How do water supply conditions affect evaporation?

Factors influencing evaporation at the water surface. That is to say, how the conditions of water supply will affect evaporation, the following will mainly talk about this aspect, you can refer to it.

The factors affecting water surface evaporation are complex and diverse, and there are two main ones:

1) Water supply conditions.

The prerequisite for the evaporation phenomenon is the presence of water on the evaporation surface, and the water supply conditions of the evaporation surface are usually divided into two types: adequate water supply and insufficient water supply.

Generally, the evaporation of the water surface and the evaporation of the soil with water content above the water holding capacity of the field are regarded as evaporation under the condition of sufficient water supply. The evaporation when the soil water content is less than the water holding capacity in the field is called evaporation under the condition of insufficient water supply.

In general, the maximum evaporation that can be achieved in a given meteorological environment with adequate water supply conditions is called evaporation capacity, also known as potential evaporation or maximum possible evaporation. In the case of surface evaporation, it is always under the condition of sufficient water supply, so free surface evaporation under the same meteorological conditions can be regarded as the evaporation capacity of a region (or basin).

Since the sensible heat exchange between the evaporation surface and the atmosphere and the heat exchange inside are small and negligible under the condition of sufficient water supply, the net income of the radiative equilibrium is completely consumed by evaporation, then the evaporation capacity can be determined as follows:

where EP is the evaporation capacity; r is the radiation equilibrium value; t is the length of the period; l is the latent heat of evaporation.

However, it is important to note that in practice evaporation may be equal to or less than evaporation capacity. In addition, the evaporation capacity of a particular evaporation surface is not constant, but varies with conditions such as solar radiation, temperature, water vapor pressure difference, and wind speed.

2) Kinetic and thermodynamic factors influencing evaporation.

1.The kinetic factors affecting evaporation mainly include the following three aspects.

1) Vertical diffusion of water vapor moleculesNormally, the vertical distribution of water vapor molecules over the evaporation surface is extremely uneven. The closer to the water surface, the greater the water vapor content, so there is a vertical gradient of water vapor content and a gradient of water vapor pressure. As a result, the water vapor molecules have a tendency to diffuse along the gradient direction.

The more significant the vertical gradient, the stronger the diffusion of water vapor on the evaporation surface.

2) Vertical convection of the atmosphereVertical convection refers to the temperature difference between the evaporation surface and the air, and the result of the movement is to continuously send the water vapor near the evaporation surface into the air, so that the water vapor content near the evaporation surface becomes smaller, and the saturation difference expands, thereby accelerating the evaporation of the evaporation surface.

3) Horizontal motion in the atmosphere and turbulent diffusion of air flow in the near-surface layer, both regular horizontal motion and irregular turbulent motion (eddy current). The result of the movement not only affects the horizontal and vertical exchange process of water vapor, affects the distribution of water vapor on the evaporation surface, but also affects the temperature and saturation difference, and then affects the evaporation rate of the evaporation surface.

Determinants of how fast water evaporates:

1. Temperature: The higher the temperature, the faster the water evaporates.

2. Surface area: the larger the surface area, the faster the water evaporates.

3. The air flow speed on the liquid surface: the greater the air flow speed on the liquid surface, the faster the water evaporates. The amount of water dispersed into the air by evaporation over a certain period of time is usually expressed in millimeters of the thickness of the evaporated water layer, and the amount of water evaporation from the water surface or soil is measured by different evaporators.

Generally, the higher the temperature, the lower the humidity, the greater the wind speed, and the lower the air pressure, the greater the evaporation; Conversely, the evaporation will be smaller. Microscopically, evaporation is the process by which liquid molecules leave the liquid surface. Since the molecules in the liquid are constantly moving irregularly, the magnitude of their average kinetic energy is adapted to the temperature of the liquid itself.

Extended information: According to the mechanism of evaporation, the factors affecting evaporation can be divided into two categories: one is the meteorological conditions above the surface of the object, such as solar radiation, temperature, humidity, wind speed, air pressure, etc.

The other type is the factors of the object itself, for water surface evaporation, there are factors such as the area and shape of the water surface, the depth of the water, the quality of the water and the condition of the water surface. The difference between the water vapor pressure between the water surface and the air is larger, and the number of water molecules escaping from the water surface is larger. Conversely, the number of water molecules returning to the surface from the air is smaller.

It is generally believed that the difference between the number of water molecules escaping from the surface and the number of water molecules returning to the surface is the actual observed evaporation or evaporation intensity.