Water evaporation is an important physical phenomenon that occurs in nature and several industrial applications such as food drying processes, cooling in air-conditioning systems and desalination. In all these systems, it is necessary to have a good prediction and control of evaporation rate as a function of various system parameters. Attempts to understand the affecting factors have mostly focus on the flow rates of gas or water streams, relative humidity of the air, presence of dissolved or suspended material in the water, temperatures of the air and water streams. However, as water surface partially covered (less surface area) is generally thought to have lower evaporation rate, little notice has ever put on it.

Here we consider the evaporation case of water surface covered with nano-through-hole lid (NHL) of which the radius size is nearly equal to the average free path of the vapor. Using a gravimetric method, we experimentally measured the evaporation rate of water at the orifice of the nano-holes. The results indicate that the evaporation rate is 1–6 times faster than the non-sheltered water surface with the same liquid area. Moreover, with the porosity of the lid decreasing, the evaporation rate per unit area increases. A theoretical model is developed for this novel phenomenon from the view of molecular dynamics during evaporation and vapor diffusion. We envision that this finding may have new inspirations on phase change phenomenon in nano-confined space and put forward one new way for promoting evaporation of liquid.

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