On the suitability of steady RANS CFD for forced mixing ventilation at transitional slot Reynolds numbers

Accurate prediction of ventilation flow is of primary importance for designing a healthy, comfortable, and energy‐efficient indoor environment. Since the 1970s, the use of computational fluid dynamics (CFD) has increased tremendously, and nowadays, it is one of the primary methods to assess ventilation flow in buildings. The most commonly used numerical approach consists of solving the steady Reynolds‐averaged Navier–Stokes (RANS) equations with a turbulence model to provide closure. This article presents a detailed validation study of steady RANS for isothermal forced mixing ventilation of a cubical enclosure driven by a transitional wall jet. The validation is performed using particle image velocimetry (PIV) measurements for slot Reynolds numbers of 1000 and 2500. Results obtained with the renormalization group (RNG) k‐ε model, a low‐Reynolds k‐ε model, the shear stress transport (SST) k‐ω model, and a Reynolds stress model (RSM) are compared with detailed experimental data. In general, the RNG k‐ε model shows the weakest performance, whereas the low‐Re k‐ε model shows the best agreement with the measurements. In addition, the influence of the turbulence model on the predicted air exchange efficiency in the cubical enclosure is analyzed, indicating differences up to 44% for this particular case.     

Adaptive Comfort Degree-Days: A metric to compare adaptive comfort standards and estimate changes in energy consumption for future UK climates

This paper introduces the concept of the Adaptive Comfort Degree-Day, a temperature difference/time composite metric, as a means of comparing energy savings from Adaptive Comfort Model standards by quantifying the extent to which the temperature limits of the thermal comfort zone of the Predicted Mean Vote Model can be broadened. The Adaptive Comfort Degree-Day has been applied to a series of climates projected for different locations (Edinburgh, Manchester and London) under different emissions scenarios in the United Kingdom for the 2020s, 2030s, 2050s and 2080s. The rate at which energy savings can be achieved by the European adaptive standard EN15251 (Category II) was compared with the ASHRAE 55 adaptive standard (80% acceptability) during the cooling season. Results indicate that the wider applicability of the European standard means that it can realise levels of energy savings which its counterpart ASHRAE adaptive standard would not achieve for decades.     

A comparative study of three advanced controllers for the regulation of hypnosis

The anesthetic state is a dynamic combination of hypnosis, analgesia and neuromuscular blockade that is maintained by infusing a cocktail of drugs. This work focuses on controlling the hypnosis during a surgical procedure by automatic regulation of isoflurane and employs Bispectral Index (BIS) as the primary controlled variable. A seventh-order nonlinear pharmacokinetic–pharmacodynamic representation has been used for the hypnosis dynamics of patients. This study uses a model predictive control structure for the regulation of BIS. Performance of this controller has been tested for a range of patients and compared with two previously employed control strategies (cascade internal model controller and cascade controller with modeling error compensation). Performance of the three controllers has also been studied for a step change in BIS, measured disturbances and noise in the measured variables. Numerical simulations show that the model predictive controller performed better than the other two controllers.     

丙烯腈反应器新型两级旋风分离器大型冷模试验研究

针对丙烯腈装置扩能的要求 ,分析了用新型两级旋风分离器取代原三级旋风分离器的必要性 ,采用PV型和PV E型旋风分离器组成新型两级旋风分离器。根据旋风分离器尺寸分类优化设计法 ,设计了一种工业尺寸规模的两级旋风分离器 ,并将它和Ducon型三级旋风分离器在冷态条件下进行了对比试验。结果表明 ,新型两级旋风分离器不仅性能优异 ,而且结构简单、占据空间小、工作可靠 ,适合现有丙烯腈装置扩能改造的需要。     

Effect of Molecular Weight on the Strength of Nylon 6 and PET Fibers

Abstract

The mechanical properties of polymers depend on their morphological characteristics. With many systems and especially with semicrystalline polymers, it is possible to achieve significant changes in structure and properties by varying their thermal and stress histories. Considering the broad range of polymer applications it would, therefore, be desirable to have a quantitative understanding of the effects of structure on the properties of polymers in the solid state. The morphology of polymers is, however, often so complex that the interpretation of the mechanical responses must be restricted to qualitative considerations. In particular, the analysis of strength of un-oriented semicrystalline polymers is quite complex because of large plastic deformations which usually precede the rupture. However, by orienting the polymers in the form of fibers, it is possible to achieve structures which can be ruptured in tension with minimum plastic deformation. Under these conditions, the analysis of mechanical properties is greatly facilitated for fibers. Nevertheless, we still lack a quantitative understanding of the mechanical responses of polymeric fibers mainly because their structure has not yet been described with a precision allowing rigorous treatments.     

