73 research outputs found

    Retrofit of a Heat-Exchanger Network by Considering Heat-Transfer Enhancement and Fouling

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    Many design methods for the retrofit of heat-exchanger networks have been proposed during the last 3 decades. Conventional retrofit methods use additional area to accommodate the increasing heat duty. However, the implementation of additional area may prove difficult because of topology, safety, and downtime constraints. This problem can be mitigated through the use of heat-transfer enhancement. This Article investigates the influence of heat-transfer enhancement on fouling in heat-exchanger networks. A novel design approach is used to solve heat-exchanger network retrofit problems on the basis of heat-transfer enhancement by considering fouling. Simulated annealing is used to optimize the retrofit problem under fouling conditions. The results show that heat-transfer enhancement is a very attractive option for retrofitting when fouling is considered. The consideration of fouling in heat-transfer enhancement has the potential to make a significant impact on retrofit design and to make the design more cost-effective than conventional design approaches

    Interfacial Structure and Energy Determine the Heterogeneity in the Electrochemical Metal Dissolution Activity at Grain Boundary

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    Grain boundaries are defects present in polycrystalline materials that often possess unique electrochemical activity, including in metal dissolution reactions. The structural origin of the enhanced activity at some grain boundaries is often experimentally elusive because of the ambiguity in attributing the activity to a specific grain boundary due to ensemble averaging. Herein, we experimentally elucidate the structural and energetic effect of grain boundary on metal dissolution reaction by colocalized scanning electrochemical cell microscopy (SECCM) and electron microscopy assisted by focused ion beam (FIB). The local dissolution activity at isolated locations containing only single grain boundaries is measured from SECCM. The structure and orientation of the same grain boundary planes are characterized by electron backscatter diffraction and FIB, which is confirmed by transmission electron microscopy (TEM). The relative interfacial energy of these grain boundaries is also measured via the thermal grooving method. Using anodic dissolution at Ag grain boundaries as a model system, we found that the dissolution rate increases with grain boundary energy and the density of broken bonds at the grain boundary plane. The results explain the heterogeneity in the activity of metal dissolution at different grain boundaries, elucidating the initiation sites of metal dissolution. The method developed here is generally applicable to revealing the structure–activity correlation of electrochemical reactions at grain boundaries

    Developing low-carbon cities through pilots

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    <p>Nationwide rapid urbanization has been a key driver of economic growth, energy consumption, and carbon emission in China. To avoid the high energy consumption and pollution present in other industrialized countries, China is making the economic and social transition from a high-carbon model to a low-carbon model. The low-carbon city pilots (LCCPs) programme was launched by the National Development and Reform Commission (NDRC) to resolve the dilemma between economic development and transitioning to a low-carbon model. The status quos of these pilots in different regions have set CO<sub>2</sub> intensity per unit of gross domestic product (GDP), CO<sub>2</sub> emissions per capita, CO<sub>2</sub> reduction targets, and CO<sub>2</sub> discharge peak times. Traditional policies, including those aimed at improving energy efficiency, applying renewable energy, adjusting sector structure, and increasing carbon sequestration capacity, are being widely applied in the form of command-mandatory tools, market-economic tools, and voluntary tools. By summarizing these policies, low-carbon development plans, LCCP governments reports, and a case study focusing on Zhenjiang (practical experiences based on city features), this article proposes implications for how to achieve the LCCPs’ low-carbon goals.</p> <p><b>Policy relevance</b></p> <p>China has launched a low-carbon city pilots (LCCPs) programme to promote its future low-carbon urbanization, but the cities concerned have not yet managed to achieve true ‘low-carbon' status in terms of CO<sub>2</sub> per unit of GDP and CO<sub>2</sub> per capita. To improve the performance of LCCPs, central government should provide guidance on institutional framework and policies, while local governments should establish carbon management systems. Both central and local governments should establish a policy assessment system and use integrated policy tools as part of their low-carbon development plans.</p

    Cooperative Catalytic Alkyne Hydrosilylation by a Porphyrinic Metal–Organic Framework Composite

