Melt cavitation at its volumetric crystallization

It is shown that at volumetric crystallization of the undercooled melt the high negative pressures are generated in this melt; they are caused by matter shrinkage at solidification, what leads to intensive cavitation of uncrystallized melt. The mechanisms are studied and the kinetic model of this process is presented here. Considerable dependence of cavitation intensity on the cooling rate is shown. Numerical solutions to the problem are found at the example of cavitation of crystallizing metal melts. The sizes of crystalline grains and formed cavitation inclusions in the solidified material are determined.     

SAHPPA: a novel power pinch analysis approach for the design of off-grid hybrid energy systems

This work proposes a novel approach called stand-alone hybrid system power pinch analysis (SAHPPA), which is particularly applicable for the design of off-grid distributed energy generation systems. The enhanced graphical tool employs new ways of utilising the recently introduced demand composite curve and supply composite curve while honouring and adapting fundamental energy systems engineering concepts. The SAHPPA method is capable of optimising the capacity of both the power generators and energy storage for biomass (i.e. non-intermittent) and solar photovoltaic (i.e. intermittent) energy technologies, which is a contribution to the emerging area of power pinch analysis. In addition, the procedure considers all possible efficiency losses in the overall system encompassing the charging–discharging and current inversion processes.     

Layered Nanoprobe for Long‐Lasting Fluorescent Cell Label

A long‐lasting particle‐based fluorescent label is designed for extended cell imaging studies. This onion‐like nanoprobe is constructed through layer‐by‐layer fabrication technology. The nanoprobes are assembled with multiple layers of optically quenched polyelectrolytes, the fluorescence signal of which can be released later by intracellular proteolysis. Upon incubation with cells, the assembled nanoprobes are taken up efficiently. The tight packing and layered assembly of the quenched polyelectrolytes slow subsequent intracellular degradation, and then result in a prolonged intracellular fluorescence signal for up to 3 weeks with no noticeable toxicity.     

Dual Toll Pricing for Hazardous Materials Transport with Linear Delay

In this paper, we propose a dual toll pricing method to mitigate risk of hazardous materials (hazmat) transportation. We aim to simultaneously control both regular and hazmat vehicles to reduce the risk. In our model, we incorporate a new risk measure to consider duration-population-frequency of hazmat exposure. We first formulate the model as a Mathematical Program with Equilibrium Constraints (MPEC). Then we decompose the MPEC formulation into first-stage and second-stage problems. Separate methods are developed to solve each stage. A numerical example is provided and possible extensions are discussed.     

Investigation of P3HT/n-Si heterojunction using surface photovoltage spectroscopy

Surface photovoltage spectroscopy (SPS) was used to investigate the interactions of the interface between regioregular poly(3-hexylthiophene) (P3HT) and n-type single crystalline silicon. The SPS responses of silicon and the P3HT/n-Si heterojunction caused by band to band transition of silicon are 30 mV and 160 mV respectively. The band-bending in the silicon side of the P3HT/n-Si structure is larger than that of bare n-Si. The density of the interface states of the P3HT/n-Si heterojunction increased significantly after the deposition of P3HT. Based on the contact potential difference (CPD) transient results, charge transport and separation processes are fast in the silicon substrate and slow in the P3HT layer respectively.     

中国电力行业CDM潜力分析

构建了一种能够评估我国清洁发展机制(clean development mechanism,CDM)项目潜力的分析评价模型,该模型由两个主要模型"能源环境系统的综合评价模型"和"CDM项目潜力最优分析模型"组成。以此模型为基础,分析评价了我国电力行业CDM的实施潜力。结果表明,我国电力行业未来CDM项目的潜力巨大,且对节能的效果也非常显著。     

An experimental investigation on the effects of exponential window and impact force level on harmonic reduction in impact-synchronous modal analysis

