PARTICLE MOTION IN WATER-PARTICLE, GAS-PARTICLE AND GAS-DROPLET TWO-PHASE FLOWS

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1 ISTP-6, 5, PRAGUE 6 TH INTERNATIONAL SYMPOSIUM ON TRANSPORT PHENOMENA PARTICLE MOTION IN WATER-PARTICLE, GAS-PARTICLE AND GAS-DROPLET TWO-PHASE FLOWS Tsuneaki ISHIMA*, Masaaki YOKOTA**, Toshimichi ARAI***, Ismail M. Youssef****, Waleed A. Abdel-Fedeel***** and Tomio OBOKATA* *Gunma University, JAPAN, **Graduate school of Gunma University, JAPAN, ***MAX Co., Ltd, JAPAN, ****Minia University, EGYPT, *****High Institute of Energy in Aswan, EGYPT Corresponding author: ishima@me.gunma-u.ac.jp, , Keywords: LDA, PDA, Particle motion, Two-phase jet flow, Two-phase pipe flow Abstract Three kinds of the two-phase flow, waterparticle, gas-particle and gas-droplet flows are analyzed experimentally in the study. The carrier fluid phase is water or air and the discrete phase is glass particle or water droplet. The difference in the local mass loadings indicates the variation in the particle dispersion for the each type of flows. The newer measuring techniques to discriminate the two-phase velocities are also proposed. Introduction Particle motion in the fluid is one of the most popular problems in the fluid engineering. Some previous works are performed in pipe flow [], shear layer [, 3, 4], free jet [5], confined jet [6] and axisymmetric jet [7]. All of the studies indicate the important parameters are particle size and density. They caused a change in the particle inertia. However, each work is carried out only one carrier fluid. The aim of the present study is to clarify the effect of difference of material types of the carrier fluid and particle. In the experiments, water and air are chosen for the carrier fluid and glass particle and water droplet are chosen for discrete particle. Then three types of the flow as watersolid, air-solid and air-liquid flows are tested. Laser measuring techniques like as laser Doppler anemometer (LDA) and phase Doppler anemometer (PDA) provides very effective experimental data in the two-phase flow [, 3, 4, 6, 7]. In the two-phase flow study, the instantaneous velocities of both particle and fluid are necessary for analyzing the detailed interaction between both phases. In the present study, a newer measuring technique is also proposed. Experimental Conditions. Flow Types and Experimental Setups Three types of water-solid, air-water, and airsolid of two-phase flows have been tested in this study by using three kinds of measuring setups. Two of them are designed for jet flows and one of them are used for pipe flows. Figure shows a schematic of the watersolid flow apparatus, which has a vertical tank made of optically clear transparent acrylic resin. The internal dimensions of the sides of the test section have 5 x x x mm with trapezoid shape. The height of the tank is 68 mm filled with water and is large enough to treat the flow as the free jet. Figure shows the scheme of the test section used in air-liquid and air-solid jet flow experiments. As shown in the figure, it consists of two main parts, one is main measuring

2 Particle Feeder Particle Controller Over Flow Pipes 6 pipe φ =56 Nozzle φ =9 Nozzle D=5mm x y Honeycomb Test section Blower Measured Flow Humidifier Water Manometer Blower Valve Particle Collector Pumps Fig. Experimental apparatus for water-solid flow Fig. Experimental apparatus for gas-solid and gas-liquid flow. Table Flow types. Flow type carrier fluid Discrete Particle density Particle mean Initial volume phase [kg/m 3 ] diameter [µm] ratio[%] water-solid water glass particle and.9 air-solid air glass particle air-liquid air water droplet 3. water-solid (pipe) air glass particle 5. chamber and another is mist-air mixing chamber. Both chambers are connected together through a pipe, which has a pipe nozzle of mm or 9mm in diameter for air-liquid flow and airsolid flow, respectively.. Flow Conditions Table shows the experimental conditions. Discrete particle was glass particle with 59 kg/m 3 in density for water-solid and air-solid flows or water droplet for air-liquid flow. In all of the experiments, the origin was set on the center of the nozzle exit. The x-, y-directions are set to vertical (streamwize) and perpendicular directions, respectively. In the case of water-solid flow, two nozzles with the diameter of 5 and 8 mm were used. Two initial water velocities at the nozzle exit were adopted.8 and.5 m/s for 5 and 8 mm nozzles, respectively. The Reynolds numbers were 7.8x 3 and.x 4 for 5 and 8 mm nozzle diameters, respectively. The glass Fig.3 Experimental apparatus for water-solid pipe flow. particles with about 395 µm in mean diameter d p were mainly used in the experiments. Two cases of particle volume ratios of.6 and.9% at the initial position were reported in the paper. In the case of air-solid flow, a nozzle with 9mm in diameter was used. The mean velocity on the centerline of the nozzle exit was about

