Water vapor condensation is a ubiquitous process in nature and industry. Over the past century, methods achieving dropwise condensation using a thin (<1 µm) hydrophobic “promoter” layer have been ...developed, which increases the condensation heat transfer by ten times compared to filmwise condensation. Unfortunately, implementations of dropwise condensation have been limited due to poor durability of the promoter coatings. Here, thin‐film condensation which utilizes a promoter layer not as a condensation surface, but rather to confine the condensate within a porous biphilic nanostructure, nickel inverse opals (NIO) with a thin (<20 nm) hydrophobic top layer of decomposed polyimide is developed. Filmwise condensation confined to thicknesses <10 µm is demonstrated. To test the stability of thin‐film condensation, condensation experiments are performed to show that at higher supersaturations droplets coalescing on top of the hydrophobic layer are absorbed into the superhydrophilic layer through coalescence‐induced transitions. Through detailed thermal‐hydrodynamic modeling, it is shown that thin‐film condensation has the potential to achieve heat transfer coefficients approaching ≈100 kW m−2 while avoiding durability issues by significantly reducing nucleation on the hydrophobic surface. The work presented here develops an approach to potentially ensure durable and high‐performance condensation comparable to dropwise condensation.
Thin‐film condensation on hydrophobic‐coated nickel inverse opal structures enables heat transfer performance approaching that of dropwise condensation while achieving higher robustness by confining the condensate film and reducing nucleation on the hydrophobic layer.
A multicomponent reaction of beta-naphthol, dimethyl malonate, and aromatic aldehydes in the presence of NbCl5 as promoter is described. Under similar conditions, aromatic aldehydes with different ...substituents exhibited different behaviors than beta-naphthol and dimethyl malonate. In these MCRs, 4-aryl-3,4-dihydrobenzofcoumarins are obtained as the major products (41-93%) and 14-aryl-14H-dibenzoa,jxanthenes as the minor products (1-38%).
Bionic condensate microdrop self‐propelling (CMDSP) surfaces are attracting intensive interest due to their academic and commercial values. Up to now, it is still a great challenge to design and ...fabricate CMDSP nanostructures with superior condensation heat transfer (CHT) efficiency. Here, it is reported that the CHT coefficient of copper surfaces can be enhanced maximally ≈320% via in situ growth and geometric regulation of closely packed aligned nanoneedles with CMDSP function. These experiments and theoretical analyses indicate that reducing the interspaces of nanoneedles can help reduce the departure diameters of condensate microdrops and increase their nucleation density, both of which are beneficial to enhance CHT. In contrast, increasing the tip size and height of nanoneedles can increase drop departure diameters and film‐layer thermal resistance, respectively, either of which is disadvantageous to enhance CHT. Clearly, only considering superhydrophobic effect is insufficient and both choosing ideal nanoarchitectures and optimizing their geometric parameters are very crucial to realize high‐efficiency CHT, which optimization can be achieved via simply controlling growth time of nanostructures. These findings offer new insights into the design and development of first‐rank CHT interface nanomaterials.
Bio‐inspired closely packed aligned nanoneedles are demonstrated to be an ideal structure that exhibits a condensate microdrop self‐propelling function and an up to 320% enhancement in condensation heat transfer (CHT) coefficient as compared with flat copper surfaces. Experiments and theoretical analyses reveal respective and synergistic effects of geometric parameters to CHT enhancement. These findings help to design and develop high‐efficiency CHT surfaces.
Since an atomic Bose-Einstein condensate, predicted by Einstein in 1925, was first produced in the laboratory in 1995, the study of ultracold Bose and Fermi gases has become one of the most active ...areas in contemporary physics. This book explains phenomena in ultracold gases from basic principles, without assuming a detailed knowledge of atomic, condensed matter, and nuclear physics. This new edition has been revised and updated, and includes new chapters on optical lattices, low dimensions, and strongly-interacting Fermi systems. This book provides a unified introduction to the physics of ultracold atomic Bose and Fermi gases for advanced undergraduate and graduate students, as well as experimentalists and theorists. Chapters cover the statistical physics of trapped gases, atomic properties, cooling and trapping atoms, interatomic interactions, structure of trapped condensates, collective modes, rotating condensates, superfluidity, interference phenomena, and trapped Fermi gases. Problems are included at the end of each chapter.
1-Substituted 3-3-methyl-1H-pyrazol-5-ylthioureas react with omega-bromoacetophenones forming N-substituted(thiazol-2-ylidene)pyrazol-5-amine derivatives. Rational for these conversations are ...presented. PUBLICATION ABSTRACT
Cloud condensation nuclei (CCN) can affect cloud properties and therefore Earth's radiative balance
. New particle formation (NPF) from condensable vapours in the free troposphere has been suggested ...to contribute to CCN, especially in remote, pristine atmospheric regions
, but direct evidence is sparse, and the magnitude of this contribution is uncertain
. Here we use in situ aircraft measurements of vertical profiles of aerosol size distributions to present a global-scale survey of NPF occurrence. We observe intense NPF at high altitudes in tropical convective regions over both Pacific and Atlantic oceans. Together with the results of chemical-transport models, our findings indicate that NPF persists at all longitudes as a global-scale band in the tropical upper troposphere, covering about 40 per cent of Earth's surface. Furthermore, we find that this NPF in the tropical upper troposphere is a globally important source of CCN in the lower troposphere, where CCN can affect cloud properties. Our findings suggest that the production of CCN as new particles descend towards the surface is not adequately captured in global models, which tend to underestimate both the magnitude of tropical upper tropospheric NPF and the subsequent growth of new particles to CCN sizes.
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•Simultaneous dropwise and filmwise condensation behavior on a completely hydrophilic configuration.•Continuous dropwise condensation achieved without the assistance of a hydrophobic ...coating.•Thermodynamics principles are applied for the design of microstructured condensation surfaces.•Enhanced heat transfer performance by simultaneous dropwise and filmwise condensation.
While wicking or spreading of a liquid through microstructures has been found to be promising for applications such as textiles, microelectronics or heat sinks, the effects of such structured surfaces on condensation phase change has received less attention. On a hydrophilic surface and for a fixed micropillar aspect ratio (height/diameter), the spacing between pillars is found to have a strong impact on the dynamics of condensation and on the final morphology of the condensate. In the case of micropillars with a large spacing between pillars, the condensate grows initially dropwise, and thereafter, as condensation develops, the condensate overcomes the pillars’ height flooding the substrate, and condensation continuous in a filmwise condensation (FWC) fashion. In contrast, filmwise condensation and the continuous nucleation, growth, and departure of drops at the pillars’ tops in a dropwise condensation (DWC) fashion occurs when the spacing between pillars is decreased. In this configuration, the geometry of the microstructures constrains the condensate between the pillars and rise of the condensate interface above the micropillars’ height is not thermodynamically favorable, while the top of the pillars act as nucleation sites. We refer to this latter condensation behavior as simultaneous dropwise/filmwise condensation. These observations were enabled by the excellent spatial and temporal resolution of Environmental Scanning Electron Microscopy. A heat transfer model is proposed to demonstrate the greater heat transfer performance of the simultaneous dropwise/filmwise condensation behavior on these surfaces when compared to solely filmwise condensation. The enhanced heat transfer is realizable due to the ability to maintain a thin film within the microstructures and to the active dropwise condensation at the micropillars’ tops. We report for the first time the occurrence of dropwise condensation on a completely hydrophilic wettability configuration without the assistance of a hydrophobic coating. Our findings pave the way to the development of microstructures for enhanced condensation heat transfer.
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