Evaluating the Evaporation Reduction through Combined Methods of Floating Balls and Monolayer in Class A Pan (Case Study of Khorramabad City)

In arid and semi-arid regions, surface evaporation can be considered the main cause of water loss. Evaporation occurs at temperatures lower than the boiling point of water and it is an inevitable phenomenon and it plays an important role in the loss of water resources in countries according to their geographical and meteorological conditions. One of the main methods to reduce evaporation from the surface of open tanks, which is used in many hot and dry regions, is the use of physical and chemical coatings. In the current research, which was conducted with the aim of reducing the rate of evaporation from class A evaporation pans, it was tried for the first time to investigate the efficiency of three types of balls with monolayer composition of hexadecanol as an evaporation reducing coating. Three types of balls with a diameter of 7 cm made of propylene were used; balls with two holes, six holes, and no holes. In order to investigate the performance of these coatings in reducing the evaporation of class A pans, they were investigated for 2 months from 1400/6/1 to 1400/7/30 (two months). The measurement of evaporation has been repeated once every hour from 8:00 am to 5:00 pm and the resulted times series were analyzed statistically. The measured evaporation values were analyzed in SAS software and the comparison of averages was done at the 99% probability level based on Duncan's average comparison test. Results showed that the combination of hexadecanol monolayer and three ball samples had a significant difference at the 5% level in terms of changes in evaporation rate and temperature. The results of comparing the average effect of different coatings on the rate of evaporation showed that the control pan had the highest amount of evaporation among other pans, while the pans covered with the monolayer combination of hexadecanol and non-porous balls showed the lowest amount of evaporation. The comparison of average evaporation values in Duncan's test did not show any common letters which means that all pairs of coatings have a significant difference at the 5% level. The results showed that the combination of hexadecanol monolayer and non-porous balls with an efficiency of 86.7% contributed the most in reducing evaporation. While the combination of hexadecanol monolayer with two-hole and six-hole balls with efficiency of 59.6% and 56.7% were placed in the next priorities. Finally, the combination of hexadecanol monolayer and balls without holes were identified as the best evaporation reducing coating in the present study due to the appropriate surface roughness and the constant percentage of empty spaces over time.