Numerical and experimental study on the falling film flow characteristics with the effect of co-current gas flow in hydrogen liquefaction process

Liquid hydrogen storage and transportation is an effective method for large-scale transportation and utilization of hydrogen energy. Revealing the flow mechanism of cryogenic working fluid is the key to optimize heat exchanger structure and hydrogen liquefaction process(LH2). The methods of cryogenic visualization experiment, theoretical analysis and numerical simulation are conducted to study the falling film flow characteristics with the effect of co-current gas flow in LH2spiral wound heat exchanger.The results show that the flow rate of mixed refrigerant has a great influence on liquid film spreading process, falling film flow pattern and heat transfer performance. The liquid film of LH2mixed refrigerant with column flow pattern can not uniformly and completely cover the tube wall surface. As liquid flow rate increases, the falling film flow pattern evolves into sheet-column flow and sheet flow, and liquid film completely covers the surface of tube wall. With the increase of shear effect of gas-phase mixed refrigerant in the same direction, the liquid film gradually becomes unstable, and the flow pattern eventually evolves into a mist flow.

Balanced Fracturing and Cold-welding of Magnesium during Ball Milling Assisted by Carbon Coating:Experimental and Molecular Dynamic Simulation

The lignite-derived carbon from self-protection pyrolysis was employed to balance the fracturing and cold-welding of magnesium during ball milling.Particle size analysis indicates that the introduction of lignite-derived carbon can effectively reduce the particle size of Mg while the introduction of graphite does no help.Besides,the effect of lignite-derived carbon on crystallite size reduction of Mg is also better than graphite.A moderate cold-welding phenomenon was observed after ball-milling Mg with the lignite-derived carbon,suggesting less Mg is wasted on the milling vials and balls.Molecular dynamic simulations reveal that the balanced fracturing and cold-welding of magnesium during ball milling is mainly attributed to the special structure of the lignite-derived carbon:graphitized short-range ordered stacking function as dry lubricant and irregular shape/sharp edge function as milling aid.The preliminary findings in current study are expected to offer implications for designing efficient Mg-based hydrogen storage materials.

Decentralized Optimal Control and Stabilization of Interconnected Systems With Asymmetric Information

The paper addresses the decentralized optimal control and stabilization problems for interconnected systems subject to asymmetric information.Compared with previous work,a closed-loop optimal solution to the control problem and sufficient and necessary conditions for the stabilization problem of the interconnected systems are given for the first time.The main challenge lies in three aspects:Firstly,the asymmetric information results in coupling between control and estimation and failure of the separation principle.Secondly,two extra unknown variables are generated by asymmetric information(different information filtration)when solving forward-backward stochastic difference equations.Thirdly,the existence of additive noise makes the study of mean-square boundedness an obstacle.The adopted technique is proving and assuming the linear form of controllers and establishing the equivalence between the two systems with and without additive noise.A dual-motor parallel drive system is presented to demonstrate the validity of the proposed algorithm.

Attenuation of Chlorinated Contamination in Three Different Depths of Aquifers at Remediation Site

The cleanup of carbon tetrachloride(CCl4)in groundwater is challenging due to its high volatility and tendency to form a dense nonaqueous liquid phase.From the engineering applications perspective,the pump-and-treat(PAT)technology has substantial advantages owing to its large-scale implementation ability to solve groundwater contamination.However,few studies focused on the variation in chloride contaminants in remediation sites after the contaminated groundwater was pumped and treated.Herein,we monitored the changes in chlorinated contamination in groundwater from 12 aquifers at the field level for 6 months.Considering that the natural attenuation of chlorinated contamination is inseparable from the action of microorganisms,the major environmental factors influencing biodegradation were also evaluated.A redundancy analysis(RDA)showed that inorganic salts(DS,DN,and DF)were the most important factor(>60%)affecting the concentration of chloride contaminants,including the negative correlation between DN and the degradation of contaminants in shallow aquifers.In deep aquifers,DS,DF,and pH explained most of the degradation of chloride contaminants.For bedrock layers,DCl was positively relevant to the chloride contaminants in wells PTJ2 and PTJ10.In addition,EC and DS accounted for 73.2%and 92.4%of the contaminant’s variance in wells PTJ4 and PTJ8,respectively.Moreover,the concentrations of the corresponding contaminations and physicochemical variation in three different depths of aquifers were compared;the shallower aquifers showed a higher biodegradation.The in situ monitoring and analysis of contaminated groundwater in remediation sites under PAT will promote practical wastewater treatment technologies in engineering applications.

