Energy Transfer Coefficient Research Articles

Secondary lock-in of vortex-induced vibration and energy transfer characteristics of a vibrating cylinder subject to cross buoyancy

The hydrodynamic and thermal characteristics of a freely vibrating circular cylinder subject to cross buoyancy are numerically investigated at low Reynolds numbers. The structural responses and onset of vortex-induced vibration (VIV) are documented over a range of parameter space, 2.0≤ reduced velocity (Ur) ≤10.0, 0.7≤ Prandtl number (Pr) ≤10.0 and 0.5≤ Richardson number (Ri) ≤2.0. The fluid and structural coefficients are chosen as Reynolds number (Re)=100, mass ratio (m*)=10.0, and damping ratio (ζ)=0.01. A phenomenon of secondary VIV lock-in is found in the cases of Ri = 2.0 (the cross buoyancy effect becomes influential), Pr≲2.0 and Ur≳7.0. An extended VIV lock-in region is formed over a wide range of reduced velocity values together with a tremendous kinetic energy transfer between fluid and structure. This finding is significant for the research of hydropower harvesting. On the other hand, the influence of structural dynamics on heat convection over the surface of a heated circular cylinder is recorded and discussed as well. The significance and mutual influence between Prandtl and Richardson numbers on hydrodynamics, structural dynamics, and heat convection are discussed in detail. The temperature contours are found concentrating around the cylinder's surface in the cases of high Prandtl numbers, which are also associated with higher mean Nusselt number (Nu¯) values. The influence on heat convection over a cylinder's surface is quantified via the computation of Nu¯ and its fluctuation for different circumstances. The energy transfer coefficient is employed to quantify the kinetic energy transfer between the fluid and a heated structure in mixed convective flow. The phase angle difference between the transverse displacement and lift force is used to support the discussions of energy transfer in fluid.

Klein–Nishina formula and Monte Carlo method for evaluating the gamma attenuation properties of Zn, Ba, Te and Bi elements

Abstract In this work, the Klein–Nishina (K–N) approach was used to evaluate the electronic, atomic, and energy-transfer cross sections of four elements, namely, zinc (Zn), tellurium (Te), barium (Ba), and bismuth (Bi), for different photon energies (0.662 MeV, 0.835 MeV, 1.170 MeV, 1.330 MeV, and 1.600 MeV). The obtained results were compared with the Monte Carlo method (Geant4 simulation) in terms of mass attenuation and mass energy-transfer coefficients. The results show that the K–N approach and Geant4 simulations are in good agreement for the entire energy range considered. As the photon energy increased from 0.662 MeV to 1.600 MeV, the values of the energy-transfer cross sections decreased from 81.135 cm2 to 69.184 cm2 in the case of Bi, from 50.832 cm2 to 43.344 cm2 for Te, from 54.742 cm2 to 46.678 cm2 for Ba, and from 29.326 cm2 to 25.006 cm2 for Zn. The obtained results and the detailed information of the attenuation properties for the studied elements would be helpful in developing a new generation of shielding materials against gamma rays.

Energy transfer coefficients in thulium-doped silica fibers

Energy transfer coefficients in thulium-doped silica fibers are key parameters for a reliable numerical modeling and optimization of high-power fiber lasers pumped at 790 nm and emitting around eye-safer wavelength of 2 µm. We report on determination of the energy transfer coefficients by comparing experimental values and rate-equation-based modeling of thulium fluorescence decays. The study was performed using two pump, 792 nm and 1620 nm, and two signal, 800 nm and 2 µm, wavelengths. The following values were obtained k3011 = (1.9 ± 0.2) × 10−22 m3s-1, k1130 = (1.4 ± 0.2) × 10−23 m3s-1 and k1120 = (3.5 ± 0.1) × 10−23 m3s-1. To the best of our knowledge, this study involves so far the most comprehensive comparison of various fluorescence decays in terms of excitation and detection wavelengths as well as excitation powers.

