| 1. |
- Cao, Zhen, et al.
(författare)
-
Pool boiling heat transfer of FC-72 on pin-fin silicon surfaces with nanoparticle deposition
- 2018
-
Ingår i: International Journal of Heat and Mass Transfer. - : Elsevier BV. - 0017-9310. ; 126, s. 1019-1033
-
Tidskriftsartikel (refereegranskat)abstract
- In the present study, two types of micro-pin–fin configurations were fabricated on silicon surfaces by a dry etching method, i.e., staggered pin fins (#1) and aligned pin fins with empty areas (#2). The micro-pin–fin surfaces were then further modified by depositing FeMn oxide nanoparticles (∼35 nm) electrostatically for 8 h and 16 h, respectively, namely #1-8h, #1-16h, #2-8h and #2-16h. Subcooled pool boiling heat transfer was experimentally studied on these surfaces at atmospheric pressure, using FC-72 as the working fluid. The results showed that in comparison to the smooth surface, pool boiling heat transfer was significantly enhanced by the micro-pin-fin surfaces and the maximum superheat was considerably decreased. Additionally, critical heat fluxes were also greatly improved, e.g., the critical heat flux on #1 was almost twice of that on the smooth surface. Generally, the nanoparticle deposition could further enhance pool boiling heat transfer, including the heat transfer coefficient and critical heat flux (CHF). High speed visualizations were taken to explore the mechanisms behind the heat transfer performance. The bubble behavior on the micro-pin–fin surfaces with and without nanoparticles was compared at low, moderate and high heat fluxes, respectively. The wickability of FC-72 on the test surfaces was measured, based on which, a modified CHF model was proposed to predict the experimental CHFs. Accordingly, a possible mechanism of CHF enhancement was described.
|
|
| 2. |
- Cao, Zhen, et al.
(författare)
-
Pool Boiling Heat Transfer of Water on Copper Surfaces With Nanoparticles Coating
- 2017
-
Ingår i: ASME 2017 International Mechanical Engineering Congress and Exposition. - 9780791858431 ; 8
-
Konferensbidrag (refereegranskat)abstract
- Saturated pool boiling heat transfer is investigated experimentally on a copper substrate with copper nanoparticle coatings at atmospheric pressure, in terms of critical heat flux (CHF) and heat transfer coefficient (HTC). Experiments are carried out on the substrate surface with a diameter of 12 mm using DI water as the working fluid. The coating is formed by stacking copper nanoparticles generated by an aerosol method. The aerosol nanoparticles are generated by a spark discharge generator with nitrogen gas as carrier gas and size-selected prior to electrostatic deposition. The thickness of the coating is quantified by the deposition time. In the present study, copper particles with diameter 35± 5 nm are selected, considering better coverage on the surface, while the deposition time is controlled as 4h and 8h, respectively.The boiling curves and heat transfer coefficient of MS-1 (4h deposition) and MS-2 (8h deposition) were compared with the BS (bare surface). The results show that CHFs of MS-1 and MS-2 are increased by 24% and 36%, respectively compared with the BS, while heat transfer is enhanced as well. High speed visualization tells that the coating provides more active nucleate sites and the hydrophobicity of the coating helps bubbles departure from the surface at low and moderate heat flux. At high heat flux, a hollow well occurs on MSs to supply liquid effectively to avoid dryout. Therefore, CHF and heat transfer are both improved.
|
|
| 3. |
- Deppert, Knut
(författare)
-
Metallic nanocrystals via an aerosol route
- 2019
-
Konferensbidrag (refereegranskat)abstract
- Mass production of nanocrystals with accurate size control is a central problem in nanotechnology. Aerosol technology offers the possibility to produce nanocrystals with well-controlled composition and size distribution.An aerosol is defined as solid or liquid particles suspended in a gas, and aerosol science and technology has been used since over 60 years, primarily to study the size, shape and composition of airborne particles [1]. For this purpose, tools have been developed, which allow scientists to fabricate and precisely classify particles in the micro- and nanometer size ranges according to size, and to measure their concentration in the carrier gas [2]. The aerodynamic properties of nanoparticles depend almost exclusively on their size and shape and only to a small extent on their mass and composition, which means that the same generic characterization and production tools can be applied to a variety of different materials [3].Here, I will present a setup of aerosol tools and methods that can be used to generate well-defined metallic nanocrystals.References[1] W.C. Hinds, Aerosol Technology: Properties, Behavior, and Measurement of Airborne Particles, John Wiley & Sons, 2007.[2] R.C. Flagan, Aerosol Sci. Techn., 28, 301-380, 1998.[3] P. Kulkarni, P.A. Baron, and K. Willeke (Eds.), Aerosol Measurement: Principles, Techniques, and Applications, John Wiley & Sons, 2011.Acknowledgments: This work was performed in NanoLund at Lund University and the author would like to thank all aerosol colleagues from Lund for their support.
|
|
| 4. |
- Deppert, Knut, et al.