Synergistic defect passivation and strain compensation toward efficient and stable perovskite solar cells

Rational interface engineering is essential for minimizing interfacial nonradiative recombination losses and enhancing device performance.Herein,we report the use of bidentate diphenoxybenzene(DPOB)isomers as surface modifiers for perovskite films.The DPOB molecules,which contain two oxygen(O)atoms,chemically bond with undercoordinated Pb^(2+) on the surface of perovskite films,resulting in compression of the perovskite lattice.This chemical interaction,along with physical regulations,leads to the formation of high-quality perovskite films with compressive strain and fewer defects.This compressive strain-induced band bending promotes hole extraction and transport,while inhibiting charge recombination at the interfaces.Furthermore,the addition of DPOB will reduce the zero-dimensional(OD) Cs_4PbBr_6 phase and produce the two-dimensional(2D) CsPb_(2)Br_5 phase,which is also conducive to the improvement of device performance.Ultimately,the resulting perovskite films,which are strain-released and defect-passivated,exhibit exceptional device efficiency,reaching 10.87% for carbon-based CsPbBr_(3) device,14.86% for carbon-based CsPbI_(2)Br device,22,02% for FA_(0.97)Cs_(0.03)PbI_(3) device,respectively.Moreover,the unencapsulated CsPbBr_(3) PSC exhibits excellent stability under persistent exposure to humidity(80%) and heat(80℃) for over 50 days.

In-situ doping-induced lattice strain of NiCoP/S nanocrystals for robust wide pH hydrogen evolution electrocatalysis and supercapacitor

Developing high-efficiency multifunctional nanomaterials is promising for wide p H hydrogen evolution reaction(HER) and energy storage but still challenging. Herein, a novel in-situ doping-induced lattice strain strategy of NiCoP/S nanocrystals(NCs) was proposed through using seed crystal conversion approach with NiCo_(2)S_(4) spinel as precursor. The small amount of S atoms in NiCoP/S NCs perturbed the local electronic structure, leading to the atomic position shift of the nearest neighbor in the protocell and the nanoscale lattice strain, which optimized the H* adsorption free energy and activated H_(2)O molecules, resulting the dramatically elevated HER performance within a wide p H range. Especially, the NiCoP/S NCs displayed better HER electrocatalytic activity than comical 20% Pt/C at high current density in 1 M KOH and natural seawater: it only needed 266 m V vs. reversible hydrogen electrode(RHE) and660 m V vs. RHE to arrive the current density of 350 m A cm^(-2) in 1 M KOH and natural seawater, indicating the application prospect for industrial high current. Besides, NiCoP/S NCs also displayed excellent supercapacitor performance: it showed high specific capacity of 2229.9 F g^(-1) at 1 A g^(-1) and energy density of87.49 Wh kg^(-1), when assembled into an all-solid-state flexible device, exceeding performance of most transition metal phosphides. This work provides new insights into the regulation in electronic structure and lattice strain for electrocatalytic and energy storage applications.

Boosting the Ni-Zn interplay via O/N dual coordination for high-efficiency CO_(2) electroreduction

Design of supportive atomic sites with a controllably adjusted coordinating environment is essential to advancing the reduction of CO_(2) to value-added fuels and chemicals and to achieving carbon neutralization.Herein,atomic Ni(Zn)sites that are uniquely coordinated with ternary Zn(Ni)/N/O ligands were successfully decorated on formamide-derived porous carbon nanomaterials,possibly forming an atomic structure of Ni(N_(2)O_(1))-Zn(N_(2)O_(1)),as studied by combining X-ray photoelectron spectroscopy and X-ray absorption spectroscopy.With the mediation of additional O coordination,the Ni-Zn dual site induces significantly decreased desorption of molecular CO.The NiZn-NC decorated with rich Ni(N_(2)O_(1))-Zn(N_(2)O_(1))sites remarkably gained>97%CO Faraday efficiency over a wide potential range of -0.8 to -1.1 V(relative to reversible hydrogen electrode).Density functional theory computations suggest that the N/O dual coordination effectively modulates the electronic structure of the Ni-Zn duplex and optimizes the adsorption and conversion properties of CO_(2) and subsequent intermediates.Different from the conventional pathway of using Ni as the active site in the Ni-Zn duplex,it is found that the Ni-neighboring Zn sites in the Ni(N_(2)O_(1))-Zn(N_(2)O_(1))coordination showed much lower energy barriers of the CO_(2) protonation step and the subsequent dehydroxylation step.

