1,721,197 research outputs found
Numerical study of heat and mass transfer in rising inert bubbles using a conjugate flow model
No full textIn order to study the mechanisms of heat and mass transfer at the gas-liquid interfaces, flows inside and around a rising inert bubble are considered and calculated using the numerical algorithm developed in a companion paper. Studies on heat and mass transfer are carried out while special attention has been paid to the effects of wake vortices. Recoveries of the Sherwood and Nusselt numbers are observed in the wake zone behind bubbles and a physical explanation is proposed
Experimental investigation of vapor chambers with different wick structures at various parameters
No full text© 2016 Elsevier Inc. In this study, copper water vapor chambers (VCs) with two wick structures (copper foam and copper powder) are manufactured. An air-cooled test rig is designed to investigate the thermal performance. For copper-foam-based VCs (CFVCs), samples with filling rates ranging from 50% to 190% are manufactured; for copper-powder-sintered VCs (CPVCs), copper powders with particle sizes ranging from 66 ± 9 μm to 265 ± 85 μm are sintered. The VC samples are tested at heat loads ranging from 60 W to 200 W under 20 mm × 20 mm heating area; CFVC with 120% filling rate and CPVC with 66 ± 9 μm particle size are also tested at heat loads ranging from 60 W to 140 W under 10 mm × 10 mm heating area, to evaluate the effect of heating area. Response time, temperature uniformity of the condenser zone, and thermal resistance are used as performance indicators. Results show that CFVCs exhibit good temperature uniformity and that CPVCs exhibit low thermal resistance. CFVCs with moderate filling rates ranging from 90% to 120% outperform those with other filling rates; CPVCs with fine-particle powders outperform those with coarse-particle powders. Furthermore, an increased heating area enhances the performance
Electro-osmotic Non-isothermal Flow in Rectangular Channels with Smoothed Corners
No full textMicrochannel heat sinks are able to provide high cooling capabilities in terms of heat flux rates. This makes them particularly interesting for the thermal management of electronic devices, owing to the latter’s ever-increasing compactness and, consequently, power density
Photoacoustic response optimization of gold nanorods in the near-infrared region
Full text linkPhotoacoustic imaging (PAI) combines the advantage of optical and ultrasonic imaging, which has a high signal-to-noise ratio, and spatial resolution. To further improve the performance of PAI, gold nanorods can be utilized as exogenous contrast agents, and their size can be controlled. The size change of gold nanorods will change their absorption and heat transfer characteristics, and then affect their photoacoustic characteristics. Therefore, in the present work, the influences of absorption characteristics (absorption cross section and volume absorption coefficient) and heat transfer characteristics (specific surface area) of gold nanorods on photoacoustic response are studied by FDTD (FDTD Solutions, Lumerical) and FEM (Comsol Multiphysics). Results show that the increase of specific surface area will enhance the thermal coupling between gold nanorods and water, so as to improve the heat transfer and produce different photothermal responses without significantly affecting the photoacoustic quantum yield (As the specific surface area increases by about 10 times, the temperature increases by about 12 times, while the photoacoustic quantum yield increases by about 24%). On the contrary, absorption characteristics are decisive factors for both photothermal and photoacoustic responses. Therefore, in terms of improving photoacoustic quantum yield, when the size of gold nanorods changes, more attention should be paid to the improvement of the absorption characteristics rather than the specific surface area. In addition, increasing the specific surface area can significantly improve the photostability of gold nanorods, which is very important for practical applications
Nanoparticle manipulation using plasmonic optical tweezers based on particle sizes and refractive indices
Full text linkAs an effective tool for micro/nano-scale particle manipulation, plasmonic optical tweezers can be used to manipulate cells, DNA, and macromolecules. Related research is of great significance to the development of nanoscience. In this work, we investigated a sub-wavelength particle manipulation technique based on plasmonic optical tweezers. When the local plasmonic resonance is excited on the gold nanostructure arrays, the local electromagnetic field will be enhanced to generate a strong gradient force acting on nanoparticles, which could achieve particle sorting in sub-wavelength scale. On this basis, we explored the plasmonic enhancement effect of the sorting device and the corresponding optical force and optical potential well distributions. Additionally, the sorting effect of the sorting device was investigated in statistical methods, which showed that the sorting device could effectively sort particles of different diameters and refractive indices
