38 results on '"Zeng, Yao"'
Search Results
2. Experimental and numerical analysis of the hydraulic and thermal performances of the gradually-varied porous volumetric solar receiver
- Author
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Shen Du, Dong Li, Zeng-Yao Li, Ya-Ling He, Xiang-Qian Xie, and Yang Gao
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Thermal efficiency ,Materials science ,Convective heat transfer ,General Engineering ,02 engineering and technology ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,0104 chemical sciences ,chemistry.chemical_compound ,chemistry ,Thermal ,Radiative transfer ,Silicon carbide ,General Materials Science ,Astrophysics::Earth and Planetary Astrophysics ,Composite material ,0210 nano-technology ,Porosity ,Penetration depth ,Recoating - Abstract
A gradually-varied porous structure is designed to increase the thermal performance of the porous volumetric solar receiver. Based on the replica method and multilayer recoating technique, the silicon carbide porous ceramic with linear-changed geometrical parameters is fabricated. The performances of the uniform and gradually-varied porous volumetric solar receivers are studied by both experiment and numerical simulation. An optimization method combining genetic algorithm and computational fluid dynamics analysis is applied to determine the optimum porosity distribution. The results present that porous volumetric solar receiver with linear-changed geometrical parameters exhibits better thermal performance than the uniform porous volumetric solar receivers, especially when the thickness of the receiver is small. Larger porosity in the front is beneficial for increasing the solar radiation penetration depth, which limits the reflectance and thermal radiative losses. Smaller porosity in the rear traps more solar radiation and increases the convective heat transfer. When the receiver’s thickness is larger, the performance of the gradually-varied volumetric solar receiver is nearly identical to that of the uniform receiver with largest porosity. The double-layer configuration is found to be the optimized structure of the gradually-varied porous volumetric solar receiver. The thermal efficiency could be further improved using genetic algorithm with an 11 K increase of the outlet temperature.
- Published
- 2020
3. Numerical modeling of the gas-contributed thermal conductivity of aerogels
- Author
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Hao-Qiang Pang, Ning Pan, Chuan-Yong Zhu, and Zeng-Yao Li
- Subjects
Fluid Flow and Transfer Processes ,Coupling ,Work (thermodynamics) ,Materials science ,020209 energy ,Mechanical Engineering ,Aerogel ,02 engineering and technology ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,Microstructure ,Thermal conduction ,Thermal conductivity ,Heat transfer ,0202 electrical engineering, electronic engineering, information engineering ,Composite material ,0210 nano-technology ,Porosity - Abstract
Due to the complex microstructure in aerogels and the intricate heat transfer mechanism of solid-gas coupling heat conduction, modeling of the gas-contributed thermal conductivity of this type of material is quite difficult. The present work introduces a novel numerical methodology for computing the gas-contributed thermal conductivity of aerogels by analyzing their microstructural characteristics and heat transfer mechanism of the thermal coupling between the gas phase and the solid backbone of the system. Specifically, structures of aerogels are reconstructed by an improved three-dimensional diffusion-limited cluster-cluster aggregation (DLCA) method, and the contribution of the solid-gas coupling heat transfer to the gas-contributed thermal conductivity of aerogels is quantified. The present numerical model is fully validated by the available experimental data for different aerogels with porosity ranging from 78% to 97.7%. The proposed numerical method is flexible and versatile because it is capable to account for both the geometrical and topological details of the aerogel structure.
- Published
- 2019
4. Coupled MLPG–FVM simulation of steady state heat conduction in irregular geometry
- Author
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Zeng-Yao Li, Wen-Quan Tao, Xue-Hong Wu, and Zheng-Ji Chen
- Subjects
Physics ,Steady state ,Finite volume method ,Applied Mathematics ,Numerical analysis ,General Engineering ,Dirac delta function ,Geometry ,02 engineering and technology ,Thermal conduction ,01 natural sciences ,Domain (mathematical analysis) ,Numerical integration ,010101 applied mathematics ,Computational Mathematics ,symbols.namesake ,020303 mechanical engineering & transports ,0203 mechanical engineering ,symbols ,Test functions for optimization ,0101 mathematics ,Analysis - Abstract
The two-dimensional steady-state heat conduction in irregular geometry is solved by a MLPG–FVM coupled method. The meshless local Petrove–Galerkin (MLPG) method is applied to the sub-region with skewed wall surface while the finite volume method (FVM) is used in the rest of the domain. The Dirichlet–Dirichlet method is adopted to couple the temperature between MLPG and FVM methods. In MLPG method, the Dirac's Delta function is taken as the test function to avoid the local domain integration which does not need the numerical integration and the solution is independent of the size of the test function. The proposed MLPG–FVM method is validated and proved to be an efficient numerical method for 2-D heat conduction in irregular geometry, which can exert their own advantages of MLPG and FVM.
- Published
- 2019
5. A novel flux mapping system for high-flux solar simulators based on the indirect method
- Author
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Zeng-Yao Li, Xiudong Wei, Jun Xiao, and Huiqiang Yang
- Subjects
Physics ,Renewable Energy, Sustainability and the Environment ,business.industry ,020209 energy ,Radiant energy ,Energy flux ,Flux ,02 engineering and technology ,Repeatability ,021001 nanoscience & nanotechnology ,Optics ,0202 electrical engineering, electronic engineering, information engineering ,Light beam ,General Materials Science ,Astrophysics::Earth and Planetary Astrophysics ,Solar simulator ,0210 nano-technology ,business ,Solar power ,Interpolation - Abstract
It is an important and challenging work to measure the energy flux density distribution of the concentrated radiation during the concentrating solar power applications. In order to evaluate the performance of a multi-lamps high-flux solar simulator, a novel flux mapping system based on the indirect method has been developed. It features two Lambertian targets. One is a stationary water-cooled Lambertian target where there is a circular hole in the center used to install a flux sensor. The other is a movable Lambertian target used to cover the flux sensor when shooting the concentrated light beam image. This kind of design can obtain the gray value of flux sensor region directly and does not require the interpolation in the sensor-influencing area. The design theory and principle, the hardware implementation and the experimental validation of this flux mapping system have been presented in detail. The repeatability experiments and the error analyses showed that the total relative errors of this flux mapping system were ±8.1% with a repeatability of 1.1%, and ±8.5% with a repeatability of 2.7%, for evaluating the flux and the total radiant power, respectively.
- Published
- 2019
6. Design and characterization of a high-flux non-coaxial concentrating solar simulator
- Author
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Yan Zhang, Jun Xiao, Raúl Navío Gilaber, Xiudong Wei, and Zeng-Yao Li
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Materials science ,business.industry ,020209 energy ,Monte Carlo method ,Photovoltaic system ,Energy Engineering and Power Technology ,Flux ,02 engineering and technology ,021001 nanoscience & nanotechnology ,Ellipsoid ,Industrial and Manufacturing Engineering ,Characterization (materials science) ,Physics::Space Physics ,Thermal ,0202 electrical engineering, electronic engineering, information engineering ,Astrophysics::Earth and Planetary Astrophysics ,Solar simulator ,Aerospace engineering ,Coaxial ,0210 nano-technology ,business - Abstract
To improve the spatial uniformity of the concentrating solar simulators, a concept of non-coaxial deflection angle was introduced to the typical ellipsoidal reflectors. Based on this idea, a new-type 42 kWe high-flux non-coaxial concentrating solar simulator was designed and built. The Monte Carlo ray-tracing technique was applied to optimize the value of the non-coaxial deflection angle and simulate the flux distribution of this new-type solar simulator. A flux mapping system based on the indirect method was used to characterize the solar simulator optically. The relative deviation for the measured and the simulated results of this new-type solar simulator, as well as the simulated results of a conventional concentrating solar simulator, were compared and analyzed. The results show that the spatial nonuniformity of this new-type solar simulator over a circular target of 50 mm in diameter, improved to 7.2% from 40.3% of a conventional one. This non-coaxial concentrating solar simulator is considered very suitable for high-temperature solar thermal, thermochemical and high-concentration photovoltaic applications, especially where there are strict requirements for spatial uniformity.