Thermal boundary conductance across solid–solid interfaces at high temperatures: A microscopic approach

The existing theories for the thermal boundary conductance (TBC) of solid–solid interfaces lead to diverse values deviating from experimental measurements. In this paper, we propose a simple mechanism to evaluate the TBC contributed by phonons at room temperatures, where the microscopic structure of the interface layers between two dissimilar solids is treated as amorphous by taking into account the mismatches of the elastic modulus, the atomic masses, and the lattice spacing. Our theory explains well the observed magnitude of the TBCs across various solid–solid interfaces in the range from 107 to 109Wm−2K−1. The coordination number density and the energy transfer coefficient across interfaces are key parameters for determining the TBCs.

Non-linear Radiation and Navier-slip effects on UCM Nanofluid Flow past a Stretching Sheet under Lorentzian Force

In the present article, the novel contributions are modelling of Upper convected Maxwell nanoflow under Lorentzian influence over a stretching surface and investigating it using bvp4c procedure with MATLAB software. The boundary is set fixed with axial slip. Non-linear energy distribution is incorporated. Similarity variables are utilized to transmute non-linear PDEs of the basic fluid model to coupled system of ODEs. Computed numerical results are better compared with the past literature work to evidence its efficacy. The nanoflow momentum, energy, species diffusion are visualized graphically and analyzing the performance of proficient physical quantities on shear stress, energy dispersion coefficient, mass diffusion coefficient scatter of the system are seen through tables. Presence of magnetic field reduces friction at the wall and acts as a cooling agent.Navier slip increases the friction factor near the wall. Non-linear radiation transfers more heat from the system. Energy transfer coefficient is high in linear thermal rather than non-linear thermal distribution.

2.0 μm Ultra Broadband Emission from Tm3+/Ho3+ Co-Doped Gallium Tellurite Glasses for Broadband Light Sources and Tunable Fiber Lasers

A flat 2.0 μm ultra broadband emission with a full width at half maximum (FWHM) of 329 nm is achieved in 1 mol.% Tm2O3 and 0.05 mol.% Ho2O3 co-doped gallium tellurite glasses upon the excitation of an 808 nm laser diode. The influence of Tm3+ and Ho3+ contents on 2.0 μm spectroscopic properties of gallium tellurite glasses is minutely investigated by absorption spectra, emission spectra, and lifetime measurement. In addition, emission cross section and gain coefficient of Ho3+ ions at 2.0 μm are calculated, and the maximum values reach 8.2 × 10−21 cm2 and 1.54 cm−1, respectively. Moreover, forward and backward energy transfer probability between Tm3+ and Ho3+ ions are qualitatively evaluated by the extended spectral overlap method. Large ratio of the forward energy transfer from Tm3+ to Ho3+ to the backward one (19.7) and high forward energy transfer coefficient (6.22 × 1039 cm6/s) are responsible for effective 2.0 μm emission from Ho3+ ions. These results manifest that Tm3+/Ho3+ co-doped gallium tellurite glass is suitable for potential applications of broadband light sources and tunable fiber lasers operating in eye-safe 2.0 µm spectral region.

Integrating photoluminescent nanomaterials with photonic nanostructures

Photoluminescence is a light-matter interaction phenomenon of utmost interest for research and technological innovation. Luminescent materials posses several characteristics, such as the quantum yield, Stokes shift, bandwidth, energy transfer coefficients and lifetime of excited states, among others. These factors, though dependent on intrinsic properties of each material, are not immutable; they are highly sensitive to the optical constraints imposed by its surroundings. In particular, nearby surfaces can modify the local electromagnetic field and the density of optical states, strongly affecting the luminescent emission spectrum, intensity and directionality. Different strategies have been developed to control the emission of molecular or nano-sized photoluminescent materials, making use of recent progress in the field of plasmonics, photonic crystals and optical microcavities. The purpose of this article is to summarize the fundamental underlying physical concepts leading to modified photoluminescent properties, as well as to review the latest experimental advances aiming for the synergistic combination of luminescent nano-sources and either photonic or plasmonic nanostructures. Special attention to hybrid structures, such as those combining plasmonics and photonic crystals, will also be addressed.

