Due to their high effectiveness and compact size, printed circuit heat exchangers (PCHEs) appear promising to be employed as intermediate heat exchangers (IHXs) in High-Temperature Gas-cooled Reactors (HTGRs). In the ...
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Due to their high effectiveness and compact size, printed circuit heat exchangers (PCHEs) appear promising to be employed as intermediate heat exchangers (IHXs) in High-Temperature Gas-cooled Reactors (HTGRs). In the literature, PCHEs of zigzag mini-channel designs have demonstrated superior performance in heat transfer and pressure drop. In this research, a three-dimensional numerical simulation was performed for a PCHE using computational fluid dynamics (CFD) tool ANSYS FLUENT to study the effects of the zigzag pitch and angle, and channel diameter on its thermal-hydraulic performance. The mass, momentum, and energy equations were solved using a finite volume method by considering steady-state, incompressible laminar {1.. The FLUENT numerical model was validated by comparing the simulation results with the experimental data obtained in a high-temperature helium test facility. The comparison showed overall good agreement between the simulations and experiments. In addition, it was challenging to obtain accurate correlations/models for the Nusselt number and friction factor with various geometrical and operational parameters considered. In our study, two artificial neural network (ANN) models were applied by utilizing the CFD results to predict the Nusselt number and friction factor in PCHE zigzag channels with different geometrical configurations and operational parameters. Consequently, the computation time needed for the PCHE design optimization process could be significantly reduced. The comparison between the ANN predictions and CFD results showed that the ANN models could predict the numerical data with good accuracies. Furthermore, to achieve an optimal heat exchanger design, two conflicting evaluation criteria were proposed based on the capital and operational costs. Finally, the Non-dominated Sorting Genetic Algorithms (NSGA-II) and the proposed ANN models were combined and utilized to optimize the geometrical design parameters of the zigzag-channel PCHEs.
Local hydrodynamics in the riser of an external loop airlift reactor (EL-ALR) are identified and the performances of three drag models are evaluated in computational fluid dynamics simulation. The simulation results...
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Local hydrodynamics in the riser of an external loop airlift reactor (EL-ALR) are identified and the performances of three drag models are evaluated in computational fluid dynamics simulation. The simulation results show that the Schiller-Naumann drag model underestimated the local gas holdup at lower superficial gas velocity whereas the Tomiyama drag model overestimated that at higher superficial gas velocity. By contrast, the dual-bubble-size (DBS)-local drag model gave more reasonable radial and axial distri-butions of gas holdup in all cases. The reason is that the DBS-local drag model gave correct values of the lumped parameter, i,e., the ratio of the drag coefficient to bubble diameter, for varying operating conditions and radial positions. This ratio is reasonably expected to decrease with increasing superficial gas velocity and be smaller in the center and larger near the wall. Only the DBS-local drag model correctly reproduced these trends. The radial profiles of the axial velocity of the liquid and gas predicted by the DBS-local model also agreed well with experimental data.
The basic characteristics of differential pressure signals and the limitation of flow rate metering methods based on differential pressure are studied analytically and experimentally. Through the investigation into di...
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Coal chemical properties show conspicuous impacts on its reactivity and thermal conversion. Nevertheless, the quantitative analysis of coal property indice in China is insufficient. Here, we quantitatively analyzed th...
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Coal chemical properties show conspicuous impacts on its reactivity and thermal conversion. Nevertheless, the quantitative analysis of coal property indice in China is insufficient. Here, we quantitatively analyzed the correlations of various chemical properties of coals from thousands of data. Noteworthy variations were captured with some quantified expressions between coal properties obtained.
Photocatalysis is an emerging technology that enables a wide variety of applications,including degradation of organics and dyes,antibacterial action,and fuel generation through water splitting and carbon dioxide *** i...