- Published
- 2018
7. Design and optimization of core/shell structures as highly efficient opacifiers for silica aerogels as high-temperature thermal insulation
- Author
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Chuan-Yong Zhu, Zeng-Yao Li, Ning Pan, and Hao Qiang Pang
- Subjects
010302 applied physics ,Materials science ,business.industry ,Composite number ,General Engineering ,Opacifier ,chemistry.chemical_element ,Aerogel ,02 engineering and technology ,Carbon black ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,Thermal conduction ,Condensed Matter::Disordered Systems and Neural Networks ,01 natural sciences ,Condensed Matter::Soft Condensed Matter ,Thermal conductivity ,chemistry ,Thermal insulation ,0103 physical sciences ,Composite material ,0210 nano-technology ,business ,Carbon - Abstract
Opacifiers are usually doped in the silica aerogels to reduce the radiative heat transfer at high temperature. However, the doped opacifiers will enhance the heat conduction in the solid phase and increase the density of silica aerogels dramatically. For developing lightweight and efficient opacifiers, in this paper, different types of core/shell opacifiers are designed, and their extinction performance is investigated, theoretically. Then the optimal temperature-dependent particle size and doping amount of these opacifiers are obtained by maximizing the Rosseland mean extinction coefficient and minimizing the total thermal conductivity of silica aerogel composite. The results show that the hollow carbon black opacifiers might greatly reduce the densities of the opacifier-doped silica aerogels without deteriorating appreciably their insulating capability, and the carbon/SiC, carbon/TiO2 and carbon/Al2O3 core/shell opacifiers exhibit excellent extinction performance and would be strong candidates for high temperature due to their high extinction performance, low density and high-temperature stability. Finally, a core/shell opacifier-gradient-doped silica aerogel based on the optimal opacifier types and doping amount is designed, which significantly improves the insulating performance and reduces the density of silica aerogel composite. The results of this paper present important references for the process design and improvement of comprehensive performance of opacifier-doped silica aerogels.
- Published
- 2018
8. Modeling of the apparent solid thermal conductivity of aerogel
- Author
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Chuan-Yong Zhu and Zeng-Yao Li
- Subjects
Fluid Flow and Transfer Processes ,Materials science ,Laplace transform ,Physics::Instrumentation and Detectors ,020209 energy ,Mechanical Engineering ,Thermodynamics ,Aerogel ,02 engineering and technology ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,Boltzmann equation ,Thermal conductivity ,Thermal ,Heat transfer ,0202 electrical engineering, electronic engineering, information engineering ,Heat equation ,0210 nano-technology - Abstract
This paper provides an insight into the heat transfer in the solid backbone of aerogel and an effective approach to model the apparent solid thermal conductivity of aerogels. First, a model for the thermal conductivity of aerogel solid backbone is developed based on thermal constriction resistance between interconnected nano-particles by taking into account the size effect of a single particle, and validated by the numerical solutions of the gray Boltzmann transport equation (BTE). Then, combined with the analytical expression derived based on the Laplace heat conduction equation, the proposed model is used to predict the apparent solid thermal conductivity of aerogels, and the predictions are in good agreement with the available experimental data of different kinds of aerogels.
- Published
- 2018
9. Study on the consistency between field synergy principle and entransy dissipation extremum principle
- Author
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Zeng-Yao Li, Peng Wang, Wenjing Zhou, Zhi-Qiang Yu, and Wen-Quan Tao
- Subjects
Fluid Flow and Transfer Processes ,Computer simulation ,Field (physics) ,Turbulence ,020209 energy ,Mechanical Engineering ,Laminar flow ,02 engineering and technology ,Mechanics ,010502 geochemistry & geophysics ,Condensed Matter Physics ,01 natural sciences ,Classical mechanics ,Heat flux ,Flow (mathematics) ,Consistency (statistics) ,0202 electrical engineering, electronic engineering, information engineering ,Constant (mathematics) ,0105 earth and related environmental sciences ,Mathematics - Abstract
This paper is aiming at numerically demonstrating the interrelationship and consistency between field synergy principle (FSP) via the field synergy number (Fc) and the entransy dissipation extremum principle (EDEP). Numerical simulation is conducted by using the FLUENT software and the user defined function programs (UDF) for fin-and-tube surfaces (plain plate and slotted fins) and composite porous materials. The thermal boundary conditions include given heat flux and given surface temperature. The flow includes laminar and turbulent. The air properties may be constant or vary with temperature. Based on the numerical data the analyzed results from the FSP via Fc are totally consistent with the results analyzed by the EDEP for all the cases studied. Such consistency between the FSP and the entransy theory can be regarded as a kind of demonstration of the reliability and correctness of both the FSP and the entransy theory.
- Published
- 2018
10. High-throughput cell focusing and separation via acoustofluidic tweezers
- Author
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John D. Mai, Kejie Chen, Zeyu Wang, Tony Jun Huang, Shujie Yang, Zeng-Yao Li, Mengxi Wu, and Po-Hsun Huang
- Subjects
Erythrocytes ,Materials science ,Microfluidics ,Separation (aeronautics) ,Biomedical Engineering ,Bioengineering ,Nanotechnology ,Cell Separation ,02 engineering and technology ,01 natural sciences ,Biochemistry ,Article ,Cell Line, Tumor ,Lab-On-A-Chip Devices ,Tweezers ,Leukocytes ,Humans ,Particle Size ,Throughput (business) ,010401 analytical chemistry ,Acoustics ,General Chemistry ,021001 nanoscience & nanotechnology ,Biocompatible material ,0104 chemical sciences ,0210 nano-technology ,Sorted Cells - Abstract
Separation of particles and cells is an important function in many biological and biomedical protocols. Although a variety of microfluidic-based techniques have been developed so far, there is clearly still a demand for a precise, fast, and biocompatible method for separation of microparticles and cells. By combining acoustics and hydrodynamics, we have developed a method which we integrated into three-dimensional acoustofluidic tweezers (3D-AFT) to rapidly and efficiently separate microparticles and cells into multiple high-purity fractions. Compared with other acoustophoresis methods, this 3D-AFT method significantly increases the throughput by an order of magnitude, is label-free and gently handles the sorted cells. We demonstrate not only the separation of 10, 12, and 15 micron particles at a throughput up to 500 μl min-1 using this 3D-AFT method, but also the separation of erythrocytes, leukocytes, and cancer cells. This 3D-AFT method is able to meet various separation demands thus offering a viable alternative with potential for clinical applications.
