Chương trình học tiếng Anh: Anh ngữ đặc biệt của VOA hôm nay phúc trình về công nghệ với tựa đề Solar Water Heater.
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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 a design developed some years ago in Afghanistan. Since then, it has been built and used in many countries.
It can heat seventy liters of water to sixty degrees Celsius. It can do this between sunrise and noon on a clear day with an average air temperature of thirty-two degrees Celsius.
There are two parts to the solar water heater. One part is made of a sheet of metal painted black. Black surfaces become hotter in the sun than surfaces painted any 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. Corrugated metal will work very well. Corrugated 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 one hundred liters. Two rubber pipes are attached to the 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 at 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 rubber pipes need to be replaced.
There is also something else you will need to make the solar water heater work -- the sun. As you might expect, the heater will heat water only on sunny days.
You can get more information about solar water heaters and other projects from EnterpriseWorks/VITA. This group works internationally to fight poverty. The website is enterpriseworks.org. Choose the link for News & Resources, then click on Publications.