Experimental dew condensation using radiative cooling

The increasing need of fresh water in the world and especially in arid regions led recently to seriously consider rain and dew precipitations as new source of water. Collecting rain water is simple, but harvesting dew is much challenging as it requires (i) cooling a surface below the dew point so that the vapor in the air condenses; (ii) tailoring the surface properties to promote water condensation and drainage. In order to reproduce and study this phenomenon, a commonly used way is to cool the substrate by contact. However the method has thermal and geometrical limitations and diverges from the natural phenomenon which involves radiative heat exchange. In order to reproduce radiative cooling in the laboratory a novel setup has been designed. It uses a cold plate at 200K exchanging heat with the substrate. The latter is set in a humidity-controlled chamber where heat exchange is made through a window transmitting 8-13 μm radiation. The device is then used to condense water on complicated shapes as needles, insects or curved surfaces what wouldn't be possible by contact cooling. This work will be concerned with basic questions on the influence of surface chemistry and efficiency of radiative cooling, and will explore the efficiency of this coupled strategy for water harvesting.