Airflow Visualization Research Articles

96/01770 Thermal and optical consequences of the introduction of baffles into compound parabolic concentrating solar energy collector cavities

Concerning the solar air collectors, various techniques favorise and increase the heat transfer coefficient between the caloporting fluid (air) and the absorber; such as the fixation of small wings to the absorber, the manner in which the air flows vis à vis the absorber, the shape of the collector itself and those of its inlets and outlets. Studies achieved at the University of Valenciennes–France, Laboratory of Aerodynamic, Energetic and Environmental (current naming), were especially interested in another factor: the creation of turbulence in the air channels by using obstacles or baffles. The efficiency reached 80% for an air flow rate of 50 m3/h/m2, allowing a temperature increase of 70 °C to be achieved. All the configurations of baffles are subjected to visualizations of air flow, measurement of pressure drop and instantaneous energetic efficiency. The best configuration is the one that permits extending the trajectory of the air flow and increases the speed of the air within the collector and therefore the heat transfer.

Visualization of Supersonic Flow Using O2-LIPF.

As a method for analysis of supersonic flow, visualization of the flow field structure using LIF of tracers seeded in a carrier gas has been employed. In this study, the capability of imaging of supersonic flow using O2-LIPF (laser-induced predissociative fluorescence) is examined. Since oxygen is one of the main constituents of air, O2-LIPF may enable visualization of air flow in a high-speed wind tunnel without tracers. However, because the visualization of the flow field below room temperature using O2-LIPF is very difficult, it has been applied only to high enthalpy and combustion flow, not to high-speed flow at low temperature. In this study, the supersonic oxygen flow is visualized by O2-LIPF using an ArF excimer laser and a high-sensitivity CCD camera. If the CCD camera is set at a long exposure time (1200 sec) and the scattered laser beam is suppressed sufficiently, the supersonic oxygen flow below room temperature can be imaged successfully using O2-LIPF.

Air Flows and Particle Distribution Around a Rotating Grinding Wheel

ABSTRACT The grinding of iron with a rotating grinding wheel was studied. Measurements were performed to determine air movements and the transport of grinding particles. Particles are spread around a rotating grinding wheel. Visualizations of airflow show that radial air transport off the surface of a grinding wheel circumference is not negligible and therefore affects the transport of particles. This was supported by the results of particle concentration measurements. Concentration measurements showed that very small particles were spread more rapidly than in a computer simulation of particle transport.

245 可視化画像上のパターン追跡による三次元速度計測の可能性

Since the life of tracer particles is very short in an airflow visualization using smoke or mist particles, it is difficult to fill the whole space with tracer particles. Therefore, tracer particles are supplied locally by predicting flow direction and the plane which is expected to include main flow is illuminated by a light sheet. Although velocity vectors are usually assumed to be two-dimensional in an airflow measurement through pattern tracking, the velocity componen tperpendicular to the visualized plane exists frequently in a real situation. In this paper we propose a new technique in which two planes perpendicular to camera axis are visualized simultaneously and the velocity component perpendicular to the planes is calculated from the differenc eof two images. The performance of the technique is investigated by a numerical experiment.

IMPINGING JET DRYER

ABSTRACT In coating and gravure printing, an impinging jet nozzle with high thermal efficiency for drying of coated film was developed. Trial production 0f 40 kinds of nozzle enables to develop a high-performance impinging jet nozzle with heat transfer coefficient 1.5 times larger than that of current slit nozzle, through measurement of heat transfer coefficient, visualizations of air flow and heat transfer, and measuremenu of jet velocity and turbulence distribution. The purpose of the trial production was to expand a range of high heat transfer and promote turbulence compared with the current nozzle. Paying attention to mass transfer within gravure ink coated film, drying characteristic of the film was analyzed by numerical solution of a set of equations governing the drying process in which concentration dependencies 0f the diffusion coefficient and the equilibrium vapor pressure were considered. Applying these analyses. an industrial scale dryer with excellent drying efficiency has finally been developed.

Buoyancy effect on forced convection in the leaf boundary layer

Abstract. Mixed convection (forced convection plus free convection) in the leaf boundary layer was examined by air flow visualization and by evaluation of the boundary layer conductance at different leaf‐air temperature differences (TL‐TA) under low wind velocities. The visualized air flow was found to become more unstable and buoyant at higher TL‐TA. An ascending longitudinal plume was induced along the upper surface, and the air flow along the lower surface ascended after passing the trailing leaf edge. The air flow modified by buoyancy was considered to result in an increase in boundary layer conductance (GA) for mixed convection, which became higher with higher TL‐TA as compared with the conductance for pure forced convection without buoyancy. This increase in GA appeared larger at larger Grashof number (Gr) and at smaller Reynolds number (Re). The dependences of buoyancy effect on Gr and Re were related to ‘edge‐effects’.

