Experimental study on the heat transfer and flow characteristics of nanorefrigerants inside a corrugated tube

The heat transfer and flow characteristics of MWCNT-R141b nanorefrigerant with different mass fractions have been studied through experiments. Experimental results were compared with existing correlations. A two-step method was used to prepare the nanorefrigerants. Span-80 was used as surfactant with an average particle diameter of 20 nm. Transmittance method was used to evaluate the stability of nanorefrigerants. Results showed that the stability of MWCNT-R141b nanorefrigerant, which is the added dispersant, was good during the experiments. The 0.3 wt% MWCNT-R141b nanorefrigerants had optimal heat transfer enhancement effects compared with pure refrigerants. The maximum Nusselt number increased by 40%. The specific pressure drop of nanorefrigerant increased as the Reynolds number (Re) increased, and the specific pressure drop of the pure refrigerant was minimum, which is similar to R141b.     

Automatic generation of variants depending on changes of product properties in a flexible manufacturing environment

Competition forces manufacturing systems to be flexible and to increase product variety and process complexity. These tasks depend on the flexible design of a bill of materials (BOM), one of the most important inputs in manufacturing planning and control systems. Product variety forces systems to generate BOMs with regard to product properties through a BOM pattern. A variant bill of materials provides a structure to manage product variability. In this study, an algorithm is designed to build a BOM pattern using computer-aided design and computer-aided manufacturing (CAD/CAM) data, and another algorithm is designed to generate variants with regard to product specifications. Genetic algorithm is used to generate new products to provide high product variability for testing algorithms. After the test, both algorithms are applied to a real industry problem. The BOM pattern is built automatically using CAD/CAM data, and variants are generated with regard to the pattern, and the results are discussed.     

CineCubes: Aiding data workers gain insights from OLAP queries

In this paper we demonstrate that it is possible to enrich query answering with a short data movie that gives insights to the original results of an OLAP query. Our method, implemented in an actual system, CineCubes, includes the following steps. The user submits a query over an underlying star schema. Taking this query as input, the system comes up with a set of queries complementing the information content of the original query, and executes them. For each of the query results, we execute a set of highlight extraction algorithms that identify interesting patterns and values in the data of the results. Then, the system visualizes the query results and accompanies this presentation with a text commenting on the result highlights. Moreover, via a text-to-speech conversion the system automatically produces audio for the constructed text. Each combination of visualization, text and audio practically constitutes a movie, which is wrapped as a PowerPoint presentation and returned to the user.     

A physically-based model for global collision avoidance in 5-axis point milling

Although 5-axis free form surface machining is commonly proposed in CAD/CAM software, several issues still need to be addressed and especially collision avoidance between the tool and the part. Indeed, advanced user skills are often required to define smooth tool axis orientations along the tool path in high speed machining. In the literature, the problem of collision avoidance is mainly treated as an iterative process based on local and global collision tests with a geometrical method. In this paper, an innovative method based on physical modeling is used to generate 5-axis collision-free smooth tool paths. In the proposed approach, the ball-end tool is considered as a rigid body moving in the 3D space on which repulsive forces, deriving from a scalar potential field attached to the check surfaces, and attractive forces are acting. A study of the check surface tessellation is carried out to ensure smooth variations of the tool axis orientation. The proposed algorithm is applied to open pocket parts such as an impeller to emphasize the effectiveness of this method to avoid collision.     

Active disturbance rejection based trajectory linearization control for hypersonic reentry vehicle with bounded uncertainties

This paper investigates a novel compound control scheme combined with the advantages of trajectory linearization control (TLC) and alternative active disturbance rejection control (ADRC) for hypersonic reentry vehicle (HRV) attitude tracking system with bounded uncertainties. Firstly, in order to overcome actuator saturation problem, nonlinear tracking differentiator (TD) is applied in the attitude loop to achieve fewer control consumption. Then, linear extended state observers (LESO) are constructed to estimate the uncertainties acting on the LTV system in the attitude and angular rate loop. In addition, feedback linearization (FL) based controllers are designed using estimates of uncertainties generated by LESO in each loop, which enable the tracking error for closed-loop system in the presence of large uncertainties to converge to the residual set of the origin asymptotically. Finally, the compound controllers are derived by integrating with the nominal controller for open-loop nonlinear system and FL based controller. Also, comparisons and simulation results are presented to illustrate the effectiveness of the control strategy.     

