要不断打开教学思路——《压缩空气》教后随感

《压缩空气》这一课我共教了10次,因此感触也特别深,想得最多的便是怎样使学生能动地自行获取知识。在和许多老师一起研究和试教这一课的过程中,我也得到了很多启示,概括起来,主要有以下几点:

《压缩空气》课堂实录与评析

师:(出示瘪篮球)这是什么? 生:瘪篮球! 师:让它圆起来,怎么办? 生:打气! 师:打什么气? 生:空气! 师:什么地方的空气? 生:打气筒里面的。 师:打气筒里的气是哪里来的? (评:这个问题改为:“打气筒里的空气够吗?”可能要好一些。后面还会说到。)

研究《压缩空气》教学时的两点体会

教课前两天接到通知,黄山市的老师要来听课,按进度正好是《压缩空气》,匆匆试教了一次,课后座谈时,黄山市的老师们说了许多鼓励的话,促成我们对这个课的教学作进一步的研究,以下记述研究中的一些体会。 一、为什么先不给球打气?

让“空气压缩”看得见

在教《压缩空气》时,为了帮助学生看得见空气的压缩,我改进了实验,效果很好。我先在烧瓶内烧一张纸,用纸板盖住瓶口,产生浓浓的烟雾,然后用注射器对着瓶口吸进带有烟雾的“空气”,这样学生便可以直接观察烟雾“空气”渐渐吸入这一过程,用橡皮或手堵住出口,用力把活塞向内压,带有烟雾的“空气”的体积便缩小些。

《空气占据空间》教学体会

上了《空气占据空间》一课后,感受颇多,下面就我体会最深的两点谈一谈。 一、博学、深研、勤奋、认真 小学自然课的内容涉及的学科众多,知识面很广。教师除了要理解所教的知识。

压缩空气

空气之间也有距离，而且空气也可以被压缩在一起，你知道吗？让我们来动手做做看。

香蜜湖畔的一点感受

近几年,听了不少的自然课,发现不少的教师,把参加观察实验的若干个学生编成1、2、3、4等若干个号码,观察实验开始了,老师往往不喊学生的姓和名,而直截了当地叫:1号拿烧杯,2号划火柴,3号拿抹布……,如此等等。教学上,课堂纪律有条不紊,实际上,是小学自然实验教学的误区。 值得欣慰的是,去年12月18日在深圳市召开的全国小学自然教育研讨会上,武汉市水果湖二小的刘晋斌老师、温州市永中小学的李玉字老师有意识地走出了这个误区。

New Respirable Dust Suppression Systems for Coal Mines

Dust suppression in coal mines is a worldwide problem which has not been solved effectively. The applica-tion of negative pressure secondary dust removal (NPSDR) is a breakthrough in the coal mine safety field. In this paper,NPSDR technology and ultrasonic dust suppression systems are introduced. High pressure water is supplied to the NPSDR device which is mounted on the shearer. A negative pressure field is formed in the device. At the same time,the dusty air around the shearer drum will be sucked into,and purged from,the NPSDR device by the negative pressure field. An ultrasonic dust suppression system uses water and compressed air to produce micron sized droplets which suppress respirable coal dust effectively. The NPSDR technology can be used for shearer dust suppression while ultra-sonic dust suppression can be applied in areas such as the transportation positions. These dust suppression methods have the following advantages: high efficiency,wide applicability,simple structure,high reliability and low cost.

Theoretical and numerical simulation of critical gas supply of refuge chamber

The personnel in refuge chamber absorb O_2 and exhale CO_2 all the time. Supplying O_2 and removing CO_2 are the basic function of refuge chamber. After disaster occurs, the supply of the compressed air or oxygen for personnel in refuge chamber is limited. Thus, how to effectively use the compressed air and oxygen and try to improve the time of supply has a great significance. Supplying more oxygen will result in waste, while supplying less oxygen will cause its concentration to be lower, and harm life safety. This research uses the theoretical calculation and numerical simulation, finds critical gas supply for refuge chamber, and illuminates the change law of gas concentration with critical gas supply in refuge chamber,which provides theoretical guidance for effective use of compressed air and oxygen in refuge chamber.

Experimental Study of the Controlling Characteristics of Inverter-Driven Multi-type Air Conditioner

The controlling algorithm was studied for the inverter-driven multi-type air conditioner using electronic expansion valve(EEV) in outdoor unit. The performance of inverter-driven air conditioner with two different units was investigated by varying the outdoor ambient temperature and compressor speed. Based on the test results, the effect of EEV opening on the indoor unit exit superheat was discussed. For the specified outdoor ambient temperature scope and the EEV opening, the superheats of indoor units decrease with the outdoor ambient temperature rising. Improper distribution of refrigerant into each indoor unit will causes excessive superheat difference between two indoor units. Suggestions were then given for the controlling of the superheat.

Reaction Crystallization of Struvite in a Continuous FB MSZ Type Crystallizer with Jet Pump Driven by Compressed Air

The results of struvite reaction crystallization from diluted water solutions of phosphates （V） （0.20 mass% of PO43-） by means of magnesium and ammonium ions are presented. Continuous FB MSZ crystallizer with jet pump driven by compressed air was used. Influence of pH and mean residence time of suspension on the crystal product quality was determined. Increase in pH from 9 to 11 resulted that mean crystal size decreased nearly two-time： from 27.1 to 15.1μm for mean residence time of suspension 900 s. Elongation of this time from 900 to 3,600 s influenced struvite crystal size advantageously-it increased from 27.1 to 41.2 μm at pH 9. From the population density distributions nucleation and growth rates of struvite were calculated based on the simplest SIG model of mass crystallization kinetics in MSMPR crystallizer. Linear growth rate ofstruvite crystals decreased nearly two-time with the increase in environment pH from 9 to 11, and more than 2.5-time with the elongation of mean residence time of crystal suspension in a crystallizer from 900 to 3,600 s from 1.34× 10-8 m/s （pH 9, τ= 900 s） to 2.60×10-9 m/s （pH 11, τ= 3,600 s）.

