Effect of Wind Flow and Solar Radiation on Functionality of Water Evaporation Suppression Monolayers

Abstract

The average evaporation in Iran is 3 times higher than the world average. Applying chemical monolayers on water surfaces is one of the promising methods for suppressing the evaporation. Literature studies have shown that the mixture of cetyl and stearyl (ratio of 1 to 9) is the state-of-the-art monolayer to minimize the evaporation. Adding calcium hydroxide increases the spreading rate and self-healing of the monolayer. Despite long study and investigation on monolayers, there are inconsistencies in explaining the mechanism by which monolayers decrease the evaporation. The mechanisms used to explain the evaporation reduction are: (i) increasing the reflected solar radiation, (ii) dampening the waves formed by winds and decreasing the water surface area, consequently, and (iii) limiting the escape of water molecules. In this paper, by design of experiments (DOE), we try to answer the above question. Evaporation rate from a container in absence of wind or low wind (~0.2 m/s) and at moderate temperature and relative humidity (~20 °C and 45%) is ~10 mm/day. Utilization of the monolayer can save 41% of the evaporated water. Also, in absence of radiation, a 9 m/s wind caused ~15 mm/day evaporation. By increasing the wind speed from 0 to 9 m/s, effectiveness of the monolayer deteriorated from 60 to 13%. Therefore, the main mechanism is neither reflecting the radiation (as in absence of radiation, monolayer was still effective) nor dampening the waves and decreasing the surface area (as in absence of wind, monolayer was effective; also, at higher wind speeds where the surface area increases, monolayer efficiency decreases). Therefore, the main mechanism by which monolayers decrease the evaporation rate is limiting the escape of water molecules. So, monolayers may be effective even during the nights even though radiation is at its lowest.

Lake Evaporation Mitigation Using Self-Assembled Films: Case Study Of Chitgar Lake

“…So, a considerable drop was observed in both pans on the SD because of the rst windy day. Since the oating pans experience waves inside, more cracks or holes will appear in the lm, therefore using a component to ll in cracks and help respreading becomes important (Mozafari et al, 2019). In order to overcome this problem St and Ce can be mixed in which the shorter one (Ce) helps spreading rate and ll in the cracks and the longer one (St) acts more as an evaporation retardant (Prime et al, 2012).…”

“…It also disappeared on the SD in the oating pan due to emerging into wavy water in windy condition (Brzozowska et al, 2012) and didn't achieve to save appropriate TW. In order to improve stability and increase spreading rate of the layer, the CH were added to F4 to make F6 (Mozafari et al, 2019) which indicated more than 50% R in the FD on both land and oating pans. The CH dissolves in the water and make positive charged Calcium ions that makes the F4 spread all over the surface because of positive repel force and can resist against wind up to 4.5 m/s (Waheeb Youssef and Khodzinskaya, 2019).…”

“…These technologies are suitable for use in water reservoirs which are less than 10 ha while chemical covers are recommended as an economical technique for large water bodies (Craig et al, 2007). In the chemical method, a nanometric monolayer consists of long-chain self-spread molecules is dispersed on water to form a molecular lm, which prevents the water molecules from evaporating (Mozafari et al, 2019;Mohammadi et al, 2022). One tail of these molecules is hydrophilic that will settle on the water surface and another tail is hydrophobic which extends in the air-water interface thus they stand next to each other on the water surface and acts as a unique thin layer (Pittaway and Ancker, 2010).…”

“…They spontaneously spread on the surface and could decrease evaporation up to 45% on reservoirs and lakes which areas are less than 10 km 2 (Mcjannet et al, 2008). Also, evaporation reduction of the monolayers has been reported up to 70% in smaller scales and limited conditions such as in class A evaporation pans and lab scale tests (Gallego-Elvira et al, 2013; Mozafari et al, 2019). Using such layers are more reasonable than physical covers in periods that evaporation is higher and wind ow is not too heavy, since they display better stability on lower wind speed (Prime et al, 2012;Mozafari et al, 2019).…”

“…Also, evaporation reduction of the monolayers has been reported up to 70% in smaller scales and limited conditions such as in class A evaporation pans and lab scale tests (Gallego-Elvira et al, 2013; Mozafari et al, 2019). Using such layers are more reasonable than physical covers in periods that evaporation is higher and wind ow is not too heavy, since they display better stability on lower wind speed (Prime et al, 2012;Mozafari et al, 2019). Small amount of these materials are enough to cover wide area, for instance about 20 g of Stearyl alcohol is enough to cover a hectare.…”