- Published
- 2018
11. Pool boiling heat transfer of R134a outside reentrant cavity tubes at higher heat flux
- Author
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Ding-Cai Zhang, Zeng-Yao Li, Ya-Ling He, Chuang-Yao Zhao, Wen-Tao Ji, Wen-Quan Tao, and Peng-Fei Zhao
- Subjects
Materials science ,Critical heat flux ,020209 energy ,Plate heat exchanger ,Energy Engineering and Power Technology ,02 engineering and technology ,Heat transfer coefficient ,021001 nanoscience & nanotechnology ,Industrial and Manufacturing Engineering ,Heat flux ,Heat transfer ,0202 electrical engineering, electronic engineering, information engineering ,Micro heat exchanger ,Composite material ,0210 nano-technology ,Nucleate boiling ,Shell and tube heat exchanger - Abstract
An experimental investigation on the pool boiling heat transfer of refrigerant R134a outside three enhanced tubes is conducted. The heat flux is from 10,000 to 370,000 W / m 2 . The heat transfer is substantially enhanced at the heat flux less than 200 kW/m2. An increase of heat transfer coefficient up to 330% above the plain tube is observed. However, at the heat flux higher than 200 kW / m 2 , it is found that the heat transfer coefficient of enhanced tubes is even lower than the plain tube. The same features are also observed for other enhanced tubes in the literature.
- Published
- 2017
12. A general effective thermal conductivity model for composites reinforced by non-contact spherical particles
- Author
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Zeng-Yao Li, Bin Ding, Liang Gong, Chuan-Yong Zhu, Wen-Xin Yang, and Hai-Bo Xu
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Materials science ,020209 energy ,General Engineering ,02 engineering and technology ,Thermal management of electronic devices and systems ,Condensed Matter Physics ,01 natural sciences ,Energy storage ,010305 fluids & plasmas ,Matrix (geology) ,Thermal conductivity ,0103 physical sciences ,Volume fraction ,0202 electrical engineering, electronic engineering, information engineering ,Particle ,Thermal protection ,Composite material - Abstract
Particle reinforced materials are widely used in many areas, including energy storage, energy saving, thermal protection, and thermal management. These applications tend to require an accurate foreknowledge of the effective thermal conductivity of these materials. Although there exist many different effective thermal conductivity models for this kind of materials, a general and accurate model for the composites reinforced by different types of spherical particles, including mono-particles, hybrid particles, and core-shell particles, is still lacking. This paper firstly collected some commonly used effective thermal conductivity models and tested their scope of use by numerical results. Then, a general and easy-to-use effective thermal conductivity model was provided by extending the model of Meredith and Tobias. This extended Meredith and Tobias's model was proven to be able to accurately predict the effective thermal conductivity of multi-phase composites reinforced by different types of spherical particles with large ranges of particle volume fraction and thermal conductivity ratio of particles to the matrix.
- Published
- 2021
13. The effective thermal conductivity of coated/uncoated fiber-reinforced composites with different fiber arrangements
- Author
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Hai-Bo Xu, Ze-Kai Gu, Zeng-Yao Li, Liang Gong, Chuan-Yong Zhu, and Bin Ding
- Subjects
Materials science ,020209 energy ,Mechanical Engineering ,02 engineering and technology ,Building and Construction ,Fiber-reinforced composite ,engineering.material ,Thermal energy storage ,Pollution ,Industrial and Manufacturing Engineering ,General Energy ,Thermal conductivity ,020401 chemical engineering ,Coating ,Volume fraction ,Heat transfer ,Thermal ,0202 electrical engineering, electronic engineering, information engineering ,engineering ,Fiber ,0204 chemical engineering ,Electrical and Electronic Engineering ,Composite material ,Civil and Structural Engineering - Abstract
Fiber-reinforced composites are attractive for many applications in energy fields, such as thermal energy storage and building energy-saving. In these applications, their effective thermal conductivity is extremely important; however, research addressing the effect of various parameters on effective thermal conductivity is scarce. In this paper, the influences of different parameters, including volume fraction, aspect ratio, and orientation of fibers, and the thickness of coating layers on the effective thermal conductivity of fiber-reinforced composites, are numerically investigated by the Lattice Boltzmann method. Based on numerous numerical results, a correlation of the effective thermal conductivity is proposed for the composites with fibers randomly distributed in space. It is found that the thermal conductivity of fiber and coating layers are the two most dominant factors which influence the effective thermal conductivity of fiber-reinforced composites. The thickness of the coating layer affects the effective thermal conductivity of composites with fibers randomly distributed in space remarkably, while its effect on the effective thermal conductivity of composites with fibers arranged perpendicular to the heat transfer is negligible. The results of this work could provide important references for the process design and improvement of thermal performance of fiber-reinforced composites.
- Published
- 2021
14. A theoretical and numerical study on the gas-contributed thermal conductivity in aerogel
- Author
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Xinpeng Zhao, Zeng-Yao Li, and Chuan-Yong Zhu
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Fluid Flow and Transfer Processes ,Coupling ,Materials science ,020209 energy ,Mechanical Engineering ,Thermodynamics ,Aerogel ,02 engineering and technology ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,Thermal conduction ,Thermal conductivity ,0202 electrical engineering, electronic engineering, information engineering ,Kinetic theory of gases ,Direct simulation Monte Carlo ,0210 nano-technology - Abstract
In this paper, a modified model for predicting the gaseous thermal conductivity in aerogel pores is proposed based on the kinetic theory of gases and the data from Direct Simulation Monte Carlo (DSMC) method. With the proposed modified model and the classical Effective Medium Theory (EMT) model, a gas-contributed thermal conductivity model which includes the equivalent gaseous thermal conductivity and the solid-gas coupling thermal conductivity is derived. The present gas-contributed model is validated by available experiment results for different types of aerogels. Comparisons between the present model and existing models show that the present gas-contributed model has a higher accuracy without complex calculations and assumptions.
- Published
- 2017
15. Numerical investigations on fully-developed mixed turbulent convection in dimpled parabolic trough receiver tubes
- Author
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Zhen Huang, Wen-Quan Tao, Guang-Lei Yu, and Zeng-Yao Li
- Subjects
Materials science ,Convective heat transfer ,Turbulence ,020209 energy ,Grashof number ,Energy Engineering and Power Technology ,Reynolds number ,Thermodynamics ,02 engineering and technology ,Mechanics ,Heat transfer coefficient ,021001 nanoscience & nanotechnology ,Nusselt number ,Industrial and Manufacturing Engineering ,symbols.namesake ,Heat flux ,Heat transfer ,0202 electrical engineering, electronic engineering, information engineering ,symbols ,0210 nano-technology - Abstract
The fully-developed mixed turbulent convective heat transfer characteristics in dimpled tubes of parabolic trough receiver are numerically studied at a certain Reynolds number of 2 × 104 and different Grashof numbers ranged from 0 to 3.2 × 1010 to produce substantial surface heat transfer augmentations with relatively small pressure drop penalties. The Boussinesq approximation is applied, in which variations in fluid properties other than density are ignored. The Realizable k-e two-equation turbulence model with enhancement wall treatment is adopted. The influences of outer wall heat flux distributions and dimple depth on flow resistance and heat transfer rate are illustrated and analyzed. The results indicate that the average friction factor and Nusselt number in dimpled receiver tubes under non-uniform heat flux (NUHF) are larger than those under uniform heat flux (UHF). In most cases, the comprehensive performance of dimpled receiver tube under NUHF is also better than that under UHF. The deep dimples (d/Di = 0.875) are far superior to the shallow dimples (d/Di = 0.125) at a same Grashof number.
