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发表于 2011-4-25 13:07
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[Homework]SENEWS-2011-04-25
THIS IS THE VOA SPECIAL ENGLISH TECHNOLOGY REPORT
Solar water heaters are used around the world, and are not very difficult to build. the system we are going to describe is based on the design develop some years ago in Afghanistan. Since then, it has been built and used in many countries.
It can heat 70 liters of water to 60 degrees Celsius, it can do this between sunrise and noon on the clear day with an average air temperature of 32 degrees Celsius, there are two parts to the solar water heater, one part is made of the sheet of the metal painted black, black surfaces become hotter in the sun than surfaces painted in the other color, this black metal plate is called a collector, the collector is placed in contact with the water. There are several kinds of metal sheets that can be used for the collector, x metal will work very well, sheets are often used as roofs on housing.
Once the water is heated, it is kept hot with insulation material, this allows the water to stay warm for a long time, the second part of the solar water heater holds the water for the system. this storage tank can be a container that holds about 100 liters, two rubber pipes are attached to water storage tank, one pipe lets water flow into the system, the other lets water flow out , when the water heater is working correctly, water will flow from the storage tank to the collector and back again. you can use the hot water as the top of the tank for washing and cleaning ,you can change the flow of water so that the temperature is hot or warm as desired , this solar water heater is easy to build and operate, it will last about two years before the rubble pipes need to be replaced, there are also something else you will need to make the solar water heater work, the sun, as you might imagine, the heater will heat the water only on sunny days, you can get more information about solar water heaters and other projects from enterprise works vita , this group works internationally to fight poverty, the website is enterpriseworks.org, choose the link for the news and resources then click on publications, and that the VOA special English technology report.
tell us if you have ever built a solar water heaters or have ideas for improvements, post you comments at VOA SPECIAL ENGLISH.COM, or you can also find transcript at pm three and pose casts of our program, we also offer English teaching activities in the classroom section about our set.
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