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In this paper, the heat transfer enhancement (HTE) of supercritical nitrogen flowing downward in a vertical small tube (diameter 2 mm) is studied using the commercial software CFX of Ansys16.1, to provide theoretical guidance on the design of high-performance heat transfer systems. An effective numerical simulation method, which employs the SSG Reynolds stress model with enhanced wall treatment, is applied to study the heat transfer of supercritical nitrogen under typical working conditions. The objective is to evaluate the effect of the main parameters taking into account the buoyancy and flow acceleration effects. Simulation results are compared with results calculated from three well-known empirical correlations and the applicability of empirical correlation is discussed in detail. It is discovered that the Watts and Chou correlation accurately fits the simulation results of supercritical nitrogen and the Dittus-Boelter and Jackson correlations can only be used for high-pressure conditions. The HTE of supercritical nitrogen is closely related to the laminar sub-layer and buffer layer of a boundary layer. The buoyancy effect on the HTE should be considered at low mass flux conditions, and thermal acceleration can be completely ignored for the cases studied. The special HTE featured by the increment in heat transfer coefficient with increasing heat flux is discovered at low pressure, and simulation results proved that this HTE is caused by the combined actions of buoyancy as well as significant variations in specific heat and viscosity.

With high concentrations of salinity, heavy metals, and refractory organics, the nanofiltration (NF) concentrate in electroplating wastewater is difficult to be treated using the traditional methods. The aim of this study was to investigate the feasibility to treat the NF concentrate using the microbial electrolysis desalination and chemical production cell (MEDCC) combined with the Fenton process. Results showed that heavy metals of nickel and zinc were efficiently removed using the proposed method. The maximum current density reached 9.4 A/m2 in the MEDCC fed with the pretreated NF concentrate. Within 20 h, 94%, 82%, and 91% of nickel, zinc, and calcium were removed in the desalination chamber of MEDCC. The dilute acid with pH = 0.9 and alkali with pH = 12.9 were recovered in the MEDCC. The Fenton oxidation process with and without the MEDCC removed COD 79% and 30%, respectively. In the MEDCC and Fenton combined system, refractory organics were transformed to linear alkanes and efficiently degraded. With high removal of COD and heavy metals, acid and alkali recovery, and low energy consumption, our combined MEDCC and Fenton process should provide a promising method to efficiently treat the NF concentrate in electroplating wastewater.

The aim of this study was to establish the relationship between spatial distribution of Geobacter and electric intensity in the microbial electrolysis desalination and chemical-production cell (MEDCC) and to investigate the effect of enlarged volumetric anode on the performance of MEDCC. The MEDCC was constructed with nine carbon brush anodes (length × diameter = 11 cm × 3 cm) as enlarged volumetric anode, and operated by feeding with 1 g/L acetate as substrate and 35 g/L NaCl as artificial seawater under the applied voltages of 1.2-4.5 V. Spatial distribution of Geobacter in the anodic biofilm was determined according to the bacterial community analysis on 27 biofilm samples from the top, middle and bottom layers of anodes (i.e., with distance of 4.5, 10, and 15.5 cm to the cathode, respectively). Results showed that the enlarged volumetric anode significantly improved the performance of MEDCC. The maximum desalination rate and current density reached 338.5 ± 21.8 mg/L∙h and 55.7 ± 3.7 A/m

Clogging is a common and difficult problem in subsurface flow wetlands. In this study, 2-4mm, 4-8mm, 8-10mm lightweight ceramsite were used as suspended media beds and 5-10mm gravel was used as traditional substrate bed as control. The effects of these four substrate beds on the purification of water quality and the change of flow capacity in the clogging process in the non-deformable inorganic particle wastewater, deformable inorganic particle wastewater and organic particle wastewater were studied. After the beds were clogged, using the characteristics of lightweight ceramsite floating up and down with water level, the mitigation effect of clogging with water level fluctuation at different heights (10 cm, 20 cm, 30 cm, 40 cm) was explored. The results showed that four kinds of beds had effect on the removal of turbidity and suspended particles. The beds in the treatment of non-deformable inorganic particle wastewater were more likely to cause wetland gap clogging; In the absence of plants, compared with inorganic particles, the clogging degree of substrate in the treatment of organic suspended particulate wastewater was not obvious. After clogging, lightweight ceramsite floats up and down with the water level, three kinds of wetland clogging have been alleviated to some extent.