(författare)
-
One-step Gas-phase Synthesis of Core-shell Nanoparticles via Surface Segregation.
- 2019
-
Konferensbidrag (refereegranskat)abstract
- A great amount of research effort has been devoted to theproduction of core-shell nanoparticles for applications in variousfields including biomedical imaging, catalysis, and plasmonics.Such attention to core-shell nanoparticles arise from the fact thatthey can exhibit enhanced physical and/or chemical properties.Furthermore, core-shell particles with distinctly new propertiescompared to those of the constituent materials can be designedby tuning, for example, their size, shell thickness, and structure [1,2].Although chemical synthesis techniques are currently the mostpopular methods for fabricating core-shell nanoparticles,interface and surface contaminations are often an unavoidableissue in the solution-based approaches. Aerosol based methodsare cleaner alternatives and have been used to produce core-shellnanoparticles [3-6]. Here we present aerosol core-shellnanoparticles generated via spark discharge generation (SDG) [7].Cu-Ag core shell nanoparticles were fabricated via surfacesegregation using SDG accompanied by sintering directly in thegas phase. The surface segregation employed in this methodrefers to the phenomenon of the enrichment of one componentof a mixture in the surface region and is attributed to theinterplay between the atomic radii, cohesive energy, and surfaceenergy of the core and shell materials [8].Depending on the sintering temperature, the SDG-generatednanoparticles form Janus-like or core-shell structures. Themorphology, crystallinity, and composition of the SDG-generatedbimetallic nanoparticles were investigated by scanning electronmicroscopy, high-resolution transmission electron microscopy,and energy-dispersive X-ray spectroscopy. Molecular dynamicssimulations were carried out to investigate the structuralevolution of Cu-Ag nanoparticles during heating and coolingprocesses corresponding to the sintering. This appealingly simpleone-step gas-phase synthesis method presented here can beemployed for other bimetallic systems.
|
|
| 5. |
- Dubrovskii, Vladimir G., et al.
(författare)
-
Length Distributions of Nanowires Growing by Surface Diffusion
- 2016
-
Ingår i: Crystal Growth & Design. - : American Chemical Society (ACS). - 1528-7483 .- 1528-7505. ; 16:4, s. 2167-2172
-
Tidskriftsartikel (refereegranskat)abstract
- We present experimental data on the time and radius-dependent length distributions of Au-catalyzed InAs nanowires grown by metal organic vapor phase epitaxy. We show that these distributions are not as sharp as commonly believed. Rather, they appear to be much broader than Poissonian from the very beginning and spread quickly as the nanowires grow. We develop a model that attributes the observed broadening to the diffusion-induced character of growth. In the initial growth stage, the nanowires are fed from their entire length, leading to a Polya-like length distribution whose standard deviation is proportional to the mean length. After the nanowire length exceeds the adatom diffusion length, the growth acquires a Poissonian character in which the standard deviation scales as a square root of the mean length. We explain why wider nanowires have smaller length dispersion and speculate on the length distributions in Au-catalyzed versus self-catalyzed growth methods.
|
|
| 6. |
- Eom, Namsoon, et al.
(författare)
-
A Continuous One-Step Aerosol Method for Producing Core@Shell Cu@Ag Nanoparticles
- 2019
-
Konferensbidrag (refereegranskat)abstract
- The synthesis of core@shell nanoparticles has predominantly been carried out by chemical methods or physical deposition of a shell material post-growth onto core particles. By combining immiscible materials that differ in surface energy, we demonstrate the spontaneous atomic rearrangement to monodisperse Cu@Ag core@shell particles directly in the aerosol phase, starting from pure Cu and Ag electrodes with the spark discharge generation (SDG) method. The morphology and crystallinity were investigated by SEM and HRTEM, and the composition was confirmed by STEM EDX, which indicated that the Ag shell acts as an oxidation barrier for the Cu core. The current material system may find applications in antibacterial coatings. The method presented can be extended to other bimetallic systems with applications in catalysis, plasmonics and as seed-particles for nanowire growth. Owing to the simple, zero-waste and continuous production method, SDG is an ideal platform for such nanoparticle generation and investigation.
|
|
| 7. |
- Eom, Namsoon, et al.
