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Promoting the development and utilization of solar energy is a practical way to alleviate the energy crisis and achieve the goal of carbon neutrality. Recently, interest has arisen in the dual-functional active solar thermal façade (ASTF) system that produces hot water throughout the whole year and reduces cooling and heating load as a function of the building façade. Here, a mathematical model of the ASTF system is built and validated by the experimental data, and the annual performance of the ASTF system in representative cities in three climate regions is evaluated. The results are that compared with the common solar water system, the ASTF system adds passive energy savings, which accounts for 5.8%, 7.2% and 11.4% of the total primary energy savings of the system for Shanghai, Beijing and Lanzhou. Compared with the traditional wall, the ASTF saves 16.4% and 23.0% of cooling energy consumption and 102.3% and 92.4% of heating energy consumption for Shanghai and Beijing, respectively. Additionally, it saves 74.7% of heating energy consumption for Lanzhou. Lastly, the impact of the design parameters and operation parameters of the system are investigated, respectively. This study demonstrates a viable path to promoting cost-effective active solar thermal façades in different climates, and the results can be beneficial to further research. [ABSTRACT FROM AUTHOR]

Mass exchange network (MEN) synthesis is an important technique to ensure efficient purification of industrial waste gas sources and water streams. However, most existing models for MEN synthesis are not capable of dealing with multi-component problems and achieving optimal designs. In this study, an innovative process integration strategy based on a node-based vertical non-structural model (NV-NSM) is proposed. The developed strategy allows for a more random representation of process configuration and aids in handling both single- and multi-component problems. The NV-NSM arranges several groups of main nodes in the process streams and the sub-nodes in their branches and results in design configurations by connecting any two sub-nodes on the rich and lean streams at the same main node number. When dealing with multi-component synthesis, the number of tray column is directly optimized to balance the mass transfer needs of different components. As part of the current investigation, the random walk algorithm with compulsive evolution (RWCE) is established to realize the simultaneous optimization of multiple variables, including the mass transfer loads, the number of trays, the stream split ratios, and the flowrates of lean streams. Furthermore, the fine-search strategy based on the RWCE is applied to improve global and local optimization performance. Finally, the proposed method is applied to four MEN cases featuring different exchanger specifications and considering both single and multiple components. The implementation and analysis result in more optimal solutions compared to those published in the literature, demonstrating the feasibility and effectiveness of the proposed method in analyzing and evaluating different MEN problems, including multi-component ones. • A node-based vertical non-structural model is presented for mass exchange networks. • The proposed model is feasible for both single and multiple component problems. • Random walk algorithm with compulsive evolution is used to optimize the new model. • The proposed method can balance the mass transfer needs of different components. • Four cases with single and multiple component are solved with lower system costs. [ABSTRACT FROM AUTHOR]

A novel method combined signal flow graph of a single heat exchanger with the transfer function of streams is developed for the dynamic behaviors of heat exchanger networks problems, which are determinate factors of the process control and operation optimization in the processing industries. The transfer functions between any two nodes of heat exchanger networks including the inlet and the outlet are obtained based on the signal flow graph of the networks by block-diagram reduction, Mason's rule and the seeking-up method. The developed method is solved by a numerical inverse Laplace transform and the analytical solution to the dynamic behavior of heat exchanger networks is presented in the time domain. The numerical results demonstrate that the presented method is more efficient and more accurate for the dynamic behaviors of heat exchanger networks problems. [ABSTRACT FROM AUTHOR]

This paper proposes novel microencapsulated phase change material slurries (MPCSs) as both the energy storage media and heat transfer fluids. The flow and heat transfer characteristics of MPCSs have been experimentally investigated. A series of experiments were conducted in laminar, transition and turbulent flow conditions for MPCSs in a circular tube under constant heat flux, respectively. The results of pressure drop measurements showed that transportation costs of slurries were close to pure water. The heat transfer experiments demonstrated that proposed MPCSs could enhance the heat transfer performance as the heat transfer fluids for thermal system applications in comparison with pure water. The average enhancement percentages of the Nusselt number were 23.9%, 20.5% and 9.1% for MPCS of 5 wt%, and enhancement of the Nusselt number was achieved when phase change material in the microcapsules were in solid, solid/liquid and liquid states, respectively. However, heat transfer enhancement of MPCS depends on the following combination factors: the slurry concentration, the flow rate, the pumping power and the heating rate. Importantly, the phase change process must be carefully controlled in the heat transfer test section with above combination factors in order to take advantages of MPCS over pure water. [ABSTRACT FROM AUTHOR]

• A new separation technology is applied in process integration system. • Two variant of non-structural models are adapted in the mass exchanger network system. • The advantages of two variant models are analyzed. • A two-step optimization approach for mass exchanger network synthesis is proposed. Mass exchanger networks have been considered a promising solution for reducing impurity in streams and maximizing energy recovery in the chemical industry. This paper adjusts two non-structural models with distinct optimization variables and a heuristic algorithm according to the MEN synthesis characteristics. Considering the requirement of the objective function, a two-step optimization method that combines these two models is proposed. In the first step, a feasible solution is determined by the model using the transferred mass as an optimization variable. In the second step, the aforementioned model is employed to maximize tray utilization by adopting the tray number as an optimization variable. The results of the two cases obtained by the proposed method are 406,330 $/yr and 329,326 $/yr, which are lower than the published results, and is verified on two cases regarding quality and efficiency. [ABSTRACT FROM AUTHOR]

Highlights • A NLP for optimal heat load distribution is solved by a Cuckoo Search Algorithm. • An improved Cuckoo Search Algorithm is proposed for optimal HENS. • An efficient stream arrangement strategy is used to depress the demand of stages. • Four benchmark cases are solved with a lower TAC compared with previous methods. • A special characteristic from two case studies is analyzed to lower the TAC. Abstract Heat exchanger network synthesis (HENS) is still a challenging task for minimizing the Total Annual Cost (TAC). In this work, a Cuckoo Search Algorithm (CSA) is introduced to solve the NonLinear Programming (NLP) problem of the fixed heat exchanger network design to determine the optimal heat load distribution, which can help improve the heat load configurations of previously found optimum configurations. The improved CSA (ICSA) is used to solve the Mixed Integer NonLinear Programming (MINLP) problem for optimal HENS, which can simultaneously optimize continuous and integer variables, and the proposed stream arrangement strategy aims to optimize the stream match search space by lowering the stage demands, i.e. reducing the number of independent variables, which is a promising means for an easier solution of large and medium sized HENS problems. Four large and medium sized benchmark cases have been investigated, obtaining no-splits results with lower TAC in a shorter computational time. In addition, a special feature from case 3 and 4 is analyzed, which is useful in order to achieve a lower TAC by using modified Stage-Wise Superstructure (SWS) models with flexible utility placement. [ABSTRACT FROM AUTHOR]

The major difficulty in the heat exchanger network synthesis (HENS) is dealing with the simultaneous optimization of large-scale continuous and integer variables. Heuristic algorithms are used in HENS due to their efficient global search ability and the step size (Δ L ) constitutes one of the critical concepts in it. In this paper, by analyzing the influence of Δ L in Random Walk Algorithm with Compulsive Evolution (RWCE), it was pronounced that evolution speed got faster when Δ L increased in the early stage and evolution accuracy was higher by Δ L declination, in the late stage. Hence, five new different Δ L adjustment functions were proposed. This case-study concluded that Δ L adjustment functions in an upward parabola declination could maintain high speed in the early stage and improve the accuracy of solutions in late stage respectively. However, during the late stage, the minor Δ L led to the decline of the global search ability and it was difficult to jump out of the local minimum. Furthermore certain individuals in the population were randomly given a relatively large Δ L in late stage. Thus, an integrated RWCE algorithm with Δ L adjustment strategy was presented and demonstrated satisfying global and local search ability. [ABSTRACT FROM AUTHOR]

