All power production, refrigeration, and advanced electronic systems depend on efficient heat transfer mechanisms for achieving high power density and best system efficiency. Breakthrough advancement in boiling and quenching phase-change heat transfer processes by nanoscale surface texturing can lead to higher energy transfer efficiencies, substantial energy savings, and global reduction in greenhouse gas emissions. This paper reports breakthrough advancements on both fronts of boiling and quenching. The critical heat flux (CHF) in boiling and the Leidenfrost point temperature (LPT) in quenching are the bottlenecks to the heat transfer advancements. As compared to a conventional aluminum surface, the current research reports a substantial enhancement of the CHF by 112% and an increase of the LPT by 40 K using an aluminum surface with anodized aluminum oxide (AAO) nanoporous texture finish. These heat transfer enhancements imply that the power density would increase by more than 100% and the quenching efficiency would be raised by 33%. A theory that links the nucleation potential of the surface to heat transfer rates has been developed and it successfully explains the current finding by revealing that the heat transfer modification and enhancement are mainly attributed to the superhydrophilic surface property and excessive nanoscale nucleation sites created by the nanoporous surface.
We study the dynamics of a supersonic molecular beam in a low-finesse optical cavity and demonstrate that most molecules in the beam can be decelerated to zero central velocity by the intracavity optical field in a process analogous to electrostatic Stark deceleration. We show that the rapid switching of the optical field for slowing the molecules is automatically generated by the cavity-induced dynamics. We further show that ∼ 1% of the molecules can be optically trapped at a few millikelvin in the same cavity.The generation of ultracold molecules is opening up new directions in ultracold physics and chemistry. Ultracold molecules offer the possibility of studying exotic quantum phases through anisotropic electric dipole-dipole interactions [1]. These interactions, however, only become important when they are in the submillikelvin range. The ability to create cold molecules and subsequently trap them in external electric and magnetic fields allows long interaction and interrogation times and therefore high-resolution spectroscopic measurements. Such measurements have already been undertaken with OH radical in the millikelvin temperature range [2], which could be used to constrain the time variation in fine structure constant [3]. Such trapped cold molecules are anticipated to be also important in the search for parity violation [4], and for tests of physics beyond the standard model [5]. Although yet to be explored experimentally, chemistry at ultracold temperatures is dominated by resonance and tunneling phenomena, with reaction rates predicted to be many orders of magnitude larger than at room temperature for some species [6].Cooling of molecules has proven to be considerably more difficult to achieve than laser cooling of atoms [7]. Ultracold molecules can be created from association of laser-cooled atomic species by photoassociation and on magnetic Feshbach resonances at microKelvin temperatures [8]. Recently, progress has been made to transfer these molecules in high vibrational levels to low rovibrational states [9,10]. The methods are, however, limited to atoms that can be laser cooled. Buffer gas cooling is a general method, which can dissipatively cool complex molecular species. This method utilizes elastic collisions within a buffer gas in a cryogenic cell in the 100-mK range [11]. Another technique for creating complex cold molecules is via phase space filtering, in which conservative electrostatic, magnetic, or optical potentials are used to filter out a narrow energy distribution of a hotter gas and then transfer them to zero velocity in the laboratory frame [12][13][14][15][16]. Electrostatic Stark deceleration is a well-developed scheme of this type where gas of 10 6 cm −3 polar molecules in a single quantum state at 10 mK is produced [12]. This scheme uses rapidly switched electrical fields to create a moving potential that traps and slows a subset of the initial molecular distribution. The rate and duration of the switched field change as the trapped molecules are brought to rest. * lanzhihao7@...
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