太陽曬着水

是水量*被曬面積*時間

當然導熱係數有關聯

你先計算管内的水量
再計算被曬得面積
最後就要計算被曬的時間

你就可以自己製造太陽熱水器了

For the case of a tank of water under the sun, only the water surface absorbs heat from the sun. Because water is a poor thermal conductor, heat absorbed is hardly conducted to the other parts (especially the bottom) of water.

Moreover, because the water on surface is at a higher themperature that below the water, this cannot produce a convection current. Hence, heat from the surface cannot be transferred to the rest of the water. The heat absorbed by the water is thus used mainly in evapourating the water away rather than in raising its temperature.

For the case of water in a metallic pipe, because metal is a good conductor, the heat absorbed by the metallic pipe conducts quickly to the rest of the pipe and which in turn heat up the water inside in all directions. Also, the enclosed water is prevented from evapouration by the pipe and hence the heat absorbed is conserved. Thus the water could reach a higher temperature when it is inside a pipe than when it is in an open tank.