We propose a novel model control with dynamic adaptation to improve the control accuracy and speed of heat exchangers. The proposed method first applies an accurate mathematical model of heat exchanger as a motion model to create the inverse problem algorithm of manipulated variable. Subsequently, it improves the transient performance using a dynamic adaption of manipulated variable. Compared the control performance to feedback control method, the dynamic adaptation of manipulated variable fed in an exponential function resulted in both approximately a 100% reduction in overshoot and settling time elimination in response to inlet temperature and flow rate disturbances of objective fluid. [ABSTRACT FROM AUTHOR]

Multipopulation differential evolution combined with opposition-based learning is developed to improve the convergence efficiency and optimization accuracy for heat exchanger network synthesis. The algorithm is based on a stagewise superstructure simultaneous optimization model without considering stream splitting. The candidate population and its opposite population are searched in parallel. Mutation operations are implemented on both populations to provide a full information exchange among populations at each generation. A regrouping schedule is introduced to avoid premature convergence. The algorithm is applied to five heat exchanger network cases of different sizes. More economic networks are found using this method with less computational time. [ABSTRACT FROM AUTHOR]

The study of radiation property of particles is of great significance in the field of solar thermo-chemistry. In this study the randomly dispersed particle system is obtained by the KBr tablet method, and the transmittance of activated carbon particle systems in 0.4–25 μm wavelength are measured by the spectrophotometer and FTIR to obtain their radiation property. The extinction coefficient of the particle systems and the efficiency factor for extinction of single particle are calculated through experimental data. The results show that the activated carbon particles have higher absorption ability in the visible light spectrum. Above investigation will not only be beneficial to the simulation of solar thermo-chemistry hydrogen production process, but also provide an experimental basis for inverse calculation of optical constants of the activated carbon particles. [ABSTRACT FROM AUTHOR]

The synthesis of heat exchanger networks (HENs) is a complex problem because of the nonlinearity that results from the integer and continuous variables. Here, a bi-level algorithm for the optimal design of a HEN is proposed that attempts to optimize separately the integer and continuous variables on two levels. The master level is a problem-oriented evolution method generating new candidate HEN structures. The slave level is a memetic particle swarm optimization, an improved particle swarm optimization combined with a local search component, improvement of neighbourhood topologies and control parameter preference. The slave level minimizes the total annual cost (TAC) of a given structure received from the master level, and then sends this value back to the master level for structure evolution. The proposed bi-level method is applied to several cases taken from the literature, which demonstrate its reliable search ability in both structure space and continuous variable space and its ability to optimize the system, producing generally lower TACs than previously used methods. [ABSTRACT FROM AUTHOR]

Gel-supported surfactant dry solution (GDS) was prepared by mixing gelling agent, sodium dodecyl sulfate (SDS) solution, hydrophobic silica nanoparticles and air in a high speed blender. GDS has the merits of surfactant dry solution (DS) and gel-supported dry water (GDW). The stack of micron-sized GDS droplets provides abundant gas transport channels and large surface area for gas–liquid contacting. Each droplet is a micro system with active surface and gelling structure. Methane storage in clathrate hydrates using GDS was investigated in a stainless steel vessel without stirring under the condition of 5.0 MPa and 273.15 K. The results demonstrated that the dispersed GDS droplets could significantly enhance formation kinetics, storage capacity and storage repeatability of methane hydrate. In addition, GDS exhibited faster storage rate (4.5221 m 3 m −3 min −1 ) and higher storage capacity (152.23 m 3 m −3 ) than GDW. Compared with SDS-DS, GDS has similar storage rate and better storage repeatability (by experiment of 9 cycles), but its storage repeatability slightly became poor and capacity decay occurred due to the agglomeration of droplets after these cycles of hydration/dissociation. [ABSTRACT FROM AUTHOR]

The optimization of distributed energy systems (DES) is challenging because of the diversity of the types of energies involved and the complexity of the structure. Mathematically, the optimization of DES is a mixed-integer non-linear programming problem (MINLP). The optimal tradeoff between precision and computational efficiency, to find the global optimal solution, is a core issue that needs to be solved. This present work proposes a two-stage superstructure model which is solved by the random walk algorithm with compulsive evolution (RWCE), to better approximate the global optimal solution of the MINLP. The paper is divided into two parts; the first focuses on the modeling methodology and model solving strategy. Moreover, to confirm the applicability and effectiveness of the recommended method, DESs for three case studies, i.e. , business park, residential building, and hotel, were optimized from system planning point of view. On comparison with literatures, it was found that the proposed method had positive effects on further improving the economy of the system at different scales and configurations. The resulting decrease in the total annual cost of the three systems was 12%, 36%, and 2%, respectively. Further research on system operation optimization will be published as the second part of this paper. • A two-stage superstructure model is established for the optimization of renewable energy integrated DES. • RWCE algorithm is used to solve the proposed model to better approximate the global optimal solution of the MINLP. • The applicability and effectiveness of the proposed method are proved by three case studies. • The economy of DESs at different scale and configurations has been improved. [ABSTRACT FROM AUTHOR]

The global optimization of heat exchanger network synthesis remains a hotspot and challenge in the field of chemical process integration. The random walk algorithm with compulsive evolution has shown good performance in avoiding entrapment in the local optima by accepting imperfect solutions with a certain mutation probability. This work first investigates the detailed effects of accepting imperfect solutions on the continuity of optimization and the efficiency of global optimization by analyzing the imperfect solutions generated in the optimization process. Then, a novel parallel optimization route is established to balance the global and local search ability by combing basic and fine-search optimization levels. Additionally, enhancing strategies promoted by accepting imperfect solutions and large step lengths are integrated into the parallel optimization route to further improve the efficiency of structure evolution and global optimization. Finally, three case studies are presented to verify the effectiveness of the proposed method and discuss the roles of each module and different module combinations in facilitating the global search. Many promising results with more structure possibilities are obtained in each case study, with the obtained optimal solutions being lower than most reported in the literature. This indicates the effectiveness of the proposed method in facilitating the structure evolution and global optimization for heat exchanger network synthesis. • Accepting imperfect solutions affects structure mutation and evolution continuity. • Parallel optimization route uses basic/fine-search level for global/local search. • Modules for enhancing structure evolution are optional in the optimization route. • The method performs well in the global optimization of heat integration problems. [ABSTRACT FROM AUTHOR]

Traditional pinch design method of heat exchanger networks is improved, the composite curve is divided into several segments for individual treatment, the network of every segment using the uniformity factor of temperature difference of heat exchanger networks as the evaluation index is designed, the structures of every segment and the matches far form the pinch re combined into an integrated original heat exchanger network, the original structure using Newton method as regulation optimization is optimized, and an optimal cost heat exchange network finally is obtained. From a specific example, the heat exchanger network designed according to the uniformity principle of temperature difference field is of better heat transfer performance, the final annual cost is better than that of other literature, and the availability of this method is validated. [ABSTRACT FROM AUTHOR]

The non-structural model of a heat exchanger network randomly selects a position of a node on hot and cold streams to generate a heat exchanger and an existing heat exchanger to participate in the evolution. Despite the model being more random and flexible, this selection method cannot easily find a good solution. In addition, the heat exchangers participating in the evolution might not be involved in all streams in each evolutionary process. A stream that does not participate in the evolution will have no significance to the current iteration. Therefore, many iterations are required to make each stream participate in the evolution, which limits the evolution efficiency of the optimization algorithm. In view of this shortcoming, this study proposes a participatory evolutionary strategy for streams based on hot streams. The proposed strategy reorders the existing heat exchangers on hot and cold streams and takes the corresponding measures to ensure that a heat exchanger is selected for each stream to participate in the evolution in every cycle. The proposed participatory evolutionary strategy for streams improves the global optimal solution for designs based on non-structural models. The effectiveness of the proposed strategy is demonstrated in two cases. [ABSTRACT FROM AUTHOR]

