Evolving simple-to-apply models for estimating thermal conductivity of supercritical CO2

Today, due to extensive applications of supercritical fluids technology in various chemical engineering process and industrial fields, predicting thermal conductivity of supercritical carbon dioxide is vital. In this research, two simple-to-apply models have been developed to estimate thermal conductivity of supercritical CO₂ as a function of temperature, pressure and density over broad ranges. This research presents a predictive tool based on LSSVM to predict thermal conductivity of supercritical CO₂. Genetic algorithm is employed to determine hyper-variables which are included in the LSSVM approach. In this regard, a set of accessible data containing 745 data points has been gathered from the previous published papers. Estimations are found to be in excellent agreement with reported data. Moreover, statistical analyses have been applied to evaluate the performance of two models. The obtained values of Mean Squared Error and R-Square were 7.415866, 0.9935 and 0.046527, 1.00 for the correlation and LSSVM model, respectively. The developed tools can be of immense practical value for chemical engineers to have a quick check of thermal conductivity of supercritical CO₂ at an extensive range of conditions.     

Air-water flows in circular drop manholes

Drop manholes, a typical element of urban drainage networks in steep catchments and in reaches of supercritical flow, enhance air entrainment and entrapment. The air flow across drop shafts can be remarkably high.

This paper discusses the air transport phenomena and the effects of ventilation absence in drop manholes. Based on an extensive experimental study, air entrainment mechanisms have been accurately described and air demand has been evaluated in different flow regimes. In addition, the effects of ventilation absence on the hydraulics of circular drop manholes, with emphasis on sub-atmospheric pressure onset and pool depth raising, have been investigated. The effects of a possible air flow recirculation have also been evaluated. Issues regarding any scale effects have been discussed.

The influence of the main hydraulic and geometric parameters on drop manhole performance was contemplated to provide improved design concepts for sewer systems.     

Hydraulic design aspects for supercritical flow in vortex drop shafts

ABSTRACT

Vortex drop shafts, as special sewer manholes, operate optimally if an adequate energy dissipation is guaranteed and the integrity of the structural components is safeguarded. The results of an experimental study on a vortex drop shaft with supercritical inflow are discussed herein. The hydraulic behaviour of the spiral inlet, the vertical shaft and the dissipation chamber is described. Based on detailed flow observations, useful recommendations for designing these structures are provided. It is demonstrated that a relation adopted for supercritical bend flows provides a reliable estimation of the maximum wave height along the inlet. A procedure for predicting the rotational flow angles and the velocity distribution along vertical shafts with swirling flows is developed. Water levels and pressure measurements in the dissipation chamber are further analysed to identify maximum forces acting on the chamber invert and to derive preliminary design equations.     

气温骤降对薄壁混凝土结构温度应力的影响

采用有限单元法,对气温骤降时薄壁混凝土结构的温度场及应力场进行了仿真计算分析,结果显示,气温骤降会引起混凝土表面拉应力急剧增长,对施工期防裂十分不利,进一步论证了气温骤降时,对混凝土表面采取保温措施的必要性,该研究可为同类工程施工提供有益参考。     

Data-based mechanistic modelling of indoor temperature distributions based on energy input

Energy used for building heating, ventilating and air conditioning contributes to a great share in the total energy consumption worldwide. Better understanding and management of energy distribution in those processes is essential for the improvement of process quality and efficiency of energy use. This paper presents the data-based mechanistic modelling approach which has been developed to model the dynamic indoor temperature distribution in an imperfectly mixed ventilated airspace based on energy input to the system. The combination of classical heat balance differential equations and the data-based modelling techniques for continuous-time system has brought a robust dynamic model suitable for model-based controlling and yet providing a profound insight at the energy and temperature distributions in ventilated systems. The effect of changing heat input on the temperature distribution inside a ventilated structure was studied. Dynamic response of indoor temperature to varying energy input could be explained by a second order transfer function model with a high coefficient of determination (R² > 0.99), a low Young Identification Criterion (YIC < −2.3) and a low model standard error (SE < 0.028 °C). The physically meaningful model parameters as local heat load fraction γ and the coefficient of local temperature change h (°C J⁻¹) were revealed. This modelling approach is very useful for future design of model-based predictive controller for zonal control of indoor temperature by the direct adjustment of heat load into ventilated structures.     