The effects of gravity on the heat transfer performance of supercritical CO2 flowing within a vertical tube with a diameter of 4.75 mm are numerically studied in this paper. The main objectives are to comprehensively investigate the action of gravity and buoyancy on the supercritical heat transfer. An effective numerical method, which employs a modified Shear Stress Transfer k-&omega, model (SST k-&omega, ), is applied at various gravity conditions. It is found that, for both upward and downward flows, the heat transfer of supercritical CO2 is improved with increased gravity magnitude. The effect of gravity on heat transfer are more pronounced under a low mass flux condition than that under a high mass flux condition and it is closely related to the variations of thermal properties. For the upward flow, the increased gravity magnitude accelerates the near wall fluid and creates a classic &ldquo, M-shaped&rdquo, radial velocity distribution. For the downward flow, the increased gravity magnitude decelerates the near wall fluid and creates a parabola-like radial velocity distribution. On one hand, the turbulent kinetic energies of both the upward and downward flows are enhanced as the gravity magnitude increases, which benefits heat transfer dominated by turbulent eddy diffusion. On the other hand, high-density fluid with high thermal conductivity occupies the near wall region as the gravity magnitude increases, which benefits heat transfer dominated by molecular diffusion. The results might provide some instructive advice to improve the design and operation safety of heat exchanger at various gravity conditions.

There are some problems in the thermal system of Huabei Oilfield, such as high energy consumption, high operation cost and poor production safety. With more stringent requirements for energy conservation and emission reduction, it is particularly important to replace fuel oil projects and improve the efficiency of heating system.The utilization of waste heat and waste heat resources in Huabei Oilfield and the application conditions of various heat pump technologies were investigated, according to the characteristics of large amount of sewage and high temperature produced by crude oil dehydration in Huabei Oilfield. Aiming at the characteristics of large amount of sewage and high temperature produced by crude oil dehydration in Huabei Oilfield, Pilot Application of Optimized Extracted Water Source Heat Pump Technology, the research results are applied to the the He Yi Station in the third oil production plant, estimating the scale and benefit of saving, finally, the purpose of reducing cost and increasing efficiency is achieved, and the data basis and technical guidance for energy saving renovation of thermal system in the future are improved.

Phosphorus is the main element for eutrophication of water bodies. Aluminate cement is a cheap building material rich in aluminium and calcium which have significant effects on phosphate adsorption. This study aimed at the investigation of removal behavior of phosphate by thermally dehydrated aluminate cement granules, treated at different temperatures, and the adsorption mechanisms. It was found that 600 °C was the optimal temperature, producing excellent granules with a particle size of 0.6-1.5 mm (T600), giving a great adsorption capacity of phosphate of 49.1 mg P per g and presenting fast and high initial adsorption, reaching a capacity of 23.7 mg P per g within 30 min at 20 °C. The phosphate adsorption process was dominated by chemical adsorption, mainly through inner-sphere complexion and phosphate precipitation on the surface of the adsorbent. Compared with other phosphate adsorbents, T600 may be an economical and efficient adsorbent.

Laboratory experimentation was used to investigate the impact of the organic loading rate shock on extracellular polymeric substances (EPSs) and the physicochemical characteristics of nitrifying sludge (NS) treating high-strength ammonia wastewater. The increased organic loading rates (OLRs) strongly influenced the stability of the NS with regard to nutrient removal, biomass-liquid separation, and surface properties, leading to the sludge system collapse at the OLR of 0.75 kg COD per kg MLVSS d. However, an incomplete recovery of the NS after the high OLRs shock was observed when decreasing the OLRs. In addition, the variations of OLRs resulted in relatively stable amounts of tightly bound EPS (TB-EPS), but a significant change in loosely bound EPS (LB-EPS). Both in LB-EPS and TB-EPS, the proteins (PN) contents and proteins to polysaccharides (PN/PS) ratios decreased with the increase in OLRs. Results from the excitation emission matrix spectra implied that the tryptophan PN-like substances were the major components in EPS at low OLRs, while the humic acid-like and fulvic acid-like substrates increased markedly at high OLRs. Furthermore, correlation analysis demonstrated that PN and the PN/PS ratio were the most important factors in determining the physicochemical properties of the NS. It was indicated that the PN could accurately reflect the sludge properties of the NS, and thus effectively change the surface properties of the sludge, contributing to the cohesion between the aggregates to maintain a stable structure.

Manganese oxides have been applied in advanced oxidation processes (AOPs), however, underlying oxidation regimes are still debatable. In this work, we synthesized various crystalline manganese oxides and single or dual metal-doped amorphous MnO2 (M-AMO, M = Fe, Co, Ni, and Cu) for organic oxidation with peroxymonosulfate (PMS). M-AMO at 1 mol% exhibited much higher activities than crystalline manganese oxides and Cu-AMO displayed the rate constant at 3.5 times as high as that of AMO. Different from conventional radical oxidation, nonradical degradation occurred via two pathways. Cu-doping resulted in relatively higher-crystallized structure, more oxygen vacancies, and a higher ratio of Mn4+/Mn3+ for a faster redox cycle between MnⅣ(s) and MnⅢ(s) to boost PMS activation and direct/indirect (Cu-AMO–PMS complex-based) phenol oxidation. This study contributes to a new insight to the structure-catalysis relationship in manganese-catalyzed PMS oxidation. The outcomes will direct the rational synthesis of reaction-oriented catalysts for nonradical AOPs and novel remediation technologies.