• A new optimization concept for heat exchanger network synthesis is proposed. • Functional sequential method is used in simultaneous optimization. • The new concept arranges optimization route by combining functional modules. • The optimization route varies according to the optimization requirement of different stages. Heuristic algorithms are widely used in the global optimization of heat exchanger network synthesis (HENS). However, since heuristic algorithms are often characterized by a divergent search and a combination of multi-parameters, it is difficult to weigh and balance the global and local search in the process. In existing algorithms, the global and local search weight is commonly fixed during optimization. As a result, the algorithms hardly distribute the structural and continuous variables optimization suitably, sometimes even becoming invalid. Even more so, such algorithms fail to realize functions enhancing the searching ability. Therefore, this paper proposes a new, phased, modular concept that supports functional and sub-functional combinations to timely escape the stagnant status and obtain satisfying solutions with high efficiency and high quality. The concept's main goal is to achieve flexible combining and sequencing of different functions during the optimization process. Hence, the optimization route arrangement emphasizes the functions' distribution, which differs from the sequential methods decomposing the whole problem. Each route's components are not unique, and the structure's current needs can change the modules' sequences and categories. Such coordination of modules improves the algorithm's exploration and exploitation abilities, enabling the proposed method to attain better results within less computational time and rendering. Therefore, the proposed method is more suitable in large-scale HENS owing to much local optima involved in cases. Three cases are used to demonstrate the proposed routes' validity, which shows that the optimization route arrangement successfully decreases the total annual cost and improves computational efficiency. [ABSTRACT FROM AUTHOR]

• A life cycle analysis on recycling and secondary use of lithium-ion batteries. • Based on the recycling in China, the LCA of different methods has been established. • Compared to other recovery, the secondary use has the lowest environmental impact. • Secondary use has the greatest impact on assessment results in dynamic situations. With the rapid development of the global new energy vehicle industry, how to minimize the environmental impact of the recovery has become a common concern and urgent concern. China is a major production and consumption market for electric vehicles, there are no specific and extensive resource and environmental assessment system for batteries. In this paper, the retired Electric vehicles lithium-ion batteries (LIBs) was the research object, and a specific analysis of the recycling treatment and gradual use stages of power batteries were based on life cycle assessment. Different battery assessment scenarios were established according to the development of battery recycling in China. The results showed that the secondary use has the optimal performance compared to the full-component physical, pyrometallurgical and hydrometallurgy recycling. The results showed that direct recycling has a GWP of 0.037 kg-CO 2 eq·kg LIB-1, which is lower than others. Secondary use of LIB accounts for the most emission reductions with Global warming (GWP) as 12.134 kg-CO 2 eq·kg LIB-1. The secondary use has the greatest impact on the assessment results, especially in dynamic scenarios. Through a comprehensive comparison of different recycling technologies, the secondary use, increasing the recycling rate, reducing resource, energy consumption and pollution emissions. [ABSTRACT FROM AUTHOR]

Enhanced greenhouse effects by anthropogenic emissions of greenhouse gases (GHGs) resulted in global warming since the Industrial Revolution. However, the influence of the spectral characteristics of the Earth's surface radiation on the greenhouse effect has not been completely explored. This work uses the surface temperature as the variable of model and investigates the response mechanism of the greenhouse effect. According to the GHGs' different selective spectral absorption of earth's infrared radiation (IR) band and the distribution characteristic of spectral radiant intensity with the temperature increases, some quantified analysis shows that the greenhouse effect is highly dependent on two factors: the radiation intensity enhancement (RIE) and the spectral absorption enhancement (SAE). RIE is determined by the spectral radiant intensity of earth's IR while SAE represents the GHGs' spectral absorption change under different wavelength. As the results show, RIE always enhances the greenhouse effect, while SAE, as a result of the spectral shift in the Earth's radiant energy, can enhance or weaken the greenhouse effect depending on the positive or negative total SAE integrated over the entire spectral region. The quantified data of this work also explain the reason why greenhouse effect has greater impact on extreme cold areas from the aspect of spectral characteristics: when the surface temperature drops below −20 °C, SAE of CO 2 has an enhancing effect, so that both RIE and SAE exert positive influences with the temperature increase in the polar region for its extremely low surface temperature, which doubly enhances the global warming. • Analyzing the mechanism of the greenhouse effect from the aspect of GHGs' spectral characteristics. • Temperature increase is attributed to radiation intensity enhancement (RIE) the spectral absorption enhancement (SAE). • RIE always enhances the greenhouse effect, while SAE can either enhance or weaken greenhouse effects. • In the polar region, the RIE and the SAE of CO 2 doubly enhance on the greenhouse effect. [ABSTRACT FROM AUTHOR]

For more than three decades, heat exchanger network (HEN) synthesis has been primarily addressed by defining initial structures that embed different design alternatives, and near optimal HEN configurations are extracted from these structures during the optimization process. However, such initial structures are prone to missing necessary design alternatives and may require simplifying assumptions to ease the computational burden of optimization algorithms. This paper presents a non-structural model (NSM) for synthesis of HEN considering stream splitting and non-isothermal merging of branch streams. The model exhibits randomness in stream matching, generation and elimination by which potential matches are realized. Random walk algorithm with compulsive evolution is used for optimization of both integer variables (number of heat units) and continuous variables (heat duties and split fractions). The effectiveness of the approach is tested for small- and medium-size literature cases. The method demonstrates results comparable to or better than those reported in literature. • Non-structural model with stream splitting is proposed for heat exchanger network synthesis. • Split regions are used in process streams to decide stream splitting and mixing. • HENs are optimized using random walk algorithm with compulsive evolution. • Solutions are comparable to or better than those previously published in literature. [ABSTRACT FROM AUTHOR]

Heat exchanger network (HEN) synthesis is a vibrant research field in process system engineering, with substantial contributions to energy conservation and emissions reduction initiatives. The optimal design of a heat exchanger network is not an easy task due to the abundance of local optima in the solution space caused by the non-linear, non-convex, and discontinuous nature of the problem. Generally, several heuristic algorithms employ a greedy evolutionary mechanism, optimize through greedily accepting the decrease in the objective function, and converge to obtain the optimal solution. The Random Walk algorithm has a simple evolutionary mechanism, is prone to mutation, and exhibits high flexibility. However, the algorithm's inherent persistent greediness in searching restrict the scope of the search. Thus, this paper proposes an anti-greedy concept based on the Random Walk method to serve as the basis of a new synthesis approach called the Anti-greedy Random Walk algorithm. Two strategies are proposed in the algorithm, which broaden the solution domain by slowing down rapid unit reduction and accepting imperfect solutions, respectively. One strategy is to thoroughly search for the integer and continuous variables of the HEN problem by covering a much larger search space. Another is to escape the local extrema and move forward to discover more possibilities. Quantitative data demonstrates the algorithm's ability to avoid the local extrema and enhance the search effectiveness. Three different scales of classical cases are used in this work and the obtained results are superior to the published ones. [Display omitted] • An improved Random Walk algorithm is presented for heat exchanger network synthesis. • Two anti-greedy strategies are proposed from an objective and structural perspective. • Both integer and continuous variables are explored by covering a larger search space. • Three benchmark cases were solved with better results than previously literature. [ABSTRACT FROM AUTHOR]

An electrochemical method for improving the durability of cement mortar by injection of nanoparticles (alumina (Al2O3)-coated silica (SiO2)) is presented. In this method, nanoparticles are injected into cement mortar pores under an external electrical field, refining the pore structure of cement mortar. The efficiency of electro-injection nanoparticle treatment with different applied electric fields was evaluated by monitoring the evolution of cement mortar resistivity. The improvement of cement mortar durability after electro-injection of nanoparticles was assessed by examining the resistance to water absorption, carbonation, sulfate attack and chloride diffusion. The microstructure of cement mortar after the electro-injection treatment was analysed using scanning electron microscopy (SEM), mercury intrusion porosimetry (MIP), X-ray diffraction (XRD) and differential thermo-gravimetric analysis (DTG). The results show that cement mortar durability can be improved by the injection of nanoparticles under external electric field. The efficiency of electro-injection nanoparticle treatment increased with the increase of applied electric field. The resistance to water absorption, carbonation, sulfate attack and chloride diffusion were significantly improved by using the electro-injection method. The improvement in cement mortar durability can be attributed to the filling effect of nanoparticles. [ABSTRACT FROM AUTHOR]

