Begell House Inc.
Journal of Flow Visualization and Image Processing
JFV
1065-3090
11
2
2004
NUMERICAL VISUALIZATION OF SWIRLING FLOWS IN MACROLAMINATED ATOMIZERS
20
10.1615/JFlowVisImageProc.v11.i2.10
Pei-Yuan
Tzeng
Department of Aeronautical Engineering, Chung Cheng Institute of Technology, National Defense University Ta-Hsi, Tao-Yuan 33509, Taiwan, ROC
Chung-Ho
Liu
Department of Biomedical Engineering, Yuanpei University of Science and Technology, 306 Yuanpei Street, Hsinchu 300, Taiwan, ROC
Yu-Jui
Chu
Graduate School of Defense Science Studies, Chung Cheng Institute of Technology, National Defense University Tahsi, Taoyuan 33509, Taiwan, ROC
Internal and external flow fields of macrolaminated atomizers are visualized and investigated by using CFD tools. Although for the three-dimensional turbulent flow calculations there is a lack of measurement data to quantitatively verify the accuracy, the numerical visualizations can still be very valuable in providing insight into this complicated flow situation. The distinctive features of air-core-like formation and hollow cone spray structure are well captured. The effects of orifice diameter (Dor) on the flow velocities, turbulence kinetic energy (TKE), and spray cone angle (2θ) in the exit region are also examined. With increasing the Dor, in general, the intensity of TKE and swirling effect are smaller, whereas the spray cone angle is wider. The results of this numerical research provide better understanding of the complex flow characteristics of swirl atomizers that are not easily accessible experimentally, and may be useful for practical atomizer design and improvement.
THERMOCAPILLARY CONVECTION AROUND A HORIZONTAL HEAT SOURCE IN A LIQUID CAVITY
12
10.1615/JFlowVisImageProc.v11.i2.20
Wen-Jei
Yang
Department of Mechanical Engineering and Applied Mechanics University of Michigan, Ann Arbor, Michigan 48109-2125, U.S.A.
Numerical and experimental studies are performed on thermal fluid-flow transport phenomena around a heating wire set on the free surface of a liquid cavity. Emphasis is placed on the effects of the Marangoni number, Ma, the aspect ratio, H/L, and the Rayleigh number, Ra, on the flow and isothermal fields. The mechanism is theoretically investigated by numerically solving the two-dimensional governing equations through discretization by means of a finite-difference technique. Experimentally, flow patterns are disclosed by means of a tracer method. It is found that (i) the thermal fluid flow is affected by the aspect ratio, that is the thermal fluid flow in the lower region of the cavity with H/L = 2 is almost stable, and (ii) natural convection around the wire is induced by the Marangoni force, i.e., the surface tension, while the effect of Ra on the velocity field is minor.
A TIME-AVERAGED TECHNIQUE FOR GAS-LIQUID FLOW STRUCTURE RECONSTRUCTION FROM LOCAL VOID FRACTION MEASUREMENTS
20
10.1615/JFlowVisImageProc.v11.i2.30
Volfango
Bertola
Laboratory of Technical Physics, School of Engineering, University of Liverpool, Brownlow Hill, Liverpool L69 3GH, UK
The structure of gas-liquid, two-phase flow is studied by means of a time-averaged tomographic technique, which provides a representation of the local flow structure on a given cross section. Single-fiber optical probes, sensitive to the refractive index of the surrounding medium, were used to measure the local void fraction distribution, which corresponds to the time-averaged gas concentration. The spatial resolution was enhanced by bi-harmonic spline interpolation of the experimental data; the flow structure in a generic position between two reference cross sections was obtained by linear interpolation. The proposed measurement technique was applied to the investigation of an air-water intermittent flow in horizontal pipes of large diameters (0.06 and 0.08 m i.d.). The water mass flow rate was 3 kg/s, while the gas fraction of volume flow ranged from 20% to 85%. Test sections with a constant diameter and with a sharp-edged abrupt area contraction were used.
FLOW SIMULATION AND VISUALIZATION OF A MICRODROPLET GENERATOR
12
10.1615/JFlowVisImageProc.v11.i2.40
Chung-Chu
Chen
E. L. Ginzton Laboratory, Stanford University, Stanford, California 94305, USA
Chen-Kuei
Chung
Department of Mechanical Engineering, National Cheng Kung University, Taiwan 701, ROC
Shih-Huei
Chen
Department of Power Mechanical Engineering, National Tsing Hua University, Hsinchu, Taiwan 300, ROC
Tong-Ming
Liou
Department of Power Mechanical Engineering, National Tsing Hua University, Hsinchu, Taiwan 300, ROC
This paper investigates droplet characteristics and refill time of the microdroplet generators with different shape of actuator and actuation amplitude. The simulation results show that a ring-type actuator provides the best performance on the droplet trajectory and ink refill time. Droplets generated by the ring-type actuator have the shortest initial pillar length and the least velocity inconsistency. Hence, the occurrence of satellite droplet is diminished. Square- and circle-type actuators have a refill time of 67 and 61 μs, respectively, up to 37% larger than the value of 49 μs of the ring-type actuator. For the ring-type actuator, the droplet size, tip velocity, and refill time are in proportion to the actuation amplitude for a given nozzle diameter.