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The solution of a task No. 3. "Invent yourself: curved mirrors"
12FM team Novosibirsk, 8th class
Slide 1. Hello, my name is Suluyanova Ksenia. I am the member of the 12MP team from Novosibirsk. Let me represent the solution of the problem "Invent yourself: curved mirrors."
Slide 2. The statement of the problem you can see on the slide. Studied the theoretical material on the research topic, the following hypothesis was put forward: if you send a concave mirror of large dimensions under the stream of solar rays, then their energy concentrated at the point of focus can be used to heat various objects.
Slide 3. Purpose: to perform the melting of snow using a solar concentrator made on the basis of a concave mirror.
The research objectives are presented on the slide:
1. Study the theoretical justification of the phenomenon under investigation;
2. Consider the principle a solar concentrator`soperation of manufactured on the basis of a concave mirror of large dimensions;
3. Suggest a way to using a concave mirror for heating different objects;
4. Make a concave mirror of large dimensions;
5. Calculate the thermal power of concave mirrors of different diameters.
Slide4.Let us consider the basic physical concepts underlying the solution of this task.
A spherical mirror is a mirror reflecting the surface of which has the form of a sphere`ssegment. Spherical mirrors are divided into convex and concave. The slide shows the path of the rays in a concave mirror. The rays incidenting on the surface of the concave mirror parallel to the optical axis.After the reflection they are collected in focus F.
The focus F of a concave mirror is a point on the optical axis through which the ray (or its continuation), passes after reflection from the mirror.The ray is incident on the mirror parallel to the optical axis
Slide 5. This year we had a snowy winter. The amount of precipitation exceeded the average 1.5-2 times. Therefore, starting to solve this problem, it was decided to direct the Sun`senergy to the struggle with snowdrifts.
In the reference books, one can find the energy density that reaches the surface of the Earth. It is equal to 800-1000 W per 1 m2, perpendicular to the sun's rays.
Starting to make the construction, we stopped on a parabolic mirror, which is quite simple to manufacture. The mirror is made of plywood and pasted with household foil for baking. The coefficient of its reflection of infrared rays is 90-95%.
To build a parabola we will use the method from the site Do it yourself (the link is presented on the slide). To do this, draw a right angle on the plywood sheet; On one side we put the marks in 10 cm and denote them with letters; On the other - after 20 cm, denoted by numbers. Then we connect the marks with the lines a1, b2, b3, and so on. The forming lines will give us the desired parabola. The obtained points are smoothed out using a pattern and we mirror the forming part.
Using the materials presented on the slide for the patterns, a concave mirror with 1 meter diameter was made.
Slide 6. Let us pass to the experimental part of our study. As a water tank, a black aluminum can is used.
The purpose of the first experiment is to determine the thermal power of the installation. The experiment was made on April 10, the environmental temperature was + 3.40C. Before the experiment, determine the location of the focus point of the mirror produced (first by hand, and then - using an electronic thermometer). We put in the focus point a jar with a small amount of water (60 ml), we measured its initial temperature and the heating time.
The data obtained during the measurements made it possible to obtain the value of the thermal power generated by the installation. It turned out to be 10.6 W, which correspond to 10.6 W / 0.691 m 2 = 15.4 W / m2.
Slide 7. During the measurements and calculations, we used the following notation, constants, and formulas. They are universal for computations, so it was decided to present them on a slide, and then to show only the computed result. Slide 8. The purpose of the second experiment was to determine the thermal power of concave mirrors of different sizes.
Equipment: concave mirrors, centimeter tape, thermometer, stopwatch.
The slide shows the parameters of the concave mirrors used by us in the experiment.
To reduce the errors affecting the value of thermal power in each experiment, one set of materials and the same amount of waterwere used.
Slide 9. The results of calculating the heat output are presented on the slide. Analysis of the obtained values allows us to make the following conclusions:
1. A round open can is ineffective for obtaining a good result. Some part of the energy for the heating and some is radiated into the environment, including airflow.
2. The formed parabolic mirror with a diameter of 1 m is covered with food foil, which has low reflecting qualities.It explains the low thermal power at the longest chord length. Another reason that affects the process of heating water is that the focus of this mirror is outside the bowl. At the same time, the sun's rays from the parabola laid on the round surface of the cans not everywhere evenly. The part of the rays passed by, the part fell on the tangent. At the same time, the can was cooled by the wind on one side, while it was heated on the other.
3. A concave mirror with a chord length of 37 cm has a focus located inside the bowl, so the heating of the container with water was more uniform. This explains the greatest value of heat output.
4. With the concave mirrors sizes increase, the thermal power of the solar concentrator also increases.The quality of the coating remains unchanged (mirrors 1-4).
Slide 10. This slide shows photo of the experiment.
Slide 11. The third experiment was made on April 14, the air temperature was + 7ᵒC. The experiment started on 2pm.
The purpose of the experiment is to effect the melting of snow by means of a concave mirror.
The melting time of snow with a mass of 100 grams was 18 minutes 15 seconds.
Slide 12. According to the measurements and the above formulas, we calculated the thermal power of the solar concentrator. It is equal to 30 W. The intensity of the heat flow - the heat flow, per unit area of the concave mirror is about 400 W / m2. (The power was divided by the surface area of the concave mirror). The analysis of the experiments results of the made it possible to come into the following conclusions:
1. With increasing the surface area and the time of using of the solar concentrator at the same time reducing the height of the segment of the concave mirror (so that the focus leaves the mirror) we can melt snow in hard-to-reach places.
Slide 13. Conclusions of the work.
1. We consider the principle a solar concentrator`s operation of manufactured on the basis of a concave mirror of large dimensions;
2. Large mirrors (from 10 to 100 cm) were produced.
3. According to the experiments carried out, the thermal power of the concave mirrors of different diameters was calculated.
4. On the basis of formed and industrial concave mirrors, a mobile snow melting unit has been developed. The model certainly has drawbacks. Low power can be compensated by the number of mirrors that direct the light flux to one point, but this leads to a large flow of material.
Slide 14. The slide shows a list of used literature and Internet sources. Thank you for your attention, I'm ready to listen to your questions.