A novel nano phase change material emulsion (NPCE) with low supercooling and high thermal conductivity was prepared by sonication method. N -octadecane was employed as phase change material, multi-walled carbon nanotubes (MWCNTs) were utilised as high thermal conductivity material, and octadecanol was utilised as nucleating agent. The characterization and thermal properties of the nanoemulsions prepared with various concentrations of MWCNTs and octadecanol were measured and analysed by scanning electron microscopy (SEM), transmission electron microscopy (TEM), particle size analyser, differential scanning calorimeter (DSC) and thermal conductivity meter. The results indicated that the nanoemulsions prepared had great stability, low supercooling and enhanced thermal conductivity. The thermal conductivity was enhanced by 4.32% for 10 wt% nanoemulsion with addition of 1 wt% MWCNTs. The supercooling degree of 20 wt% nanoemulsion was decreased by 36.4% from 17.3 °C to 11.0 °C with addition of 1 wt% octadecanol. It can be concluded that the nanoemulsions prepared were able to be utilised as heat transfer and energy storage fluids, with great potential in thermal system applications. • The enhancement ratio of thermal conductivity was 4.32% for 10 wt% nanoemulsion. • The supercooling of 20 wt% nanoemulsion was decreased by 36.4% with addition of 1 wt% octadecanol. • Fabricated nanoemulsions presented good stability and thermo-physical properties. • Fabricated nanoemulsions have great potential application in the thermal systems. [ABSTRACT FROM AUTHOR]

• A non-structural model (NSM) was presented for HEN synthesis. • A general implementation method was proposed to make NSM feasible for optimization. • NSM is flexible and not restricted by the predefined and staged framework in SWS. • The proposed method can achieve better results with relatively higher efficiency. Simultaneous synthesis of heat exchanger network (HEN) is an indispensable strategy to improve energy efficiency and realize high techno-economic performances. The structural models that involve a stage-wise superstructure have some limitations concerning the global optimization for the HEN, including the flexibility of configurations and computational efficiency of synthesis methods. Therefore, a novel non-structural model (NSM) is proposed in this work for the simultaneous synthesis of the HEN. Firstly, the concept of a non-structural HEN configuration is described based on an analysis of the drawbacks of structural models. Then, the mathematical formulation of the NSM is provided. Finally, a general implementation method is proposed to realize the simultaneous synthesis of an NSM-based HEN and make it a feasible synthesis method. Six medium and large scale case studies are used to demonstrate the flexibility of configurations in the proposed model and its performance concerning the global optimization of HEN synthesis using a random walk algorithm with compulsive evolution. The combination of the NSM and the heuristic method has led to better optimal solutions than those that exclude the stream splits as published in previous works, achieving high quality and efficiency in the synthesis of HEN problems. [ABSTRACT FROM AUTHOR]

Random walk algorithm with compulsive evolution (RWCE) performs better for global optimization of heat exchanger network synthesis than other stochastic methods though it faces the inevitable decrease in optimization efficiency during the late period. This paper aims to analyze the relationship between population diversity and optimization performance. Firstly, population diversities are contrasted to explain the relatively satisfactory performance of RWCE. It is found that the optimal structures for individuals become significantly similar with evolution. Secondly, key evaluation indexes are established to identify similar individuals and clusters formed during the evolution. A noteworthy observation of the study is the clustering phenomenon in RWCE where most individuals cluster together with structural community while 5% individuals alone are excluded from the clusters. Finally, a population-diversity enhancement strategy is established to weaken the negative effect of the clustering phenomenon and enhance the global optimization efficiency. The new strategy is efficient in achieving more economical solutions compared to those in literatures. [ABSTRACT FROM AUTHOR]

Abstract Hydrogen sorption and storage in a solid matrix can greatly improve its safety and efficiency when compared to the compressed gas or liquid hydrogen storage system, and kinetics mechanisms are of interest towards the development of such materials. In this study, the composites of Mg-Ni-Cu doped with singe-walled carbon nanotubes (Mg-Ni-Cu/CNTs) were synthetized. The activation performance, isothermal hydrogen sorption and desorption were systematically tested, and the experimental data were analyzed using the shrinking core model. The results show that three cycles of hydrogen sorption and desorption may be enough to fully activate Mg-Ni-Cu/CNTs and the stability can be kept for 150 cycles. A 10.1 wt% of Cu and 50.3 wt% of Ni in Mg-Ni-Cu/CNTs facilitates the hydrogen sorption and a reversible hydrogen capacity of ∼3.35 wt% can be achieved at 310 °C and 3.0 atm, and hydrogen capacity and kinetics shows significant decline during contact with 1.0 vol% CO impurity. Considering desorption at 600 °C, the kinetic profiles are about linear and desorption is completed within minutes. The gas-solid reaction processes for hydrogen sorption undergo three different rate-limiting stages, and hydrogen desorption can only be divided into two stages of surface chemical reaction and product layer diffusion. Highlights • MgNiCu/CNTs are active in H 2 sorption at 310 °C and 3.0H 2 pressure. • Cu, Ni and CNTs can facilitate H 2 sorption of Mg and increase stability. • H 2 sorption and kinetics are deteriorated during contact with CO impurity. • Kinetics mechanisms and rate-limiting steps were determined by SCM. [ABSTRACT FROM AUTHOR]

This paper presents a tradeoff grassroots design of cost-effective and low-CO 2 emissions heat exchanger networks for crude oil distillation units (CDUs) to address high energy consumption in CDUs. To reduce the impact of the objective's magnitude on the optimization searching direction, a normalization process handling the objectives to the dimensionless indexes to assess the performance of CDU is presented. An originally designed random walk algorithm with compulsive evolution (RWCE) and a special superstructure nodes-based non-structural model (NNM) is adopted for the multi-objective optimization problem. The comparison analysis shows that the proposed model and the heuristic algorithm are robust in solving the global optimization problem. In addition, aiming to investigate the evolution mode of utilities in RWCE, an active evolution strategy of utilities (RWCE-AU) is proposed to promote structural evolution by altering the heat loads of utilities by a certain probability. Finally, several industrial CDU cases are optimized by RWCE and RWCE-AU in this work. The continuous improvement solutions have highlighted that the RWCE could yield a better optimal total annual cost (TAC) compared to the reported initial case. Moreover, the RWCE-AU enhances the searching ability of RWCE and provides a better tradeoff between the economic benefits and the environmental impacts. • A multi-objective approach is proposed for crude oil distillation units. • Economic benefit and CO 2 emissions are simultaneously considered in the design. • A new algorithm and optimization model are adopted in the problem. • An active utilities evolution strategy is proposed to enlarge the energy recovery. [ABSTRACT FROM AUTHOR]

Photovoltaic (PV) power generation coupled with proton exchange membrane (PEM) water electrolysis favors improving the solar energy utilization and producing green hydrogen. But few systems proposed focus on achieving all-day stable hydrogen production, which is important for the future large-scale hydrogen utilization. Herein, a PV-Battery-PEM water electrolysis system for hydrogen production was constructed. An energy management strategy (EMS) was proposed to achieve the goal of all-day stable hydrogen production, improve energy utilization efficiency and reduce light discard rate. The PV power generation system, battery system and PEM electrolyzer for hydrogen production system were first established by Matlab/Simulink platform. Then, the overall PV-Battery-PEM electrolyzer system for hydrogen production was constructed, and the effectiveness of EMS was verified. The energy efficiency of the system under different working conditions with and without battery for energy storage was analyzed. The results show that the proposed energy management strategy can meet the purpose of all-day stable hydrogen production. Under the same working conditions, the energy efficiency of the system with battery for energy storage increases by 2–4% compared with the system without battery for energy storage, which indicates that the addition of energy storage can improve the energy utilization and reduce the light discarding. [Display omitted] [ABSTRACT FROM AUTHOR]

