Swing-like pool boiling on nano-textured surfaces for microgravity applications related to cooling of high-power microelectronics

Abstract

Here, we demonstrate that heat removed in pool boiling from a heater mimicking high-power microelectronics could be used to facilitate a swing-like motion of the heater before being finally dissipated. This swing-like motion could be beneficial for shedding a large vapor bubble that encapsulates high-power heaters in microgravity where buoyancy force is unavailable for vapor bubble removal. The swing-like motion is propelled by vapor bubble recoil, the force which exists irrespective of gravity and buoyancy. We also demonstrate that this force could be significantly enhanced by depositing on the heater surface supersonically blown polymer nanofibers with cross-sectional diameters below 100 nm. These nanofibers provide additional nucleation sites, resulting in much more frequent bubble nucleation and departure, and thus a higher overall vapor recoil force propelling the heater motion. Such nanofibers strongly adhere to the heater surface and withstand prolonged harsh pool boiling. The measured velocity of the model swing-like heater in Novec 7300 fluid is about 1 cm/s.

Cooling microelectronics with nanofibers

As microelectronics get smaller, there is an urgent need to develop efficient methods to keep them cool without extra power input. Under normal gravity, excess heat can be removed by vapor bubbles rising through a coolant. In space however, due to the lack buoyancy force, vapor bubbles remain attached to the submerged heater and prevent heat removal. Prof. Alexander Yarin, at the University of Illinois at Chicago, and his team show that in heaters mimicking high-power microelectronics, the thrust of vapor bubble release (the vapor recoil force, which exists irrespective of gravity) helps shedding merger vapor bubbles by generating a swing-like motion of the heater. Moreover, they demonstrate how nanofiber coatings can increase heat transfer by providing more bubble nucleation sites, and thus enhance the swing-like motion.