A comprehensive review of solar‐driven desalination technologies for off‐grid greenhouses

This paper is motivated by the crisis of freshwater in remote areas around the world and responds to the growing need for sustainable food production in arid lands. It focuses on utilizing solar energy to yield freshwater from the sea or brackish water with less environmental impacts, for greenhouses, which can produce sustainable food all over the year. The integration of various solar‐driven desalinations such as solar still, humidification‐dehumidification, reverse osmosis, electrodialysis, and multieffect and multistage flash with greenhouses are evaluated, for better sustainability towards greenization. The paper first discusses the specifications of solar‐driven desalinations and compares their advantages and limitations. Then, different types of greenhouses are introduced, and their total water requirement is discussed based on their locations, crop type, greenhouse technology, irrigation type, and environmental conditions, as well as their cooling and heating strategies. Later, the existing integration of solar‐driven desalinations with greenhouses are reviewed, and their advantages and limitations are deliberated. Finally, the paper discusses the criteria to be considered when selecting solar‐driven desalinations for greenhouses and presents a detailed comparison between the water production rate and cost as well as the energy consumption of these systems. In the end, the most appropriate combinations of solar‐driven desalinations with greenhouses are recommended based on their water requirement and production cost.     

浅埋深薄基岩高强度开采工作面压架机理分析

为解决浅埋深薄基岩高强度开采影响下引起的压架事故,采用数值模拟和理论分析的手段,分析了工作面推进过程中覆岩的破坏过程及压架事故发生机理。结果表明:在煤层开采过程中,不同岩性的岩层中应力分布差异很大,其破断冒落条件也不相同;覆岩中上行裂隙、下行裂隙同时发育贯通是压架事故发生的前提;覆岩载荷传递因子的变化、基本顶破断岩块架后切落、地表厚风积沙的存在以及水沙对基本顶破断岩块运动形式的影响,均增加了顶板沿煤壁大范围切落并导致压架事故发生的概率。通过对乌兰木伦煤矿31402工作面局部压架事故进行分析可知,采高增大而破断岩块长度减小,基本顶结构仅以单关键块形式出现,是基本顶结构容易发生切落的主要原因。     

液压支架与工作面顶板耦合分析

根据液压支架支护特性和工作原理,给出将支架简化为具有一定弹性系数的弹性体的理论依据,充实了采场围岩与液压支架整体力学模型理论基础。在此基础上,推导出了液压支架顶梁载荷分布规律,理论结果与实验数据基本一致,从而验证了液压支架与顶板耦合关系模型的正确性,为相关研究深入开展创造了条件。     

Self‐Powered Trace Memorization by Conjunction of Contact‐Electrification and Ferroelectricity

Triboelectric nanogenerator (TENG) is a newly invented technology that can effectively harvest ambient mechanical energy from various motions with promising applications in portable electronics, self‐powered sensor networks, etc. Here, by coupling TENG and a thin film of ferroelectric polymer, a new application is designed for TENG as a self‐powered memory system for recording a mechanical displacement/trace. The output voltage produced by the TENG during motion can polarize the dipole moments in the ferroelectric thin film. Later, by applying a displacement current measurement to detect the polarization density in the ferroelectric film, the motion information of the TENG can be directly read. The sliding TENG and the single‐electrode TENG matrix are both utilized for realizing the memorization of the motion trace in one‐dimensional and two‐dimensional space, respectively. Currently, the ferroelectric thin film with a size of 3.1 mm² can record a minimum area changing of 30 mm² and such resolution can still be possibly improved. These results prove that the ferroelectric polymer is an effective memory material to work together with TENG and thereby the fabricated memory system can potentially be used as a self‐powered displacement monitor.     

Self‐Recovering Triboelectric Nanogenerator as Active Multifunctional Sensors

A novel self‐recovering triboelectric nanogenerator (STENG) driven by airflow is designed as active multifunctional sensors. A spring is assembled into the STENG and enables the nanogenerator to have self‐recovering characteristic. The maximum output voltage and current of the STENG is about 251 V and 56 μA, respectively, corresponding to an output power of 3.1 mW. The STENG can act as an active multifunctional sensors that includes a humidity sensor, airflow rate sensor, and motion sensor. The STENG‐based humidity sensor has a wide detection range of 20%–100%, rapid response time of 18 ms, and recovery time of 80 ms. Besides, the STENG could be utilized in the application of security monitoring. This work expands practical applications of triboelectric nanogenerators as active sensors with advantages of simple fabrication and low cost.     

Performance analysis of a supersonic ejector cycle working with R245fa

A supersonic ejector chiller for industrial use is currently being developed and tested as part of a project cooperation between Frigel s.p.a and DIEF (Department of Industrial Engineering, University of Florence). The refrigerator was built following a “ready to market” setup criterion and is intended for applications on the industrial refrigeration market or in air conditioning. The plant has a nominal cooling power of 40 kW and is powered by low temperature heat (from 90 up to 100 °C). The ejector is equipped with a movable primary nozzle and 9 static pressure probes along the mixing chamber/diffuser duct. The working fluid is R245fa. An extensive numerical campaign was performed to analyze the internal dynamics of the ejector. All the simulations were carried out by accounting for the real gas properties of the refrigerant. Comparison with experimental data resulted in close agreement both in terms of global and local parameters. Analyses showed that in order to achieve an accurate matching with the experimental data, it is necessary to correctly account for the surface roughness of the ejector. This is especially true for off-design operating conditions.     

钒自给能探测器延迟信号数字处理算法与实验研究

钒自给能探测器（VSPND）输出电流信号的慢响应特性严重影响反应堆内中子通量的实时测量，不利于反应堆的控制和安全管理。采用反函数计算或各种补偿方法改进其响应特性，有利于VSPND的使用。本文研究了前向差分变换法、后向差分变换法、阶跃响应不变法及双线性变换法等4种数字处理算法，提出了两次处理的方法，有效缩短了VSPND输出信号的响应时间，时间常数由325.47 s减少到7 s以内，其中阶跃响应不变法算法的时间常数最小为5.2 s。设计了数字实验系统，验证了算法的正确性，为该探测器用于反应堆内中子通量测量的快速响应提供了可行性。