Recent research progress in the area of nano/micro scale nucleate boiling is reviewed and an up-to-date summary is provided with a focus on the advances of fundamental boiling physics. This review examines nano/micro scale pool boiling experimental and theoretical/numerical work reported in the open literature. On the experimental side, the topics covered are moving contact line, critical heat flux, boiling curve, nucleation, single bubble boiling cycle, bubble coalescence boiling cycle, heater size effect, nanofluid, and nanoscale-structured heater surface. For the theoretical/numerical work, continuum mechanics modeling of the micro-region and molecular dynamics modeling of the nano-region are included.
Pool boiling experiments from a platinum wire heater in FC-72 liquid were conducted under terrestrial and microgravity conditions, both with and without the presence of a high-intensity acoustic standing wave within the fluid. The purpose of this research was to study the interaction between an acoustic field and a pool boiling system in normal gravity and microgravity. The absence of buoyancy in microgravity complicates the process of boiling. The acoustic force on a vapor bubble generated from a heated wire in a standing wave was shown to be able to play the role of buoyancy in microgravity. The microgravity environment was achieved with 0.6 and 2.1-s drop towers. The sound was transmitted through the fluid medium by means of a half wavelength sonic transducer driven at 10.18 kHz. At high enough acoustic pressure amplitudes cavitation and streaming began playing an important role in vapor bubble dynamics and heat transfer. Several different fixed heat fluxes were chosen for the microgravity experiment and the effects of acoustics on the surface temperature of the heater were recorded and the vapor bubble movement was filmed. Video images of the pool boiling processes and heat transfer data are presented.
The purpose of this paper is to form a more general understanding of the effect an electric field has on boiling heat transfer by considering non-boiling electroconvection and boiling bubble dynamics separately. In an attempt to decouple these two heat transfer mechanisms, an electric field was utilized which produced a uniform dielectrophoretic force (DEP force) across a horizontal platinum wire. Boiling curves were produced with FC-72 as the working fluid for variable DEP and buoyancy forces by varying the electric field geometry (with a constant potential of 23 kV), by varying the orientation of the electric field with respect to gravity, and by performing experiments in a drop tower with very small buoyancy forces. In order to elucidate the relative contributions of the individual forces and correlate the data, an effective gravity g′(b,e) was defined which represents the ratio of the total DEP and buoyancy body forces on the vapor bubbles to the constant terrestrial-gravity buoyancy force.
It was concluded that the effect of the DEP force on the bubbles is analogous to reducing or increasing the gravity locally or inducing vapor flow across the heater surface similar to forced-convection. In semis of the relationship between the bubble dynamics and the heat transfer, it was concluded that nucleate boiling heat transfer will be enhanced if the effective gravity acts to hold the vapor bubbles near the heater surface, while at the same time permitting access of the liquid to the surface in order to prevent dryout. However, a large electroconvective effect can dominate and possibly reverse this trend. For the critical heat flux (CHF) it was discovered that for 1 < g′(b,e) < 3 a quarter power dependence is a reasonable engineering approximation for the increase in CHF with effective gravity.
Based on these results and support from the literature, we concluded that the overall heat transfer coefficient for boiling in the presence of an electric field can be considered as the summation of a heat transfer coefficient due to bubble dynamics and a heat transfer coefficient due to electroconvection. Furthermore, the heat transfer coefficient due to the bubble dynamics can be modeled with current theory based on variable gravity results and/or forced convection.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.