- Published
- 2017
16. Multi-scale numerical analysis of flow and heat transfer for a parabolic trough collector
- Author
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Xinpeng Zhao, Zeng-Yao Li, Wen-Quan Tao, and Zhen Tang
- Subjects
Fluid Flow and Transfer Processes ,Materials science ,020209 energy ,Mechanical Engineering ,Flow (psychology) ,Thermodynamics ,02 engineering and technology ,Mechanics ,Condensed Matter Physics ,Heat flux ,Heat transfer ,0202 electrical engineering, electronic engineering, information engineering ,Parabolic trough ,Emissivity ,Boundary value problem ,Direct simulation Monte Carlo ,Envelope (mathematics) - Abstract
This paper numerically investigated the coupled flow and heat transfer of a parabolic trough collector (PTC), with the non-uniform heat flux boundary condition on the absorber wall and the rarefied gas effects in the annular vacuum gap being taken into consideration. A fully coupled cross-sectional heat transfer model is established with Direct Simulation Monte Carlo (DSMC) method for the rarefied gas flow and heat transfer in the vacuum annual gap. The PTC tube efficiency can be obtained from the above simulation for a given HTF temperature. Such simulation is conducted for several specified HTF temperature and different efficiency data are obtained. These data are fitted by an equation. This equation is then used to advance the HTF temperature in the axial direction. In such a way a simplified 3D model for the design of a PTC receiver is obtained. Cross-sectional simulation results show that when the gas pressure is less than 0.1 Pa further decrease in pressure makes no further contribution to reduce the heat loss. The effects of periphery non-uniform distribution of heat flux, coating material emissivity, envelope diameter and HTF inlet velocity on the PTC efficiency are discussed. An operation variant is proposed by using the 3D model by which the total PTC tube length can be reduced for a given thermal load.
- Published
- 2017
17. Propulsion of copper microswimmers in folded fluid channels by bipolar electrochemistry
- Author
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Mei-Hong Guo, Jin-Zhi Jiang, Jian-Jun Sun, Fen-Zeng Yao, and Ju Li
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Work (thermodynamics) ,Chemistry ,Linear channel ,General Chemical Engineering ,Bubble ,chemistry.chemical_element ,Nanotechnology ,02 engineering and technology ,General Chemistry ,Mechanics ,Propulsion ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,Copper ,0104 chemical sciences ,Electrode ,Bipolar electrochemistry ,Hydrogen bubble ,0210 nano-technology - Abstract
We report for the first time that conducting objects could be propelled in folded liquid filled channels by bipolar electrochemistry. This approach was based on controlling the formation of hydrogen bubbles at one extremity of a bipolar electrode. In this work, copper wires used as microswimmers could move in folded channels with angles from 30° to 180° by bubble propulsion and the velocity fluctuated over time. A proportional relation between polarization voltage and average velocity in linear channel was verified. The motion of microswimmers could be controlled within these types of channels in space and time, which might broaden the applications of micromachines in bipolar electrochemistry.
- Published
- 2017
18. Numerical study on combined natural and forced convection in the fully-developed turbulent region for a horizontal circular tube heated by non-uniform heat flux
- Author
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Zhen Huang, Wen-Quan Tao, and Zeng-Yao Li
- Subjects
Materials science ,Natural convection ,Convective heat transfer ,Meteorology ,Critical heat flux ,020209 energy ,Mechanical Engineering ,02 engineering and technology ,Building and Construction ,Mechanics ,Heat transfer coefficient ,Management, Monitoring, Policy and Law ,Forced convection ,Physics::Fluid Dynamics ,General Energy ,Heat flux ,Combined forced and natural convection ,0202 electrical engineering, electronic engineering, information engineering ,Nucleate boiling - Abstract
The present work focuses on the fully developed mixed turbulent flow and heat transfer in receiver tube heated by non-uniform heat flux, especially the effect of local buoyancy force induced by the non-uniform heat flux at Reynolds number of 2 × 104–105, Prandtl number of 1.5 and Grashof number of 0–1012. The friction factor and Nusselt number between forced convection and mixed convection under uniform heat flux and non-uniform heat flux are analyzed quantitatively. The effect of solar elevation angle on the fluid flow and heat transfer is also investigated. It is concluded that the mixed fluid flow and heat transfer under non-uniform heat flux is different from that under uniform heat flux. The solar elevation angle has strong influence on the mixed fluid flow and heat transfer characteristics. A criterion for the buoyancy free is proposed. It is not feasible to perform the heat transfer design and prediction for parabolic trough solar collector based on the experimental correlations for forced convection or conventional mixed convention.
- Published
- 2017
19. Numerical analysis and experimental validation of heat transfer characteristic for flat-plate solar air collector
- Author
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Zeng-Yao Li, Bau-Shei Pei, Tsung-Jie Huang, Duen-Sheng Lee, Tzu-Chen Hung, and Chih-Hung Lin
- Subjects
Solar chimney ,business.industry ,020209 energy ,Nanofluids in solar collectors ,Energy Engineering and Power Technology ,02 engineering and technology ,Mechanics ,Industrial and Manufacturing Engineering ,Thermal radiation ,Heat transfer ,0202 electrical engineering, electronic engineering, information engineering ,Emissivity ,Mass flow rate ,Passive solar building design ,business ,Simulation ,Thermal energy ,Mathematics - Abstract
This study combines both concepts of solar ventilation technology and solar air collector. This is a quite innovative and potential facility to effectively use thermal energy and reduce the accumulation of heat in the indoor space simultaneously. The purpose of this study is to create a prototype and implement the experiments. Computational fluid dynamics (CFD) approach is employed to validate the characteristics of the flow and heat transfer. For the accuracy of numerical predictions, the method of Solar Ray Tracing was used for thermal radiation flux as boundary condition on the wall. The local heat transfer correlation was investigated to predict surrounding wind speed upon device cover. Three sorts of glasses and several aspect ratios of flow channels have been compared to conclude the optimal configuration. In addition, four important factors, such as the stagnant layer thickness, emissivity on the illustrated surface, mass flow rate and the height of the device, are also considered and discussed in detail. The result showed that the optimal design is dominated by the combination of an aspect ratio of 50 mm:10 mm, and appropriate mass flow rate to the height of the device. The present work on thermal energy collection can assist us in designing a powerful solar air collector in some potential applications.
- Published
- 2017
20. Fabrication and characterization of Au–Fe/Ni/(Mo/Co) alloy microsphere motors (AMSM) based on physical vapor deposition
- Author
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Yang Sen, Jin-Zhi Jiang, Ju Li, Fen-Zeng Yao, Jian-Jun Sun, and Qing Xiao
- Subjects
Permalloy ,Fabrication ,Chemistry ,General Chemical Engineering ,Alloy ,Metallurgy ,Nanowire ,chemistry.chemical_element ,02 engineering and technology ,engineering.material ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,0104 chemical sciences ,Analytical Chemistry ,Nickel ,Chemical engineering ,Physical vapor deposition ,Specific surface area ,Electrochemistry ,engineering ,0210 nano-technology ,Electroplating - Abstract
Au–Fe/Ni/(Mo/Co) alloy microsphere motors (AMSM), having an average diameter of 7 ~ 9 μm, were fabricated though a rapid and effortless method than the template direct electroplating (TDEP), which only requires physical vapor deposition (PVD) of inert metal coat on commercially available microspheres; thus, several kinds of AMSM with different alloy composition can be manufactured readily. Via co-catalytic decomposing reaction in the mixed fuel of hydrogen peroxide and hydrazine, the ejection of oxygen bubbles generated from the Fe/Ni/(Mo/Co) alloy hemisphere provides a powerful directional propulsion. The AMSM's moving ability closely depends upon the content of mixed fuel and the composition of alloy, especially the content of nickel. The AMSM can move as fast as 548.63 μm/s (ca. 64 body-lengths/s). Because of the permalloy composition, the AMSM also can be guided by the magnetic force besides controlled with the propelling force generated by the bubble thrust. Compared with the nanowire motor, the AMSM could facilitate different biomedical applications, such as targeted drug delivery in future research, because of its bigger specific surface area.
