Laser-induced convection flow in micro-enclosures

The heat supply through a laser has attracted attentions for last decades. Diverse patterns of temperature gradient due to a laser are related to a variation of material properties. By generating highly non-uniform temperature field in fluid, many phenomena can be generated because of the variation of material properties. This report is composed of four experimental results and discussions regarding laser heating that is supplied by 1064nm continuous wave laser. Velocity is analyzed by 2D &mgr;PIV (Micro Particle Image Velocimetry). First, the Marangoni flow in non-evaporated droplet is studied. Herein, the Marangoni flow is induced from a focused laser. The Marangoni flow is generated due to a gradient of surface tension that is generally inversely proportional to temperature. Consequently, fluid flow in a droplet is generated. To observe a phenomenon only due to laser effect, a droplet is covered with oil layer. By covering a droplet using an oil layer, an evaporation of the droplet is blocked. When a highly focused laser is applied in micro size enclosures, natural and forced convection is generated. Convection study area has been used traditional heating methods such as a heat from a surface or a sphere or a line. Otherwise, laser induce natural and forced convection is novel and can be utilized into many ways by manipulating laser power or shape. Characteristic of convection flow due to a focused laser heating will be investigated. Once AC electric field is applied to a sharp thermal gradient due to a focused laser heating, electrothermal (ET) flow is generated. Physics of the ET flow and relationship between the ET flow and Vpp, frequency, and laser power will be discussed. In addition, material effects on electrothermal flow are performed by changing ITO coated glass to different materials

Effects of Turbulent Flow Regimes on Pilot and Perforated-Plate Stabilized Lean Premixed Flames

An experimental study of the effects of turbulent flow regime on the flame structure is conducted by using perforated-plate-stabilized hydrogen-piloted lean premixed methane/air turbulent flames. The underlying non-reacting turbulent flow field was investigated using two-dimensional three-components particle imaging velocimetry (2D3C-PIV) with and without three perforated plates. The non-reacting flow data allowed a separation of the turbulent flow regime into axial velocity dominated and vortex dominated flows. A plate with 62% blockage ratio was used to represent the stream-dominant flow regime and another with 86% blockage ratio was used to represent the vortex-dominant flow regime. OH laser-induced fluorescence was used to study the effects of the turbulent flow regime on the mean progress variable, flame brush thickness, flame surface density, and global consumption speed. In comparison with the stream-dominant flow, the vortex-dominant flow makes a wider and shorter flame. Also, the vortex-dominant flow has a thicker horizontal flame brush thickness and a thinner longitudinal flame brush thickness. Especially, the horizontal flame brush thickness for the vortex-dominant flow does not follow the turbulence diffusion theory. Then, the vortex-dominant flow shows a relatively constant flame surface density along the stream-wise direction, while the stream-dominant flow shows a decreasing flame surface density. Lastly, the vortex-dominant turbulent flow improves the consumption speed in comparison to the stream-dominant turbulent flow regime with the same velocity fluctuation level