3 PARTICLE MOTION IN WATER-PARTICLE, GAS-PARTICLE AND GAS-DROPLET TWO-PHASE FLOWS.5.5.9% u f/u m u/um, uf /Um, up /U m.5.5.6% Fig. 4 Results of diameter measurement by PDA in water-solid jet flow. 7m/s and the Reynolds number was about.x 4. Glass particle with 93 µm in diameter were released at the upstream of the nozzle. The volume ratio was set to. %. In the case of air-droplet flow, the jet flowed out from the nozzle with mm in diameter. The mean velocity on the centerline of the nozzle exit was about.3 m/s and the Reynolds number was about.x 4. Water mist was used as the discrete particles. Since it was difficult to obtain a narrow size distribution, a size classified discrimination method was applied. In the method, droplet velocity information was classified by using diameter size windows with µm width. In the liquid-air flow, it was difficult to obtain the exact particle volume ratio, because a nozzle (Ikeuchi: AKIJet) provided the mist with wide range particle size distribution. In the experiment, the flow rate of the water droplets was set to.35 cc/s. In the water-solid flow, a pipe flow experiments were also performed for a proposal of the new measuring techniques. Figure 3 shows the experimental setup for the pipe flow. The inner diameter of the pipe was 6 mm. The velocity of the center of the pipe was set to.m/s and the Reynolds number was.6 x Fig 5 Mean velocity of water-solid flow for.9% Fig. 6 Mean velocity of water-solid flow for.6%. The mean diameter of the glass particle was 5 µm and the particle volume ratio was.%..3 Measurement Techniques A phase Doppler anemometer (PDA) and a laser Doppler anemometer (LDA) are applied to measure the flows. In the LDA measurements, size discrimination method based on difference on signal intensities between large particle and small tracer particles. Since the PDA provides both of the particle size and the velocity, the velocity information is classified into discreteand continuous-phases by using the particle size. Figure 4 shows an example of the results of diameter measurement by PDA. The flow type is water-solid flow. The measuring positions of the figure are from the jet center y = mm to the jet boundary y = 6 mm at the axial distance of x = mm from the nozzle exit. It is shown two distinct peaks in the figure. The first one is the data of the tracers which are represented by the smallest class bars at the left hand side. The second one is larger particles at the right hand side. At y = 6 mm the peaks by the glass particles disappeared due to the decrease of the number density of the particles at the border of the jet. By using diameter information, the separation between the velocity data of glass particles or tracers is carried out. 3 Results and Discussions 3. Mean Velocity Distributions 3.. Water-solid flow: Figure 5 shows the mean velocity of the water-solid flow at x/d = 5 3

4 .5.5 d = 9 mm.% u f/u m u p /Um.5.5 d = mm.% u m/s Diameter range in µm Fig. 7 Mean velocity of air-solid flow. 3 Fig. 8 Mean velocity of air-liquid flow. 3 Fig. 9 Diameter-classified mean velocity of air-liquid flow at x =mm. with particle volume ratio of.9%. The velocity is normalized by the mean velocity on the axis for single-phase flow. Lateral positions are also normalized by the half width of the jet velocity profile. In the figure, u, u f and u p indicate mean velocities of single-phase, fluidphase and particle, respectively. Particle has larger velocity around the centerline than the water-phase. No effect on the water-phase mean velocity can be observed. Figure 6 shows the same expressions as used in the Fig. 5 and the particle volume ratio of.6 %. Around the axis, the particle velocity is smaller than the single-phase flow. The water-phase has also smaller mean velocity than the single-phase flow. When the particle volume ratio increases, the influence on the water-phase becomes important. In this experiment, the particle cannot affect the water-phase motion for the dilute condition but it can affect the water-phase motion for dense condition. 3.. Air-solid flow: Figure 7 shows the same expression as shown in the Figs. 5 and 6 for the air-solid flow. The particle has larger velocity around =. In the air-solid flow, the particle has smaller velocity on the nozzle exit. At x/d = 5, the particle accelerates at all of the regions but it cannot exceed the air velocity around the axis. The previous studies indicate the particle has flat velocity distribution because of the mass-transfer in lateral direction [4]. Then the particle has larger velocity around =. The air-phase has the same velocity distribution as that of single-phase flow. The particle cannot affect the air-phase motion Air-liquid flow: Figure 8 shows the same expression as used in the Figs. 5, 6 and 7 for the air-liquid flow. In the figure, the particle data includes all of the droplets. The particle velocity is slightly larger than those of single-phase and air-phase at <. The particle has almost the same velocity on the nozzle exit for the airliquid flow. Then the particle has larger velocity around the axis because the particle accelerates by the gravity force. Figure 9 shows diameter- u/u m, uf/u m, up/u m.5.5.9% Parthasarathy and Feath x/d Fig. Velocity decay of the water-solid flow. 4

