduced in diameter from the outer diameter of the cylindrical body portion to an apex which is smaller in diameter than the orifice. The axial position of the valve member body is adjusted relative to the valve body62by rotating the valve member relative to the valve body to displace the valve member in the axial direction of the outlet opening relative to the valve seat68. When fully open the valve opening or orifice is unobstructed by the valve member. By advancing the valve member towards the outlet opening, the reduced diameter working end74of the valve member can be inserted into the valve opening of the seat68by varying amounts to obstruct the orifice by varying amounts. By varying the portion of the orifice unobstructed by the valve member, the effective size of the valve opening is adjusted to optimize the sonic flow through the valve body to reduce agglomerations of tracing material within the carrier fluid.

In use, the sump area is initially filled with tracing material through the inlet coupling, for example to a level indicated by the broken line inFIG. 4(a). Once the cap of the inlet coupling is replaced and the pressure chamber is pressurized, fluid flow can be introduced through the seeding chamber primarily in the flow area from the inlet coupling to the outlet coupling. Rotating the agitator by varying speeds will vary the concentration of tracing material which is lifted from the sump area into the flow area for being collected within the flow of carrier fluid exiting the seeding chamber. Substantially all of the carrier fluid flow can be directed through the seeding chamber for slower flows if desired; however, adjustment of the first and second valves permits varying amounts of the carrier fluid to be re-directed through the by-pass line in parallel to the seeding chamber for higher speed carrier fluid flows. The position of the valve member within the sonic valve is adjusted to optimize sonic flow through the valve body and break up agglomerates of tracing material as described above.

The main objective of the present invention is the design a new seeder which aims to resolve the seeding issues briefly discussed above. The design adopted in the new seeder aims at i) enlarging the flow operability range, ii) ensure steady and uniform supply of particles, and iii) having control over the concentration and size of particles independently of the volumetric flow rate and moisture content in a gaseous flow. A schematic diagram of the new seeder is shown inFIG. 4(a). The concept of this seeder is to mechanically agitate solid particles inside a horizontal container to producing fluidized particles. The seeding particles concentration is controlled by the speed of a rotating brush independently of the flow rate. To break up the particle agglomerates, a sonic valve is used at the exit/outflow of the seeder as shown inFIG. 4(b). In addition, the flow direction in the sonic valve is altered to avoid the clogging problem.

A photographic picture of the new seeder is provided inFIG. 5. As shown in this figure, the seeder mainly consists of a horizontal cylinder divided into two compartments. The cylinder diameter is about 90 mm. The smaller compartment connects to a pressurized supply line of air or nitrogen, which is needed to balance the pressure between the two compartments for the purpose of sealing the seeder. The larger compartment contains solid particles and a rotary brush (seeFIG. 4(a)) which mechanically agitates the particles and hence produces aerosols of particles agglomerates. When a gaseous flow passes through this compartment it mixes and consequently carries the suspended particle agglomerates. The concentration of particles in the flow is controlled by varying the speed of a DC motor connected to the brush. The design includes also a bypass line to control the over flow through the seeder for extremely high speed flows. The technique of high shear stress of a sonic flow is adopted in this design to break the large agglomerates to smaller ones. Moreover, a variable sonic valve is employed to achieve a choked flow over a wide range of jet flow conditions.

