Abstract Three different numerical models for simulating the well-known experimental flash method are presented and compared. These models consider conduction-radiation coupling and are applied ...within a one-dimensional grey semi-transparent slab enclosed between two opaque surfaces. The first model (A) is deterministic, dating back to about a decade, and is based on three assumptions regarding radiation transfer: isotropic intensity within each of the two hemispheres, the scattering phenomenon is supposed to be isotropic, and linearization of terms involving differences of temperatures to the fourth power. The other two models are completely new and do not make these assumptions. While the first one (B) is purely deterministic and serves as a reference for validation, the other one (C) is fully stochastic, and is the focus of this paper. A comparison shows excellent agreement between (B) and (C), validating our new model of interest (C). On the other hand, (A) exhibits significant discrepancies with the other two, highlighting the importance of its limiting assumptions.
Abstract
A power upgrade project (CSNS-II) has been approved in 2021 to increase the beam power to 500 kW for the China Spallation Neutron Source (CSNS), for which the Linac energy will reach 300 MeV ...and the beam intensity is expected to be 50 mA. In this study, the beam measurement results given by the wire scanners at various current intensities, and the numerical modeling and fitting methods to obtain the evolution of the beam envelope and emittance along the CSNS medium energy beam transfer (MEBT) are given and discussed. Finally, new matching results have been given to control the emittance blowup.
Microplastics (MPs), a new class of emerging pollutants, have attracted exponentially increased attention due to the adverse ecological impacts on biota, not only by themselves but also by the ...combined corrosive substances. However, the occurrence mechanisms, numerical models and influencing factors of MPs adsorbing organic pollutants (OPs) show a significant variation with literatures. Therefore, this review is focused on the adsorption of OPs on MPs, including mechanisms, numerical models, and influencing factors, to obtain a comprehensive understanding. Research shows that MPs with strong hydrophobicity have high adsorption capacity for hydrophobic OPs. Hydrophobic distribution and surface adsorption are considered to be the main mechanisms by which MPs adsorb OPs. The available literature suggests that the pseudo-second-order model describes the adsorption kinetics of OPs on MPs better than the pseudo-first-order model, while the choice of Freundlich or Langmuir isotherm model depends mainly on the specific environmental conditions. Moreover, the characteristics of MPs (composition, particle size, aging, etc.), the nature of OPs (concentration, polarity, hydrophilicity, etc.), the environmental conditions (temperature, salinity, pH, ionic strength, etc.), and the substances co-existing in the environment (e.g., DOM and surfactants) are all important factors affecting the adsorption behavior of MPs for OPs. Environmental conditions can also indirectly affect the adsorption of hydrophilic OPs adsorbed on MPs by causing changes in the surface properties of MPs. Based on the current knowledge, the perspective shortening the knowledge gap is also suggested.
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•Studies on the adsorption of OPs by MPs in aquatic environment were reviewed.•Mechanisms, kinetic and isotherm models, and influencing factors were discussed.•Hydrophobic distribution and surface adsorption are the main adsorption mechanism.•The pseudo-second-order kinetic model and Langmuir isotherm model are favorable.•The knowledge cap and further study needed are suggested.
In this study, we design a hybrid thermal management system that combines liquid cooling and phase change materials (PCMs) for a battery pack of 20 Li-ion cylindrical cells. This system integrates a ...cold plate through which water flows into a PCM matrix composed of expanded graphite/RT44HC composites. The study aims at exploring factors that influence the temperature rise and the temperature uniformity of batteries. Experiments have been conducted to study the effect of water inlet temperature and flowrate, as well as the PCM content in a battery. The results show that the best control strategy would be to limit the water temperature less than 40 °C and as close to the ambient temperature. The high water flowrate reduces Tmax and ΔTplanar slightly but can significantly increase ΔTaxial and power consumption; therefore, a low flowrate is preferred. Composite PCMs with a high mass fraction of RT44HC perform better, especially under high discharge current up to 2.9C. A numerical model has also been proposed for the hybrid thermal management system to visualise temperature distribution and heat transfer routines and for system optimisation.
•Experimentally test a liquid-PCM hybrid cooling system for cylindrical batteries.•Separately study impacts of water and PCM on 3D battery temperature distribution.•Discuss the temperature difference in a single battery and between different cells.•Present a numerical model with high accuracy to guide the system design.•Numerically study the effects of the thermal conductivity and latent heat.
Traditional deep learning models are trained at a centralized server using data samples collected from users. Such data samples often include private information, which the users may not be willing ...to share. Federated learning (FL) is an emerging approach to train such learning models without requiring the users to share their data. FL consists of an iterative procedure, where in each iteration the users train a copy of the learning model locally. The server then collects the individual updates and aggregates them into a global model. A major challenge that arises in this method is the need of each user to repeatedly transmit its learned model over the throughput limited uplink channel. In this work, we tackle this challenge using tools from quantization theory. In particular, we identify the unique characteristics associated with conveying trained models over rate-constrained channels, and propose a suitable quantization scheme for such settings, referred to as universal vector quantization for FL (UVeQFed). We show that combining universal vector quantization methods with FL yields a decentralized training system in which the compression of the trained models induces only a minimum distortion. We then theoretically analyze the distortion, showing that it vanishes as the number of users grows. We also characterize how models trained with conventional federated averaging combined with UVeQFed converge to the model which minimizes the loss function. Our numerical results demonstrate the gains of UVeQFed over previously proposed methods in terms of both distortion induced in quantization and accuracy of the resulting aggregated model.
