Presentation on Evaporation, its process and factors affecting evaporation.pptx

It's presentation on evaporation, process and measurement methods of evaporation

1. Student profile Sohail Akhtar 20PWCIV5453 Class roll number: 175

2. Topic Evaporation

3. Topics to be presented Evaporation Factors affecting evaporation Measurement of evaporation

4. Introduction Evaporation happens when a liquid substance becomes a gas. When water is heated, it evaporates. The molecules move and vibrate so quickly that they escape into the atmosphere as molecules of water vapor. Evaporation is a very important part of the water cycle. Heat from the sun, or solar energy, powers the evaporation process. It soaks up moisture from soil in a garden, as well as the biggest oceans and lakes. The water level will decrease as it is exposed to the heat of the sun.

5. Process of Evaporation Evaporation is a form of vaporization that usually happens on the surface of liquids and it involves the transition of the liquid particles into the gaseous phase. Therefore, this process is said to involve a change in the state of matter of liquids. The surrounding gas must not be saturated with the substance which is evaporating. They transfer energy to each other as the molecules of the liquid collide, depending on how they collide with each other.

6. Continued…. The liquid particles will generally escape and enter the surrounding air as a gas when a molecule near the surface consumes enough energy to overcome the vapour pressure. The energy extracted from the vaporized liquid as evaporation occurs will decrease the temperature of the liquid, resulting in a process known as evaporative cooling.

7. Examples of Evaporation Drying of clothes in sun:  We all dried up our clothes in the sun, the wet clothes get dries up because of evaporation where the water turns into water vapor. Drying of water bodies:  We have seen in summer water in the ponds and lake get decrease or sometimes dried up due to evaporation. Water cycle:  This is a very good example of evaporation, in the above two we discussed how evaporation turns water into water vapor. This water vapor further goes to the sky and gets condensed to form a cloud, and later it got precipitated. So, evaporation is significant to regulate the water cycle.

8. Factors affecting Evaporation Evaporation eases our life in many ways, and even it is contributing to the water cycle too. But evaporation is dependent on some factors which will be going to control the rate of evaporation. One more thing to note evaporation is a slow process but some external factors increase or slow down the rate of evaporation. Let’s discuss all these factors of evaporation

9. Factors affecting Evaporation The following are the main factors affecting evaporation Temperature Surface Area of the Liquid Wind Speed Humidity

10. Temperature The very first factor is temperature since we know evaporation can happen at any temperature before the boiling point, but the temperature has a role in evaporation too. It will determine the rate of evaporation, the more the temperature more is the rate of evaporation. Now the question is how? We all know the temperature will increase the kinetic energy, as the energy used to break intermolecular forces that bind the liquid molecule. So, when we apply more temperatures the molecule fastly breaks its intermolecular forces and get evaporated.

11. Surface area Earlier we discussed that evaporation is a surface phenomenon, and the surface plays a role in the rate of evaporation. The more a surface area more will be the rate of evaporation. So, if more surface area will be there then more liquid molecules will present on the surface, meaning more molecules break their intermolecular bonds which will increase the rate of evaporation. So we can write it as; Surface area of liquid ∝ Evaporation

12. Humidity Humidity refers to the amount of wetness or water vapor in the air. The more water vapor in the air we will say more humidity. With more humidity, the rate of evaporation gets decreased. Humidity ∝ 1/Evaporation For example, in the rainy season when our surrounding is more humid than it is very difficult to dry up our clothes.

13. Wind speed Wind speed is directly proportional to evaporation means with the increase in wind speed there would be an increase in the rate of evaporation. Wind Speed ∝ Evaporation For example, on a windy day, clothes get quickly dried up than on normal days. This is because the wind decreased the humidity which will increase the rate of evaporation.

14. Measurement of Evaporation It is measured as rate of evaporation. The rate of evaporation is defined as the amount of water evaporated from a unit surface area per unit of time. It can be expressed as the mass or volume of liquid water evaporated per area in unit of time, usually as the equivalent depth of liquid water evaporated per unit of time from the whole area. The unit of time is normally a day. The amount of evaporation should be read in millimeters (WMO, 2003). Depending on the type of instrument, the usual measuring accuracy is 0.1 to 0.01 mm.

15. Direct methods Rate of evaporation measurement Indirect methods Measurement of Evaporation

16. Direct method of evaporation measurement The following are the main direct methods of evapo r ation measurement Water budget Technique lysimeter Pan evaporation method

17. Water budget technique This technique involves the maintenance of a water budget. Mathematically it is stated as E = I - O ± Δ S E = Evaporation I = inflow into soil reservoir E= Irrigation water + precipitation + incoming soil water contribution from surrounding + G.W O = deep percolation (inside soil runoff) Δ S = Change in storage Now I = i + P + SFI + SSQ + GW O = RO + SSQ + DP + L + E

18. Lysimeter A lysimeter is a measuring device which can be used to measure the amount of actual evapo -transpiration which is released by plants, usually crops or trees. By recording the amount of precipitation that an area receives and the amount lost through the soil, the amount of water lost to evapotranspiration can be calculated. Monolithic weigh-able lysimeters are a tool for water balance studies and solute transport determination. Lysimeters are of two types: Weighing Non-weighing

19. Pan Evaporation 1.Setup: A standard pan, often painted white to reduce solar absorption, is filled with a known amount of water. The pan is placed in an open, level area with minimal obstruction to air circulation. 2. Measurement of Initial Water Level: The initial water level in the pan is carefully noted before the start of the measurement period. This serves as the reference point for calculating evaporation. 3. Exposure: The pan is left exposed to the atmosphere for a specified period, usually 24 hours. During this time, water evaporates from the pan's surface into the air.

20. Continue… 5. Correction Factors: To account for factors that may affect the evaporation rate, correction factors are often applied. Common corrections include adjusting for temperature, wind speed, humidity, and solar radiation. These corrections help provide a more accurate estimate of evaporation. 6. Calculation of Evaporation: The evaporation rate (E) is calculated using the formula: E =(Initial water level) - (Final water level) + Precipitation - Runoff - Infiltration 7. Recording and Analysis: The evaporation data, along with any correction factors, are recorded. Long-term records of pan evaporation can be analyzed to identify trends, seasonal variations, and climatic influences on evaporation in the specific location.

21. Pan Evaporation method

22. Indirect methods of evaporation measurement Following are indirect methods of evaporation measurement Aerodynamic method Energy budget method Hargreaves method Jensen Haise method