EXPERIMENTAL PROCEDURE

To assess the performance of the new seeder, an existing atmospheric flame/burner test rig was employed and used in a laboratory for studying the stability of turbulent jet flames. Details of the test apparatus is reported in [13,14]; however, a brief description is provided as follows. The atmospheric burner consists mainly of an interchangeable fuel nozzle attached to a central supply pipe, which is, in turn, connected to a supply cylinder of fuel (or to a compressed air supply line; which what was used in the present tests). The central pipe is surrounded by an annulus which is used for supplying co-airflow delivered from a laboratory compressed supply line. However, in the present tests only the central air jet is used. The flow rate along with the exit cross-sectional area of the nozzle (or pipe, see Table 1) is used to determine the exit velocity (i.e. bulk velocity). The selected jet airflow rate, which is supplied to the burner from a laboratory compressed air line, mixes with the seeding particles in the seeder, and then flows through the central pipe before discharging into the atmosphere from the nozzle/pipe. The existing seeder, which is a mechanically agitated fluidised bed seeder was described in [15]. A Dantec Dynamics two-dimensional particle image velocimetry (PIV) was used to measure the flow instantaneous velocity profiles. The PIV system consists mainly of a 120 mJ/pulse laser with 532 nm wavelength to illuminate the flow field, and a 12-bit high-resolution digital camera (Dantec Dynamic NanoSense MKIII camera) with a 1024 pixels×1260 pixels CCD and 12 μm pixel pitch. The laser sheet was located in the symmetry plane of the jet. Instantaneous image pairs of about 2000 were used to determine the jet flow velocity information. The instantaneous images were processed using 8 pixels×8 pixels interrogation window with a 50% overlap and adaptive correlation. The analysis of 8 pixels×8 pixels and 16 pixels×16 interrogation windows demonstrated that the results were grid independent. The present test conditions are summarized in Table 1 as follows:

Results and Discussions

A series of experiments were carried out to assess the newly designed seeder in terms of its ability in 1) performing adequately at low and high flow rate, 2) controlling the particles concentration, and 3) breaking up the larger agglomerates in order to reduce the size of particles.

Particles Concentration

Instantaneous images of air jet flow into a stationary atmospheric ambient is shown inFIG. 6. The jet issues from a pipe with a flow rate of 3.70 LPM. These images illustrate the performance of the new seeder in controlling the concentration of solid particles fed into a gaseous jet flow without changing the flow rate.FIG. 6(a) shows a very weak concentration of particles in the jet which can be achieved by keeping the rotational speed of the brush at low RPM. It is clear that the jet flow is not sufficiently seeded (FIG. 6(a)) and hence any attempt in using laser-based velocity measurements technique will fail. Further increasing the brush rotational speed results in an increase in the concentration of particles in the jet as shown inFIG. 6(b). This figure shows that the flow is sufficiently seeded as the jet is clearly identifiable from its quiescent atmospheric environment. The same figure, however, reveals a relative drop in the seeding particles in the very far-field of the jet. This is due to the fact that the ambient surrounding the jet is unseeded and hence the jet loses seeding particles to the ambient as a result of entrainment/mixing.FIG. 6(c) shows that the concentration of seeding particles in the jet flow's far-field is enhanced by increasing further the rotational speed of the brush without varying the jet flow rate. This feature of the new seeder makes it superior to the existing/published seeders.

FIG. 7compares the contours of the number of PIV valid velocity vectors for the jet's half between the mechanical agitated fluidized bed seeder (MFS) and the new seeder (NS) at three different flow rates (i.e., jet exit velocity). This figure shows clearly that the new seeder provides much better contours at any jet flow rate. The same figure shows also that the number of PIV valid vectors with the MFS seeder becomes comparable to that of the NS at medium range of jet flow rates (e.g., 15 m/s).

The number of valid vectors along the centerline of the jet for the jet conditions explored inFIG. 7is presented inFIG. 8. It confirms that, at sufficiently high/medium jet flow rate (e.g., 15 m/s), the mechanically agitated fluidized bed (MFS) provides comparable seeding to that of the NS. However,FIG. 8clearly demonstrates that the MFS seeding quality deteriorates as the jet flow rate drops quickly farther downstream of the jet, which is an indication that MFS performance depends on the jet flowrate. The effect of the concentration of particles on PIV velocity measurements is presented inFIG. 9for a laminar regime (Re=1800) and inFIG. 10for a transient laminar-turbulent regime (Re=3900). Figures (a) and (b) present, respectively, the jet decay along the centreline and the corresponding valid PIV velocity vectors.FIGS. 9 and 10show that as the seeding concentration in the jet drops below a certain concentration level (FIGS. 9(b) and10(b)), the mean-velocity profile (FIGS. 9(a) and10(a)) deviates or fluctuates noticeably around the one that corresponds to adequate concentration level.