- Published
- 2016
21. Thermal hydraulic characteristics of intermediate heat exchanger with coaxial bending tubes in a pool-type sodium-cooled fast reactor
- Author
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Guang-Lei Yu and Zeng-Yao Li
- Subjects
Nuclear and High Energy Physics ,Work (thermodynamics) ,Materials science ,020209 energy ,Mechanical Engineering ,02 engineering and technology ,Bending ,Mechanics ,Concentric ,01 natural sciences ,010305 fluids & plasmas ,Thermal hydraulics ,Sodium-cooled fast reactor ,Nuclear Energy and Engineering ,0103 physical sciences ,Heat transfer ,0202 electrical engineering, electronic engineering, information engineering ,General Materials Science ,Tube (fluid conveyance) ,Coaxial ,Safety, Risk, Reliability and Quality ,Waste Management and Disposal - Abstract
The intermediate heat exchanger (IHX), which consists of thousands of tubes assembled along concentric circles, has a complex geometry that makes it extremely difficult to analyze through the 3-D CFD approach, especially when there exists coaxial expansion bends. The motivation of this work is to study its thermal hydraulic characteristics and figure out the influence of the coaxial bends on its performance. In addition, both of the 3-D detail simulation method and the distributed parameter method are employed in this research. And the respective results by these two methods show that the shell-side main flow direction is generally consistent with the tube direction and the rear straight tube section is the main working section with the heat transfer rate of nearly 45% of the total heat transfer rate, and that the bending section plays an important role in controlling the non-uniformity of temperature field.
- Published
- 2021
22. Modeling of the Conductive Heat Transfer between Two Touching Nanoparticles in Nanoparticle-Based Materials
- Author
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Zeng-Yao Li and Chuan-Yong Zhu
- Subjects
Fluid Flow and Transfer Processes ,Materials science ,business.industry ,020209 energy ,Mechanical Engineering ,Nanoparticle ,02 engineering and technology ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,Thermal conduction ,Boltzmann equation ,Thermal conductivity ,Thermal insulation ,Heat transfer ,Thermal ,0202 electrical engineering, electronic engineering, information engineering ,Particle size ,Composite material ,0210 nano-technology ,business - Abstract
Nanoparticle-based materials (NBMs), whose thermal insulating performance is dominated by the heat transfer between two neighboring nanoparticles, have attracted tremendous attention in recent decades due to their potential applications in thermal insulation. This work provides an insight into the conductive heat transfer between two touching solid or hollow nanospheres by solving the gray phonon Boltzmann transport equation (BTE). The influence of some factors, including particle size, contact ratio, and shell thickness on the temperature distribution and effective thermal conductivity of two touching particles, is examined. Based on the thermal constriction resistance theory and numerical results, a prediction model for the effective thermal conductivity of two touching solid nanospheres is then proposed and proved to have high accuracy with a relative error less than 3.0%. Finally, a brand new effective thermal conductivity model for two touching hollow nanospheres with the same form as that of two touching solid spheres and an acceptable prediction error of 6.5% is also proposed.
- Published
- 2021
23. Design calculation and thermal-hydraulic analysis of 290 MW intermediate heat exchanger for pool-type sodium-cooled fast reactor
- Author
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Zeng-Yao Li and Guang-Lei Yu
- Subjects
Work (thermodynamics) ,Materials science ,020209 energy ,Flow (psychology) ,Energy Engineering and Power Technology ,02 engineering and technology ,Mechanics ,Industrial and Manufacturing Engineering ,Thermal hydraulics ,Sodium-cooled fast reactor ,020401 chemical engineering ,Heat exchanger ,Thermal ,0202 electrical engineering, electronic engineering, information engineering ,Tube (fluid conveyance) ,0204 chemical engineering ,Porous medium - Abstract
The intermediate heat exchanger (IHX) is a type of shell-and-tube heat exchanger. It is assembled with thousands of straight or expansion bend tubes in concentric circles and extremely huge and complex in geometry which leads to the non-uniform flow in the shell-side. The motivation of this work is to design a 6 m long, 290 MW IHX and clarify the influence of the tube specification on its performance. Traditional thermal design method is employed here for the design process, while 2-D porous medium model with anisotropic properties is adopted for simulation to support the design process adjusting the tube specification. The results show that the tube specification mainly affects the flow uniformity in the inlet region but has little effects on outlet region flow distribution. Comparing the IHX thermal-hydraulic performance under different tube specifications, it is found that the specification with 19 mm outer diameter, 25 mm radial pitch and 0.8 mm wall thickness is the best choice.
- Published
- 2020
24. Effective thermal conductivity modeling of hollow nanosphere packing structures
- Author
-
Xue-Hong Wu, Zeng-Yao Li, Junhua Jiao, Mengyao Hu, and He Liu
- Subjects
Fluid Flow and Transfer Processes ,Fabrication ,Nanostructure ,Materials science ,Nanoporous ,business.industry ,Mechanical Engineering ,Physics::Optics ,02 engineering and technology ,Cubic crystal system ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,01 natural sciences ,Spherical shell ,010305 fluids & plasmas ,Thermal conductivity ,Thermal insulation ,0103 physical sciences ,Heat transfer ,Composite material ,0210 nano-technology ,business - Abstract
Nanoporous insulating materials are of importance for applications such as energy-efficient buildings, energy storage and savings, and cryogenic engineering. Recent progress on manufacturing technology has enabled the fabrication of ordered nanostructures to be practical, providing a possibility to fabricate high-performance insulation materials. In this work, three kinds of nanoporous insulating materials with regular geometric structures and controllable thermal conductivities, including a simple cubic packing, a face-centered cubic packing, and a cubic array of intersecting spheres packing of uniform-sized hollow nanospheres, were designed. The effective thermal conductivity models of each packing structure were developed according to the assumption of one-dimensional heat transfer, in which the following factors including material types, size of the hollow nanosphere packing structure (e.g., sphere size, spherical shell thickness, contact ratio), gas pressure, the rarefaction effect of gas and the mean free path of phonons were considered. The developed models of the hollow nanosphere packing structures were validated by the experimental results from the literature. It is found that the effective thermal conductivity can be lowered to ~ 0.01 W/(m⋅K) by tuning the packing style and size of hollow nanosphere packing structures in the room environment, showing excellent thermal insulation performance. The work provides a new strategy for the design of super-insulation materials.
