Thermal analysis of a solar parabolic trough receiver tube with porous insert optimized by coupling genetic algorithm and CFD

In this paper, the heat transfer enhancement in a solar parabolic trough receiver tube with porous insert and non-uniform heat flux condition was investigated. A new optimization method, which couples genetic algorithm (GA) and computational fluid dynamics (CFD) based on Socket communication, was proposed to optimize the configuration of porous insert. After the acquisition of the optimal porous inserts, some performance evaluation criterions such as synergy angle, entransy dissipation and exergy loss were introduced to discuss the heat transfer performance of the enhanced receiver tubes (ERTs) with optimal and referenced porous inserts. The results showed that, for a large range of properties of porous insert (including porosity and thermal conductivity) and Reynolds number, the heat-transfer performance of ERT with porous insert optimized by GA is always higher than that of the referenced ERTs. Better heat-transfer performance can further improve the solar-to-thermal energy conversion efficiency and mechanical property of the solar parabolic trough receiver. When some porous materials with high thermal conductivity are adopted, ERT can simultaneously obtain perfect thermal and thermo-hydraulic performance with using the same optimized porous insert, which cannot be achieved by using the referenced porous insert. In the view of those introduced evaluation criterions, using the optimized porous insert can obtain better synergy performance and lesser irreversibility of heat transfer than using the referenced porous insert. Entransy dissipation per unit energy transferred and exergy loss rate have equivalent effects on the evaluation of irreversibility of heat transfer process. These evaluation criterions can be used as optimization goals for enhancing the comprehensive performance of the solar parabolic trough receiver.     

石材加工及相关技术专利统计分析

本文通过对近几年来关于石材加工及相关专利文献的分析,进一步阐明我国石材行业知识产权面临的问题和所要解决的重点问题。为进一步提升我国石材行业科技发展和技术水平提高提供参考依据。     

WCDMA和TD-SCDMA中HSDPA的比较

高速下行分组接入(HSDPA)技术是针对第三代移动通信系统上、下行链路业务量不平衡的特点提出的,能够大幅提高下行传输速率。在R5版本中WCDMA和TD-SCDMA分别引入了HSDPA。两系统中的HSDPA技术在MAC层、物理层和技术上有一致性,但同时二者在物理层信令参数、物理信道种类、时隙调整、技术和整体性能上存在着一些差异,而差异的产生源于WCDMA和TD-SCDMA系统本身特点的不同。主要阐述了WCDMA和TD-SCDMA HSDPA的异同,并进行分析。     

一种基于三层结构的本地电信网销帐系统

基于三层结构的C／S系统由于其各层功能分离、维护方便、系统结构灵便的特点成为解决的较为理想的方案，该设计模式提高了系统的扩展性，提高了事务处理的能力。其特点对于本地电信网的销帐系统结构是一种比较好的设计模式。本文介绍了一个基于三层结构的设计模式的电信本地网的销帐系统的设计实例。     

E时代的馆藏设计——沈阳少儿图书馆方案设计

网络触角无处不在的今天，阅读的方式及形式也受到了极大的冲击。因而对于图书馆这一建筑的设计就提出了更高的要求。本文以“激情”为设计理念，注重设计灵活性和功能实用性的同时，力求最大限度的激发人们的求知热情。     

Determination of difenoconazole residue in tomato during home canning by UPLC-MS/MS

The effects of different steps in canned tomato paste production on difenoconazole levels were investigated. And residues were determined by using ultra-performance liquid chromatography coupled with tandem mass spectrometry (UPLC-MS/MS) after each stage including washing, peeling, homogenization, simmering and sterilization. Results showed that washing and peeling process reduced the amount of residue by 99%, whereas homogenization, simmering, and sterilization process had little effects on the removal of difenoconazole residue. Difenoconazole mostly remained in tomato skin, therefore, washing and peeling significantly reduced difenoconazole, especially peeling resulted in nearly 94.6% difenoconazole removal from tomatoes, with the processing factor of peeling at < 0.05.     

新视觉高清频道播出系统设计与实现

介绍了上海文广互动新视觉系列高清轮播频道播出系统建设的设计方案以及具体实施过程。遵循全台制播网络一体化的思想,由光纤和千兆以太网构建了全无带化的播出网络系统。其中,二级存储系统选择了统一存储的硬件结构。由于采用了嵌入式音频技术,系统链路结构更加趋于简单。另外,入侵防御系统的使用将网络安全提升到了崭新的高度。运行2年以来,给广大观众带来了稳定的播出质量和美妙的视觉享受。     

Optical properties of MgO doped near-stoichiometric LiTaO3 single crystals

Comparative study of the optical properties of undoped and 1-3 mol% MgO doped near-stoichiometric LiTaO₃ (SLT) crystals were undertaken. It was observed that the red shift in the absorption edge occurred with the increasing MgO doping concentration. The infrared absorption spectrum of the OH-stretch-mode in SLT was measured for crystals of undoped and 1-3 mol% MgO doped compositions. The coercive field for the crystals was measured to be 0.913, 0.610 and 0.735 kV/mm for 1-3 mol% MgO doped SLT, respectively. Photorefractive damage of SLT single crystals with 1-3 mol% MgO doping levels was measured to be 136.29, 180.25 and 222.54 MW/cm².     

面向消息的中间件技术在告警网管中的设计与实现

MDCN作为一个公共信息传输平台,将各个业务系统整合到了一起,在移动通信网络管理中起到了非常重要的作用。当前,如何监控MDCN上的设备正常工作,已经成为研究的热点问题。本文利用面向消息的中间件技术对设备告警的管理平台进行了设计与实现。     

An entransy dissipation-based optimization principle for solar power tower plants

The entransy theory,which can be used to optimize the heat transfer network of a solar power tower system(SPTS)and improve its energy efficiency,was introduced in this paper.Firstly,the irreversibility of the heat transfer processes in a SPTS was analyzed and the total entransy dissipation equation of a SPTS was derived.Then,two types of optimization problems(reducing the total circulating flow rate or the total heat-exchanging area)of a SPTS were solved with conditional extremum model based on the formulas of total entransy dissipation.Finally,the entransy dissipation-based optimization principle was applied to a simple SPTS without re-heater and a complex SPTS with a re-heater.The results showed that under the chosen calculation conditions the minimum total thermal conductance was 19306.03 W K?1 for a SPTS without re-heater when the total heat capacity rate of heat transfer fluid(HTF)was 3200 W K?1.The minimum total thermal conductance was about 7.9%lower than the value predicted based on the typical outlet temperature of a receiver.This meant that the total heat exchange area or initial investment could be effectively reduced under the prescribed total HTF circulating flow rate.We also studied the variation trends of the two optimized results including minimum total HTF heat capacity rate and minimum total thermal conductance.The minimum total HTF heat capacity rate decreased with the given total thermal conductance,the minimum total thermal conductance decreased first and then increased with the given total HTF heat capacity rate.We also found that for a SPTS with a re-heater,the mixing temperature and the mixing position of HTF had significant effects on the two types of optimization problems.