Particles Size

FIG. 11illustrates the effect of the new seeder sonic valve in breaking up the agglomerated particles into smaller size. These instantaneous images are an illustration of the effect of the sonic valve on the size of TiO2particles in the near field of a jet at low flow rate.FIG. 11(a) shows that when the valve is fully open, the flow appears to be seeded by a wide range of particles size including large particles.FIG. 11(b) shows that even though the valve is not in sonic position, the increased shears stress at valve by reducing the exit cross sectional area, breaks down many larger agglomerates into smaller ones. In other words, the concentration of the very large particles seen inFIG. 11(a) is reduced. On the other hand,FIG. 11(c) clearly shows that maximum shear stress at a sonic condition of the valve breaks down all particle agglomerates into small agglomerated particles. Moreover, sonic position of the valve results in a uniform size distribution of particles in the jet flow (FIG. 11(c)).

The effects of the sonic valve on the velocity measurements along the centerline of the jet are shown inFIG. 12.FIG. 12(b) shows that although, there are enough particles to generate valid PIV vectors (this is done by adjusting the brush rotational speed to increase the particles concentration when the valve is fully or half open) in all positions of the valve (FIG. 12(b)),FIG. 12(a) shows that the corresponding jet velocity decay profiles do not overlap. This is because of the larger particles formed when the sonic valve is either fully or half open.

New Seeder Versus Existing Seeders

In order to evaluate the performance of the new seeder (NS) at different flow rates, the profiles of the jet mean-velocity decay are compared between the mechanically agitated fluidized-bed seeder (MFS) and new seeder (NS).FIG. 13, which is for a very low flow rate with a jet exit velocity of about 3.7 m/s (Re=800), shows that the mechanically agitated fluidized bed has a fluctuating profile of the jet centerline velocity decay. This is mainly due to its poor seeding as it can be seen inFIG. 13(b); whereas the NS results in a smoother jet velocity decay profile.FIG. 14, which is for a moderately higher flow rate (i.e., with a jet velocity of about 8 m/s; that is for Re1800), shows that the MFS performs better than before as its corresponding mean-velocity decay profile's fluctuations decreased but still not enough to provide a smooth profile. This clearly shows the dependence of the seeding of the flow by the MFS on the jet flow rate.FIG. 15presents the profiles for a much higher flow rate than in the cases ofFIGS. 13 and 14where the jet exit velocity is about 15 m/s (Re3900).FIG. 15(b) shows that, at this relatively high flow rate, the MFS supplies enough particles into the flow.FIG. 15(a), however, shows that the MFS jet has a decay profile that is still slightly different than its NS counterparts. This is due to larger particles agglomerates generated by the MFS.

Performance and Validations

The new seeder is tested for flowrates between 3.70 LPM and 150 LPM. The seeder could operate bellow 3.70 LMP but the flow rate was restricted by the minimum range of the flowmeter. Also, the higher range of 150 LPM is limited by the speed and resolution of the camera due to the high speed of the jet; however, the new seeder could operate at higher than 150 LPM. Measuring the mean velocity and turbulence intensity of a jet at high speed can be achieved by using a bypass line in order to reduce the over flow into the seeder.

FIG. 16presents a comparison of the centreline mean-velocity decay (FIG. 16(a)) and its corresponding turbulence intensity (FIG. 16(b)) for a jet seeded by MFS or NS with their counterparts published results obtained using hot wire anemometry, which is an independent technique (as it does not employ seeding). FIG.16(a) clearly shows that both the centreline decay of the jets seeded by the NS with a sonic valve agree well with their counterparts obtained by hot wire anemometry [16] over the range of Re=3,900-17,500; whereas the centreline decay profile of the jet seeded by the MFS shows lower values than the corresponding published profiles. The same figure shows also that the decay profile of the jet flow seeded with the new seeder but with the sonic valve fully open has a noticeably lower profile than that of the jet with a sonic valve configuration.FIG. 16(b) shows that the centreline turbulence intensity of the jet seeded by the new seeder overlaps its corresponding published counterpart at Re=17,500. The same figure shows that the centreline turbulence intensity of the jet seeded by the MFS is not in agreement with that seeded with the new seeder when a sonic valve is used. The same figure shows also that the jet seeded by the new seeder with the sonic valve not used (i.e., fully open) has a different (higher) turbulence intensity profile than its counterpart with the sonic valve being used. This figure is evidence of the superior performance of the new seeder, not only in generating adequate/proper particles to seed the jet flow, but also in breakup up large particles and hence provide uniform particles size.