Combined effect of pulsed electric fields and ultrasound on mass energy transfer and diffusion coefficient of plum

The aim of the study was to investigate the impact of combined application of pulsed electric fields (PEF) and ultrasound (US) pre-treatment on drying kinetics, mass transfer and convective water diffusion coefficient on plum fruit. The treatment was performed by using plum fruit in water for uniform distribution of electric conductivity and PEF treatment was applied at 1, 2 and 3 kV/cm, 50 pulses followed by US, 40 kHz with 99% frequency for 30 min and 27 ± 2 °C. Cell disintegration, drying kinetics, mass transfer and diffusion coefficient were calculated, and results showed that plums treated at 3 kV/cm intensity exhibited higher cell disintegration followed by 2 and 1 kV/cm. Furthermore, the investigation of PEF and US pre-treatment for drying kinetics and convective diffusion coefficient revealed that plums treated at 3 kV/cm contributed higher drying rate and convective water diffusion coefficient at uniform, pulse number, temperature and sonication time followed by 2 and 1 kV/cm. This study stated that combined treatment of PEF and US increased the cell disintegration, drying rate and also facilitate convective water diffusion as compared to untreated intact tissues.

Erbium-ytterbium co-doped aluminum oxide thin films: Co-sputtering deposition, photoluminescence, luminescent lifetime, energy transfer and quenching fraction

Abstract Erbium-ytterbium co-doped aluminium oxide (Al2O3:Er3+:Yb3+) thin films were deposited on thermally oxidized silicon wafers using reactive radio frequency co-sputtering deposition. The effects of deposition parameters (including oxygen flow rate, substrate temperature and substrate bias) were investigated to obtain low loss Al2O3 films (~0.15 dB/cm at 1550 nm). A set of singly- and co-doped Al2O3 films (surface roughness: ~144.8 p.m.) with various Er3+ concentrations (1.4, 2.0 and 2.5 × 1020 cm−3) and/or Yb3+ concentrations (1.3, 2.1, 3.2, 4.3 and 5.8 × 1020 cm−3) were deposited and investigated. The Er3+ photoluminescence (PL) spectrum around 1550 nm exhibits a pump power-independent full width at half maximum (FWHM) of ~40 nm with and without the presence of Yb3+ as a sensitizer. The luminescent lifetime of Er3+ (4I13/2, 6.52–7.14 m s) exhibits a power-dependent characteristic, while that of Yb3+ (2I5/2, 0.514–0.716 m s) is power-independent. A power-dependent role of energy transfer upconversion is concluded from both the power-dependent Er3+ PL intensity trend and its power-dependent PL decay rate. Yb3+-Er3+ ion energy transfer also exhibits power-dependent characteristics. The energy transfer coefficient (up to ~3.2 × 10−17 cm3s−1) and energy transfer efficiency (up to ~80%) depend on the Yb3+ and Er3+ concentrations. The PL intensity trend and power-dependent absorption of Er3+ and Er3+-Yb3+ under 1469-nm excitation can be well described by using a three-energy-level model. The derived Er3+ quenching fraction based on the fittings of the measured absorption and PL intensity, decreases with the presence of Yb3+ ions. In addition, the Yb3+ quenching fraction was derived based on a two-energy-level model for 973-nm absorption. This work provides parametric references and insights regarding deposition, characterization, and design of the evolving rare-earth-doped Al2O3 platform for on-chip near-infrared applications.

