Calculating Evaporation: Pressure, Vapor Pressure & Temperature

In summary, the formula for quantifying the evaporation of a liquid is m-dot=(A)(42.6+37.6V)(Pw-Pa)/Hv, where various factors such as surface area, air velocity, and saturation vapor pressure are taken into account. However, it may not directly address the issue of contaminants in the mixture.
  • #1
marlene0311
1
0
Hi,

I would like to know how to quantify the evaporation of a liquid.

I assume it would depend on pressure, liquid vapor pressure & temperature but I can't find a formula.

Can somebody help?

I need to find out if some possible oil contaminant would show up in an RGA analysis

Thanks a lot

Marlene
 
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  • #2
Try this:
m-dot=(A)(42.6+37.6V)(Pw-Pa)/Hv
Where:
m-dot=evaporation rate kg/hr
A=surface area, square meters
V=air velocity over water surface, m/s
Pw=saturation vapor pressure at water temperature, mm Hg
Pa=saturation vapor pressure at dew point, mm Hg
Hv=latent heat of vaporization of water at surface temperature, from 2257-2270 Kj/Kg

This same formula is contained in other parts of the evaporation rate thread.

I'm not sure if this addresses the issue you are asking about--the contaminant in the mixture.
 

Related to Calculating Evaporation: Pressure, Vapor Pressure & Temperature

What is evaporation and how is it calculated?

Evaporation is the process by which a liquid changes into a gas. It is calculated using the equation: E = P x A x K x (Pw - Pa), where E is the evaporation rate (in mm/hr), P is the windless water surface pressure (in mmHg), A is the surface area (in cm²), K is the Kofler coefficient (a unitless factor that takes into account the specific conditions of the evaporation site), Pw is the vapor pressure of water (in mmHg), and Pa is the atmospheric pressure (in mmHg).

What role do pressure and temperature play in evaporation?

Pressure and temperature have a direct impact on the rate of evaporation. As pressure decreases, the boiling point of a liquid decreases, causing it to evaporate more quickly. Similarly, as temperature increases, the kinetic energy of the liquid molecules increases, leading to faster evaporation.

What is vapor pressure and how does it relate to evaporation?

Vapor pressure is the pressure exerted by a vapor in equilibrium with its liquid or solid form. It is directly related to the rate of evaporation, as a higher vapor pressure means there are more molecules escaping from the surface of the liquid, leading to a faster rate of evaporation.

How does humidity affect evaporation?

Humidity refers to the amount of water vapor present in the air. A higher humidity means that there is already a significant amount of water vapor in the air, making it more difficult for water to evaporate. This is because the air is already saturated with water molecules and there is less room for more to evaporate from the liquid surface.

What are some factors that can affect the accuracy of evaporation calculations?

The accuracy of evaporation calculations can be affected by various factors, including wind speed, surface area, and the specific conditions of the evaporation site. Changes in these factors can alter the rate of evaporation and therefore impact the accuracy of the calculations. Additionally, the Kofler coefficient, which takes into account the specific conditions of the evaporation site, may need to be adjusted for different locations or situations.

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