Hydrogen production and reduction of Ni-based oxygen carriers (OCs) during chemical looping steam reforming (CLSR) of ethanol were studied in a fixed-bed reactor using four OCs with different supports including NiO/SBA-15, NiO/MCM-41, NiO/MMT and NiO/Al 2 O 3 . The OCs prepared were characterized by N 2 adsorption-desorption, TPR, TPO, XRD, TEM, FTIR and TGA-DSC. The results demonstrated that NiO component in all the OCs was first reduced by ethanol and the reduced OCs were responsible of catalytic steam reforming and water gas shift for hydrogen production. Mesoporous NiO/SBA-15 presented increasing conversion of NiO reduction and the highest selectivity of hydrogen production. The conversion of ethanol increased with reactions proceeding until the highest value is reached after about ∼300s, and the negative steam conversion obtained was resulted from H 2 O formation from ethanol oxidation by OCs. Compared with MMT and Al 2 O 3 supports, the oxidization of NiO with MCM-41 and SBA-15 supports was very fast and less carbon was formed and deposited. Enhancement in hydrogen production from CLSR process was achieved by in-situ CO 2 removal. Shrinking Core model (SCM) based on the constant pattern model for fixed-bed reactor indicated the rates of OCs reduction with ethanol were mainly controlled by surface chemical reaction and product layer diffusion. The reduction process was found to undergo three different rate-limiting stages, and the critical times for changes in the rate-limiting steps were determined. [ABSTRACT FROM AUTHOR]

Biochar-assisted water electrolysis (BAWE) facilitates the high-value utilization of biomass and energy-saving hydrogen production. However, the BAWE efficiency is hindered by slow kinetics of biochar oxidation reaction (BOR) at anode. Herein, to improve the overall efficiency of BAWE, three-dimensional porous nanosheets modified on nickel foam (Ni 1 Fe 2 -LDH@NF) was developed for BOR, and its mechanism was identified. Impressively, the BAWE system exhibited remarkable activity, including a low potential of 1.387 V vs. RHE for BOR over as-synthesized electrocatalyst at current density of 10 mA·cm−2, and excellent long-term stability over 20 h at a high current density of 200 mA·cm−2 and after 1000 CV cycles. The required electricity input was 3.29 kWh·Nm−3H 2 at 10 mA·cm−2 for BAWE with Ni 1 Fe 2 -LDH@NF toward BOR. In addition, the reaction mechanism of BOR including biochar direct oxidation on the electrocatalysts surface and indirect oxidation in the electrolyte was deduced, according to the surface chemistry and composition changes of electrocatalysts and biochar, as well as the products. This work provides an effective strategy towards the enhancement of the BOR process by designing the binder-free electrocatalysts, and facilitates the development of BAWE for energy-efficient hydrogen production and biomass utilization. [Display omitted] • 3D porous Ni–Fe nanosheets modified on nickel foam was developed for enhancing BOR. • Ni 1 Fe 2 -LDH@NF favored the adsorption of OH− and accelerated the charge transfer rate. • Ni 1 Fe 2 -LDH@NF toward BOR demonstrated a potential of 1.387 V vs. RHE@10 mA·cm−2 and stability over 20 h@200 mA·cm−2. • The BOR mechanism including biochar direct oxidation on electrocatalysts and indirect oxidation in electrolyte was deduced. [ABSTRACT FROM AUTHOR]

Highly-efficient and stable non-noble metal electrocatalysts for overcoming the sluggish kinetics of oxygen evolution reaction (OER) is urgent for water electrolysis. Biomass-derived biochar has been considered as promising carbon material because of its advantages such as low-cost, renewable, simple preparation, rich structure, and easy to obtain heteroatom by in-situ doping. Herein, Ni 2 P–Fe 2 P bimetallic phosphide spherical nanocages encapsulated in N/P-doped pine needles biochar is prepared via a simple two-step pyrolysis method. Benefiting from the maximum synergistic effects of bimetallic phosphide and biochar, high conductivity of biochar encapsulation, highly exposed active sites of Ni 2 P–Fe 2 P spherical nanocages, rapid mass transfer in porous channels with large specific surface area, and the promotion in adsorption of reaction intermediates by high-level heteroatom doping, the (Ni 0.75 Fe 0.25) 2 P@NP/C demonstrates excellent OER activity with an overpotential of 250 mV and a Tafel slope of 48 mV/dec at 10 mA/cm2 in 1 M KOH. Also it exhibits a long-term durability in 10 h electrolysis and its activity even improves during the electrocatalytic process. The present work provides a favorable strategy for the inexpensive synthesis of biochar-based transition metal electrocatalysts toward OER, and improves the water electrolysis for hydrogen production. [Display omitted] • Ni 2 P–Fe 2 P spherical nanocages encapsulated in N/P-doped biochar is synthesized. • High-level heteroatom ((N + P + O): C) doping of 30.61 at% is achieved. • OER over (Ni 0.75 Fe 0.25) 2 P@NP/C demonstrates an overpotential of 250 mV@10 mA/cm2. • The synergistic effect of Ni 2 P–Fe 2 P and N/P-doped biochar promotes OER. [ABSTRACT FROM AUTHOR]

To improve the process and performance of CO 2 capture with ammonia by chemical absorption, a vortex flow-based multistage spray reactor was designed to evaluate the enhancement effect for post-combustion CO 2 capture with ammonia. The process intensification analysis based on flow patterns from a CFD (computational fluid dynamics) simulation indicated that the vortex flow presented multi-dimensional velocities including a V-shaped tangential velocity profile and non-uniform axial velocity profile, which resulted in enhancement of gas–liquid contact, mixing, mass transfer, and reaction compared to non-vortex flow. Furthermore, the CO 2 capture characteristics were examined at varied operating parameters. It was found that the capture efficiency E increased with increasing ammonia concentration and liquid flow rate but decreased with increasing CO 2 inlet concentration and gas flow rate. Meanwhile, the overall gas phase mass transfer coefficient K g a increased with increasing ammonia concentration, liquid flow rate, and gas flow rates but decreased with increasing CO 2 inlet concentration. Within the measured range, the E and K g a varied from 72.05 to 86.72% and 0.31–0.49 × 10 −3 kmol/m 3 kPa s, respectively. Importantly, vortex flow presents relative enhancements of 7–15% in E and 18–33% in K g a compared with non-vortex flow depending on the operating parameters. [ABSTRACT FROM AUTHOR]

The electrochemical Bunsen reaction has been proposed as an innovative and promising method compared with the traditional Bunsen reaction for the sulfur–iodine cycle, and its kinetics were studied in this work. Polarization curves were measured using platinum electrode in the different concentrations of SO 2 –H 2 SO 4 –H 2 O and I 2 –HI–H 2 O solutions at a temperature range of 303–353 K. Fundamental kinetic parameters, namely exchange current density, Tafel slope, asymmetry factor, were determined for anodic SO 2 oxidation reaction and cathodic I 2 reduction reaction according to the Tafel plots. The activation energy and pre-exponential factor for the electrode reactions were also analyzed using Arrhenius relation. Results indicated that an increase in the SO 2 concentration in the anolyte and the I 2 concentration in the catholyte reduced the activation energy, contributing to the easier anode and cathode reaction. Take high electrode reaction rate and easier electrode reactions into account, the initial SO 2 concentration of 1.509 mol/L and the I 2 /HI molar ratio of 0.5 could be optimal. [ABSTRACT FROM AUTHOR]

Ca/Zr mixed oxide catalysts were prepared using three different methods and were employed in the transesterification of rapeseed oil with methanol for biodiesel production. To elucidate their composition, morphology and basic properties, the resulting materials were characterized using: thermogravimetric analysis, N 2 -adsorption, X-ray diffraction, scanning electron microscopy, temperature programmed desorption of CO 2 and X-ray photoelectron spectroscopy. A birch template method was found to improve the pore structure and dispersion of basic sites. The highest biodiesel yield reached 92.6% over CaO/ZrO 2 catalyst prepared by template method with a Ca-to-Zr molar ratio of 0.3 under the optimal reaction conditions: catalyst mass fraction 8%, 72:1 M ratio of methanol to rapeseed oil, reaction temperature 120 °C and a reaction time of 6 h. [ABSTRACT FROM AUTHOR]

