# The Naked Scientists Forum

### Author Topic: Is evaporation affected by surface area?  (Read 6386 times)

#### Tim Thielen

• Guest
##### Is evaporation affected by surface area?
« on: 14/01/2010 18:30:02 »
Tim Thielen  asked the Naked Scientists:

Hi Chris,

My name is Tim Thielen from Salem, Oregon.

My question is does the surface area affect the evaporation rate of water?

For example, a long tube with 500ml of water compared to a bowl with 500ml of water. Will they evaporate the same amount of water in a period of time?

Cheers!

What do you think?
« Last Edit: 14/01/2010 18:30:02 by _system »

#### CoughSyrup

• First timers
• Posts: 1
• I think, therefor I exists.
##### Is evaporation affected by surface area?
« Reply #1 on: 16/01/2010 22:05:33 »
Yes, of course surface area affects the rate at which water evaporates.
In fact there's a formula for calculating the evaporative loss of a body of water, called the evaporative loss formula. Although this formula can vary greatly depending on the number of variables you want to consider, surface area is one of the variables.

Below are a couple I have found using google. None of these are perfect and I encourage someone to post their evaporative loss formula.

Formula:
E = k A (xs - x)
Where:
E = amount of evaporated water (kg/h)
k = (25 + 19 v) = evaporation coefficient (kg/m2h)
v = velocity of air above the water surface (m/s)
A = water surface area (m2)
xs = humidity ratio in saturated air at the same temperature as the water surface (kg/kg)
x = humidity ratio in the air (kg/kg)

-----

Formula:
Rate = P*( 1- H/100 )
Where:
P = the vapor pressure of water at the given lake temperature
H = the relative humidity.

-----

Formula:
W = ((Pw - Pa)*(0.089+0.0782*V)/Y)*3600
Where:
W = Rate of evaporation at the surface of the water level (kg/h m2)
Pw = Vapor pressure at saturation taken at the temperature of surface of water in kPa
Pa = Vapor pressure at the dew point according to the temperature of the ambient air in kPa
V = Air velocity above at the surface of water in m/s
Y = Latent heat necessary according to the change of state of the water vapor at the temperature of surface of water in kJ/kg