Multi-phase flow and heat transfer of a micro-pump thermally-driven by pulse laser

This paper presents an experimental study of multi-phase flow and heat transfer in a micro-pump thermally driven by a multi-output pulse laser. The test-section is a copper micro-tube with inner diameter less than 1 mm. Distilled water is used as the working fluid. The pumping power is provided by phase change of the fluid in the copper tube due to surface heating by a multi-output pulse laser. The pulse laser is a diode embattling type laser with a high-power GaAs/AlGaAs/InGaAsP quanta trap. The laser wavelength is λ=940 nm, the pulse width, the pulse-interval and the output-power are adjustable within the range of 50 ∼ 1000 ms, -10 ∼ +10 ms and 0 ∼ 40W, respectively. The laser has five output channels with each delivering a beam of linear geometry of 12 mm × 1 mm. With each channel of the laser targeting a segment of the test section, the micro-pump can be driven with a controlled energy distribution along the tube. Extensive flow and heat transfer measurements and visualization experiments have been carried out to characterize the micro-pump behavior under various conditions. The experiments reveal extremely unsteady and complex flow patterns in the microtube with the flow correlating closely with the bubbles' generation and collapse. It is found that the flow rates are controlled by the heating and condensation condition within the tube. The laser pulse width, pulse interval and output-power as well as the tube diameter all show a strong influence on the flow rate of the micro-pump. This study provides a basis for the design of thermally-driven micro-pump induced by pulse-laser.