• The addition of metal oxide particles greatly improves the thermal conductivity of MPCS. • MPCS with metal oxide particles can enhance heat transfer under different flow conditions. • Heating power and flow rates are crucial to the heat transfer of MPCS. • MPCS with metal oxide particles can be used as heat transfer medium and energy storage fluid. ZnO, nano ZnO and nano Al 2 O 3 were mixed with microencapsulated phase change material slurry (MPCS) for improving the heat transfer performance of slurries in this paper. The thermal and rheological properties of MPCS were measured using DSC, thermal conductivity meter and rheometer. The results show that the thermal conductivity of 5 wt% MPCS with 1 wt% ZnO, nano ZnO and nano Al 2 O 3 was 17.9 %, 19.4 % and 23.5 % higher than that of 5 wt% MPCS, respectively. The forced convection heat transfer experiment of slurries was carried out in a loop system with various heat flux and flow conditions. The influences of heat flux, flow rate and metal oxide particles on the flow and heat transfer behaviour of slurries were investigated. The results show that the heat transfer was significantly enhanced for all slurries with metal oxide particles under three flow conditions. Compared with water, the local heat transfer coefficient (h x) of MPCSs with 1 wt% ZnO, nano ZnO and nano Al 2 O 3 increased by 6.5 %, 9.1 % and 12.4 % under laminar flow, 6.6 %, 15.5 % and 14.9 % under transition flow, and 15.7 %, 19.0 % and 21.6 % in turbulent condition, respectively. [ABSTRACT FROM AUTHOR]

[Display omitted] • Electrochemical activation of biochar was achieved via limited electrooxidation. • Biochar-assisted water electrolysis reduced electricity consumption for hydrogen production. • Oxygen-containing groups enriched on biochar during its electrooxidation. • Upgraded biochar by electrochemical activation enhanced its removal of Cr(VI). • Cr(VI) removal mechanism by upgraded biochar follows attraction-reduction-complexation. Biochar-assisted water electrolysis (BAWE) has the potential to reduce the electricity consumption of hydrogen production. However, prolonged electrolysis leads to over-oxidation of biochar, reduced reactivity, and decreasing hydrogen production at cathode. Herein, we proposed the electrochemical activation of biochar via limited biochar oxidation reaction (BOR) and hydrogen evolution reaction (HER) in BAWE process, and the upgraded biochar was employed to remove Cr(VI). Distinct biochar was first pyrolyzed from three kinds of representative biomass components, cellulose, lignin, and their mixture at different temperatures. All of them exhibited excellent BOR activity, especially the biochar derived by the pyrolyzed cellulose and lignin at 800 °C (MBC-800) required a potential as low as 1.319 V vs. RHE@1 mA cm−2 using Pt electrode in 1 M KOH and achieved a Faraday efficiency almost 100% for hydrogen production. BAWE presented an energy-saving electrical consumption of 4.98 kWh Nm−3 H 2 compared to the conventional water electrolysis of 5.32 kWh Nm−3 H 2. Electrochemical oxidation enriched the oxygen-containing groups on biochar surface, which significantly improved its reductivity towards Cr(VI) and complexation with Cr(III), leading to the removal rate of Cr(VI) more than doubled. Results showed the achievement of electrochemical activation of biochar by limited electrooxidation. These findings provide a new route for the high-value utilization of biochar and energy-saving electrolytic hydrogen production. [ABSTRACT FROM AUTHOR]

SO 2 -depolarized electrolysis (SDE) is the key process in the hybrid sulfur cycle for green hydrogen production, but the detailed SDE characteristics including products generation, current efficiency variation, and side reactions are unclear. Herein, a continuous SDE process was experimentally conducted and theoretically modelled. The H 2 and H 2 SO 4 production was accelerated and the current efficiency for both electrodes was improved with a proper increase in current density (50−100 mA/cm2) or temperature (293−318 K), but further increasing current density to 150 mA/cm2 or temperature to 333 K led to a negative trend because of the anode corrosion or declined SO 2 solubility. The increasing initial H 2 SO 4 concentration (10−40 wt%) facilitated the cathodic H 2 production and current efficiency, while negatively influenced the anodic SO 2 conversion. The parasitic reactions occurred at cathode consumed H 2 and resulted to the cathodic current efficiency well below 100%. A rigorous mathematical regression model correlating the production rates of H 2 and H 2 SO 4 with current density, temperature, and initial H 2 SO 4 concentration was developed, and combined with the analysis of variance, current density was suggested the biggest factor affecting products generation in SDE process. These findings demonstrate a practical avenue for efficient SO 2 conversion and H 2 production in SDE process of hybrid sulfur cycle. [Display omitted] • H 2 and H 2 SO 4 production, current efficiency, and side reactions during SDE process were characterized. • Influence of current density, temperature, and initial H 2 SO 4 concentration on SDE process were emphasized. • Rigorous mathematical regression models concerning H 2 and H 2 SO 4 production rates were developed. • Current density was the biggest influencing factor toward products generation during SDE process. [ABSTRACT FROM AUTHOR]

Three nanoscale metal oxides composed of nano TiO 2 , nano Al 2 O 3 , and nano MgO were added to the phase change microcapsule slurry for optimising the heat transfer behaviour. The thermal and rheological properties of the resulting microencapsulated phase change materials (MPCMs) and microencapsulated phase change material slurries (MPCSs) were characterized to determine the effects of added metal oxides in optimising the performance of MPCSs. The impacts of factors like metal oxides, concentrations, and flow rates on the heat transfer behaviour of MPCSs were investigated by forced convective heat transfer experiment with various working conditions. Compared to 6 wt% MPCSs, the heat transfer coefficients (h x) of 6 wt% slurries containing 1 wt% TiO 2 , 1 wt% Al 2 O 3 , and 1 wt% MgO increased by 4.0 %, 2.5 %, and 7.13 %, respectively. Nano-MgO showed the most significant heat transfer enhancement effect on MPCSs. Moreover, the heat transfer performance gradually enhanced as a function of the concentration for nano MgO. Overall, the addition of metal oxides enhanced heat transfer by increasing the thermal conductivity of the slurry, as well as improved the micro-convection effect. The proposed MPCSs are promising for applications in solar photovoltaic/thermal (PV/T) systems, chip cooling, thermal management, buildings, and automotive cooling. [Display omitted] • Forced convection heat transfer experiment were conducted with bonded triangular tubes. • Heat transfer enhancement achieved by optimising heat transfer medium and tube structure. • Metal oxide type and concentration have significant effect on heat transfer of slurries. • Nano-MgO showed the most significant heat transfer enhancement effect on slurries. [ABSTRACT FROM AUTHOR]

• A flowsheet of SI cycle considering the Bunsen reaction kinetics was developed. • A user-defined Fortran module concerning Bunsen reaction kinetics was established. • Internal heat exchange network was created using pinch point temperature difference analysis. • The theoretical thermal efficiency of SI system was obtained in the range of 14.0–57.4 %. Thermochemical sulfur-iodine (SI) cycle is one of the large-scale, clean, and efficient hydrogen production routes. The Bunsen reaction process is always simulated by a stoichiometric reaction, without considering the realistic Bunsen reaction kinetic process. Herein, a user-defined Fortran module concerning Bunsen reaction kinetics was developed and embedded into a continuous stirred tank reactor (RCSTR), and then a SI flowsheet with 100 L/h hydrogen production was modeled. The key parameter optimization, mass and energy balance were analyzed, the internal heat exchange network was created using the pinch point temperature difference analysis and the principle of energy cascade utilization, along with thermal efficiency evaluation. Bunsen reaction process reaches equilibrium after a period, which is consistent with experiments. The increase of H 2 SO 4 decomposition ratio is beneficial to reduce the energy consumption of system. Increase in temperature has less effect on increasing the equilibrium decomposition ratio of HI. The theoretical thermal efficiency of system reaches 14.0–57.4 % considering the recovery of exothermic heat. This work provides a theoretical basis for the optimization of SI cycle. [ABSTRACT FROM AUTHOR]