- Published
- 2020
25. Local relation network with multilevel attention for visual question answering
- Author
-
Lejun Yu, Zeng Yao, Yinghui Zhang, and Bo Sun
- Subjects
Computer science ,business.industry ,020207 software engineering ,02 engineering and technology ,Machine learning ,computer.software_genre ,Rendering (computer graphics) ,Signal Processing ,0202 electrical engineering, electronic engineering, information engineering ,Media Technology ,Question answering ,Visual attention ,020201 artificial intelligence & image processing ,Computer Vision and Pattern Recognition ,Artificial intelligence ,Electrical and Electronic Engineering ,Semantic information ,business ,computer - Abstract
With the tremendous success of the visual question answering (VQA) tasks, visual attention mechanisms have become an indispensable part of VQA models. However, these attention-based methods do not consider any relationship among regions, which is crucial for the thorough understanding of the image by the model. We propose local relation networks for generating context-aware image features for each image region, which contain information on the relationship among the other image regions. Furthermore, we propose a multilevel attention mechanism to combine semantic information from the LRNs and the original image regions, rendering the decision of the model more reasonable. With these two measures, we improve the region representation and achieve better attentive effect and VQA performance. We conduct numerous experiments on the COCO-QA dataset and the largest VQA v2.0 benchmark dataset. Our model achieves competitive results, proving the effectiveness of our proposed LRNs and multilevel attention mechanism through visual demonstrations.
- Published
- 2020
26. Geometric optimization of aerogel composites for high temperature thermal insulation applications
- Author
-
Junhua Jiao, Zeng-Yao Li, Mengyao Hu, and He Liu
- Subjects
010302 applied physics ,Work (thermodynamics) ,Materials science ,business.industry ,Infrared ,Aerogel ,02 engineering and technology ,Radiation ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,Thermal conduction ,01 natural sciences ,Electronic, Optical and Magnetic Materials ,Thermal conductivity ,Thermal insulation ,Thermal radiation ,0103 physical sciences ,Materials Chemistry ,Ceramics and Composites ,Composite material ,0210 nano-technology ,business - Abstract
Silica aerogel has attracted great interest in thermal insulation applications due to its ultralow thermal conductivity. However, silica aerogel is transparent to the infrared radiation in the range of 3-8 µm, making them be not suitable for high temperature thermal insulation applications. Here, we developed an optimization method considering both thermal radiation and heat conduction to design the geometric structures of aerogel composites with minimized thermal conductivity. The results show that when the ambient temperature is lower than ~ 600 K, the additives with low thermal conductivity are preferred. When the ambient temperature is higher than ~ 600 K, the additives with high extinction coefficients are needed. The additives with a broad size distribution could enable the aerogel composites to have an optimal thermal insulation performance in the environment with a changing temperature. The work provides a guideline for the geometric design of aerogel composites for high temperature thermal insulation applications.
- Published
- 2020
27. Three-dimensional numerical study on fully-developed mixed laminar convection in parabolic trough solar receiver tube
- Author
-
Zhen Huang, Zeng-Yao Li, and Wen-Quan Tao
- Subjects
Natural convection ,Materials science ,Convective heat transfer ,Meteorology ,020209 energy ,Mechanical Engineering ,Grashof number ,02 engineering and technology ,Building and Construction ,Mechanics ,Heat transfer coefficient ,Rayleigh number ,Pollution ,Industrial and Manufacturing Engineering ,Fin (extended surface) ,Forced convection ,Physics::Fluid Dynamics ,General Energy ,020401 chemical engineering ,Combined forced and natural convection ,0202 electrical engineering, electronic engineering, information engineering ,Astrophysics::Solar and Stellar Astrophysics ,0204 chemical engineering ,Electrical and Electronic Engineering ,Civil and Structural Engineering - Abstract
In this paper, a numerical investigation is presented, aiming at the effect of the buoyancy force induced by the non-uniform heat flux on the laminar flow and heat transfer characteristics in the solar receiver tube of parabolic trough collector. The flow and heat transfer performances are analyzed for forced and mixed laminar convection in receiver tube heated by uniform and non-uniform heat fluxes with different Grashof numbers, Reynolds numbers and solar elevation angles. The results show that the natural convection can increase heat transfer rate of laminar forced convection by more than 10% when the Grashof number is greater than a threshold value. The mixed fluid flow and heat transfer characteristics vary with solar elevation angle. Heat transfer deterioration occurs when the Richardson number is greater than 12.8.
- Published
- 2016
28. Investigation of the effect of the gas permeation induced by pressure gradient on transient heat transfer in silica aerogel
- Author
-
Wen-Quan Tao, Zeng-Yao Li, Xinpeng Zhao, and He Liu
- Subjects
Fluid Flow and Transfer Processes ,Materials science ,Nanoporous ,Mechanical Engineering ,Aerogel ,02 engineering and technology ,Permeation ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,Thermal conduction ,01 natural sciences ,010305 fluids & plasmas ,Permeability (earth sciences) ,Thermal radiation ,0103 physical sciences ,Heat transfer ,Composite material ,0210 nano-technology ,Pressure gradient - Abstract
A fractal permeability model considering both the tortuous gas transport path and the gas slippage effect for nanoporous silica aerogel is developed. The fractal model is verified by experimental results and existing models. Then, a one-dimensional macro model, which combines the influence of heat conduction, thermal radiation and gas permeation, is developed to investigate the influence of gas permeation induced by pressure gradient on transient heat transfer within bulk silica aerogel with the acquired gas permeability by the present model. It is found that gas transport within silica aerogel exerts important effect on the temperature response performance of bulk silica aerogel, which is mainly reflected on changing the pressure distribution and inducing energy migration within the bulk material. For silica aerogel, energy migration has remarkable effect on unsteady heat transfer process when the gas permeability reaches the order of 10−14 m2. The dynamic temperature response of the cold wall will be strengthened when the directions of gas flow and heat transfer are the same, and vice versa.
- Published
- 2016
29. Experiment and optimization study on the radial graded porous volumetric solar receiver matching non-uniform solar flux distribution
- Author
-
Dong Li, Tian Xia, Shen Du, Xiang-Qian Xie, Zeng-Yao Li, and Ya-Ling He
- Subjects
Thermal efficiency ,Materials science ,Convective heat transfer ,020209 energy ,Mechanical Engineering ,Mass flow ,02 engineering and technology ,Building and Construction ,Management, Monitoring, Policy and Law ,Physics::Geophysics ,General Energy ,020401 chemical engineering ,Heat transfer ,0202 electrical engineering, electronic engineering, information engineering ,Fluid dynamics ,0204 chemical engineering ,Composite material ,Porosity ,Porous medium ,Inconel - Abstract
Radial graded porous volumetric solar receiver is designed to match the non-uniform solar flux distribution. Based on the computed tomography and image-processing techniques, uniform and radial graded porous volumetric solar receivers are reconstructed. The 3D printing technique and suitable post processing are implemented to fabricate complex porous samples using super-alloy Inconel 718 as material. Both experimental and numerical studies are conducted to investigate the fluid flow and heat transfer processes in porous volumetric solar receivers. The results present that the 3D printed porous samples are suitable for solar thermal energy absorption and high temperature utilization. As for uniform porous receivers, porous media with small pore diameter has larger thermal efficiency because of enhanced convective heat transfer. Compared with the uniform porous receiver with highest thermal efficiency, the radial graded porous volumetric solar receiver with large pore diameter inside could further relatively increase the thermal efficiency by 4.1% while relatively decreases the flow resistance by 8.6%. The reasonable distribution of pore diameter of porous media could regulate the mass flow distribution and direct more air to the high heat flux region. Moreover, local overheating phenomenon is observed in the uniform porous receiver using air as heat transfer fluid. By applying the coupled optimization method, an optimum pore diameter distribution is determined for the radial graded porous volumetric solar receiver.
