# A Formula for Rate of Evaporation

1. Jun 4, 2012

### marvolo1300

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?

2. Jun 4, 2012

### marvolo1300

Here's what I found so far:

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.

3. Jun 4, 2012

### genericusrnme

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!

4. Jun 4, 2012

### marvolo1300

What a coincidence! It seems you may have a unit for the rate of evaporation.

5. Jun 5, 2012

### marvolo1300

Well, it was worth a shot.

6. Dec 31, 2013

### mfg88

i neeeeeeeeeeeeeeeeeeeeeeeed relationship that relates between evaporation rate and pressure ...all this equations indicate the relationship between the temperature and evaporation rate

7. Dec 31, 2013

### mfg88

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?

8. Dec 31, 2013

### Staff: Mentor

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