5 PARTICLE MOTION IN WATER-PARTICLE, GAS-PARTICLE AND GAS-DROPLET TWO-PHASE FLOWS classified results of the mean velocity. An increase in the droplet diameter causes the large mean velocity. 3. Velocity Decay 3.. Water-solid flow: Figure shows the axial mean velocity along the axis of the jet at the particle volume ratio of.9% for watersolid flow. The mean axial velocity is normalized by U m which is mean velocity of single-phase flow at the center of the nozzle exit. The axial distance is also normalized by nozzle diameter of d. The result by the previous researchers [5] is also indicated in the figure. In the upstream, there is a zone where the decreasing ratio of the velocity is small. Since the jet at the outlet of the nozzle is not flat shape in the velocity distribution in the experiment, the detail is different from the potential core but the region has similar phenomena as the potential core. In the figure, the linear velocity decay from x/d = 3 can be observed. The mean velocity at the center is decreased linearly until 63.5% of the initial velocity value at x/d = 7. Comparison between the previous and the present data indicates that the tendencies agree with the previous data. Under this particle concentration, there is less difference in the mean velocity. The result with.6% of particle concentration indicates almost the same tendency with this case. 3.. Air-liquid flow: Figure shows the same expression as the Fig. 9 for the air-liquid Mass Flux kg/m s 8 6 x/d = x/d = x/d = x/d = 3 x/d = 5 x/d = 7 x/d = x/d = 5 Mass flux kg /m s x/d Fig. Velocity decay of the air-solid flow. flow. In the figure, the particle data includes all of the droplets. The particle velocity is slightly larger than single-phase and air-phase velocities at x/d = 5 and 7. The results seem to be related with the droplet inertia. In the air-liquid flow, difference in the densities of the particle and the fluid is large compared with the water-solid flow. Then, the particle can keep the velocity in the upstream. 3.3 Mass Flux 3.3. Water-solid flow: The particle mass flux versus the nozzle diameter at different positions is shown in figure. The results are obtained with the particle volume ratio of.6%. The nozzle of the jet is 5 mm. The glass particle is concentrated around the axis of the jet at the upstream and then slowly spreading to the out region with increasing the axial distance of x/d. x/d = x/d = 5 x/d = 5 Mass Flux kg/m s 3 x/d = x/d = x/d = 7 x/d = x/d = Fig. Mass flux of water-solid flow. Fig. 3 Mass flux of air-solid flow. Fig. 4 Mass flux of air-liquid flow. 5