Anisotropic scattering characteristics of nanoparticles in different morphologies: improving the temperature uniformity of tumors during thermal therapy using forward scattering
Full text linkPrecise control of the thermal damage area is the key issue during thermal therapy, which can be achieved by manipulating the light propagation in biological tissue. In the present work, a method is proposed to increase the uniformity of the specific absorption rate (SAR) distribution in tumors during laser-induced thermal therapy, which is proved to be effective in reducing the thermal damage of healthy tissue. In addition, a better way of manipulating light propagation in biological tissue is explored. It is found that the anisotropic scattering characteristics of nanoparticles are strongly dependent on their shapes, sizes, orientations, and incident wavelengths, which will strongly affect the light propagation in nanoparticle embedded biological tissue. Therefore, to obtain a better outcome from photothermal therapy, the scattering properties of nanoparticles are very important factors that need to be taken into consideration, along with the absorption efficiency. Further investigation finds that nanoparticles that predominantly scatter to the forward direction are favorable in obtaining a larger penetration depth of light, which will improve the uniformity of SAR and temperature distributions. This paper is meaningful for the application of nanoparticle-assisted laser-induced thermal therapy
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Heat transfer in unconventional geothermal wells: a double numerical modelling approach
Full text linkGeothermal energy aims at producing electricity or heat from underground resources. Worldwide geothermal energy extraction and use is still limited, despite its estimated high potential. To date, the efficiency and viability of enhanced geothermal system (EGS) and deep unconventional geothermal resources (e.g. superheated/supercritical systems) via conventional heat recovery techniques have led to limited success due to technology issues. Research on superheated/supercritical geothermal systems is highly active in Europe, notably triggered by the Iceland Deep Drilling Project (IDDP) [1]. Supercritical resources could deliver more energy than conventional resources thanks to the increase of enthalpy and the sharp decrease of density around the critical point of water [2]. The first well from IDDP was drilled at a depth of 2072 m after unintentionally drilling into magma between 2092 and 2104 m. The wellhead temperature reached 450°CC, with a superheated steam at a pressure of 140 bars (Palsson et al. in Geothermics 49:23–30, 2014)
A Novel Horizontal Liquid–Liquid Flow Pattern Map Using Dimensionless Number Groups
No full textA thorough literature review on immiscible liquid-liquid flow in horizontal pipes shows that there are a variety of flow pattern maps that are not always consistent with one other; hence, their reconciliation would be of fundamental importance. Flow pattern maps constructed using dimensional parameters are valid only for the particular pipe sizes and fluids employed to construct the maps. Construction of flow pattern maps using the relevant dimensionless parameter groups would enable the development of more generalised flow pattern maps, which would cover a wider range of flow systems. In this study, the Buckingham π theorem was applied to the independent system variables and fundamental dimensions of oil-water flow to determine the governing dimensionless groups, based on an extensive dataset built from the open literature. Four flow pattern maps were developed by plotting the ratio of mixture Reynolds number to Eötvös number Rem/Eo, the ratio of Weber number to Eötvös number We/Eo, the mixture Froude number Frm, and the ratio of gravity force to viscous force G/V as functions of water fraction fw. The lower the oil viscosity used in the experimental studies, the higher the Rem/Eo obtained. At high We/Eo and Frm, the inertia forces dominate, and dispersed flow prevails. At low We/Eo and Frm, the gravity forces dominate, and stratified flow prevails. At low G/V, the viscous forces dominate, with the core-annular flow or slug/plug most likely to occur. At high G/V, the gravity forces dominate; the stratified and dispersed flows are the most likely flow patterns. Based on the data analysed, stratified ST, stratified mixed SM, dispersed water-in-oil Dw/o, and slug SL flow regions were captured in the graphs of We/Eo and Frm as functions fw
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