Long-Term Retardation of Water Evaporation by Ultra-Thin Layers of Polydimethylsiloxanes in the Indoor Conditions

Abstract

Global warming is affecting on the water balances in many parts of the world to exceed evaporation over rainfall, leading to negative environmental consequences and economic losses. An effective way to reduce water loss due to evaporation from the free surface of reservoirs is the use of ultra-thin surface films of special additives. Insufficiently high stability and significant cost of additives based on fatty alcohols (hexadecanol, octadecanol and their mixtures) leads to the search for new effective and more economical additives to reduce water loss due to evaporation. In the laboratory, a series of long-term (84 days) experimental studies of the effect of ultra-thin films of polydimethylsiloxanes brands PDMS-100 and PDMS-200 with a thickness of 1 μm on the rate of evaporation of water from the free surface. The dynamics of change in time of daily values of the effect of reduction of evaporation by means of PDMS films, and also total effect from the beginning of researches is received. The maximum daily effects of evaporation reduction were obtained on the 6th day of the study; they accounted for 39.5% for the PDMS-200 film and 32.9% for the PDMS-100 film, respectively. Linear correlations are obtained between the values of mass transfer coefficient and free surface temperature for water without additives, as well as for similar tanks with ultra-thin PDMS films. The total effect of evaporation reduction with the PDMS-200 film with a thickness of 1 μm for 84 days was 17.2%, while for the PDMS-100 film of the same thickness a reduction of evaporation by 5.7% was obtained. Given the long duration of action, ultra-thin films of polydimethylsiloxanes, especially PDMS-200 from an economic point of view can be a profitable alternative to the use of monofilms based on fatty alcohols.

Keywords

• evaporation retardation
• mass-exchange coefficient
• monolayer
• polydimethylsiloxane
• ultra-thin layer
• water balance