Broadband ~1.8 µm emission characteristics of Tm3+-doped bismuth germanate glass based on Ga2O3 modification

In this paper, Tm3+-doped Bi2O3-GeO2-Ga2O3Na2O glass was synthesized using melt-quenching method. Spectroscopic and thermal properties of the presented glass was characterized. The effects of Ga2O3 oxide on the glass structure and ~1.8 µm emission properties were investigated. The thermal stability and Raman spectroscopic analysis showed that partial substitution of GeO2 by Ga2O3 resulted in decreasing of glass transition temperature and maximum phonon energy (745 cm−1). It is known that relatively low maximum phonon energy is good for ~1.8 µm emission. Based on the measured absorption spectra, Judd-Ofelt intensity parameters and other spectroscopic parameters were calculated to elucidate the radiative properties of the presented Tm3+-doped glass. Moreover, under the excitation of 808 nm laser diode, broadband ~1.8 µm fluorescence was observed. For Bi2O3-GeO2-Ga2O3Na2O glass doped with 1.0 mol% Tm2O3, the large values of σemi × τmea product (8.30 × 10−21 cm2ms) and σemi × ∆λeff product (16.00 × 10−26 cm3) indicate a good gain property as well as a good gain bandwidth. Finally, the energy transfer coefficient (CD-A = 12.0 × 10−40 cm6/s) of cross relaxation (3H4, 3H6 → 3F4, 3F4) between Tm3+ ions is calculated. These results indicate that the prepared Tm3+-doped Bi2O3-GeO2-Ga2O3Na2O glass is a promising gain material for ~1.8 µm band solid-state laser applications.

Grinding temperature prediction model of high-volume fraction SiCp/Al composite

Grinding is the main processing technique for particle-reinforced composites, in which grinding force and temperature are significant for investigating the removal mechanism and surface properties. In this study, a grinding force prediction model is established based on the response surface methodology. The energy density of surface heat source in the grinding area is calculated by combining the contact area between the grinding wheel and workpiece. Based on the integration algorithm in time and space, a theoretical ideal grinding temperature prediction model is deduced. The grinding heat energy transfer coefficient is defined as the percentage of heat energy, which is transferred from the grinding heat energy to the workpiece. According to the experimental and ideal theoretical highest grinding temperatures, a prediction model of the heat energy transfer coefficient is established, and the modified theoretical highest grinding temperature prediction model is obtained. Furthermore, a finite element model of SiCp/Al composite in grinding is established. The highest grinding temperature in the finite element model is consistent with the modified theoretical highest grinding temperature, and the grinding temperature field is analysed. The highest grinding temperature increases as the wheel speed and grinding depth increase, while it decreases as table speed increases, which differs from that of some common materials. Thus, the grinding temperature prediction model provides an important reference for the study of removal mechanism and surface properties of SiCp/Al composite.

Influence of Turbulence, Density, Phase Change, and Phase Interfaces Models on the Performance of the Numerical Simulation of a Two-Phase Closed Thermosyphon

A heat pipe can be considered a highly effective thermal conduction device, which is especially desirable in heat transfer operations in order to ensure high energy efficiency. However, the operation of heat pipes comprises different heat and mass transfer phenomena, such phase change, heat conduction and convection, solid-liquid and vapor-liquid surface interactions, surface vaporization, and nucleate boiling. Therefore, modelling heat pipes is a highly complex task that demands detailed knowledge of the physical phenomena involved and choosing suitable theoretical models to obtain a good representation of the real nature of the heat and mass transfer processes. In this study, some models and parameters available in the commercial CFD software ANSYS Fluent for turbulence, density, phase change, and phase interfaces were examined to determine their influence on the prediction of the heat and mass transfer in a two-phased closed thermosyphon (TPCT). The numerical results show that using a turbulence viscous model is not necessary and that a variable density model improves the temperature distribution inside the TPCT. Furthermore, using high mass and energy transfer coefficients during condensation makes the vapor remain close to the saturation temperature. Finally, a sharp interphase model is strongly recommended for this type of process.

Cold white light emission in tellurite-zinc glasses doped with Er3+–Yb3+–Tm3+ under 980 nm

Tellurite-zinc glasses doped with Er3+, Yb3+ and Tm3+ were fabricated by conventional melt-quenching technique and characterised by absorption spectroscopy, refractive index, lifetime measurements, excitation, luminescence and up-conversion spectroscopy. Tunable blue to cold white light emission based on the colour mixing of red, green and blue light was obtained via up-conversion under 980 nm and by adjusting the laser excitation intensity. The balancing of the relative intensity of each colour is provided by the energy transfer process between the rare-earth ions. Moreover, luminescence spectroscopy was performed with a 405 nm laser to further understand the energy transfer mechanism that produce the white light. The Judd-Ofelt intensity parameters (Ω2, Ω4 and Ω6) were calculated for all samples and present the trend Ω2>Ω4>Ω6. The spectroscopic parameters were computed with the Judd-Ofelt theory as well as the energy transfer micro-parameters (critical radius of interaction and energy transfer coefficient). Such results shall be used to give a comprehensive explanation for the energy transfer process between these rare earth ions.