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Photocatalysis is an emerging technology that enables a wide variety of applications,including degradation of organics and dyes,antibacterial action,and fuel generation through water splitting and carbon dioxide *** inorganic semiconducting materials have been explored as photocatalysts,and the versatility of these materials and reactions has been expanded in recent *** the relationship between the physicochemical properties of photocatalytic materials and their performances as well as the fundamentals in catalytic processes is important to design and synthesis of photocatalytic materials.
The influences of operating conditions, such as excess air ratio and SOFA arrangement, on temperature distributions, species distributions, NO x emissions and burnout of a tangentially-fired utility boiler using bitum...
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The influences of operating conditions, such as excess air ratio and SOFA arrangement, on temperature distributions, species distributions, NO x emissions and burnout of a tangentially-fired utility boiler using bituminous and blended coal were investigated by numerical approach in the present study. The simulation results show that the fuel type exhibits certain effect on the temperature distributions and the NO x emissions. Moreover, higher excess air ratio could restrain the CO formation but promote NO x emission. The temperature and the species distributions are highly related to the SOFA arrangement. In addition, SOFA technology is still an effective approach to control the NO x emissions during blended coal combustion, while the disadvantageous effect on char burnout should be considered.
Oxy-fuel combustion is recognized as one of the most promising CO 2 capture technologies. Under oxy-fuel combustion, the concentrations of CO 2 and H 2 O are much higher, result in different temperature profiles and h...
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Oxy-fuel combustion is recognized as one of the most promising CO 2 capture technologies. Under oxy-fuel combustion, the concentrations of CO 2 and H 2 O are much higher, result in different temperature profiles and heat transfer properties. In this study, a modified computational fluid dynamics (CFD) model-was developed for a 600 MW tangentially-fired boiler. Different oxygen volume fractions and two flue gas recycle modes (dry recycle and wet recycle) were numerically investigated, focusing on the properties of combustion and heat transfer. The results indicate the peak temperature in the burner zone decreases in oxy-fuel combustion, because of the high heat capacity and chemical reactivity of CO 2 . Compared with air-fired combustion, similar total heat transfer rate in furnace can be achieved at 27.0% and 28.3% of oxygen volume fraction for wet and dry recycle. These findings indicate retrofitting an existing boiler with oxy-fuel combustion technology is entirely feasible.
Titanium dioxide(TiO_(2))has been widely investigated for photocatalytic H_(2) evolution and photoelectrochemical(PEC)water splitting since ***,its wide bandgap(3.0-3.2 eV)limits the optical absorption of TiO_(2) for ...
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Titanium dioxide(TiO_(2))has been widely investigated for photocatalytic H_(2) evolution and photoelectrochemical(PEC)water splitting since ***,its wide bandgap(3.0-3.2 eV)limits the optical absorption of TiO_(2) for sufficient utilization of solar *** TiO_(2) has been proposed as an effective strategy to enhance its solar absorption and thus the photocatalytic and PEC activities,and aroused widespread research *** this article,we reviewed the recent progress of black TiO_(2) for photocatalytic H_(2) evolution and PEC water splitting,along with detailed introduction to its unique structural features,optical property,charge carrier transfer property and related theoretical *** summarized in this review article,black TiO_(2) could be a promising candidate for photoelectrocatalytic hydrogen generation via water splitting,and continuous efforts are deserved for improving its solar hydrogen efficiency.
The ash-related issues due to the high-alkali characteristic are still unresolved during utilization of biomass and Zhundong coal. Here, the correlations of several chemical properties of high-alkali solid fuels were ...
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The ash-related issues due to the high-alkali characteristic are still unresolved during utilization of biomass and Zhundong coal. Here, the correlations of several chemical properties of high-alkali solid fuels were investigated. The distributions of ash compositions in various biomass exhibit obvious diversity, while the distribution of K 2 O content within wheat and corn straws are the most scattered. The ash content in biomass shows a decrease tendency with the increase of carbon content. Zhundong coals generally have medium but close ash fusion points despite of quite different ash compositions sometimes.
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