Feedforward-feedback control of a solid oxide fuel cell power system

One of the main challenges for wide-spread utilization of the solid oxide fuel cell (SOFC) power systems is how to achieve high electrical efficiency without increasing the degradation rate of the fuel cells. To run the SOFC power system at high efficiency over a long period of time, properly designed controllers are indispensable.Although a number of various approaches to control SOFC have been proposed so far, it seems that the design of control system, along with simple tuning procedure, has not been treated in a consistent manner. This issue is addressed in the present paper resulting in a feedforward-feedback control structure. The feedforward part is based on the stoichiometry of electro-oxidation, reforming and combustion reactions, which allow immediate response to variable current demand. The feedback part performs additional fine adjustment of fuel and air supply in order to minimize the undesired system temperatures variations. The selection of pairings of manipulated and controlled variables for control is based on physical knowledge of the system. Input/output pairing for single-loop feedback control is assessed by the relative gain analysis. An efficient procedure for tuning the parameters of the feedback controllers is suggested, relying on simple open-loop step responses of the system.The proposed low-level control is assessed on a detailed physical model of a 2.5 kW SOFC power system by simulating two nonstationary load regimes. Simulations show that the control provides a robust operation under large load variations while meeting the operating constraints. Due to its simplicity, the control is feasible for implementation on a real SOFC system.     

Accumulation mechanism for metal chalcogenide nanoparticles at Hg0 electrodes: copper sulfide example

Mercury electrodes preconcentrate metal chalcogenide nanoparticles effectively, enabling their detection at submicromolar concentrations (as Sigma chalcogenide) by adsorptive cathodic stripping voltammetry. Understanding the unique behavior of nanoparticle analytes during preconcentration is critical for lowering detection limits and for quantification. A multistep mechanism is proposed on the basis of accumulation experiments with polydisperse copper sulfide (CuxS) nanoparticles. Particles first diffuse and adsorb at the Hg0 surface. When both the electrode and particles have negative surface potentials, this process resembles charge-impeded coagulation, obeying the Schulze-Hardy rule at various electrolyte strengths. Consequently, accumulation rates are surprisingly sensitive to electrolyte concentration. Choosing accumulation potentials where the electrode and particles have opposite surface potentials greatly improves collection efficiency, especially for the smallest particles. After adsorption, particles undergo transformations. One product is a more stable (harder to reduce) form of CuxS, interpreted to consist of adclusters or adlayers. A very significant (approximately 0.3 V) negative shift in reduction potential results from this transformation. Loss of analyte to at least one nonelectroactive product is also observed. Loss is greatest for the smallest particles and is sensitive to choice of accumulation potential. To improve accumulation efficiency, accumulation potentials more positive that the potential of zero charge of Hg electrodes are advantageous but care must be taken to remove dissolved chalcogenides under these conditions in order to avoid artifacts.     

Quality of eggs coated with oil–chitosan emulsion: Combined effects of emulsifier types,initial albumen quality,and storage

Effects of mineral oil:chitosan (MO:CH at 25:75) emulsions prepared with four different emulsifiers (2 water- and 2 oil-miscible) as coatings on the internal quality (weight loss, Haugh unit, yolk index, and albumen pH) of coated eggs were evaluated during 5 weeks at 25 ± 2 °C and 20 weeks at 4 ± 2 °C. Eggs with two initial albumen qualities [Haugh unit (HU): H = 87.8 and L = 70.9] were used. At 25 ± 2 °C, Haugh unit, yolk index, and albumen pH of all coated eggs decreased with increased storage time. Coated H- and L-eggs maintained an A-grade up to 4 weeks and 1 week, respectively. Weight loss of all coated eggs remained below 1.35% after 5 weeks of storage at 25 ± 2 °C. All coated eggs maintained an A-grade with less than 2.5% weight loss during 20 weeks of storage at 4 ± 2 °C. Emulsifier types marginally affected the internal quality of coated eggs regardless of storage temperatures.     

Flow visualization and characterization for optimized MQL machining of composites

Limited information is available on the effect of Minimum Quantity Lubrication (MQL) parameters (oil flow rate OFR, air flow rate AFR, nozzle orientation and distance from the cutting zone) on flow characteristics. ‘Particle Image Velocimetry’ and ‘Phase Doppler Anemometry’ flow visualization methods were used to define the optimal MQL jet for better penetration and cooling/lubrication; coherent, small magnitude/number of vorticities, and small droplets of high velocity. Effect of flow characteristics on cutting forces, temperature, tool wear and geometric errors was examined in CFRP milling. Optimum AFR, OFR and nozzle distance from the cutting zone were established and compared to flood, pressurized air, and dry machining.     

建筑涂料市场蒸蒸日上

以产量划分,建筑涂料是涂料行业中最大的细分市场.但是,前几年,该市场却停滞不前.2020年,该市场摆脱了涂料行业的危机,建筑涂料制造商度过了 一个成功的财政年度.但是,对于这种良好发展的态势能否持续,仍存在很大的不确定性. 事实证明,建筑涂料市场在此次疫情期间表现强劲.自新冠肺炎疫情爆发以来,许多人都居家隔离,其家庭的...     

生物基涂料市场:前景光明

据ChemQuest和Orr&Boss公司等行业专家估计,生物基体系的产值约占整个涂料市场的5％,而产量则略高于1％.尽管如此,AkzoNobel、Covestro和PPG等公司的行业专家都预计生物基体系将有更多的发展机会.业内人士分享了他们对当前形势的看法,并且对该细分市场的前景进行了展望. PPG公司的Mary E...     

可再生原材料:全球增长

正在涂料领域,每天听到最多的是"可持续发展性"、"绿色"和"环境友好"等。因此,毫不意外的是,各种配方中生物基材料的含量肯定将出现增长。预计到2020年,生物基溶剂替代品的比例也会实现增长。     

Limitations of Pauling Bond Order Concept

It is shown that Kekulé structures do not realistically predict the behavior of π-electron properties of those polycyclic hydrocarbons that have many fixed double bonds. This is caused by the fact that such molecules would be destabilized by delocalization. We analyze a group of polycyclic hydrocarbons with a large number of fixed bonds, whose geometry was determined by means of an unrestricted symmetry-broken UB3LYP/6-311G(d,p) DFT method. We put forward a new concept, the unpaired bond order, and show that it is well correlated with bond lengths, but poorly correlated with Pauling bond orders. Hence, in this way we provide a simple test of the validity of the Pauling-bond-order concept for the molecule being considered.     

Comparing effects of α‐ vs. β‐chitosan coating and emulsion coatings on egg quality during room temperature storage

Effects of α‐ and β‐chitosan (CH), soybean oil (SO) and their emulsions (CH:SO = 2:3) as coating materials on selected internal quality and sensory properties of eggs were evaluated during 5 weeks storage at 25 °C. After 3 weeks of storage, α‐ and β‐CH‐coated eggs changed to B grade, while SO‐ and emulsion‐coated eggs preserved grade A quality. Weight loss of eggs coated with SO and CH:SO emulsions was <2.0% vs. 5.3–5.8% for noncoated and CH‐coated eggs after 5 weeks of storage. β‐CH (0.9%) maintained lower weight loss of eggs than α‐CH (1.2%) only at 1‐week storage. Albumen pH of eggs coated with SO and CH:SO emulsions decreased progressively throughout storage. Eggs coated with β‐CH:SO emulsion and SO were significantly glossier than noncoated eggs. Consumers indicated positive purchase intent (69.17–76.67%) for all coated eggs. Overall, α‐CH:SO and β‐CH:SO emulsions extended egg shelf life by at least 3 weeks during room temperature storage.