High temperature heat pipes are effective devices for heat transfer, which are characterized by remarkable advantages in conductivity, isothermality and passivity. It is of significance to apply heat pipes on new conc...
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ISBN:
(纸本)9780791855812
High temperature heat pipes are effective devices for heat transfer, which are characterized by remarkable advantages in conductivity, isothermality and passivity. It is of significance to apply heat pipes on new concept passive residual heat removal system (PRHRS) of molten salt reactor (MSR). In this paper, the transient performance of high temperature sodium heat pipe is simulated with numerical method in the case of MSR accident. The model of the heat pipe is composed of three conjugate heat transfers, i.e. the vapor space, wick structure and wall. Based on finite element method, the governing equations and boundary conditions are solved by using FORTRAN code to acquire the profiles of the temperature, velocity and pressure for the heat pipe transient operation. The results indicated that high temperature sodium heat pipe had a good operating characteristic and removed the residual heat of fuel salt rapidly under the accident of MSR.
In order to reduce the use of fossil fuels and meet the needs of different energy products, this paper proposes an integrated multi-generation system that can produce power, cooling, and freshwater. A mathematical mod...
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In order to reduce the use of fossil fuels and meet the needs of different energy products, this paper proposes an integrated multi-generation system that can produce power, cooling, and freshwater. A mathematical model is established to analyze the system performance from the perspectives of energy, exergy and economics. Different machine learning algorithms are used to develop prediction models of the system performance. By comparing the predictive performance of different machine learning models, the optimal model is obtained to replace the thermodynamic model of the proposed system to accelerate the optimization process. The results show that the backpropagation neural network (BPNN) model demonstrates the highest predictive accuracy and the lowest relative error fluctuation. When comparing the multi-objective optimization results of the BPNN model with those of the thermodynamic model, it can be observed that the results achieved through both models are very close. Furthermore, the optimization time using the BPNN model is significantly shorter than the thermodynamic model. Finally, under the conditions of solar radiation intensity of 950 W/m2, heliostat field area of 1000 m2, and heat source temperature of 838.15 K, the total product output, thermal efficiency, exergy efficiency, and levelized cost of energy at the final optimal point obtained through BPNN model-based optimization are 2.486 MW, 26.16 %, 23.64 %, and 0.105 $/kWh, respectively. The net power output, cooling capacity, and freshwater flow rate are 2.006 MW, 131.06 kW, and 8.27 m3/h, respectively.
CO2 gases stored underground may escape from the reservoir site to other places and even through the soil layer into atmosphere, thus identify the leakage source is therefore a crucial problem after leakage occurring....
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CO2 gases stored underground may escape from the reservoir site to other places and even through the soil layer into atmosphere, thus identify the leakage source is therefore a crucial problem after leakage occurring. The paper introduced a direct method to solve the inverse problem combined with the optimization method, which is Occam regularization method. This method was applied to estimate the source parameters. Firstly, the calculation process of Occam regularization method was introduced and then the feasibility of its application for source parameters identification was proved by simulation and experiment data. The results showed that, Occam regularization method is able to estimate source parameters successfully. (C) 2014 The Authors. Published by Elsevier Ltd.
Three-dimensional simulations of bubble formation in Newtonian and non-Newtonian fluids through a microchannel T-junction are conducted by the volume-of-fluid method. For Newtonian fluids, the critical capillary numbe...
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Three-dimensional simulations of bubble formation in Newtonian and non-Newtonian fluids through a microchannel T-junction are conducted by the volume-of-fluid method. For Newtonian fluids, the critical capillary number Ca for the transition of the bubble breakup mechanism is dependent on the velocity ratio between the two phases and the microchannel dimension. For the power law fluid, the bubble diameter decreases and the generation frequency increases with higher viscosity parameter K and power law index n. For a Bingham fluid, the viscous force plays a more important role in microbubble formation. Due to the yield stress (y), a high-viscous region is developed in the central area of the channel and bubbles deform to a flat ellipsoid shape in this region. The bubble diameter and generation frequency are almost independent of K.
Carbon monoxide is an important intermediate in supercritical water oxidation processes. Carbon monoxide oxidation in supercritical H2O/CO2 mixtures was investigated using reactive molecular dynamics simulations. The ...
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Carbon monoxide is an important intermediate in supercritical water oxidation processes. Carbon monoxide oxidation in supercritical H2O/CO2 mixtures was investigated using reactive molecular dynamics simulations. The results show that CO mainly converts into CO2 through the reaction CO + OH & RARR;HOCO & RARR;CO2 + H. The intermediate HOCO can also react with OH or O2 to form CO2. The overall activation energies of CO oxidation in the supercritical medium range from 125.3 & PLUSMN;4.0-159.4 & PLUSMN;3.6 kJ/mol, which are roughly consistent with the experimental results. Supercritical water not only provides reactive free radicals for CO conversion but also acts as a third body to induce some chemical events. The high concentration of CO2 inhibits the production of OH but highlights the oxidizing action of O and HO2. Oxygen increases the amounts of OH and HO2 through the reaction H2O + O2, thereby promoting the conversion of CO.
Carbon dioxide is the major greenhouse gas that contributes to the global warming more than 60%. Carbon dioxide from power plants is one of the main sources. Therefore it is essential to reduce the CO2 emission from p...
