Quantitative efficiency of composite plates in reducing evaporation from water surface

Background and objectives: The average annual evaporation rate in Iran is 2100 millimeters, which is three times the global average. This figure indicates that if the evaporation rate of reservoirs decreases with appropriate methods, we can make better use of these resources. Neglecting the high evaporation rate in the country has caused billions of cubic meters of water to evaporate from the reservoirs of more than 600 dams in the country every year. In this research, the effectiveness of composite plates in reducing evaporation from the free surface of water under real conditions was studied.
Materials and methods: The present study was conducted in the meteorological station of Ahvaz airport, with a geographical latitude of 31° 32', a geographical longitude of 48° 66', and an altitude of 16 meters above sea level. Class A evaporation pans with a diameter of 120.7 millimeters and a depth of 25 centimeters made of galvanized iron were used. All experiments were conducted between July and December 2022. In this study, composite plates with aluminum coating were used to reduce evaporation from the water surface with a thickness of 4 millimeters and consisted of two layers of aluminum sheet in the outer shell and a layer of polyethylene in the middle were used. In order to investigate the effectiveness of composite plates, floating balls, which are a relatively common method of reducing evaporation, used. In addition, the effect of various meteorological variables such as temperature, relative humidity percentage, average vapor pressure, wind speed and solar radiation on the efficiency of composite panels was investigated. Two-way analysis of variance was used to investigate the effect of various weather variables on the performance of composite plates.
Results: Experiments showed that square composite plates had an efficiency of 69%, triangular composite plates had an efficiency of 67%, and floating balls had an efficiency of 73% in reducing evaporation from the water surface. Therefore, floating balls had a slightly greater effect on reducing evaporation from the free surface. The empty space between square composites, due to their larger dimensions compared to triangular composites, is less, which can be considered as one of the reasons for the reduction of evaporation in square composites compared to triangular composites. According to the results of the analysis of variance, two parameters, relative humidity and wind speed, have a significant effect on the efficiency of composite plates in reducing evaporation from the water surface. Based on the results of the analysis of variance considering the interaction effects, none of the interaction effects have a significant effect on the efficiency of composite plates. However, considering the interaction effects in addition to the main effects increased the R-squared value of the created model to 0.669, which indicates that the interaction effects had a contribution of about 0.2 to this value.
Conclusion: Based on the results of the analysis of variance considering the main effects, two parameters, relative humidity and wind speed, have a significant effect on the efficiency of composite panels in reducing evaporation from the water surface. Relative humidity has an effect of 0.182, and wind speed has an effect of 0.197 on the efficiency of composite panels. Relative humidity and wind speed are among the parameters that have a significant impact on the rate of evaporation from the water surface, causing a decrease and an increase in evaporation from the water surface, respectively. The presence of composite panels has greatly reduced the effect of these two parameters on the evaporation rate from the water surface.