Evaporation - CIE125, Cagayan de Oro College PDF

EVAPORATION CIE125 - Hydrology ENGR. ARNOLD APOSTOL JR. DEPARTMENT OF CIVIL ENGINEERING COLLEGE OF ENGINEERING AND ARCHITECTURE DEFINITION PROCESS OF EVAPORATION Water molecules are constantly in motion, with velocity dependent on temperature. Molecules attract each other, and...

EVAPORATION CIE125 - Hydrology ENGR. ARNOLD APOSTOL JR. DEPARTMENT OF CIVIL ENGINEERING COLLEGE OF ENGINEERING AND ARCHITECTURE DEFINITION PROCESS OF EVAPORATION Water molecules are constantly in motion, with velocity dependent on temperature. Molecules attract each other, and the attraction between molecules in the water body causes some molecules at the surface to escape into the atmosphere. Molecules with higher kinetic energy overcome attraction forces and evaporate, a process known as evaporation. Evaporation is a cooling process as escaping molecules carry heat energy with them. Molecules continuously move between the water surface and the atmosphere, with evaporation being the net movement of molecules from water to air. When the rate of condensation (molecules returning to the water) exceeds evaporation, it leads to condensation. Evaporation is measured in terms of depth of water per unit area per unit time (e.g., mm/m²/h). NECESSITY OF ESTIMATION OF EVAPORATION DALTON’S LAW OF EVAPORATION Immediately adjacent to the water surface, there is a thin layer of air that is saturated with vapour and its temperature is the same as that of water. Evaporation depends upon the difference of vapour pressure in the atmosphere and the saturated vapour pressure of this air film. FACTORS AFFECTING EVAPORATION 1. Temperature: Evaporation increases with water and air temperature. The relationship is complex, as evaporation depends on the difference in vapor pressure between the water and the air. 2. Solar Radiation: Evaporation depends on solar energy, which heats the water. The rate changes with day, night, and seasonal variations due to varying sunlight. 3. Wind: Wind helps remove water vapor from the air, increasing evaporation. The effect is more significant with higher wind speeds, but only up to a certain limit. FACTORS AFFECTING EVAPORATION 4. Barometric Pressure & Altitude: Lower barometric pressure and higher altitudes increase evaporation due to reduced atmospheric pressure, although temperature changes at higher altitudes can counteract this effect. 5. Quality of Water: Dissolved solids in water reduce evaporation since they lower vapor pressure. Evaporation is lower in seawater compared to freshwater, with a decrease of about 2–3%. 6. Depth of Water: Deeper water absorbs more heat, which may reduce evaporation in warmer months but increase it in colder months. 7. Other Factors: Surface shape, water surface area, color, flow velocity, and wave presence affect evaporation, though the exact relationships are still under study. EVAPORIMETERS EVAPORIMETERS EMPIRICAL EVAPORATION EQUATIONS EMPIRICAL EVAPORATION EQUATIONS EMPIRICAL EVAPORATION EQUATIONS SAMPLE PROBLEM CONTROL OF EVAPORATION FROM A RESERVOIR CONTROL OF EVAPORATION FROM A RESERVOIR TRANSPIRATION LYSIMETER FACTORS AFFECTING TRANSPIRATION