Thermal Interaction of Laser Beam With Particulate Flow in Mini-Channels

Optical propulsion via laser source is a relatively new and non-contact tool for manipulation of microscopic objects. The method is based on the radiation pressure of light photons on the micron sized particles. Applications of the technique mainly cover microscopic separation, purification and cellular studies. Due to high power intensity of laser beams, absorption of light may result in heating and damage of objects to be manipulated. In addition, the difference between heated and cold zones can lead to a naturally driven flow around the objects. So precisely controlled conditions should be set up to avoid thermal effects. In this work, a theoretical study is conducted to investigate the thermal effects on a particulate flow in a mini-channel. Thermal effects are studied as a result of light absorption either in carrier fluid or dispersed phase. A continuous laser beam is considered as a radiation heat source and wave propagation and interaction with suspension of microspheres in water is simulated. The main objective of mentioned simulation is to determine the conditions of pure hydrodynamic laser-particle interaction. Especially the criteria for properties of particles and beam parameters are presented. Derivation of limits is based on the maximum allowable temperature increase and the magnitude of thermal induced flow. The results are crucial for design and selection of elements in microscopic separation by laser beam.