A novel method called Impact-synchronous modal analysis (ISMA) was proposed previously which allows modal testing to be performed during operation. This technique focuses on signal processing of the upstream data to provide cleaner Frequency response function (FRF) estimation prior to modal extraction. Two important parameters, i.e., windowing function and impact force level were identified and their effect on the effectiveness of this technique were experimentally investigated. When performing modal testing during running condition, the cyclic loads signals are dominant in the measured response for the entire time history. Exponential window is effectively in minimizing leakage and attenuating signals of non-synchronous running speed, its harmonics and noises to zero at the end of each time record window block. Besides, with the information of the calculated cyclic force, suitable amount of impact force to be applied on the system could be decided prior to performing ISMA. Maximum allowable impact force could be determined from nonlinearity test using coherence function. By applying higher impact forces than the cyclic loads along with an ideal decay rate in ISMA, harmonic reduction is significantly achieved in FRF estimation. Subsequently, the dynamic characteristics of the system are successfully extracted from a cleaner FRF and the results obtained are comparable with Experimental modal analysis (EMA).     

Integration strategies of hydrogen network in a refinery based on operational optimization of hydrotreating units

Inferior crude oil and fuel oil upgrading lead to escalating increase of hydrogen consumption in refineries. It is imperative to reduce the hydrogen consumption for energy-saving operations of refineries. An integration strategy of hydrogen network and an operational optimization model of hydrotreating (HDT) units are proposed based on the characteristics of reaction kinetics of HDT units. By solving the proposed model, the operating conditions of HDT units are optimized, and the parameters of hydrogen sinks are determined by coupling hydrodesulfurization (HDS), hydrodenitrification (HDN) and aromatic hydrogenation (HDA) kinetics. An example case of a refinery with annual processing capacity of eight million tons is adopted to demonstrate the feasibility of the proposed optimization strategies and the model. Results show that HDS, HDN and HDA reactions are the major source of hydrogen consumption in the refinery. The total hydrogen consumption can be reduced by 18.9% by applying conventional hydrogen network optimization model. When the hydrogen network is optimized after the operational optimization of HDT units is performed, the hydrogen consumption is reduced by 28.2%. When the benefit of the fuel gas recovery is further considered, the total annual cost of hydrogen network can be reduced by 3.21×10₇ CNY·a_-1, decreased by 11.9%. Therefore, the operational optimization of the HDT units in refineries should be imposed to determine the parameters of hydrogen sinks base on the characteristics of reaction kinetics of the hydrogenation processes before the optimization of the hydrogen network is performed through the source-sink matching methods.     

Bubble behaviors in direct methanol fuel cell anode with parallel design

In this paper, the Volume of Fluid (VOF) method for tracking the gas-liquid interface is employed to investigate the carbon dioxide (CO₂) behaviors inside the anode of a direct methanol fuel cell (DMFC). The CO₂ bubble emergence processes from the catalyst layer (CL) to the gas diffusion layer (GDL) and then to the flow channels are studied with two different strategies. In the first strategy, the CL and GDL are modeled as a uniform porous layer; in the second strategy, they are modeled as a well-ordered-path GDL and a uniform CL. The simulation results show that the second modeling strategy can better capture and match the fundamental phenomena of CO₂ bubble formation and evolvement observed from the experiments inside a DMFC anode.     

Study of relationship between temperature and thermal energy,operating conditions as well as environmental factors in large‐scale lithium‐ion batteries

We have developed a thermal model for a large‐scale lithium‐ion cell and have simulated its thermal behaviors during charge, discharge, and charge–discharge cycles with different current rates by using the software of COMSOL Multiphysics 3.5a. In this work, thermal energy and its distribution were firstly calculated based on experimental data under different operating conditions. A new parameter, called thermal energy conversion efficiency, was proposed to describe relative value of thermal energy in the cell. The thermal energy conversion efficiency and the temperature were plotted in a figure to show their relativity. The temperature variation was also studied systemically when the cell underwent discharge–charge cycles. A low rate charge is validated to be a favorable factor in protecting the cell from overheating during charge–discharge cycles. A connection resistance is proved to be a main factor that accelerates the rise of temperature in the spot near a terminal column, which should be eliminated as much as possible to protect the cell from local overheating. Copyright © 2014 John Wiley & Sons, Ltd.