河北省深州市地热水位下降对环境影响分析

进行了构造断裂和热储层渗透性能对地热水水位下降影响研究,对地热水水位下降潜在诱发地震、地面沉降及地热水资源枯竭等地质灾害进行了预测分析,并提出了相应的预防对策,以期避免地热开采引发的地质灾害,保障城市健康发展。     

跌落式熔断器在电网中的应用

通过分析电网中跌落式熔断器的常见故障，就熔断器在选择、安装、操作、维护管理等方面提出一些建议，并指出应定期对跌落式熔断器进行检查。     

Exergy based performance analysis of high efficiency poly-generation systems for sustainable building applications

In this study, first and second laws of thermodynamics, accompanying with Rational Exergy Management Method (REMM) were employed in developing a MATLAB based algorithm for natural gas fired, internal combustion engine (ICE) driven poly-generation systems. Two systems were studied based on a tri-generation plant built within the framework of the EU-FP6 HEGEL Project, tested at METU MATPUM (RICBED) building. This study introduces a better set of metrics for rating, evaluating, and optimizing poly-generation systems in order to minimize emissions, maximize fuel savings, and thus to accomplish an optimum sustainability metric among the factors of environment, energy, human needs and economics. Results show that with ICE poly-generation systems, exergy efficiency may increase beyond 60%. Even at part loads, minimum values of Primary energy savings (PES) are 12.4% for Case-1 and 17.7% for Case-2 (compared to minimum allowed 10%). REMM efficiency and Exergy Embedded PES (PES_R) evaluated by REMM are proven to be better indicators of the performance. When exergy destruction is lower, (waste heat is recovered) PES_R increases significantly. PES_R values are minimum 18.2% for Case-1 and 42.4% for Case-2, which reveals that both systems provide high performance energy generation and considerably lower emissions.     

Prediction performance of natural gas dehydration units for water removal efficiency using a least-square support vector machine

Natural gas dehydration unit is employed to eliminate water from natural gas liquids and natural gas, and it is needed to avoid condensation of free water and creation of hydrates in transportation and processing facilities, prevent corrosion, and meet a water content condition. In this paper, a least-square support vector machine (LSSVM) coupled with genetic algorithm (GA) was employed to estimate the water dew point of a natural gas stream in equilibrium with a triethylene glycol (TEG) solution at different TEG concentrations and temperatures. Results showed that GA–LSSVM accomplishes more reliable outputs compared with real recorded data in terms of statistical criteria.     

山区大口径高落差管道通球试压扫水要点分析

就榆济天然气管道工程八标段的山区通球试压及扫水方案进行了要点分析,首先对图纸上的理论数据进行整理,采用多分段、降压差的方法把最大高差的理论数据进行分解,然后根据现场的实际情况对分段的长度及选点进行考证,同时对现场试压用水的上水点和排水点进行落实,最后针对各段的情况选定所用通球试压及扫水设备,从而有效地解决了无法攻克的试压困难,为榆济天然气管道工程顺利投产奠定了基础。     

Direct measurements of reaeration rates using noble gas tracers in the River Lagan, Northern Ireland

Dissolved oxygen (DO) in river systems is often depleted by polluting substances, sometimes rendering the water unfit for habitats and human use. The natural mass transfer of oxygen from the atmosphere can help to alleviate this. The reaeration coefficient, K₂, which describes the rate of oxygen absorption, is an important parameter in water‐quality modelling. Owing to difficulties in the direct measurement of K₂, values for use in water quality models are typically derived using predictive equations, but these are notoriously inaccurate. This paper presents a field method for the direct measurement of K₂ by two alternative analysis methods and includes the results of eight tests conducted on a reach of the River Lagan, in Northern Ireland. The method is based on a long‐established protocol but replaces a now‐unacceptable radioactive tracer (⁸⁵Kr) with stable noble gases. K₂₍₂₀₎ values between 3 and 80/day are reported for the test reach.     

水雾雾滴粒径的分析与研究

介绍了水雾雾滴粒径的不同表征参数以及雾滴粒径的不同测量方法,并通过试验对水雾喷头以及细水雾喷头的雾滴粒径进行了测量,对通过雾滴直径这一参数如何区分描述水雾喷头和细水雾喷头的雾滴特性提出了相应的建议。     