空調機室外機からの排気流のシミュレーションによる可視化

This paper shows computer-aided air flow visualization(CAFV) of exhaust air from outdoor unit of air-conditioners which are installed on every floor of a multistory building. After generating the complicated orthogonal meshs with automated fluid/solid cell determination thermo-fluid flow analysis is carried out with the Finite Volume Method Solver specially turned for air-conditioner simulation. Then, the results obtained are visualized through a highly interactive 3-D graphic display. Three dimensional colored contours and color fringes of temperature distributions visualize the convection flow along the building surface which is induced by the hot exhaust air from the outdoor units. Three dimensional vector display also help us understand the complicated flow structure around the outdoor units.

23 空調機吹出噴流の室内気流分布に及ぼす影響の評価

Experiments were performed to evaluate the variation of air flow distribution in the room with air jet angle, air flow rate and inlet air temperature from the outlet of air conditioner for improving the human comfort.In a present study, measurement for visualizing air flow and for evaluating the air flow distribution in the room were made of by using a particle tracing method. Air flow visualization was carried out by using TV camera and then air flow distribution was evaluated with image processing based on tracer particles image data recorded by TV camera. The good agreements between the air flow distribution data obtained using the hot wire anemometer and that evaluated from the present tracer particles image processing method were obtained within the present experiment range.

26 電子機器筺体内の可視化

In order to conduct an effective computer simulation for the thermal design, flow visualization was performed. A transparent model, incorporated with boxes which could be supplied a specific heat flux, was used. The mist method by liquid paraffin was adopted for air flow visualization, and the thermo graphic method was used for temperature distribution measurments. By the comparison of analysis and experimental results, the simulation method and boundary condition were examined.

自動車のエンジンルーム内の温度分布と空気流れの可視化

自動車のエンジンルーム内の温度分布と空気流れの可視化

ゆげによる流れの観察

ゆげによる流れの観察

Visualization by means of coherent light sheets: application to different flows

Light-sheet generator systems using a sweeping, focused laser beam and spherocylindrical optical components are described and their respective performances discussed. They allow the visualization of supersonic air flows by means of light scattering. Tomographic recordings give a three-dimensional reconstruction of the flow (especially the stationary structures) and can be realized in real-time.

Vortex Attenuation Obtained in the Langley Vortex Research Facility

It has been shown by a new static airflow visualization method that a drogue device properly positioned downstream of the wing tip causes vortex breakdown. This same result has been obtained by mounting a jet engine simulator at the wing tip and directing the high-energy jet blast downstream into the vortex. These configurations, among others, are now under intensive investigation in the new Langley Vortex Research Facility. In this facility, a balance mounted vortex generating model is propelled along the 1800-ft track while a second model trailed at 160 ft (scale distance of 1 mile) measures the far-field rolling moment induced by the vortex of the generating model.

Ventilation investigations using a section of a livestock building and air flow visualization by bubbles

The design and use of an experimental full-sized section of an intensive livestock building for research on the control of environment is described. Features include an air flow visualization technique using illuminated liquid-film bubbles with photographic recording, a choice of ventilation systems, control of temperature and throughput of the ventilating air, variable pen lay-outs, and the use of simulated pigs.

A new chemical method of reducing the reflectance of glass : F.H. Nicoll ( R. C. A. Review, Vol. VI, No. 3.)

Current measurement techniques do not allow the visualization of the return air flow of open volumetric receivers in solar tower power plants. The reason is that the region of interest is irradiated by concentrated solar radiation and is located on top of a tower. Therefore, a novel method of measurement, the Induced Infrared Thermography (IIT) is introduced within this paper. With this method the return air can easily be observed with an infrared camera. As air has a very low emissivity in the infrared region the activity has to be induced by the addition of an infrared-active component, here carbon dioxide. The temperature of the infrared-active component has the greatest influence on the signal strength but the mole fraction of the component and the distance to the infrared camera are also important. Due to temperature restrictions, the measured signal to noise ratio is low and therefore several post-processing steps have to be conducted to visualize the return air. The most important step for the visualization is subtracting a background image. Furthermore, a video filter is employed in order to remove noise. A time series of ITT images can be used to obtain information on the velocity fields of the flow. The process, called Infrared Image Velocimetry (IRIV) here, is similar to Particle Image Velocimetry (PIV) and is applied in this paper to external fluid flows of the open volumetric receiver. As IRIV is in an early stage of development the depicted results are treated as qualitative vector fields.

Visualization of Airflow by Means of Concentrated Beams of Light

W sunlight is admitted through a narrow opening in a darkened room, the dust particles flying in the air and crossing the beam become visible. This phenomenon reproduced in the wind tunnel may be utilized to visualize airflow around an object. Fig. 1 shows a sketch of the arrangement used. In the two opposite sides of a darkened wind tunnel are narrow slots through which parallel beams of light are thrown on the airfoil. Aluminum dust is introduced in the airflow by means of a blower at the opening of the wind tunnel. The camera is mounted on the top of the wind tunnel. A very small amount of light and aluminum powder is necessary to make the flow visible