Balancing the trade-off between structural diversity (solution space) and optimization efficiency is an urgent challenge in the modeling and global optimization of heat exchanger network synthesis problems. This paper presents a node dynamic adaptive non-structural model without stream splitting to enhance optimization efficiency under the premise of ensuring an adequate solution space. The node-based non-structural stream matching mechanism can be used to make the solution space scalable and achieve the efficacy of multi-stage stage-wise superstructure with a finite number of nodes. Two node dynamic adaptive strategies (uniformly distributed and random) are established to periodically adjust the number of nodes in process streams and the node distribution of existing heat exchanger units, thereby preventing a decrease in computational efficiency due to an excess number of preset nodes while still satisfying the solution space requirements. The node dynamic adaptive non-structural model is optimized using the random walk algorithm with compulsive evolution. The proposed method was applied to four well-known heat exchanger network case studies. High-quality solutions were obtained, and they are more economical than most of the optimal results previously reported in the literature. These results demonstrate the enhanced computational efficiency and applicability of the proposed synthesis method based on a node dynamic adaptive non-structural model for efficiently solving large-scale heat exchanger network synthesis problems. • Node dynamic adaptive non-structural model (NDA-NSM) was presented. • NDA strategies were established to make the solution space of NDA-NSM scalable. • NDA-NSM ensures adequate solution space and enhances the optimization efficiency. • High-quality solutions were obtained by combing NDA-NSM with efficient algorithm. [ABSTRACT FROM AUTHOR]

Carbon-based fuel electrochemical reforming is considered as a promising hydrogen production method. Ethanol is one of the most appropriate carbon-based fuels. In this work, anode performance, especially the flow, ethanol electro-oxidization and energy consumption in the ethanol electrochemical reforming is numerically studied and experimental verified. Take the straight serpentine channel with square cross-section as a base structure in the electrochemical cell (EC), the effects of channel geometry and operating parameters are analyzed. Another five different configurations of flow channels, as well as another three different cross-sections are designed and explored. Results indicate that at the same cross-section area, the wider channel provides the higher effective area for proton transfer, and thereby improves the electrode reactions. The appropriate decrease of inlet velocity or increase of input voltage promotes the anode reaction and reduces the pressure drop in channel, while the operating temperature has the opposite effects on ethanol conversion and pressure drop. The arc channel is found optimal considering its highest ethanol conversion, although its pressure drop is a bit higher. The sector cross-section with uniform flow field distribution is found most favorable for the straight serpentine channel considering the ethanol electro-oxidization. These findings will favor the improvement of EC. • 3-D mathematical model for ethanol electrochemical reforming was developed. • Flow, ethanol electro-oxidization and energy consumption at anode were studied. • Effects of flow channels and operating parameters were characterized. • The favorable channel configuration and cross-section were proposed. [ABSTRACT FROM AUTHOR]

• Node-wise non-structural model is proposed for heat integration of energy system. • NW-NSM can realize free stream matching and flexible insertion of new matches. • NW-NSM can achieve the efficacy of multi-stage SWS with the finite number of nodes. • NW-NSM shows great adaptability when optimized by stochastic methods for HENS. • Uniform distribution strategy can expand solution space for structure optimization. The present paper proposes an original node-wise non-structural model (NW-NSM) with no stream splits for the heat integration of energy system. Global optimization approaches using structural models such as the stage-wise superstructure model, have limitations for heat exchanger network synthesis. Instead of complying with the typical fixed multi-stage network frameworks of stage-wise superstructures, the new model generates stream matches by randomly connecting preset nodes in the hot and cold streams. Then, the NW-NSM is optimized using the random walk algorithm with compulsive evolution. Furthermore, the effects of nodes on the solution space and performance of the NW-NSM are analyzed. Finally, a uniform distribution strategy for node locations of existing heat exchangers is used to expand the solution space and to ensure the generation of all possible stream matches. The combination of a flexible model and stochastic algorithm improves the global optimization. The model was applied to medium and large-scale case studies to verify the feasibility and high efficiency of the NW-NSM with respect to the global optimization of heat exchanger networks. The model achieved more economical results compared to other models previously presented in the literature. [ABSTRACT FROM AUTHOR]

Multi-energy system is currently under rapid development due to their potential to reduce the use of fossil fuel resources and improve system stability. A systematic simulation-based, multi-objective optimization model of for solar hybrid heat pump heating and cooling system is presented. A combined energy, economic and environmental analysis of the system is conducted to calculate the primary energy use as well as the levelized total annual cost. A multi-objective optimization model is formulated using a genetic algorithm to simultaneously minimize these objective. Linear programming technique for multidimensional analysis of preference (LINMAP) is used to select the optimal point from the Pareto front. A sensitivity analysis is also performed to assess the influence of fuel cost, capital cost of innovative components and the annual interest rate on the Pareto front of the optimal solution. • Systematic simulation and MOO model for solar hybrid heat pump system are presented. • Genetic algorithm is used for the model to minimize energy and economic objectives. • Sensitivity analysis of the influence of parameters on the Pareto front is made. [ABSTRACT FROM AUTHOR]

Summary: To improve the sulfur‐iodine (SI or IS) cycle for renewable hydrogen production, direct electrolysis of HIx solution (HI‐I2‐H2O) from Bunsen reaction has been recently proposed. This work concerns the detailed microscopic physical performance and electrolytic processes of HIx electrolysis through theoretical simulation and experimental exploration. A two‐dimensional mathematical model of the electrolytic cell for HIx electrolysis was developed, and was verified by the relevance between the simulated and experimental hydrogen production. The concentration, electric and flow field distributions were characterized. The decrease of anodic HI and increase of cathodic H2 were found along the flow direction. The local potential distribution declined from anode to cathode region. Higher pressure drop from the inlet to outlet of channel as well as the pumping power were required for anolyte than catholyte. More detailed electrolytic processes along the flow channel at different operating conditions were analyzed. Increasing temperature from 303 K to 343 K improved the H2 production rate. A low anode flow rate of 0.2 m/s was favorable for achieving high conversion rate of reactants and low consumed pumping power. The developed models and the clarified characteristics of HIx electrolysis will be further applied to the improved SI cycle. [ABSTRACT FROM AUTHOR]

The sulfur–iodine (SI or IS) thermochemical cycle assembled with solar or nuclear energy has been proposed as a large-scale, clean and renewable hydrogen production method. In present work, an improved SI cycle integrated with HI electrolysis for hydrogen production was developed according to experiments and simulation. The mathematical models of HI electrolysis using proton exchange membrane (PEM) electrolytic cell was developed, and then the user-defined module of HI electrolysis was set up through Aspen Plus and verified by experimental data. After designing and simulating the new flowsheet of the SI cycle based on HI electrolysis, 10 L/h of H 2 and 5 L/h of O 2 were obtained. The theoretic thermal efficiency of flowsheet reached 25–42% in terms of the utilization of waste heat. An ideal thermal efficiency of 33.3% through the proper internal heat exchange in the flowsheet was determined. Sensitivity analyses of parameters in the system were conducted. Increasing proton transfer number of PEM electrolytic cell in HI section improved the thermal efficiency of SI cycle. The ratio of distillate to feed rate and the plate number of distillation column in H 2 SO 4 section were the most sensitive factors to the heat duty of overall SI cycle. The proposed new flowsheet for SI cycle is competitive to the flowsheets previously proposed in the field of flowsheet simplification. • An improved flowsheet of SI cycle based on HI electrolysis was designed. • Mathematical models for HI electrolysis were developed. • User-defined module of HI electrolysis was set up and experimentally verified. • The theoretic thermal efficiency of 25–42% was estimated for the flowsheet. [ABSTRACT FROM AUTHOR]