- Published
- 2020
30. Experimental and numerical study on the reflectance losses of the porous volumetric solar receiver
- Author
-
Ming-Jia Li, Zeng-Yao Li, Shen Du, and Yan He
- Subjects
Materials science ,Computer simulation ,Renewable Energy, Sustainability and the Environment ,business.industry ,02 engineering and technology ,Radiation ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,Reflectivity ,0104 chemical sciences ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,chemistry.chemical_compound ,Optics ,chemistry ,Silicon carbide ,0210 nano-technology ,business ,Porosity ,Porous medium ,Recoating ,Distributed ray tracing - Abstract
The reflectance losses are the predominate energy losses in solar radiation transfer process for the porous volumetric solar receiver. However, few studies pay attention to the influence of geometrical parameters of porous media on the reflectance losses, and the data of reflectance losses of porous volumetric solar receiver in solar spectrum is not complete. In this paper, both experimental and numerical simulation methods are applied to comprehensively investigate the reflectance losses of the porous volumetric solar receiver. A series of silicon carbide reticulated porous ceramics (SiC RPCs) is fabricated by replica method and recoating technique. The reflectance losses are measured based on UV-VIS-NIR spectrophotometer. Meanwhile, porous models with different geometrical parameters are artificially reconstructed. Monte Carlo Ray Tracing method is used to calculate the total reflectance. The results present that the SiC RPCs exhibit small reflectance losses in the solar spectrum with a peak at about 420 nm. The geometrical parameters, such as porosity and pore diameter do not change the spectral behavior but only influence the magnitude of the reflectance. Larger porosity and larger pore diameter are beneficial for reducing the reflectance losses. The correlation of the reflectance losses as functions of pore density and porosity has been developed. Furthermore, the influence of the incident angle of radiation on reflectance losses is studied. Relatively large increase is observed as the incident angle is larger than 30°. This phenomenon becomes more obvious for the porous media with larger porosity or larger pore diameter.
- Published
- 2020
31. Correction: High-throughput cell focusing and separation via acoustofluidic tweezers
- Author
-
Po-Hsun Huang, Zeng-Yao Li, Kejie Chen, Shujie Yang, Tony Jun Huang, John D. Mai, Mengxi Wu, and Zeyu Wang
- Subjects
Physics ,business.industry ,010401 analytical chemistry ,Biomedical Engineering ,Bioengineering ,02 engineering and technology ,General Chemistry ,021001 nanoscience & nanotechnology ,Chip ,01 natural sciences ,Biochemistry ,0104 chemical sciences ,Tweezers ,Optoelectronics ,0210 nano-technology ,business ,Throughput (business) - Abstract
Correction for ‘High-throughput cell focusing and separation via acoustofluidic tweezers’ by Mengxi Wu et al., Lab Chip, 2018, 18, 3003–3010, DOI: 10.1039/C8LC00434J.
- Published
- 2020
32. A state-of-the-art overview on the developing trend of heat transfer enhancement by single-phase flow at micro scale
- Author
-
Xiao-Bin Li, Hong-Na Zhang, Zeng-Yao Li, Si-Ning Li, Jianping Cheng, Weihua Cai, and Feng-Chen Li
- Subjects
Fluid Flow and Transfer Processes ,Computer science ,business.industry ,020209 energy ,Mechanical Engineering ,Heat transfer enhancement ,Complex system ,02 engineering and technology ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,Nusselt number ,Software portability ,Robustness (computer science) ,Heat transfer ,0202 electrical engineering, electronic engineering, information engineering ,Fluid dynamics ,Electronics ,0210 nano-technology ,Process engineering ,business - Abstract
Continuous improvement of energy-efficient systems has led to various technical features such as miniaturization, integration, and portability. This development became the leading trend of the contemporary industry, with the evolvement of various new and miniaturized instruments such as micro-electro-mechanical systems and micro-satellite. Highly miniaturized and integrated electronic devices often release a large amount of heat within their micro scale inter-components areas, which under certain circumstances, may lead to the micro-device’s functional failure. This calls for techno-scientific efforts for efficient heat removal from the mentioned devices. Numerous innovatively scenarios have been so far explored to satisfy the greatly increasing heat removal demand. This paper explores two major types of heat removal technics for micro-scale single-phase flow, namely passive and active type. The passive type includes the geometry modification and working media change, where corresponding effects on heat transfer performance and fluid flow are addressed by Nusselt number and friction factor, respectively. Their most important advantages are stability and robustness in operation or integration with complex systems. For the active type, only the pulsating inlet flow and acoustic wave are considered in the present paper, which are less reviewed recently. Generally, the heat transfer enhancement is attributed to the effect of disturbed thermal boundary layers on mixing of fluids. The present review article is organized in a way that provides a historical perspective of the recent developments in this area, and advances comprehensive comments from overall situations; which may serve a substantial guidance for researchers in different background who intend to step into this area.
- Published
- 2019
33. Design and thermal insulation performance analysis of endothermic opacifiers doped silica aerogels
- Author
-
Zeng-Yao Li, Ning Pan, and Chuan-Yong Zhu
- Subjects
Materials science ,business.industry ,020209 energy ,General Engineering ,Opacifier ,Aerogel ,02 engineering and technology ,Condensed Matter Physics ,01 natural sciences ,Endothermic process ,Phase-change material ,010305 fluids & plasmas ,Thermal radiation ,Thermal insulation ,Volumetric heat capacity ,0103 physical sciences ,Heat transfer ,0202 electrical engineering, electronic engineering, information engineering ,Composite material ,business - Abstract
In order to reduce the thermal radiation and further deter the heat transfer in silica aerogel thermal insulation materials, the endothermic opacifier is designed with the shell of SiC and the core of phase change material (PCM) in this paper. Then the transient heat transfer characteristics of the endothermic opacifiers doped silica aerogel (EOSA) are numerically investigated and its short-term thermal insulation performance is estimated with a modified lattice Boltzmann method (LBM) model. The modified LBM scheme is established with a new source term to remedy the effect of the variation in the volumetric heat capacity of the specimen, and this scheme is fully validated based on the analytical results and available experimental data. The results demonstrate that adding the endothermic opacifier to silica aerogels results in a significant heat transfer delay and an improvement in short-term thermal insulation performance by suppressing radiation heat transfer and solid-liquid phase change heat absorption. With the same doping amount, the endothermic opacifiers doped silica aerogel exhibits more excellent short-term thermal insulation performance and a lower density than that of SiC opacifiers doped silica aerogels (SOSA). It indicates that the EOSA possesses great potential to be a candidate as the lightweight and efficient thermal insulation material at high temperature. Besides, exhaustively parametric studies based on the EOSA, including doping amount, latent heat of PCM, phase change temperature and endothermic opacifier particle size are conducted, and several design rules are established. This analysis could serve as a framework to develop and design silica aerogel composites with low-density and excellent short-term thermal insulation performance.
