  Boiling heat transfer is the basis of many commonly used cooling techniques.
In cooling of electronic devices, for example, it is desirable to further
miniaturize heat exchangers to achieve higher heat transfer, and thus it is
necessary to understand boiling phenomena on shorter spatial and temporal
scales. This is especially challenging at the nanometer scale because
conventional imaging techniques cannot capture the dynamics of nanobubbles,
owing to the Abbe diffraction limit. Here in this research, we utilize the
nanopore Joule heating system that enables the generation of nanobubbles and
simultaneous diagnosis of their nanosecond resolution dynamics using resistive
pulse sensing. When a bias voltage is applied across a silicon nitride nanopore
immersed in an aqueous salt solution, Joule heat is generated owing to the flow
of ionic current. With increasing voltage, the Joule heating intensifies, and
the temperature and entropy production in the pore increase. Our sensing
results show that nanopore boiling follows the theory of minimum entropy
production and attempts to settle to a minimum dissipative state. This results
in two boiling bifurcations corresponding to the transition between different
boiling states. These characteristics of nanopore boiling are represented by an
"M"-shaped boiling curve, experimentally obtained from the Joule heat variation
with the applied voltage. A theoretical framework is proposed to model the
thermodynamics of nanopore bubbles and estimate the system dissipation which
explains the four arms of the "M"-shaped boiling curve. The present study
reveals that the utilization of nanopore boiling as a benchmark platform offers
a valuable means for investigating the intricate boiling phenomenon and its
correlation with nanoscale bubble dynamics. This would provide fundamental
insights into the chaotic transition boiling regime, which is least understood.