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Carbon dioxide is the major greenhouse gas that contributes to the global warming more than 60%. Carbon dioxide from power plants is one of the main sources. Therefore it is essential to reduce the CO2 emission from power plant flue gas. Post-combustion carbon capture is the optimal choice in near-to meddle-term, since it does not need to change the configuration of the power plants essentially. Chemical absorption with amine-based solvents is currently the state-of-the-art technology for post-combustion carbon capture. This paper introduces the typical CO2 amine absorption process and analyses the main problems during the absorption process. To make the process more efficient, several improvements were investigated: increasing gas-liquid contacting area, searching for new type of reactant, and dilution of the aqueous fraction with organic liquids. The present study aims to summarize the improvements in amine scrubbing process for CO2 capture and forecast the promising research directions in the future. (C) 2013 The Authors. Published by Elsevier
A turbulence controllable premixed turbulent Bunsen burner was developed to study the separate effects of turbulence intensity and integral scale on the premixed turbulent flame. Circular and slot perforated plates wi...
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A turbulence controllable premixed turbulent Bunsen burner was developed to study the separate effects of turbulence intensity and integral scale on the premixed turbulent flame. Circular and slot perforated plates with adjustable plate positions were designed to produce quasi-isotropic and uniform turbulence field containing scale-expanded vortices with normalized turbulence intensity ranging from 5% to 40%. The method to attain the controlled turbulence with multi-layer perforated plates were discussed. Especially, the order of the plate and the distance between the plates were proposed to be vital. Eight burner configurations of the plates and twelve conditions of the CH4/air flames at two constant bulk velocities (corresponding to two Reynolds numbers 4000 and 6777) were adopted. The flame front structure of the flames was captured with OH-PLIF technique. Results show that under the same turbulence intensity, the increase of integral scale at the higher Reynolds number reduces the turbulent burning velocity and increases the flame volume, while at the lower Reynolds number it shows marginal effect. Turbulent burning velocity and flame volume both increase almost monotonously, but the flame brush thickness decreases with the increase of turbulence intensity. With both two Reynolds numbers, small integral scale leads to decreased brush thickness. Both strong turbulence intensity and small integral scale decrease the curvature radius to induce finer flame front, which should be the main reason of the increased turbulent burning velocity. However, the flame surface density seems to be ambiguously correlated with the turbulence intensity and integral scale. The turbulence intensity shows more direct and intensive effects on the flames compared to the integral scale according to the PDF distributions of the curvature radius. The present study is useful for the interpretation of the basic mechanism of turbulence intensity and integral scale as well as the evaluation of
With the vigorous progress of nuclear industry under marine environment, the ocean motion will exacer-bate the pressure oscillation phenomenon caused by the change of the steam-liquid interface during the jet, causing...
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With the vigorous progress of nuclear industry under marine environment, the ocean motion will exacer-bate the pressure oscillation phenomenon caused by the change of the steam-liquid interface during the jet, causing great harm and challenges to the security and steady operation of device related to steam submerged jets. Therefore, the effects of heave motion on the steam bubble morphology and pressure oscillation phenomenon of jets with vertically upward low mass fluxes were experimentally investigated. The experimental results show that when the heave motion is upward, the steam bubble will be stretched obviously in the necking and detachment stages;while when the heave motion is downward, the steam bubble will accumulate at the nozzle outlet during the growth initial stage. Compared with the land en-vironment, the heave motion increases the dominant frequency and pressure pulses average amplitude, and the dominant frequency and pressure pulses average amplitude have a positive correlation with the heave amplitude and a negative correlation with the heave period. In addition, there is a positive corre-lation between the Strouhal number and the heave maximum acceleration amplitude. An experimental correlation is proposed to predict the dominant frequency in heave motion, and the error is basically within +/- 30%. (c) 2022 Published by Elsevier Ltd.
Classical imbibition theory cannot describe imbibition flow dynamics in nanoporous media in tight reservoirs and other industrial applications. In this work, the two-phase imbibition flow of water-oil displacement in ...
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Classical imbibition theory cannot describe imbibition flow dynamics in nanoporous media in tight reservoirs and other industrial applications. In this work, the two-phase imbibition flow of water-oil displacement in silica nanochannels is studied by using molecular dynamics simulations. Interestingly, it is found that the two-phase imbibition length is shown to increase linearly with increasing time, which is inconsistent with the variation of single-phase imbibition length. The imbibition rate increases with the increase of external driving force, and the large channel height can accelerate the two-phase imbibition flow. As the increase of chain length of alkane molecules, the imbibition rate reduces gradually. The more oil-wet the silica surface is, the slower the imbibition rate is. Furthermore, we derive a theoretical model to describe the two-phase imbibition flow of water-oil displacement in nanochannels by considering the static force equilibrium of external driving forces, capillary forces, and viscous forces of the water and oil phases. The theoretical model can well describe the two-phase imbibition flow under various conditions using the pre-calculated oil-water interfacial tension, the viscosity of fluids, and the three-phase contact angle. This study will enrich the theoretical understanding of oil-water twophase flow at nanoscale.
Modifying the structure of photocatalyst to tune its electronic and physicochemical properties is an effective approach for efficient photocatalysis. Herein, we modify the structure of g-C3N4 by partially replacing th...
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Modifying the structure of photocatalyst to tune its electronic and physicochemical properties is an effective approach for efficient photocatalysis. Herein, we modify the structure of g-C3N4 by partially replacing the corner site C atom with P heteroatom via a simple thermal phosphorization method. Comparing with the pristine g-C3N4, the g-C3N4 after phosphorization shows an improved photocatalytic hydrogen activity, which is attributed to the narrowed bandgap and the upshifted conduction band edge, enhanced separation and transfer of photogenerated charges, and highly hydrophilic surface absorbing reactant molecule for photocatalysis. Various experimental characterizations are conducted to systemically explore the underlying essential mechanism behind the superior photocatalytic performance of g-C3N4 with phosphorization treatment. This work provides a simple approach to modifying the structure of g-C3N4, which could be applied to other semiconductors for designing photocatalyst with unique structure and enhanced activity.
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