Onset of heterogeneous nucleation in pool boiling of HFE-7100 following rapid heating on a microscale heater

Effective thermal management of electronics is crucial for maintaining their reliability, longevity, and optimal performance. As electronic devices become increasingly compact and powerful, the need to explore new and innovative methods for thermal management becomes ever more critical. Rapid transitions of power lead to temperature spikes (hotspots) of up to 100 K, and thus can dramatically increase the failure occurrence of chips. Power spikes imply that heterogeneous nucleation occurs due to rapid heating, which can vary between 10⁴ – 10⁶ K/s, and hence the coolant is in its metastable region under various degrees of superheating. Gaining ONB data with respect to the heating rate holds significance for diverse applications including nuclear installations, engines, inkjet printers, and laser-based systems. In the present paper, we have refined the definition to a heterogeneous nucleation event due to a rapid heating process, that occurs when the timescale for the wall heating is shorter than the critical bubble's significant growth time. Data pertaining to the dependence of the onset of nucleate boiling (ONB) on the heating rate is presented for the first time. Experiments are performed with HFE-7100 fluid that is rapidly heated using a uniquely designed micro-heater, 122 × 234 μm² in size. The newly designed and constructed system facilitates precise measurements of fast heating processes. In this study, we conducted a series of experiments spanning heating rates from 10⁴ to ∼10⁶ K/s. This range of heating rates was identified in our previous studies as an intermediate regime for water. The region of intermediate heating rates was previously proved in our research to be challenging to attain, due to the varying stability of the metastable zone; it is primarily attributed to pre-existing nucleation sites. Consequently, this led to a notable gap in the experimental results for water, within this particular region, in the literature. Notably, in the current study, we were able to achieve a maximum superheating degree of 14 K at a heating rate of 2.2·10⁶ K/s. Preheated liquids reach the same superheating degree with different heating rates, depending on the coexistence and spinodal curves. It was found that water and HFE-7100 differ significantly in their metastable zone, and that the first zone, for slower heating rates, spans approximately 12 K for water, but only 4 K for HFE-7100.