Aerodynamic performance of high-turning curved compressor cascade with boundary layer suction

The impact of boundary layer suction on the aerodynamic performance of a high-turning compressor cascade was numerically simulated and discussed.The aerodynamic performance of a curved and a straight cascade with and without boundary layer suction were comparatively studied at several suction flow rates.The results showed that boundary layer suction dramatically improved the flow behavior within the flow passage.Moreover,higher loading over the whole blade height,lower total pressure loss,and higher passage throughflow were achieved with a relatively small amount of boundary layer removal.The integration of curved blade and boundary layer suction contributed to better aerodynamic performance than the cascades with only curved blade or boundary layer suction used,and the more favorable effect resulted from the weakening of the three dimensional effects of the boundary layer close to the endwalls.

An Approach towards Eco-labeling of Compressed Air Filters Based on Carbon Footprint

Compressed air--a major industrial energy carrier, its filters are used to reach the required cleanliness level of compressed air. These filters, however, introduce a pressure drop which results in a loss of energy. It is shown that over the life cycle of a compressed air filter, the pressure drop dominates the total energy consumption and subsequently, the carbon footprint. From an economic as well as ecologic point of view, a reduction of the pressure drop is hence of utmost importance. Based on this finding and structuring, the wide range of applications and operational parameters, a pragmatic and technically feasible eco-labeling system for compressed air filters was developed as a decision supporting tool. Using this tool, procurement managers as well as the process engineers and environmental officers are able to steer the selection of suitable compressed air filters. The approach has been proposed to and discussed with various representatives of the compressed air filter industry nevertheless there is probably a long way to go to establish such a labeling procedure in industry.

Effect of landform on aerodynamic performance of high-speed trains in cutting under cross wind

The effects of the different landforms of the cutting leeward on the aerodynamic performance of high-speed trains were analyzed based on the three-dimensional, steady, and incompressible Navier-Stokes equation and k-e double-equation turbulent model. Results show that aerodynamic forces increase with the cutting leeward slope decreasing. The maximum adding value of lateral force, lift force, and overturning moment are 147%, 44.3%, and 107%, respectively, when the slope varies from 0.67 to -0.67, and the changes in the cutting leeward landform have more effects on the aerodynamic performance when the train is running in the line No. 2 than in the line No. 1. The aerodynamic forces, except the resistance force, sharply increase with the slope depth decreasing. By comparing the circumstance of the cutting depth H=-8 m with that of H=8 m, the resistance force, lateral force, lift force, and overturning moment increase by 26.0%, 251%, 67.3% and 177%, respectively. With the wind angle increasing, the resistance force is nonmonotonic, whereas other forces continuously rise. Under three special landforms, the changes in the law of aerodynamic forces with the wind angle are almost similar to one another.

Gigawatt Scale Storage for Gigawatt Scale Renewables

Multi-GW renewables need multi-GW storage, or fossil fuelled power stations will be needed to balance for intermittency. For the same reason, such balancing must be able to last for an entire evening peak if renewables are not generating at the same time. Batteries and DSR （demand side response） make very useful contributions and there is a large market for both, but without large scale and long duration storage, they cannot do the job. Interconnectors also contribute to the solution, and storage will make them more profitable, but （taking a UK perspective） Ofgem identified that all our neighbours have similar generation capacity crunches and similar demand patters, so if we need the electricity when they do, we’ll have to pay through the nose for it. Last winter’s ￡ 1,500/MWh prices proved that―even with only 4 GW interconnection. Following exit from the single market, our neighbours will be able to say “our consumers are more important than yours at any price”. We need UK-based storage at the right scale, to store UK-generated electricity for UK use and for export―otherwise we lose security of supply. CAES （compressed air energy storage） and pumped hydro are the only technologies currently able to deliver this scale and duration of storage. Pumped hydro is cost-effective in the long term but there are few sites, and it is （location dependent） over 3x the cost of CAES. Storelectric has 2 versions of CAES： one is a comparable price to existing CAES, but much more efficient （~70% v 50%） and zero emissions （existing CAES emits 50%-60% of the gas of an equivalent sized power station）. The other is retro-fittable to suitable gas power stations, is more efficient （-60% v 50%）, almost halves their emissions, adds storage-related revenue streams and is much cheaper. Both are new configurations of existing and well proven technologies, supported by engineering majors.

Experimental Characterization of the Action of an Artificial Wind on a Wind Turbine and Optimization of the Storage Efficiency of Compressed Air in Hybrid PV/Wind Turbine Systems

The general idea of this work is to improve the performance of CAES （compressed air energy storage） for its application in solar and wind systems through a restitution technique by creating an artificial wind. The efficiency of compressed air storage is often presented as a limit to its application. The present work describes a series of manipulations carried out in order to increase the yield. As the action of the artificial wind on the wind turbine is characterized by a reduced attack surface, a treated wind, a constant direction, an adjustable speed, it is therefore a question of acting on all the controllable parameters of the artificial wind to find the best way to use it to produce more energy from a certain quantity stored in a tank. The main manipulations consisted in determining： the optimal number of points of attack of the wind turbine; the nature of the action （continuous or interrupted） of the wind; the frequency of wind action and the duty cycle.