Explosive evaporation occurs when a thin layer of liquid reaches a temperature close to the critical temperature in a very short time. At these temperatures spontaneous nucleation takes place. The nucleated bubbles instantly coalesce forming a vapour film followed by rapid growth due to the pressure impulse. In this paper we take a closer look at the bubble nucleation. The moment of bubble nucleation was determined by both stroboscopic imaging and resistance thermometry. Two nucleation regimes could be distinguished. Several different heater designs were investigated under heat fluxes of hundreds of W mm −2 . A close correspondence between current density in the heater and point of nucleation was found. This results in design rules for effective heaters.

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Explosive Micro-Bubble Actuator proefschrift ter verkrijging van de graad van doctor aan de Universiteit Twente op gezag van de rector magnificus prof. dr. W.H.M. Zijm, volgens besluit van het College voor Promoties in het openbaar te verdedigen op vrijdag 31 oktober 2008 om 15:00 uur door Dennis Micha van den Broek geboren op 11 augustus 1979 te Vlaardingen Dit proefschrift is goedgekeurd door de promotor: prof. dr. M.C. Elwenspoek aan mijn vader Summary Samenvatting Dankwoord Chapter 1 Actuators and Bubbles A large variety of actuators can be found in literature. This chapter provides a brief overview of different actuator principles with a focus on thermo-pnuematic actuation and actuators, which utilize bubbles to provide the actuation force. The second part of this chapter will give a summary of the research on bubble nucleation and bubble dynamics under high heat-flux conditions. At the end of this chapter, an outline of this thesis is given.

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