铜绿微囊藻衰亡过程中产甲烷动态及关键影响因子

为探究铜绿微囊藻水华自然衰亡和水华堆积区藻快速衰亡对CH_4释放的影响,构建了室内模拟实验,研究了铜绿微囊藻自然衰亡和快速衰亡过程中水环境因子和CH_4、CO_2气体释放通量的变化。结果表明:高密度铜绿微囊藻衰亡中水环境因子和产气的变化遵循相似的时间模式,且衰亡对CH_4和CO_2的产生有显著的促进作用。自然衰亡和快速衰亡的CH_4累积释放量分别为对照组的22.80倍37.72倍,CO_2累积释放量分别为对照组的5.36倍和4.03倍。自然衰亡与快速衰亡的总碳(C)释放量差异不大,但快速衰亡释放的气体组分中CH_4的占比是自然衰亡的1.86倍。相关性分析表明,溶解性有机碳(DOC)是铜绿微囊藻衰亡中影响CH_4和CO_2释放的主导因子,且DOC中的芳香蛋白类物质和溶解性微生物代谢产物是CH_4和CO_2产生的主要底物来源。     

锂离子电池热失控早期预警特征参数分析

为对锂离子电池热失控状态的早期预警模型提供支撑,针对单体电池单侧受热触发热失控问题开展实体实验,分析表面温度、电池电压、气体温度等多个特征参数的变化规律,在考虑降低误报漏报率的情况下,分析其合理报警范围。结果表明,加热触发的热失控状态判定主要依赖于电池表面监测点温升速率;电池电压下降量不适用于热失控预警;电池表面温度、表面温升速率、电压降速率、气体温度等特征参数的参考报警值分别为60~90℃、0.4~1℃/s、0.05~0.16V/s、60~90℃。     

空调系统柔性风管压力损失特性实验与分析

介绍了柔性风管压力损失的理论模型。通过实验研究了两种常用柔性风管在全伸展状态时的压力损失,得出了它们的绝对粗糙度值。给出了柔性风管完全展开时的阻力计算图,可供工程设计时使用。     

Embedding built environments in social–ecological systems: resilience-based design principles

Globalization, the process by which local settlements and ecosystems are becoming linked in a global network, presents policy scientists and planners with difficult design challenges. Coping with either natural or built environments in isolation is extremely challenging in its own right (e.g. built environments at different scales: a single building, a collection of buildings, a neighbourhood or a city are in themselves very complex). In the Anthropocene era, where human activities shape the planetary system in which built and natural environments are becoming more tightly linked across scales, these complex systems need to be considered as elements in a global network, i.e. as a coupled social–ecological system (SES) at the global scale. In the context of this spiralling complexity, multi-scale and multilevel processes become more important and design/management problems become extraordinarily difficult. Preliminary ideas are explored for how research on this multilevel design problem might proceed. Specifically, based on combining insights from a collection of theories and models based on resilience and robustness concepts, the basic elements of a new approach are presented that recognizes the importance of self-organizing processes at multiple scales and emphasizes the use of feedbacks to link these processes across scales.     

Ductility reduction factor and collapse mechanism evaluation of a new steel knee braced frame

In this study, the suitability of a new structural system called the knee braced frames (KBFs) is investigated for seismic resistant steel structures. In these structural systems, ends of beams are connected to columns by hinges (simple connection) instead of rigid connections, and ends of knee braced elements are connected to columns and beams by hinges as well. In the present paper, in addition to a comparison between elastic behaviour and elastic fundamental natural period, the ductility reduction factor and the type of collapse mechanism in steel KBFs and steel moment resisting frames (MRFs) are compared. The study revealed that the stiffness of steel buildings can be increased considerably by applying knee braced elements and the effects of knee braced elements are highly dependent on knee braced configuration. By applying the pushover analysis, it was observed that the type of collapse mechanism of KBFs is very similar to the mechanism of MRFs. Furthermore in most cases, the ductility reduction factor, R_μ, obtained from steel KBFs is greater than the ductility reduction factor obtained for steel MRFs. Based on the similarity between type of collapse mechanism and the proximity of ductility reduction coefficients of the KBFs and MRFs systems, it can be concluded that the new steel knee braced frame systems can be categorised as steel MRFs with rigid connections.     

Prediction of building's temperature using neural networks models

The use of artificial neural networks in various applications related with energy management in buildings has been increasing significantly over the recent years. In this paper the design of inside air temperature predictive neural network models, to be used for predictive control of air-conditioned systems, is discussed.The use of multi-objective genetic algorithms for designing off-line radial basis function neural network models is detailed. The performance of these data-driven models is compared, favourably, with a multi-node physically based model. Climate and environmental data from a secondary school located in the south of Portugal, collected by a remote data acquisition system, are used to generate the models. By using a sliding window adaptive methodology, the good results obtained off-line are extended throughout the whole year. The use of long-range predictive models for air-conditioning systems control is demonstrated, in simulations, achieving a good temperature regulation with important energy savings.