Transition from bulk surfactant solution to gelatinous surfactant dry solution and the behavior of the methane uptake in GDS droplets during the repeated hydrate formation. • GDS droplets have the merits of the dry water, the surfactant solution and the gelling agent. • The droplets can provide abundant gas channels, considerable gas–liquid contact area and stable gel-like structure. • The droplets facilitate rapid and reversible methane storage in clathrate hydrate. • The droplets maintained relatively high methane storage capacities until the ninth cycle. A gelatinous dry solution (GDS) was prepared by blending sodium dodecyl sulfate solution, gellan gum powder, and hydrophobic silica nanoparticles in air at a high speed. It is essentially a pile of free-flowing micro surfactant droplets supported by a gelling agent. The GDS has the dispersion characteristics of dry water, activity of the surfactant solution and stability of the gel. The flour-like droplets can provide abundant micro channels for gas transfer, a considerable surface area for gas–liquid contact and stable gel-like structure for repeated hydrate formation. Multi-cycle methane consumption experiments were conducted in a stainless steel vessel at 5.0–8.1 MPa and 273.2 K, in order to study the repeated kinetics of methane hydrate formation in GDS. The results demonstrated that the dispersed GDS facilitated rapid and reversible methane storage in clathrate hydrate by enhancing the gas–liquid contact and the stability of the regular droplets. Methane uptake (152.2–163.2 m3·m−3) and maximum uptake rates (4.522–5.690 m3·m−3·min−1) were achieved in the first storage cycle at the experimental pressures. GDS maintained relatively high methane storage capacities (114.3–118.0 m3·m−3) until the ninth cycle, and the capacities only were attenuated by 24.92–27.70% with respect to the first cycle at the above pressures. A hypothesis of "droplets breakage by released gas" was proposed to illustrate the attenuation of gas storage capacity of the droplets. [ABSTRACT FROM AUTHOR]

• The channels of aluminum honeycomb (AH) can be considered as micro-vessels for the formation of gas hydrates. • Large surface area of AH provided sufficient nucleation sites for hydrate nucleation. • The excellent thermal conductivity of the metallic surface facilitates dissipation of the hydrate heat. • SDS-AH system can store more methane with the higher hydrate formation rate compared to SDS solution. In order to investigate the effect of metal honeycomb on the formation kinetics of methane hydrate, gas consumption experiments were conducted in a stainless steel vessel filled with sodium dodecyl sulfate (SDS) and aluminum honeycomb (AH) at 274.2 K in the pressure range 5.0–9.0 MPa. The honeycomb structure provides several interconnected channels with large rough surfaces for the promotion of hydrate nucleation. Meanwhile, the excellent thermal conductivity of the metallic surface facilitates dissipation of the hydrate heat. The honeycomb channels can be considered as micro-vessels for the formation of gas hydrates, and each channel provides a "free-unimpeded thermal conduction surface" for heat transfer in the hydration system. When AH is introduced in the SDS system, the methane consumption and its rate surpassed the values recorded in the absence of AH. The maximum gas consumption and the rate reached 157.0 ± 1.9 cm3·cm−3 and 29.65 cm3·cm−3·min−1, respectively. Comparison with the SDS system under similar conditions revealed that the maximum gas consumption rates increased by 9.62–14.30%. We hope this work provides new insights into the kinetic behavior of the formation of gas hydrates in metal honeycombs. [ABSTRACT FROM AUTHOR]

Hydrogen production from the sulfur–iodine water splitting cycle integrated with solar or nuclear energy has been proposed as a promising technique. Bunsen reaction is one of the three main steps in the cycle and electrochemical method has been applied to this reaction. In present work, a three-dimensional numerical study of the electrochemical Bunsen reaction was conducted. A three-dimensional, steady state, laminar and isothermal mathematical model of electrolytic cell was developed and verified by experiments. The spatial maldistribution of species concentration was found between electrodes and proton exchange membrane (PEM). The electric power drives most H 2 SO 4 and I 2 to the anode and cathode surface, respectively, while the proton attraction contributes to HI enrichment on the surface of PEM. At the high inlet H 2 SO 4 concentration of 50 wt%, the transformation of flow channel from single serpentine to single entry & double serpentine with the same inlet flow rate cannot solve the insufficient problem of SO 2. But the increase of the overall inlet flow rate in the double entry & double serpentine flow channel make SO 2 sufficient for anode reaction. Further decreasing the inlet H 2 SO 4 concentration to 40 wt% and 30 wt% make the initial SO 2 sufficient for overall reactions. The single serpentine channel gives the highest SO 2 conversion rate, followed by the single entry & double serpentine and double entry & double serpentine flow channels. The single serpentine flow channel at the H 2 SO 4 inlet concentration of 40 wt% is found optimal for achieving a high electrochemical Bunsen reaction performance. • Three-dimensional study of electrochemical Bunsen reaction was first conducted. • A 3-D, steady state, laminar and isothermal model of EC was developed. • Transformation of flow channel and key initial conditions were analyzed. • Single serpentine flow channel at inlet H 2 SO 4 of 40 wt% was optimal. [ABSTRACT FROM AUTHOR]

[Display omitted] • Correlation between biochar oxidation reaction (BOR) and electrolytes was determined. • Alkaline electrolyte was more favorable for biochar-assisted water electrolysis. • The higher concentration of H 2 SO 4 and S O 4 2 - slowed down the BOR kinetics. • The highest diffusion coefficient of 3.11 × 10−3 cm2∙s−1 for biochar was obtained at pH of 13.98. Biochar-assisted water electrolysis (BAWE) for hydrogen production is employed to reduce energy consumption by replacing the oxygen evolution reaction (OER) with thermodynamically more favorable biochar oxidation reaction (BOR). Electrolyte, as a carrier to dissolve the biochar particles and form conductive solution, is essential for the transfer and transformation of biochar particles and free radical precursors. Herein, the effects of electrolyte type, concentration, and pH on the BOR performance of BAWE system were investigated. Results show that 1 M KOH solution as an electrolyte was more suitable for the BAWE system, and the BOR of the alkaline BAWE system had the higher electrochemical activity (E 10 = 1.649 V vs RHE, 56 mV∙dec−1) compared with the OER in conventional water electrolysis system (E 10 = 1.982 V vs RHE, 189 mV∙dec−1). The anion adsorption phenomenon appeared in acidic media restricted the BOR kinetics. In addition, the diffusion coefficient of anodic reaction components showed a first decrease and then increase trend when the pH increased. And the diffusion coefficient reached the maximum value of 3.11 × 10−3 cm2∙s−1 at pH of 13.98, which was favorable for accelerating the diffusion of reaction components from the bulk solution to the electrode surface. This work can provide guidance for further improving the diffusion of reaction components, the biochar oxidation rate and hydrogen production in BAWE process. [ABSTRACT FROM AUTHOR]

• A homemade microsensor measures CCL dynamic temperature. • An improved transient thermal model is developed to analyze the process. • Both experiment and simulation indicate 0–7 °C temperature variation. • Temperature variation is dramatically affected by cathode operation. • Underlying mechanisms for temperature variation are analyzed. Temperature variation inside the cathode catalyst layer (CCL) is significant, which could greatly damage fuel cell performance and durability. However, limited by CCL microstructure and complex physicochemical processes, the knowledge regarding CCL dynamic temperature is indeed insufficient. Thus, this work integrates a pre-prepared thin-film microsensor into the fuel cell to measure CCL surface temperature under dynamic load. At the same time, an improved transient thermal model considering local mass transport and liquid effect on thermal contact resistance (TCR) is established for the first time to analyze the internal process. Results show that CCL temperature is greatly affected by local resistance and interface accumulated water. And, as confirmed by both experiment and simulation, the CCL surface exhibits 0–7 °C temperature variation, whose profile changes sharply at the beginning and then evolutes slowly, eventually taking tens or hundreds of seconds to reach a new steady state due to thermal inertia. Moreover, the temperature is further increased by ∼1 °C as cathode humidity increases or stoichiometric ratio decreases, but only slight changes with the anode condition. The significant role of cathode operation is attributed to the greater mass transfer resistance and more sensitive intrinsic oxygen reduction reaction to reactant change. This study is expected to provide a deeper understanding of CCL dynamic temperature, thus improving fuel cell thermal management. [ABSTRACT FROM AUTHOR]