A New Approach to Suppress Tip Leakage Flow Utilizing Induced Shock Wave in Tip Region of a TransonicCompressor Rotor

Tip leakage flow affects the flow stability of high-loading compressors significantly.Therefore,a novel approach via induced shock wave near suction-side edge of blade tip was proposed to suppress the strength and influence range of leakage flow in a transonic rotor.Three new schemes with different circumferentially diverging degrees of clearance were designed to reveal the mechanism of the new approach.Through the action of the circumferentially diverging clearance(from the pressure side to the suction side over blade tip),a much more dramatic acceleration of the supersonic leakage jet flow appeared over blade tip of the new schemes.An induced shock wave was produced near the suction side edge of blade tip due to the pressure difference between the discharging leakage flow and the surrounding high-pressure mainflow in tip channel.As a result,both the mass flow rate and the outlet velocity of leakage flow were reduced significantly via the induced shock wave.Meanwhile,the suppressing effect of the new approach on the tip leakage jet flow was closely related to the strength and circumferential location of the induced shock wave.With the aids of the induced shock wave,the largest improvement of tip flow characteristics with an over 5%increase in stall margin was realized in new transonic rotor when the circumferential divergence angle equals 8°,accompanied with no more than a 0.4%decrease in isentropic efficiency.

P-band center theory guided activation of MoS_(2) basal S sites for pHuniversal hydrogen evolution

The edge S sites of thermodynamically stable 2H MoS_(2)are active for hydrogen evolution reaction(HER)but the active sites are scarce.Despite the dominance of the basal S sites,they are generally inert to HER because of the low p-band center.Herein,we reported a synergistic combination of phase engineering and NH_(4)^(+) intercalation to promote the HER performance of MoS_(2).The rational combination of 1T and 2H phases raises the p-band center of the basal S sites while the intercalated NH4+ions further optimize and stabilize the electronic band of these sites.The S sites with regulated band structures afford moderate hydrogen adsorption,thus contributing to excellent HER performance over a wide pH range.In an acid medium,this catalyst exhibits a low overpotential of 169 mV at 10 mA·cm^(−2)and Tafel slope of 39 mV·dec^(−1)with robust stability,superior to most of recently reported MoS_(2)-based non-noble catalysts.The combined use of in/ex-situ characterizations ravels that the appearance of more unpaired electrons at the Mo 4d-orbital reduces the d-band center which upshifts the p-band center of the adjacent S for essentially improved HER performance.This work provides guidelines for the future development of layered transition-metal-dichalcogenide catalysts.

Micro/nanostructured amorphous TiNbZr films to enhance the adhesion strength and corrosion behavior of stainless steel

To improve the corrosion resistance of key components and ensure the service safety of marine equipment,here we combined femtosecond(fs)laser fabrication and magnetron sputtering deposition to develop micro/nanostructured amorphous TiNbZr films.Analysis of the compositional,microstructural,corrosion,and mechanical properties was conducted.The results showed that the TiNbZr films were amorphous,and spherical TiNbZr nanoparticles uniformly covered the fs laser-induced periodic fringe structure.A complex hierarchical micro/nanostructure was formed that was hydrophobic and showed enhanced adhesion strength.The TiNbZr films deposited on fs laser-treated substrates provided the best corrosion resistance,showing a self-corrosion current density of 116 nA/cm^(2),excellent passive ability,and pitting resistance.The microscratch test revealed that the micro/nanostructures doubled the binding strength of the TiNbZr/316L interface due to the compositional and structural gradients induced by an approximately 20 nm transition layer formed during fs laser processing.This work provides a new method for obtaining anti-corrosion films with a high adhesion strength for marine applications.

Molecular coordination-doping engineering enables adjustable ion transport channel based on MOFs-derived UIOLiTF-LLZTO ionic conductor

The inferior ionic conductivity of composite polymer electrolytes(CPEs)caused by grain boundary impedance is one of the critical issues.Adjustable ion transport channels at the molecular level can improve ionic conductivity and lithium-ion transference number.Herein,UIO-66-NSO_(2)CF_(3)LiLi_(6.4)La_(3)Zr_(1.4)Ta_(0.6)O_(12)(UIOLiTF-LLZTO)ionic conductor derived from metal-organic frameworks(MOFs)was designed by a covalent grafted strategy of trifluoromethylsulfonyl(TF)group on UIOLiTF and a doping process of LLZTO,showing two new lithium-ion transfer channels driven by molecular coordinationdoping engineering.The first channel along UIOLiTF-UIOLiTF was constructed due to the existence of the TF group on UIOLiTF.The second channel along UIOLiTF-LLZTO was constructed due to the direct nanometer contact interface between the opened channel of UIOLiTF and LLZTO.Then TF group acts as“claws”to capture and transfer lithium-ion along the different channels,facilitating improving ionic conductivity and reducing grain boundary impedance.Benefiting from the molecular coordination-doping engineering,UIOLiTF-LLZTO exhibits high ionic conductivity of 9.86×10^(-4)S cm^(-1),a large lithium-ion transference number of 0.79,and a wide electrochemical window of 5.35 V.Meanwhile,all-solid-state Li|UIOLiTF-LLZTO|LiFePO4 batteries show a high specific capacity of 164.5 mAh g^(-1)and 155.6 mAh g^(-1)at 0.2 C and 0.5 C,respectively.Therefore,UIOLiTF-LLZTO demonstrates the way towards the development of MOFs-based CPEs for all-solid-state lithium batteries with high performance.