Down-conversion luminescence of Yb3+ in novel Ba4Y3F17:Yb:Ce solid solution by excitation of Ce3+ in UV spectral range

Abstract The down-conversion luminescence under UV excitation was demonstrated in single-phase Ba4Y3F17 solid solution nanoparticles codoped with Ce3+/Yb3+. The complex photodynamic processes occurred in the samples including excited state absorption, excitons and color centers formation. The Yb doping suppressed the solarization effect. The efficiency of down-conversion from UV to near IR luminescence of Yb3+ appeared to be high due to Ce4+-Yb2+ charge transfer mechanism responsible for energy transfer between Ce3+ and Yb3+ ions. The direct measurements of down-conversion luminescence quantum yield by means of integrating sphere and calculations of energy transfer efficiency from luminescence spectra data were carried out. The down-conversion luminescence quantum yield reached the maximum value of about 1% for the sample with 0,1 mol.% of Ce3+ and 5,0 mol.% of Yb3+ ions contents, whereas energy transfer coefficient reached its maximum of about 6,3% for 0,05 mol.% of Ce3+ and 5,0 mol.% of Yb3+ ions.

Calculation of thermal boundary resistance based on the analysis of elastic waves propagating at the interface

This work presents a method for calculating thermal boundary resistance under the assumption of the acoustic mismatch model based on the propagation of elastic waves at the interface. The main problem is to determine the energy transfer coefficient from one material to another. Its solution requires an analysis of the reflection and refraction of acoustic waves at the interface. The most important feature of the presented model is the consideration of all types of waves propagating in solids. When the solid-solid interface is smooth at low temperature, the obtained results are in good agreement with the experiment.

Cellular automata model-based numerical analysis for breaching process of embankment dam

It is of great significance to study the process and cause of embankment dam breach in order to ensure the dam safety. In this paper, the overtopping failure mode of embankment dam is selected as the research object, and the cellular automata (CA) method is introduced to explore the development law and influencing factors of the overtopping failure mode. Based on the physical and mechanical characteristics of embankment dam and the energy evolution law of the dam soil failure process, this paper discusses the realization method of CA for simulations of dam body heterogeneity, soil anisotropy, stress environment, etc., and proposes the determination method of cellular failure threshold, energy dissipation rate and energy transfer coefficient. Afterward, the loading mode of the CA model is determined based on the relationship between generalized energy and force deformation of the dam soil. Then, energy criterion for dam erosion failure and mechanical criterion of breach slope failure are put forward. Finally, the CA model is applied to a practical project so as to analyze the development and cause for scour depth and width of the overtopping failure breach, and the influence of overtopping water level and downstream slope ratio on the development of breach.

The mean energy transfer and collisional absorption coefficient of high power laser in plasma

The absorption coefficient of high power laser incident normally onto a plasma medium is studied when electron energy distribution obeys non-extensive function. The variation of the absorption coefficient with the incident laser intensity is investigated for different electron temperatures as well as different non-extensive distribution parameter (q). The variation of the absorption coefficient with plasma density is also investigated for different q values for constant temperature. Furthermore the mean rate of energy absorption is evaluated as function of the incident laser intensity for different electron temperatures and q values. The results are compared with ones obtained in Maxwellian case and differences are shown in the corresponding diagrams.