To improve wastewater treatment efficiency by hydroponic ditches (HDs) and hybrid constructed wetlands (CWs) in cold regions and create evergreen landscape in cold periods, a research on them cultivated with Lolium perenne at depths of 10 cm and 60 cm were carried out. Water temperature of 10 °C was as the boundary between cold and non-cold periods. During the 2 years’ experiment, L. perenne grew well, with better growth characteristics in the second year than that in the first year. In the cold period of the second year, when large-area freezing occurred in the culture bed, L. perenne was still clearly proliferating and kept evergreen. Meanwhile, the removal efficiencies of COD, NH4 +-N and TP increased, especially NH4 +-N removal increasing significantly (p

Nitrate and hexavalent chromium (Cr(VI)) are potentially hazardous to human health and ecosystems. In this study, an anion exchange resin (PBO-8) was synthesized for the removal of nitrate and Cr(VI) from aqueous solution. The PBO-8 resin was characterized with Fourier transform infrared spectroscopy, scanning electron microscopy and BET surface area analyses. The results of batch adsorption experiments indicated that the maximum equilibrium uptake of nitrate and Cr(VI) in single solute solutions were 21.13 and 45.02 mg/g, respectively. The maximum quantity of PBO-8 resin for the adsorption of nitrate and Cr(VI) were, respectively, decreased to 14.17 and 27.03 mg/g in a nitrate and Cr(VI) binary solution. The increase in temperature and decrease of pH enhanced the capacity of the PBO-8 resin for Cr(VI) adsorption, but such effects were less significant for nitrate. The Gibbs free energy change, enthalpy change, and entropy change illustrated that the adsorption of aqueous nitrate and Cr(VI) were f...

The roadbed structure and construction course is a compulsory course for the major of road and bridge engineering technology in higher vocational colleges. The content of the course is theoretical, the formula is complex, and it is difficult to understand, which increases the difficulty of students’ learning, especially under the traditional “indoctrination” theoretical teaching mode , Classroom teaching efficiency is low, and students tend to lose interest and confidence in learning. With the application of BIM technology, students were visually shown the relationship between subgrade structure and construction components and construction links, with remarkable results. This article focuses on the problems related to the teaching of roadbed structure and construction courses based on BIM technology.

The biomass, bottlebrush flower, is exploited for the preparation of functionalized porous carbons by one-pot thermal activation using NaHCO3 and dicyandiamide. An intensified cross-linking effect among the precursors boosts pore (especially mesopore) formation in the pyrolysis process, producing N-doped porous carbons (NPCs) with a large specific surface area (SSA, up to 2025 m2 g−1). The biomass-derived carbon samples turn out to be highly effective in adsorption, and catalytic activation of peroxymonosulfate for degradation of aqueous phenol and p-hydroxybenzoic acid (HBA) in single and binary systems. The effects of N content, porous structure, and trace Ni species on the adsorptive and catalytic behavior of carbon are investigated. It is found that the porous structure plays a more critical role in adsorption than surface N functionality, while the contributions of various reactive species for phenol and HBA degradation are different.

In order to predict the heat transfer deterioration (HTD) of supercritical pressure fluids and to provide practical guidance for engineering applications of supercritical pressure CO2 (SC-CO2), a considerate turbulent Prandtl number (Prt) modification was proposed with the use of shear stress transport k − ω turbulent model. The proposed variable Prt model considering the effects of system pressure, fluid properties and tube diameters was validated by comparing with 26 reported experimental data, especially for HTD cases. The comparison results show that the present model not only predicts the HTD but also reproduces the onset of it. The modification of Prt in the buffer layer is the key to predict the wall temperature accurately, since the modified Prt changes in association with the molecular Pr and accommodates the contribution rate of molecular conduction to turbulent mixing on heat transfer. Moreover, the correction factors for tube diameter and system pressure are implemented to adjust the modification of Prt. The applicability of the proposed model to various operating conditions is verified in this paper, therefore the present modification for Prt may be popularized to extensive engineering applications of SC-CO2, especially for the optimization design of SC-CO2 heat exchanger.