6 Frequency MHz X/D = = Particle velocities BSA BSA u f/u m Arrival time ms Fig. 5 Simultaneous velocity measurements of both phases The maximum mass flux decreases immediately from x/d = to x/d =. After the region, the maximum mass flux decreases gradually. In the upstream of x/d =, the particle can get the force for dispersion in lateral direction. In the downstream, the force becomes weak Air-solid flow: Figure 3 shows solid particle mass flux versus normalized nozzle diameter at x/d =, 5 and 5 of the right half side of the jet in the air-solid flow. Measured data show that higher values of particle mass flux are obtaining at x/d = and x/d = 5 where solid particles concentrate near the jet center. The results are scattering however the peak can be observed around the axis. The decreasing rate of the mass flux which related with the particle dispersion seems to be smaller than that of the water-solid flow. This is caused by the relative density between the carrier-fluid and particle Air-liquid flow: Figure 4 shows droplets mass flux versus normalized nozzle diameter at three selective positions,, 7 and 5 of the right half side of the nozzle in the air-liquid flow. The data include all of the droplet size classes. The mass flux has the clear peak on the axis. The peak value decreases gradually. The tendency is similar to the air-solid flow. The forces acting to particle lateral motion related with the particle dispersion becomes less significance when the carrier fluid is air. It is indicated that the relative density between particle and fluid plays a significant role in the particle dispersion. When the density ratio between particle and fluid is small, the u/'um, u'f/um, u'p/u m y/r y/r u/'u m u' f/u m u' p /U m Fig. 6 Mean velocity and fluctuation velocity of water-solid pipe flow. particle can obtain the forces which need for the particle lateral motion. 3.4 Newer Measurement Techniques The previous experimental data are provided by PDA. The PDA is useful for the two-phase flow experiment, however there are some difficulties. The first difficulty is measurement range in the diameter. In the present study, the particle has times larger diameter than the tracers. Then, it is difficult to measure the both velocities of particle and the tracer simultaneously. The second one is the data rate. For discuss with statistical data, it is not a serious problem. However, it becomes serious when making the turbulence analyses from the time-series velocity data. In the last part of this study, newer measuring technique is proposed. The method consists of the normal type LDA optics and two signal processors (Dantec: BSA) for one-dimensional measurement. The same input signals are transferred to the two signal processors. One signal processor provides both of the particle and the tracer velocity data. The other one processes only tracer data by using the 6

7 PARTICLE MOTION IN WATER-PARTICLE, GAS-PARTICLE AND GAS-DROPLET TWO-PHASE FLOWS size discrimination function called as over size rejection. Figure 5 shows one of the examples of the results for explanation of this method. In the figure, the velocities processed by BSA provide only tracer particle data and BSA shows all Doppler signals. Remaining data subtracted the signals of BSA from that of BSA present only particle velocities. Figure 6 shows the example data measured in pipe flow. The measuring line is x/d = 5 in upward flow part. In the figure, r means pipe radial. Small difference in the mean velocity and the fluctuation velocity can be observed. The particle has small mean velocity and large fluctuation velocity. The water-phase has smaller mean velocity compared with singlephase flow. The particles affect the mean velocity of the fluid. The small velocity of the particle is caused by the gravity. The small velocity of the particle causes the small waterphase velocity. 4 Conclusions Three types of water-solid, air-solid and airliquid jet flows are tested in the present study. For proposal of the newer measuring techniques in two-phase flow, a water-solid pipe flow is also analyzed. The conclusions are summarized below:. Differences in mean velocity profiles of the particle can be clarified.. The density ratio between particle and fluid affects the particle lateral motion. 3. The proposed measuring technique is useful for the two-phase flow analysis. References [] Tsuji, Y., Morikawa and Shinomi, H., LDV measurements of air-solid two-phase flow in a vertical pipe, J. Fluid Mech., Vol. 39, pp , 984. [] Saffman, P. G. The lift on a small sphere in a slow shear flow, J. Fluid Mech., Vol., part, pp , 965. [3] Hishida, K., Ando, A. and Maeda, M., Experiments on particle dispersion in a turbulent mixing layer, Int. J. Multiphase Flow, Vol 8,, pp 8-94, 99. [4] Ishima, T., Hishida, K. and Maeda, M., Effect of particle dispersion in a plane mixing layer, Trans. of the ASME, J. of Fluids Engineering, Vol. 5, 4, pp , 993. [5] Parthasarathy, R. N. and Feath, G. M. Structure of Particle-Laden Turbulent Water Jets in Still Water, Int. J. Multiphase Flow, 3, pp , 987. [6] Hishida, K., Nakano, H., Fujishiro, T. and Maeda, M., Turbulence characteristics of liquid-solids two-phase circular confined jet, Trans. of the JSME, Part B, Vol.55, 5, pp , 989 (In Japanese). [7] Prevost, F., Boree, H., Nuglish, J. and Charnay, G. Measurements of fluid/particle correlated motion in the far field of an axisymmetric jet, Int. J. Multiphase Flow (4), pp 685 7,