基于源质的煤基中间相小球体生成与可控演化

煤全组分族分离所得的密中质组是中间相小球体生成的来源物质（即源质）。以该源质为原料，制备煤基碳质中间相。考察了炭化过程中温度、恒温时间、氮气流速、原料进样方式和添加剂等因素对中间相小球体生成过程的影响，探讨了中间相小球体演化过程的可控性。结果表明：温度、恒温时间、进样方式是影响中间相小球体生成的主要因素，能够控制生成中间相小球体粒径大小；温度升高或恒温时间延长均会加剧原料分子的热反应，促进中间相小球体的生成和融并；大面积的融并将使粒度迅速增加，部分球体解体，球体数目下降，最终形成体中间相；进样方式主要通过影响小球体演化过程中挥发性气体的逸出及原料颗粒间热传递效率影响小球体的生成和发展；氮气流速起到辅助调控作用；添加剂的加入促进了原料成核，加速了小球体的生成。     

Retrofitting of the Heat Exchanger Network with Steam Generation in a Crude Oil Distillation Unit

Steam generation through hot streams has an important impact on the utility consumption of a crude oil distillation unit. Retrofitting of the heat exchanger network with steam generation in a crude oil distillation unit is studied with regard to efficient energy usage. The grand composite curve is employed to provide insights into the steam generation problem, and a mixed‐integer linear programming model, presented previously for heat integration through hot discharges/feeds and steam generation, is used to obtain the optimal parameters for steam generation. Three heuristic rules are then proposed to determine suitable hot streams for steam generation. Finally, the heat exchanger network is modified based on pinch technology. After the retrofit, the hot and cold utility decrease.     

Assessing Cloud Transient Impacts of Solar and Battery Energy Systems on Grid Inertial Responses

To assess the dynamic impact of intermittency of rapidly increasing solar photovoltaic generation on the grid, this article presents the modeling and integration of the components that need to be considered, including the solar photovoltaic plant, battery energy storage system, grid-tied interface, and associated control systems. The complexity and accuracy of these models are suitable for evaluating the transient impact on bulk power systems. Of particular interest is the grid inertial response in such situations as different penetration levels of solar generation and fast cloud transient induced solar generation decrease coupled with outages that recurrently occur in the grid, e.g., a generator trip. The impact of such events on the grid frequency responses is investigated using a simplified simulation approach to account for the locational or spatial irradiance variation patterns and cloud movements. Responsive battery energy storage systems are recognized as an effective means to improve the inertial response.     

换能器结构参数对聚合物超声塑化黏弹生热的影响

为研究超声换能器结构参数对聚合物超声塑化过程黏弹性生热的影响，首先确定超声黏弹性生热系统的组成，进行纵振超声换能器结构设计；然后分析超声黏弹性生热过程及超声黏弹性生热原理；最后采用单一变量法分析超声换能器的主要结构参数对其纵振频率及工具头前端质点最大振幅的影响，将其实际输出的纵振激励加载于熔融聚合物，研究其结构参数对聚合物超声黏弹性生热过程及达到聚合物玻璃化转变温度所用时间的影响。结果表明，随纵振激励作用时间的增加，聚合物温度非线性升高；放大比对聚合物温度变化影响最大，前盖板厚度和工具头长度次之，影响最小的是变幅杆长度。     

热电厂供电运行故障及应对措施探讨

长期高负荷、高输出的热电厂供电运作过程中不可避免地出现设备磨损等故障。为了做好供电运行中的故障预防以及有效维护,开展了热电厂供电运行故障及应对措施探讨。分析了造成设备磨损、备用电源失效、发电设备电压不稳定、电力接地短路、发电设备温度过高等故障原因,并提出了有针对性的解决方法,以保障热电厂供电系统的正常运转。分析认为,遇到不同的电力故障问题,应具体分析、区别对待,并在检修的过程中及时总结经验;对于设备本身的问题,应最大程度以技术创新弥补自身结构缺陷。