CONCLUSIONS

The sample results of the in-house developed new seeder described herein shows that a steady amount of uniform size particles can be supplied into a gaseous jet flow independently of its flow rate. The concentration of the particles in the flow can be adjusted by a simple control of the rotational speed of a brush without affecting the jet flow rate. The designed sonic valve has also been shown to help keep the particles as small as possible and also reduces significantly the possibility of clogging. It is believed that this seeder of the present invention can perform adequately with any flow condition (i.e., ultra low, low, medium, or high flow rate). It is also believed that the seeder of the present invention can be used in large volume flows (such as in wind tunnels) where a high quantity of tracers/particles is needed.

REFERENCES

The following references referred to by number above are hereby incorporated by reference.[1] Melling A 1997 Tracer particles and seeding for particle image velocimetryMeasurement Science and Technology8(12) 1406-1416[2] Tropea C, Yarin A L and Foss J F 2007 Handbook of Experimental Fluid Mechanics, Volume 1, Springer.[3] Pierce A J and Lu F K 2011 New Seeding and Surface Treatment Methods for Particle Image Velocimetry 49th AIAA Aerospace Sciences Meeting including the New Horizons Forum and Aerospace Exposition(4-7 January, Orlando, Fla., p. 1164)[4] Smelker K P 2006 Generating Uniform Sub-micron Solid Particles for Laser-based Flow DiagnosticsUndegraduate Final Year Project ThesisThe Ohio State University, USA.[5] Willert C and Janus M 2002 Planar flow field measurements in atmospheric and pressurized combustion chambersExperiments in Fluids33 931-939[6] Crosswy F L 1985 Particle size distributions of several commonly used seeding aerosols NASA CP-2393, pp. 53-75[7] Thomas L M 2009 Flow Measurements Using Particle Image Velocimetry in the Ultracompact CombustorMSc ThesisAir Force Institute of Technology, Ohio, USA[8] McNiel C M, Peltier D W, Reeder M F and Crafton J W 2007 Clean Seeding for Particle Image Velocimetry 22nd International Congress on Instrumentation in Aerospace Simulation Facilities(IEEE, pp. 1-6)[9] DeLapp C J 2006 Particle image velocimetry using novel non-intrusive seeding MSc Thesis Air Force Institute of Technology, Ohio, USA [10] Raffel M, Willert C E, Wereley S T and Kompenhans J 2007 Particle Image Velocimetry: A Practical Guide, Springer.[11] Howison J C and Goyne C P 2010 Assessment of Seeder Performance for Particle Velocimetry in a Scramjet CombustorJournal of propulsion and power26(3) 514-523[12] Urban W and Mungal M 1997 Planar velocity measurements in compressible mixing layers 35th Aerospace Sciences Meeting(AIAA 97-0757, Reno, Nev., pp. 1-15)[13] Iyogun C O and Birouk M 2009 On the Stability of a Turbulent Non-Premixed Methane Flame Combustion Science and Technology 181(12) 1443-1463[14] Iyogun C O Birouk M and Kozinski J A 2011 Experimental investigation of the effect of fuel nozzle geometry on the stability of a swirling non-premixed methane flameFuel90(4) 1416-1423[15] Iyogun C O 2009 Effect of nozzle geometry on the stability of a turbulent jet flame with and without swirling co-flowPhD ThesisThe University of Manitoba, Canada.[16] Papadopoulos G and Pitts W 1999 Generic Centerline Velocity Decay Curve for Initially Turbulent Axisymmetric JetsJournal of Fluid Engineering121 80-85.