Effects of electric field on microbubble growth in a microchannel under pulse heating

Effects of imposed DC electric fields on microbubble growth generated from a rectangular Pt micro-heater (140 × 100 μm) fabricated on one wall of the microchannel under pulse heating are investigated experimentally in this paper. Bubble dynamics and surface temperature response of the microheater during pulse heating are observed and recorded using a high speed CCD and data acquisition system. Measurements of nucleation time and nucleation temperature and heat flux at boiling inception are taken at a fixed flow rate of 0.6 ml/min and pulse width of 1 ms, and with the electric field strength gradually increasing from zero. With increasing electric field strength, it is found that heat flux required for boiling inception is increased, boiling nucleation time is delayed, and nucleation temperature is reduced. Bubble growth is suppressed by the inward dielectrophoresis force acting at the vapor/water interface which is induced by the electric field. As a result, the diameter of the bubble becomes smaller, and the interface instability is suppressed during the bubble growth period. In addition, it is found that multiple nucleate sites appear on the surface of the micro-heater at high heat flux when the electric field is increased to a sufficiently high strength. A map showing regimes of single and multi nucleate sites in a plot of heat flux versus electric field strength is obtained.