Cutouts are made in the partitions for the absorber tubes.

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Place the radiator in a container with water and use a compressor to build up pressure of 7–8 atm. The bubbles rising at the joints indicate the tightness of the soldered joints.
If you can't find a suitable container to test the collector, you can assemble it yourself. To do this, make a box or a simple barrier from improvised means (timber trimmings, bricks, etc.) and cover it with polyethylene film.

After checking the tightness, the radiator is dried and degreased. Then they begin soldering the copper sheet. The absorber sheet should be soldered to the tubes with a continuous seam along the entire length of each element of the copper circuit.
The absorber web is welded with a continuous seam

Since the solar collector absorber is made of copper, japan mobile database blackening can be used instead of painting. This will allow obtaining a real selective coating on the surface, similar to what is obtained in factory conditions. To do this, a heated chemical solution is poured into a container for checking the tightness and the absorber is placed face down. During the reaction, the temperature of the reagents is maintained by any available method (for example, by constantly pumping the solution through a container with a boiler).
Blackening of copper is one of the most important stages of absorber manufacturing.

A solution of caustic soda (60 g) and potassium persulfate or ammonium persulfate (16 g) in water (1 l) can be used as a liquid for chemical blackening. Remember that these substances are dangerous to humans, and the copper oxidation process itself is associated with the release of harmful gases. Therefore, it is necessary to use protective equipment - a respirator, glasses and rubber gloves, and it is better to carry out the work outdoors or in a well-ventilated area.

The parts for assembling the solar collector body are cut out from the OSB sheet: a 1x2 m bottom, 0.16x2 m sides, an upper 0.18x1 m and lower 0.17x1 m panel, as well as 2 support partitions 0.13x0.98 m.
The 20x30 mm slat is cut into pieces: 1.94 m - 4 pcs. and 0.98 m - 2 pcs.
In the side walls, holes of Ø20 mm are made for the inlet and outlet pipes, and in the lower part of the collector, 3–4 drillings of Ø8 mm are made for micro-ventilation.