Transient flow boiling heat-transfer measurements in microdomains

A single channel microdevice (Dh = 230 μm) was used in this study to measure the local wall temperature in a flow boiling configuration using thin-film (70 nm titanium) thermistors. The device and experimental configuration allows the measurement of surface temperature with high spatial resolution and a temporal resolution in the kHz range with synchronized flow regime observation. A steady heat-flux was supplied to the working fluid (de-ionized water) using a thin-film heater (100 nm titanium) to study the transient temperature evolution accompanying several flow patterns, such as bubbly flow, elongated bubble (slug) flow, partial wall dryout, and critical heat flux (CHF). Transient local convective heat transfer coefficients are computed for phenomena such as bubble nucleation and bubble growth through the use of a 3-D finite element model to account for the transient conjugate heat transfer effects in the substrate.