the surface but continue to hover near the surface while pulling smaller neighboring bubbles
into it and growing in size consistent with predictions from numerical simulations. At low
superheats, bubbles at neighboring sites simply merge to yield a larger bubble. The larger
bubble mostly locates in the middle of the heated surface and serves as a sink for vapor
generated on the heated surface. The latter mode continues to persist when boiling is occurring
all over the heater surface. This behavior of vapor removal is very different from that at Earth
normal gravity where single or merged bubbles rapidly lift off from the surface. Heat fluxes for
steady state nucleate boiling and critical heat fluxes are found to be much lower than those
obtained under Earth’s normal gravity conditions and also lower than previous data obtained
on space shuttles, but higher than that predicted by the hydrodynamic theory extrapolated to
microgravity. Aside from experimental conditions, rate of nucleate boiling heat transfer will be
dependent on relative heater size and fluid confinement. This data is useful for calibration of
results of numerical simulations with the condition that correlations that are developed for
nucleate boiling heat transfer under microgravity conditions must account for the existence of
vapor escape path (sink) from the heater, size of the heater, and the size and geometry of the
chamber (Dhir 2012).
PUBLICATION(S)
Warrier GR, Dhir VK, Chao DF. Nucleate Pool Boiling eXperiment (NPBX) in microgravity:
International Space Station. International Journal of Multiphase Flow. April 2015;83:781-798.
doi: 10.1016/j.ijheatmasstransfer.2014.12.054.
Aktinol E, Warrier GR, Dhir VK. Single bubble dynamics under microgravity conditions in the
presence of dissolved gas in the liquid. International Journal of Heat and Mass Transfer.
December 2014;79:251-268. doi: 10.1016/j.ijheatmasstransfer.2014.08.014.
In Earth's gravity (image on the left) the action of buoyancy allows the bubbles to overcome surface tension
forces. The bubbles rise upward away from the heater surface. In microgravity (image on the right) the
buoyancy force is very weak. Consequently, the bubbles often remain attached to the heater because of
surface tension and become large as more vapor is produced due to the continuous input of energy from the
heater. University of California image.