Inhibited superoxide-induced halide oxidation with a bioactive factor for stabilized inorganic perovskite solar cells

Active oxygen highly affects the efficiency and stability of perovskite solar cells(PSCs)owing to the capacity to either passivate defects or decompose perovskite lattice.To better understand the in-depth interaction,we demonstrate for the first time that photooxidation mechanism in all-inorganic perovskite film dominates the phase deterioration kinetics by forming superoxide species in the presence of light and oxygen,which is significantly different from that in organic-inorganic hybrid and even tin-based perovskites.In all-inorganic perovskites,the superox-ide species prefer to oxidize longer and weaker Pb-I bond to PbO and I_(2),leaving the much stable CsPbBr_(3) phase.From this chemical proof-of-concept,we employ an organic bioactive factor,Tanshinone IIA,as a superoxide sweeper to enhance the environmental tolerance of inorganic perovskite,serving as a“skincare”agent for anti-aging organisms.Combined with another key point on healing defective lattice,the best carbon-based all-inorganic CsPbI_(2)Br solar cell delivers an efficiency as high as 15.12%and superior stability against oxygen,light,humid-ity,and heat attacks.This method is also applicable to enhance the efficiency of p-i-n inverted(Cs_(0.05)MA_(0.05)FA_(0.9))Pb(I_(0.93)Br_(0.07))_(3)cell to 23.46%.These findings not only help us understand the perovskite decomposition mechanisms in depth but also provide a potential strategy for advanced PSC platforms.

Heterojunction interface editing in Co/NiCoP nanospheres by oxygen atoms decoration for synergistic accelerating hydrogen and oxygen evolution electrocatalysis

Controllable designing of well-defined heterojunction nanostructures provides an insightful strategy for accelerating the kinetics of the hydrogen and oxygen evolution reactions(HER/OER),but such task is still challenging.Herein,we proposed a protocol of heterojunction interface editing(HIE)strategy by oxygen atoms decoration for synergistic boosting electrocatalytic HER and OER performances.A novel Co/NiCoP nanospheres(NSs)heterojunction was synthesized by crystal seed template transformation method with Ni_(5)P_(4) microspheres as seeds.The effective oxygen atoms interface editing increased the oxidation state of Co atoms and prolonged the Co-P bond length of Co/NiCoP NSs heterojunction,thus the electron localization on P sites was enhanced,leading to the dramatically elevated HER and OER performances simultaneously.The as-constructed O-Co/NiCoP NSs show excellent electrocatalytic activity with 361 and 430 mV vs.reversible hydrogen electrode(RHE)to arrive high current density of 300 mA·cm^(-2)for HER and OER in 1 M KOH as well as good stability.The proposed HIE concept could provide a new perspective on the catalyst design for energy conversion systems.

强耦合氧化钼氮碳复合材料的制备及其锂离子存储性能研究

氧化钼(MoO_(3))是一种具有吸引力的锂离子电池(LIBs)负极材料;然而,其导电性低、锂化后体积膨胀大、锂离子扩散动力学缓慢等特点严重限制了其实际应用.本文中,我们利用高量Mo/N掺杂的碳前驱材料合成了超细的MoO_(3)纳米颗粒(NPs,10–15 nm),所合成的MoO_(3)NPs被限制在原位生成的N掺杂碳网络结构中.这种设计既促进了快速的电子传导,又缩短了锂离子扩散路径;同时,MoO_(3)表面丰富的氮物种和氧缺陷有助于降低锂离子的吸附能垒,这些共同支持了MoO_(3)NPs在高电流倍率下耐久储锂性能的提升.值得注意的是,所获得的NCMoO_(3)纳米复合材料表现出1362 mA h g^(−1)(0.1 A g^(−1))的较高容量,并在10.0 A g^(−1)时保持394 mA h g^(−1)的可逆容量.全电池测试表明:在大倍率5 C下,LiFePO_(4)//NC-MoO_(3)-400电池仍可以输出81 mA h g^(−1)的比容量.我们的工作有望启发其他嵌入导电碳网络的过渡金属氧化物的设计合成及其在LIBs中的实际应用.