- Published
- 2019
34. Condensation of R134a and R22 in Shell and Tube Condensers Mounted With High-Density Low-Fin Tubes
- Author
-
Ya-Ling He, Jessica Lofton, Zeng-Yao Li, Ding-Cai Zhang, Chuang-Yao Zhao, Wen-Tao Ji, and Wen-Quan Tao
- Subjects
Fin ,Materials science ,020209 energy ,Mechanical Engineering ,Condensation ,Refrigeration ,02 engineering and technology ,Heat transfer coefficient ,Mechanics ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,Refrigerant ,Mechanics of Materials ,Heat transfer ,0202 electrical engineering, electronic engineering, information engineering ,General Materials Science ,Tube (fluid conveyance) ,0210 nano-technology ,Shell and tube heat exchanger - Abstract
In this work, the condensation of refrigerants on a single, high-density, low-fin tube and full-sized shell and tube condensers were investigated experimentally. The low-fin tube had an external fin density of 56 fins per inch (fpi) and fin height 1.023 mm. Another three-dimensional (3D) finned tube was also tested for comparison. The condensing heat transfer coefficient of the refrigerant R134a was first investigated outside a single horizontal tube at saturation temperature of 40 °C. The overall heat transfer coefficients of the two tubes were similar in magnitude. The condensing heat transfer coefficient of the low-fin tube was 16.3–25.2% higher than that of 3D enhanced tube. The experiments of the two condensers mounted with low-fin and 3D enhanced tubes were then conducted in centrifugal and screw chiller test rigs. It was found that chillers with the two different condensers generally had the same refrigeration capacity under the same experiment conditions. The refrigeration capacity of the screw chiller was smaller. It had fewer tube rows and elicited fewer inundation effects owing to the falling condensate. The heat transfer coefficients of the condensers with R134a in centrifugal chillers equipped with high-density low-finned tubes were higher than those in the screw chillers. The total number of tubes for low-fin tube condensers, in the two chillers, was reduced by approximately 15% compared with the use of domestic advanced condensers equipped with the 3D enhanced tubes.
- Published
- 2018
35. Nonlocal Effects and Slip Heat Flow in Nanolayers
- Author
-
Zeng-Yao Li, Chuan-Yong Zhu, and Wei You
- Subjects
Mathematical optimization ,Multidisciplinary ,Materials science ,Thin layers ,Characteristic length ,Mean free path ,lcsh:R ,lcsh:Medicine ,02 engineering and technology ,Mechanics ,Slip (materials science) ,021001 nanoscience & nanotechnology ,01 natural sciences ,Article ,Thermal conductivity ,Heat flux ,0103 physical sciences ,lcsh:Q ,Direct simulation Monte Carlo ,Boundary value problem ,lcsh:Science ,010306 general physics ,0210 nano-technology - Abstract
Guyer-Krumhansl (G-K) equation is a promising macroscopic model to explore heat transport in nanoscale. In the present work, a new nonlocal characteristic length is proposed by considering the effects of heat carriers-boundaries interactions to modify the nonlocal term in G-K equation, and a slip heat flux boundary condition is developed based on the local mean free path of heat carriers. Then an analytical solution for heat flux across 2-D nanolayers and an in-plane thermal conductivity model are obtained based on the modified G-K equation and the slip heat flux boundary. The predictions of the present work are in good agreement with our numerical results of direct simulation Monte Carlo (DSMC) for argon gas nanolayer and the available experimental data for silicon thin layers. The results of this work may provide theoretical support for actual applications of G-K equation in predicting the thermal transport properties of nanolayers.
- Published
- 2017
36. Theoretical and DSMC Studies on Heat Conduction of Gas Confined in a Cuboid Nanopore
- Author
-
Chuan-Yong Zhu, Zeng-Yao Li, and Wen-Quan Tao
- Subjects
Materials science ,Cuboid ,Condensed matter physics ,Mechanical Engineering ,Thermodynamics ,02 engineering and technology ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,Thermal conduction ,01 natural sciences ,010305 fluids & plasmas ,Nanopore ,Mechanics of Materials ,0103 physical sciences ,General Materials Science ,0210 nano-technology - Abstract
This paper presents a theoretical and numerical study on the heat conduction of gas confined in a cuboid nanopore, in which there exists a temperature difference between the top and bottom walls and the side walls are adiabatic. A modified gas mean free path in confined space is proposed by considering the impact of collisions between molecules and solid surfaces, with which an effective thermal conductivity model of gas in the transition regime is derived. A direct simulation Monte Carlo (DSMC) study on the heat conduction of argon and helium in a cuboid nanopore is carried out to validate the present model. The influences of the Knudsen number and the treatments of boundary conditions on the heat conduction and effective thermal conductivity of gas in nanopores are studied. The temperature jumps and the reduction of heat flux near side walls are analyzed.
- Published
- 2017
37. Particle-in-cell and Monte Carlo collision simulations of the cathode sheath in an atmospheric direct-current arc discharge
- Author
-
Heng Guo, Giovanni Lapenta, Wei Jiang, Wen Zhou, Zeng-Yao Li, and He-Ping Li
- Subjects
010302 applied physics ,Chemistry ,Monte Carlo method ,Thermionic emission ,02 engineering and technology ,Plasma ,Electron ,Hot cathode ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,01 natural sciences ,Ion ,law.invention ,Electric arc ,Physics::Plasma Physics ,law ,Physics::Space Physics ,0103 physical sciences ,Particle-in-cell ,Atomic physics ,0210 nano-technology - Abstract
A sheath is the transition region from plasma to a solid surface, which also plays a critical role in determining the behaviors of many lab and industrial plasmas. However, the cathode sheath properties in arc discharges are not well understood yet due to its multi-scale and kinetic features. In this letter, we have adopted an implicit particle-in-cell Monte Carlo collision (PIC-MCC) method to study the cathode sheath in an atmospheric arc discharge plasma. The cathode sheath thickness, number densities and averaged energies of electrons and ions, the electric field distribution, as well as the spatially averaged electron energy probability function (EEPF), are predicted self-consistently by using this newly developed kinetic model. It is also shown that the thermionic emission at the hot cathode surface is the dominant electron emission process to sustain the arc discharges, while the effects from secondary and field electron emissions are negligible. The present results verify the previous conjectures and experimental observations.
- Published
- 2016
38. Grand Canonical Monte Carlo Simulation of Nitrogen Adsorption in a Silica Aerogel Model
- Author
-
Zeng-Yao Li, Zheng-Ji Chen, Wen-Quan Tao, and Wen-Li Xie
- Subjects
Range (particle radiation) ,Materials science ,General Computer Science ,Applied Mathematics ,chemistry.chemical_element ,Thermodynamics ,Nanotechnology ,Aerogel ,02 engineering and technology ,010402 general chemistry ,021001 nanoscience & nanotechnology ,silica aerogel ,nitrogen adsorption ,DLCA ,GCMC simulation ,01 natural sciences ,Nitrogen ,0104 chemical sciences ,Theoretical Computer Science ,Adsorption ,chemistry ,Modeling and Simulation ,Specific surface area ,Cluster (physics) ,Diffusion (business) ,0210 nano-technology ,Porosity - Abstract
In this paper, the Diffusion Limited Cluster Aggregation (DLCA) method is employed to reconstruct the three-dimensional network of silica aerogel. Then, simulation of nitrogen adsorption at 77 K in silica aerogel is conducted by the Grand Canonical Monte Carlo (GCMC) method. To reduce the computational cost and guarantee accuracy, a continuous-discrete hybrid potential model, as well as an adsorbed layer thickness estimation method, is employed. Four different structures are generated to investigate impacts of specific surface area and porosity on adsorptive capacity. Good agreement with experimental results is found over a wide range of relative pressures, which proves the validity of the model. Specific surface area and porosity mainly affect nitrogen uptake under low pressure and high pressure, respectively.
- Published
- 2016
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