Some physicist correct me if I am wrong.

i always thought the reason to have clear bags was 2-fold, especially for a solar still.
1. Clear plastic lets in the infrared radiation from the sun but doesn't allow it to get out again, thereby raising the temperature of the contents in the bag which aids in evaporation of tainted water to water vapour (in the case of the solar still). That's why in solar cooking, to increase the efficiency of the cooker/pot, it is encased in glass/ clear plastic.

2. In the case of the transpiration bags, it is to allow the plant part in question to continue to photosynthesize and thus transpire and produce the water.

I think the reason why condensation occurs is because of the SATURATION of the water vapor in the air trapped in the bag and not really due to difference in temperature between the air and the bag itself. That's why you are told not to open up the bag too often, because that reduces the saturation of water vapour in the bag and thus the water producing capacity....

Please correct me if I am wrong, because that's the way I understand it from my knowledge of physics and biology....


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