Performance validation of a hybrid ventilation strategy comprising longitudinal and point ventilation by a fire experiment using a model-scale tunnel

We examined the exhaust performance of a hybrid ventilation strategy for maintaining a safe evacuation environment for tunnel users in a tunnel fire. The hybrid ventilation strategy combines the longitudinal ventilation strategy with the point ventilation strategy which is a type of transverse ventilation strategy. The model tunnel developed by this study was scaled to 1/5 the size of a full-scale tunnel. The model-scale experiment was performed taking into consideration Froude's law of similarity. Measurement items were the distribution of temperature and concentration of smoke inside the tunnel, longitudinal wind velocity, mass flow of smoke in the point ventilation duct, and the heat release rate of the fire source. The following main conclusions were obtained. The smoke height was constant even when varying the extraction rate of smoke from the ceiling vent. The backlayering length and critical velocity of the smoke flow in the hybrid strategy could be predicted by the methodology developed by using the longitudinal strategy. The hybrid strategy maintained a safe evacuation environment on both sides of the tunnel fire.     

派出所综合信息管理系统应用模型研究

随着派出所工作日趋多元化,现有应用系统已不能适应派出所当前状况,因此,提出一种松耦合、层次式的应用模型,该模型能满足云南派出所业务的特定需求。主要介绍该模型的结构,分析各层的实现方法和客户端及服务端应用平台,并简单阐述关键技术。系统的实施提高了派出所的工作效率,增强了云南公安各部门间的协同能力,真正实现了科技强警,对相关领域信息化建设有一定的借鉴作用。     

Numerical simulations of airflow and droplet transport in a wave-plate mist eliminator

In this paper, the droplet transport and deposition in the turbulent airflow inside a wave-plate mist eliminator was studied using an Eulerian–Lagrangian computational method. The Reynolds Stress Transport Model (RSTM) with standard wall functions and with enhanced wall treatment was used for simulating the airflow field. A computer code for solving the Reynolds-averaged Navier–Stokes (RANS) equations in conjunction with the RSTM on two-dimensional collocated unstructured meshes was developed. For droplet trajectory analysis, another computer code was developed that accounts for the drag and lift forces action on the droplets. The Eddy Interaction Model (EIM) was used to model the droplet dispersion in turbulent airflow. The gas flow code was validated by comparing the computational model results for a fully developed asymmetric channel turbulent flow with the experimental data. Then the airflow and droplet trajectory analysis were performed for a mist eliminator with smooth walls and the resultant removal efficiency curves were evaluated and compared with the available experimental data. The results showed that the enhanced wall treatment improved the predictions of the droplet removal efficiency especially for small droplets in which the removal efficiency was lower than 50%. On the other hand, the Reynolds Stress Transport Model (RSTM) with standard wall functions cannot predict the removal efficiency correctly, especially for low gas velocities.     

Heat rejection pressure optimization for a carbon dioxide split system: An experimental study

Recent studies indicate carbon dioxide (R744) as a valid alternative to classical substances such as HFCs used in vapour compression plants. However a transcritical refrigeration cycle is needed because the critical temperature of carbon dioxide is usually near the ambient temperature. Consequently the carbon dioxide refrigerator performances are significantly influenced by the heat rejection pressure. In this paper an experimental investigation on working optimization for a “split-system” to cool air in residential applications is presented: by varying the heat rejection pressure an optimum working condition has been found at different ambient temperatures. Furthermore a simplified model to predict the optimum heat rejection pressure is shown and a comparison with experimental results is carried out. Both the model validation and the experimental results suggest that the heat rejection pressure optimization is an convenient method to improve the performance of a carbon dioxide split system. Finally an algorithm based on the aforementioned model has been proposed in order to control an electronic back pressure valve by means of a PLC.