(författare)
-
Building superlattices from aerosol nanoparticles via evaporative self-assembly
- 2019
-
Konferensbidrag (refereegranskat)abstract
- Nanoparticle superlattices consisting of densely packed particles with periodic arrangements can exhibit interesting collective properties different from those of individual nanoparticles and thus have attracted great interest in research due to their potential applications in optoelectronic, plasmonic, and magnetic devices. Evaporation-induced self-assembly on solid substrates which employs nanoparticles produced by wet chemistry is one of the most widely used methods in nanoparticle superlattice fabrication. However, impurities are inherent in the popular wet chemistry-based method and are often a cause of lack of reproducibility. Here we present a simple but novel method to generate close-packed arrays of nanoparticles uniquely created by combining aerosol technology with evaporation-induced self-assembly. Metal and metal oxide aerosol nanoparticles (20 - 50 nm in diameter) are generated using a spark discharge generator and are subsequently deposited on liquid droplets. We demonstrate that this way of capturing aerosol nanoparticles in the gas-liquid interface of a droplet suppresses the ubiquitous ‘coffee-ring’ effect during evaporation leading to self-assemblies of nanoparticles. This simple, effective method provides a versatile strategy for fabricating various types of nanoparticle superlattices.
|
|
| 8. |
- Eom, Namsoon, et al.
(författare)
-
Core-shell Cu-Ag Nanoparticles Produced by Spark Discharge Generation
- 2019
-
Konferensbidrag (refereegranskat)abstract
- The synthesis of core@shell nanoparticles has predominantly been carried out by chemical methods or physical deposition of a shell material post-growth onto core particles. By combining immiscible materials that differ in surface energy, we demonstrate the spontaneous atomic rearrangement to monodisperse Cu@Ag core@shell particles directly in the aerosol phase, starting from pure Cu and Ag electrodes with the spark discharge generation (SDG) method. The morphology and crystallinity were investigated by SEM and HRTEM, and the composition was confirmed by STEM EDX, which indicated that the Ag shell acts as an oxidation barrier for the Cu core. The current material system may find applications in antibacterial coatings. The method presented can be extended to other bimetallic systems with applications in catalysis, plasmonics and as seed-particles for nanowire growth. Owing to the simple, zero-waste and continuous production method, SDG is an ideal platform for such nanoparticle generation and investigation.
|
|
| 9. |
- Eom, Namsoon, et al.
(författare)
-
Towards Superlattices via Evaporative Self-Assembly of Aerosol Nanoparticles
- 2019
-
Konferensbidrag (refereegranskat)abstract
- Nanoparticle superlattices consisting of densely packed particles with periodic arrangements can exhibit interesting collective properties different from those of individual nanoparticles and thus have attracted great interest in research due to their potential applications in optoelectronic, plasmonic, and magnetic devices[1, 2]. Evaporation-induced self-assembly on solid substrates which employs nanoparticles produced by wet chemistry is one of the most widely used methods in nanoparticle superlattice fabrication[3]. However, impurities are inherent in the popular wet chemistry-based method and are often a cause of lack of reproducibility. Here we present a simple but novel method to generate close-packed arrays of nanoparticles uniquely created by combining aerosol technology with evaporation-induced self-assembly. Gold aerosol nanoparticles are generated using a spark discharge generator and are subsequently deposited on liquid droplets. We demonstrate that this way of capturing aerosol nanoparticles in the gas-liquid interface of a droplet suppresses the ubiquitous ‘coffee-ring’ effect during evaporation leading to self-assemblies of nanoparticles. This simple, effective method provides a versatile strategy for fabricating various types of nanoparticle superlattices.
|
|
| 10. |
- Hamed, Tareq Abu, et al.
(författare)
-
Multiscale in modelling and validation for solar photovoltaics
- 2018
-
Ingår i: EPJ Photovoltaics. - : EDP Sciences. - 2105-0716. ; 9
-
Tidskriftsartikel (refereegranskat)abstract
- Photovoltaics is amongst the most important technologies for renewable energy sources, and plays a key role in the development of a society with a smaller environmental footprint. Key parameters for solar cells are their energy conversion efficiency, their operating lifetime, and the cost of the energy obtained from a photovoltaic system compared to other sources. The optimization of these aspects involves the exploitation of new materials and development of novel solar cell concepts and designs. Both theoretical modeling and characterization of such devices require a comprehensive view including all scales from the atomic to the macroscopic and industrial scale. The different length scales of the electronic and optical degrees of freedoms specifically lead to an intrinsic need for multiscale simulation, which is accentuated in many advanced photovoltaics concepts including nanostructured regions. Therefore, multiscale modeling has found particular interest in the photovoltaics community, as a tool to advance the field beyond its current limits. In this article, we review the field of multiscale techniques applied to photovoltaics, and we discuss opportunities and remaining challenges.
|
|
