A Formula for Rate of Evaporation

AI Thread Summary
The discussion centers on the factors influencing the rate of evaporation, including relative humidity, temperature, pressure, and surface area. A formula for evaporation rate is proposed as mass of water divided by unit area and unit time. The conversation highlights the need for a relationship between evaporation rate and pressure, referencing the Clausius-Clapeyron Equation for pressure-temperature relationships. Additionally, the importance of the mass transfer coefficient and heat transfer at the liquid-gas interface is emphasized as critical for accurate calculations. Understanding these variables is essential for determining the pressure drop required to evaporate a specific volume of water over time.
marvolo1300
Messages
15
Reaction score
0
Hi, it has been a while since I've been on PF.

I know that the rate of evaporation depends on the relative humidity, temperature, pressure and surface area.

Is there any formula that fits this criteria?
 
Physics news on Phys.org
Here's what I found so far:
LINK. CLICK ME!


Basically they define the rate of evaporation as:

massWater/(unitArea/unitTime)


Sorry about the lack of a direct link, I am using an OS without a supported PDF plugin.
 
oh wow, I was thinking about then whilst I was walking to the shops a few weeks ago
I was mainly using dimensional analysis to guide me though.. I don't really remember what I came up with though since I had to start remembering why I went to the shop once I arrived!
:biggrin:
 
What a coincidence! It seems you may have a unit for the rate of evaporation.
 
Well, it was worth a shot.
 
i neeeeeeeeeeeeeeeeeeeeeeeed relationship that relates between evaporation rate and pressure ...all this equations indicate the relationship between the temperature and evaporation rate
 
the Clausius-Clapeyron Equation relates between pressure and temperature.
i will give you example for what i want:

if i have vessel contains 100 m^3 of water and the surface area is 500 m^2 and the relative humidity is 50% and the speed of air is 0.5 m/s what is pressure drop that i need to evaporate this volume of water during 24 hours?
 
You're missing some key pieces of the puzzle. You need to know the mass transfer coefficient between the liquid and gas phases. You also need to consider heat transfer, because the temperature at the interface is going to be lower than in the bulk of the liquid (and this is going to affect the vapor pressure at the interface). See Mass Transfer Operations by Treybel. You are dealing with combined heat and mass transfer.

Chet
 
Back
Top