The traditional drinking water purification process is inefficient in removing nitrate significantly. Ion exchange may be the most practical method for the removal of nitrate from drinking water. In this study, an anion exchange resin (PBE-8) was synthesized for selective nitrate removal. The PBE-8 resin was characterized by Fourier transform infrared spectrometry, scanning electron microscopy, and BET surface area analyses. Batch adsorption experiments were carried out to evaluate the thermodynamic and kinetic behaviors of the PBE-8 resin for the adsorption of nitrate. The results indicated that the maximum equilibrium nitrate uptake of PBE-8 was 26.19 mg N/g, which was higher than that of Purolite A 520E (23.07 mg N/g), but lower than that of HZ-222 (33.57 mg N/g). PBE-8 and Purolite A 520E demonstrated better adsorption of nitrate than HZ-222 in the presence of competing anions, such as sulfate, chloride, and bicarbonate in aqueous solution. The Gibbs free energy change (−12.15 to −1.15 kJ/mol)...

Polycyclic musks are widely used for cosmetics and other personal care and household cleaning products. The occurrence and removal of two representative polycyclic musks, galaxolide (HHCB) and tonalide (AHTN) were investigated in three different processes of two sewage treatment plants (STPs) in Xi’an, China. The samples were preconcentrated by solid phase extraction procedure and analyzed using a gas chromatography mass spectrometry (GC/MS) by a modified procedure. The HHCB was in the range of 82.8 to 182.5 ng·L−1 in the influents and 22.6 to 103.9 ng·L−1 in the effluents. The AHTN ranged from 11.0 to 19.3 ng·L−1 in the influents and 2.2 to 8.8 ng·L−1 in the effluents. The removal efficiency of the two musks varied in the ranges of 43.1%–70.4% for HHCB and 54.2%–84.4% for AHTN. Concentrations of the two musks in aqueous phase of three processes slightly increased along the primary process, and significantly removed during the biologic treatment processes, revealing that the selected musks could be remarkably removed in varied activated sludge processes. Advanced processes of activated sludge did not show a significant superiority on selected musk removal compared to the conventional process. The selected musk removal mainly resulted from the adsorption function of activated sludge. There was no significant change of HHCB/AHTN ratios along the treatment flow, indicating that each sewage treatment structure had a similar removal efficiency for the two musks.

In this paper, the flexible material handling operation model on container yard is presented based on the analysis approach of flexible operation which was put forward in the first report of this research. In this model, the optimum operation scheduling plan has been carried out to realize the multi-objective optimization on operational criteria such as minimum ship waiting time and minimum operation time of transfer cranes. Meanwhile, the container information is recorded individually as the basis for operation commands from the yard production management system. Moreover, in order to enhance productivity in rehandling operation, the stack height of container block for unloaded containers is modified dynamically with fuzzy neural network according to the status and prediction of yard system. Finally, the optimal operation plan is determined by means of genetic algorithm combined with simulation analysis. The study has shown that this model can yield satisfactory operational scheduling plan for container yard by an actual case analysis.

This paper describes simulation and optimum design for system configuration on port logistics system for bulk cargo. In order to realize the multi-objective optimization on economic result, operational ability and yard utility for port logistics system, evaluation criteria are established by the following three objective functions: (1) total net present value of system; (2) average time for ship staying in port; (3) rate of yard utility. The fuzzy set theory is applied to deal with the uncertainty in human decision and to determine the reasonable Pareto optimal solution with designed degree of human preference satisfaction by tradeoff for individual objective function. Therefore, the fuzzy multiple objective optimization model with fuzzy objective functions and constraint conditions is set up. An actual case is examined to confirm the validity and reliability of the model, where the properties of objective functions are discussed. Furthermore, the sensitivity of the optimal result to system environmental parameters is analyzed.

In this paper, the analysis approach of flexible control on material handling operation in container terminal is presented. By considering the fact that container operation can be regulated by means of production management mechanism, the conventional queuing model is modified by its flexible operation model. To realize the optimum operational performance such as minimum ship waiting time, according to the variation of system status parameters, the operation rule and operation scheduling of quayside container cranes are dynamically determined with knowledge-based controller in the form of fuzzy neural network. The whole analysis process is divided into four steps: simulation execution, system status evaluation, system status prediction, and decision making on the coming operation rule. An actual case has been studied to demonstrate the effectiveness and validity of the presented model. By comparing with those from a conventional model, the results have shown that the flexible operation model can yield satisfactory oparational results.

This paper describes the optimum design on the berth configuration extension plan of materials handling systems in container terminals. The operation model with flexible controlled operation rule, which was put forward on the first report of this research, is used to analyze the margin degree of operation ability of the system to increasing operation quantity within a long period. The whole problem is divided into two parts: (a). dynamic programming is used as a basic algorithm for the optimal path of decision-making: (b). nonlinear search programming combined with discrete event system simulation is used for configuration analysis of a given year, especially for the final year's. The minimum total ship waiting time is established as the objective function. Fuzzy set theory is applied to deal with the uncertainty in decision made by terminal management, and the optimal decision-making sequence on the system configuration plan is decided. A case study is analyzed to confirm the validity and effectiveness of the approach.