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[技术] 太阳能炉灶原理

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发表于 2010-5-15 05:50:09 | 显示全部楼层 |阅读模式
今天转载一份关于太阳能炉灶的原理方面的知识与大家分享,我觉得还是用原文介绍会更有说服力,所以就不打算用google翻译了,英文水平向我一样的朋友,看看图片也是一样可以明白的。

The Scheffler-Reflector
The Idea:
The basic idea that lead to the development of the Scheffler- Reflectors was to make solar cooking as comfortable as possible. At the same time the device should be build in a way that allows it to be constructed in any rural welding workshop in southern countries after a certain period of training. The locally available materials must be sufficient.
The Technology:
To make cooking simple and comfortable the cooking-place should not have to be moved, even better: it should be inside the house and the concentrating reflector outside in the sun.
The best solution was a eccentric, flexible parabolic reflector which rotates around an axis parallel to earth-axis, synchronous with the sun. Additionally the reflector is adjusted to the seasons by flexing it in a simple way.
How does this work?
The reflector is a small lateral section of a much larger paraboloid. The inclined cut produces the typical elliptical shape of the Scheffler-Reflector. The sunlight that falls onto this section of the paraboloid is reflected sideways to the focus located at some distance of the reflector.
The axis of daily rotation is located exactly in north-south-direction, parallel to earth axis and runs through the centre of gravity of the reflector.
That way the reflector always maintains it's gravitational equilibrium and the mechanical tracking device (clockwork) doesn't need to be driven by much force to rotate it synchronous with the sun. The focus is located on the axis of rotation to prevent it from moving when the reflector rotates. The distance between focus and centre of the reflector depends on the selected parabola. During the day the concentrated light will only rotate around its own centre but not move sideways in any direction. That way the focus stays fixed, which is very useful, as it means the cooking-pot doesn't have to be moved either.
Drawing 1:
 楼主| 发表于 2010-5-15 05:53:39 | 显示全部楼层
In the course of the seasons the incident angle of the solar radiation varies + / - 23,5° in relation with the perpendicular to earth-axis. The paraboloid has to perform the same change of inclination in order to stay directed at the sun. Otherwise it's not possible to obtain a sharp focal point. But the centre of the reflector and the position of the focus are not allowed to move.
This is only possible by shaping the reflector after an other parabola for each seasonal inclination-angle of the sun, i.e. for each day of the year. This means the reflector has to change its shape.
The reflector-frame is build for equinox. By inclining and elastically deforming the reflector-frame all other parabolas can be achieved with sufficient accuracy.
Drawing 2:




Changing the inclination and deforming the reflector are mechanically combined: the two pivots A, at each side of the reflector-frame, and pivot B, in the centre of the reflector, do not form a line, but B is located below. That way inclining the reflector leads to a change in its depth, the centre of the reflector is lifted up (big radius of crossbars) or pressed down (small radius of crossbars) relative to the reflector-frame. It's enough to adjust the upper and lower end of the reflector (C and D) to their correct position to obtain a sufficiently exact reflector-shape. The setting is done by a telescopic bar at each end of the reflector.
Adjusting the reflector-shape has to be done manually every 2-3 days. When all concentrated light enters the opening of the cooking-place installed at the focal point the correct reflector-shape is achieved.
After passing the opening the light is redirected by a small reflector (secondary reflector) to the black bottom of the cooking pot. There it is absorbed and transformed into heat. The efficiency for cooking, i.e. heating water from 25°C to 100°C, can reach up to 57% and depends on the cleanliness of the reflector-surface and the state of insulation of the cooking-pot. At the focal-point itself we have measured optical efficiency of up to 75% (with 2mm ordinary glass mirrors). Depending on the season an elliptical reflector of 2,8m x 3.8m (standard size of 8m² Scheffler-Reflector) collects the sunlight of a 4,3m² to 6,4m² area, measured perpendicular to the direction of the incident light (aperture). That way the cooking power varies with the season. As an average a 8m² Reflector can bring 22 litres of cold water to boiling temperature within one hour (with 700W/m² direct solar radiation).
There are many options for the design of the cooking-place. Mostly it is integrated into a kitchen building and provides the possibility to use firewood for cooking when the sun doesn't shine. Depending on the type of food which is cooked there is no need for a secondary reflector. This increases the efficiency and simplifies maintenance. Instead of a cooking-place a backing-oven, steam-generator or heat-storage can be installed at the focal-point.
Drawing 3:



 楼主| 发表于 2010-5-15 06:10:24 | 显示全部楼层
Dissemination
The first well functioning Scheffler-Reflector (size: 1,1m x 1,5m) was built by Wolfgang Scheffler in 1986 at a mission-station in North-Kenya and is still in use .
Since then the technology has been continuously improved and passed on to many motivated people. That way the number of installed reflectors increases from year to year .
For a number of years mainly 8m² size reflectors were constructed for canteen kitchens. After the year 2000 mostly 10m² Scheffler-Reflectors are installed.
                 It´s difficult to tell how many Scheffler Reflectors exist, as there is no central registration and many workshops work independently. 2004 there were about 750 reflectors in 21 countries, that coresponds to about 200 solar kitchens, including 12 solar steam kitchens with 10 to106 reflectors per installation. The biggest solar kitchen of the world in Abu Road, Rajastan (India) is catering for up to 18 000 visiters of a Yoga center.
                        Now, 2006, there might be around 950 Scheffler Reflectors worldwide.
               
                Local Production
                During the whole time of development of the Scheffler-Reflectors - up to now 23 years- care was taken to use simple materials and construction techniques common for rural settings. For that reason Wolfgang Scheffler did a great deal of his developments in Kenya and India where he learned local construction techniques. Together with local craftsmen he built a number of first solar kitchens and installed them at interested schools.
The main construction of the reflectors (apart from the mirror surface) consists of steel. We use profiles that are common in construction of furniture, water-installation and housing. This material is relatively cheaply available everywhere.
For the reflector surface various materials can be used. Silvered glass mirrors - as they are used for bathroom-mirrors - are most common.
The combination of affordable materials, common tools and un-complicated techniques of fabrication to create a product with high-tech qualities enables interested groups to make something with their own hands which will benefit them in a sustainable way.
A good example is the construction of the worlds largest solar-kitchen in Abu Road, Rajastan, by the Brahma Kumaris. Because they did most of the work involved themselves, the whole installation ( 800m² of Reflector surface + steam system + back-up boiler) could be built for only 100 000
 楼主| 发表于 2010-5-15 06:10:52 | 显示全部楼层
Zeichnung 4:
发表于 2015-11-7 16:00:42 | 显示全部楼层
我是来刷分的,嘿嘿
发表于 2015-12-1 10:30:14 | 显示全部楼层
没看完~~~~~~ 先顶,好同志
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