In this paper, a novel fluid-thermal-electric multiphysics numerical model is presented to predict the performance of a thermoelectric generator system applied in automobile waste heat recovery. The ...model considers the complete geometry, temperature-dependent material properties, topological connection among thermoelectric modules, and impedance matching, which can simulate the actual working conditions. Numerical simulations are carried out on the COMSOL platform combined with the exhaust temperature and exhaust mass flow rate under different vehicle speeds. In addition, the detailed physical field distribution characteristics of the automobile thermoelectric generator system, as well as the variations of output power, conversion efficiency, power losses, and net power with vehicle speed, are obtained. The position of thermoelectric modules on the hot side heat exchanger plays an important role in output uniformity, and the higher the vehicle speed is, the more uniform the output will be. At the vehicle speed of 120 km h−1, the output power and conversion efficiency of the automobile thermoelectric generator system are 38.07 W and 1.53% respectively. Considering the weight power loss and coolant pumping power loss, the net power is 23.66 W. This work fills the gap in evaluating the performance of automobile thermoelectric generator systems at different vehicle speeds comprehensively.
•A fluid-thermal-electric multiphysics numerical model for automobile TEG systems is proposed.•Complete physical field distribution characteristics of the automobile TEG system is obtained.•Performance of the automobile TEG system under different vehicle speeds is investigated.•The effect of TEM location on the output performance is studied.•The net power analysis under different vehicle speeds is performed.
In this paper, we consider the Tensor Robust Principal Component Analysis (TRPCA) problem, which aims to exactly recover the low-rank and sparse components from their sum. Our model is based on the ...recently proposed tensor-tensor product (or t-product) 14. Induced by the t-product, we first rigorously deduce the tensor spectral norm, tensor nuclear norm, and tensor average rank, and show that the tensor nuclear norm is the convex envelope of the tensor average rank within the unit ball of the tensor spectral norm. These definitions, their relationships and properties are consistent with matrix cases. Equipped with the new tensor nuclear norm, we then solve the TRPCA problem by solving a convex program and provide the theoretical guarantee for the exact recovery. Our TRPCA model and recovery guarantee include matrix RPCA as a special case. Numerical experiments verify our results, and the applications to image recovery and background modeling problems demonstrate the effectiveness of our method.
•Affordable square pyramid solar still is designed, fabricated and tested.•The maximum daily water production of the portable solar still is 2.2 L/m2.•Heat transfer analysis is developed using an ...advanced simulation modelling.•The total fabrication cost of the square pyramid solar still is economical.•The efficiency of the portable solar still is significantly improved to 60%.•The square pyramid solar still has a minor effects on the environment.
In this work, a square pyramid solar still is designed, fabricated and tested during recommended days at the four seasons of Al Kufa climatic conditions (elevation is 30 m and location is 32° North and 44° East), Iraq. The proposed design of the still can be used at any remote location in Iraq where is no electricity and high solar intensity. Designing the affordable solar still was mainly due to simplicity in its operation process, long life and low cost. Data obtained from an advanced simulation modeling of multi-shaped solar stills are used to determine the temperature gradient and the heat flux distributions during unsteady-state conditions. The procedure of the modelling is included: volumetric properties of the solid and fluid regions, thermal loads on the still, mesh generation, grid convergence index and grid refinery processes. The experiments were measured during the four seasons to investigate the temperatures of water, glass, ambient, water production and solar intensity. The results show that the maximum daily water production of the designed still is 2.2 L/m2 in 17th of July with a low cost of 15 US dollars. The numerical model is predicted the thermal behavior of triangle, pyramid and pentagon types of solar stills. The results also show that the efficiency of the designed still is significantly improved to 60% compared with other experimental solar stills. The results also demonstrate that the manufacturing and transferring of the portable solar still during 20 years has a reasonable effect on the environment in terms of air acidification and water eutrophication.
Abstract Accurate prediction of scour evolution around fixed offshore foundations is a key parameter for selecting the most appropriate scour mitigation strategy. Various formulations can be used to ...estimate scour around monopiles. However, non-specific formulations have been developed for more complex foundations. In the case of jacketed offshore substations (OSS), the geometry can be one of the most complex. This paper describes a hybrid methodology (numerical model simulations, semi-empirical approaches and physical experiments) to estimate the scour evolution around OSS. The application of this methodology allows the selection of the most appropriate mitigation strategy from an early stage of the project to the final decision. The methodology is accompanied by some examples. In general, the results obtained from the semi-empirical approaches show quite good agreement with the measurements from the physical experiments. Nevertheless, considering the complex geometry of the OSS and the potential non-linearities associated with the platform geometry, physical experiments are required to ensure the correct estimation of the maximum scour (local and global).
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