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    Vinylsilanes are valuable building blocks and important structural units in organic chemistry. Herein, catalytic alkyne hydrosilylation was reported to be promoted by a porphyrin metal–organic framework with the incorporation of Pd nanoparticles (Pd@Ir-PCN-222). Catalytic results showed that Pd@Ir-PCN-222 displayed high catalytic efficiency, giving rise to the E isomer vinylsilane with an excellent turnover frequency (TOF) of 2564 h–1. The mechanism studies revealed that the enhancement of the catalytic activity originated from the cooperation between iridium porphyrin and the Pd nanoparticle in confined spaces. The iridium porphyrin was prone to absorb and condense the hydrosilane and alkyne in the inner cavities of Ir-PCN-222, not only accelerating the reaction but also promoting the Pd nanoparticle to activate the Si–H and CC bonds of hydrosilane and alkyne, respectively

    Formation of Regular Stripes of Chemically Converted Graphene on Hydrophilic Substrates

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    Chemically converted graphene (CCG), from a chemistry point of view, is a giant molecule with a unique two-dimensional (2D) configuration. The availability of CCG dispersion provides a range of scalable methods to assemble graphene-based materials but brings the challenge of understanding and control of the CCG morphology in solution processing. In this study, we found that, similar to conventional colloidal systems (e.g., spherical particles or polymers), a 2D sheet of CCG can be transferred from its aqueous dispersion to solid substrates in the form of highly regular stripe patterns by evaporation-driven deposition. The width and spacing can be defined by the concentration of the CCG dispersion and the properties of the substrate (e.g., roughness and surface charge). Furthermore, the high resolution AFM images illustrate that both 2D flattened and highly wrinkled CCG can be formed in each individual stripe, depending on the location across the stripe. The in situ optical observation of the stripe formation indicates that the morphological change of CCG may occur in the crowded meniscus of the drying front

    Kaplan-Meier curve of cumulative catheter patency.

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    <p>Patients with TDCs through left IJV (Blue, n = 28) were compared with those through right EJV (purple, n = 21). TDCs, tunneled cuffed dialysis catheters; IJV, internal jugular vein; EJV, external jugular vein.</p

    Kaplan-Meier curve of primary catheter patency.

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    <p>Patients with TDCs through left IJV (Blue, n = 28) were compared with those through right EJV (purple, n = 21). TDCs, tunneled cuffed dialysis catheters; IJV, internal jugular vein; EJV, external jugular vein.</p

    Formation of Regular Stripes of Chemically Converted Graphene on Hydrophilic Substrates

    No full text
    Chemically converted graphene (CCG), from a chemistry point of view, is a giant molecule with a unique two-dimensional (2D) configuration. The availability of CCG dispersion provides a range of scalable methods to assemble graphene-based materials but brings the challenge of understanding and control of the CCG morphology in solution processing. In this study, we found that, similar to conventional colloidal systems (e.g., spherical particles or polymers), a 2D sheet of CCG can be transferred from its aqueous dispersion to solid substrates in the form of highly regular stripe patterns by evaporation-driven deposition. The width and spacing can be defined by the concentration of the CCG dispersion and the properties of the substrate (e.g., roughness and surface charge). Furthermore, the high resolution AFM images illustrate that both 2D flattened and highly wrinkled CCG can be formed in each individual stripe, depending on the location across the stripe. The in situ optical observation of the stripe formation indicates that the morphological change of CCG may occur in the crowded meniscus of the drying front

    Improved Targeting Procedure To Determine the Indirect Interplant Heat Integration with Parallel Connection Pattern among Three Plants

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    The interplant heat integration (IPHI) problem has received growing interest for its potential to reduce energy consumption and emissions beyond heat integration within individual plants. Indirect IPHI using an intermediate energy carrier (intermedium) allows for practical implementation as opposed to direct IPHI, which may consist of multiple piping loops using process streams. Various interplant connection patterns of intermedium loops present differences in interplant heat recovery potential, pipeline costs, and the reliability of IPHI system. This work addresses that the parallel connection pattern for it presents the maximum interplant heat recovery potential and is a flexible pattern. An improved targeting procedure is proposed to determine the parallel connection pattern. This method can determine the real maximum interplant heat recovery potential for indirect IPHI among three plants and simultaneously minimizes the corresponding intermedium flow rates. Two examples from prior literatures, as well as the modified cases, are solved to demonstrate the proposed method. The proposed method can always present multiple feasible solutions for IPHI problems. Compared with the previous results for the certain case, under the same interplant heat recovery potential, a better solution in terms of the overall intermedium flow rate and/or the number of heat exchanger used can be found from all the feasible ones
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