Influence of oceanic conditions in the energy transfer efficiency estimation of a micronekton model

Abstract. Micronekton – small marine pelagic organisms around 1–10 cm in size – are a key component of the ocean ecosystem, as they constitute the main source of forage for all larger predators. Moreover, the mesopelagic component of micronekton that undergoes diel vertical migration (DVM) likely plays a key role in the transfer and storage of CO2 in the deep ocean: this is known as the “biological pump”. SEAPODYM-MTL is a spatially explicit dynamical model of micronekton. It simulates six functional groups of vertically migrant (DVM) and nonmigrant (no DVM) micronekton, in the epipelagic and mesopelagic layers. Coefficients of energy transfer efficiency between primary production and each group are unknown, but they are essential as they control the production of micronekton biomass. Since these coefficients are not directly measurable, a data assimilation method is used to estimate them. In this study, Observing System Simulation Experiments (OSSEs) are used at a global scale to explore the response of oceanic regions regarding energy transfer coefficient estimation. In our experiments, we obtained different results for spatially distinct sampling regions based on their prevailing ocean conditions. According to our study, ideal sampling areas are warm and productive waters associated with weak surface currents like the eastern side of tropical oceans. These regions are found to reduce the error of estimated coefficients by 20 % compared to cold and more dynamic sampling regions.

Enhanced 1–5 μm near- and mid-infrared emission in Ho3+/Yb3+ codoped TeO2-ZnF2 oxyfluorotellurite glasses

Intense 1–5 μm infrared emission from near- to mid-infrared was obtained from Ho3+/Yb3+ codoped TeO2-ZnF2 oxyfluorotellurite glasses which were prepared by melt-quenching method under the 980 nm LD excitation, and the emission intensity can be enhanced with the increase of ZnF2 content. Judd-Ofelt analysis was used to evaluate the radiative transition parameters of the excited levels according to the absorption spectra. The stimulated emission cross section of 5I6→5I8 (1.2 μm), 5I7→5I8 (2.0 μm), 5I6→5I7 (2.85 μm) and 5I5→5I6 (4.0 μm) transitions were calculated to reach 0.639 × 10–20, 0.760 × 10–20, 0.985 × 10–20 and 0.484 × 10−20 cm2, respectively. The energy transfer coefficients (CDA) are enhanced with the increase of ZnF2 content and phonon contribution ratios of phonon assisted energy transfer process between Ho3+ and Yb3+ were figured out. Our results demonstrate that these TeO2-ZnF2 glasses, which possess good thermal stability and transparency, low phonon energy (about 600 cm−1), excellent near- and mid-infrared emission in the range of 1–5 μm wavelength, would be promising material for infrared optical fibers and infrared lasers.

Luminescence of GdF3:Pr:Yb and YF3:Pr:Yb Solid Solutions Synthesized by Crystallization from the Melt

Spectral and luminescence characteristics of GdF3:Pr:Yb and YF3:Pr:Yb solid solutions synthesized by crystallization from the melt were investigated. Down-conversion luminescence of Yb3+ in the region of 2F5/2 → 2F7/2 transitions with 445-nm excitation was studied. The energy-transfer coefficient from Pr3+ to Yb3+ was <80% for concentration ratios Pr/Yb 0.5/10.0 and 1.0/10.0 for GdF3 and 0.5/10.0 for YF3. The absolute values of Pr3+ and Yb3+ luminescence quantum yields in the region of the greatest crystalline-silicon photosensitivity were low because of highly efficient nonradiative energy transfer. The quantum yield was <1% for Yb3+ intrinsic luminescence and <4% for total luminescence in the range 800–1050 nm (for concentration ratio Pr/Yb = 0.5/1.0 in GdF3 matrix). The low quantum yield was a consequence of the complex energy-exchange pattern between Yb3+ and Pr3+ ions, which was largely influenced by the proximity of 1G4 and 2F5/2 energy states of Pr3+ and Yb3+, respectively, in these matrices. This opened an additional pathway for nonradiative decay of Yb3+ excited states and enabled cross-relaxation between 3P0 → 1G4 transitions of Pr3+ and 2F5/2 → 2F7/2 transitions of Yb3+ that increased the lifetime of the Pr3+ 3P0 state.