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Topic: is it possible to calculate rate of evaporation ? (Read 1 time) previous topic - next topic

seaurchin

I am making a soil moisture sensor , I had a spare DHT11 , so I attached that too, I am wondering that soil will get drier faster if the rate of evaporation is high , is it possible to calculate the rate of evaporation when if we know the temperature/humidity and what else will be required ?

rw950431

Search the internet for "evaporation calculator"  There are lots of different ones for specific applications but the basic parameters are air temperature,humidity,water temperature and wind speed.


MarkT

I am making a soil moisture sensor , I had a spare DHT11 , so I attached that too, I am wondering that soil will get drier faster if the rate of evaporation is high , is it possible to calculate the rate of evaporation when if we know the temperature/humidity and what else will be required ?
Windspeed, surface boundary layer thickness - evaporation depends on the rate molecules escape
the surface, and also on the rate they diffuse back down again, which depends on transport of
humid air away from the surface, which in turns depends on the nature of the flow, turbulent or
otherwise of the air above.
[ I will NOT respond to personal messages, I WILL delete them, use the forum please ]

Delta_G

The evaporation rate also depends on the atmospheric pressure and the concentration of dissolved salts in the water. 
Ad hoc, ad loc, and quid pro quo.  So little time - so much to know!  ~Jeremy Hillary Boob Ph.D

jseery

Could you take a section of the soil you want to measure and build a pan that has a load sensor under it and record the weight loss over different time intervals? 

Delta_G

Could you take a section of the soil you want to measure and build a pan that has a load sensor under it and record the weight loss over different time intervals? 
If something is growing in the soil then we have an issue with this one because whatever plant is putting on more weight as it grows. 
Ad hoc, ad loc, and quid pro quo.  So little time - so much to know!  ~Jeremy Hillary Boob Ph.D

yv1hx

I am making a soil moisture sensor , I had a spare DHT11 , so I attached that too, I am wondering that soil will get drier faster if the rate of evaporation is high , is it possible to calculate the rate of evaporation when if we know the temperature/humidity and what else will be required ?
The DHT11 probably lacks of the precision need for that type of measurement.

The Davis Instruments Vantage Pro weather stations family is capable to offer this derived variable.
I would recommend have a look on this in page 48: Vantage Pro2 Console Manual

This document from Davis Instruments can be useful too:
DERIVED VARIABLES IN DAVIS WEATHER PRODUCTS

Also:
Measuring Evapotranspiration
Remote Sensing of Evapotranspiration

Good luck!
Marco-Luis
Researcher & Telecom Specialist at  virtual Meteorology Center and  CIDETIU

PaulMurrayCbr

Do you want to calculate the measured rate of evaporation by measuring the humidity in the soil over time; or do you want to estimate what the rate of evaporation probably is given the current conditions?

http://paulmurraycbr.github.io/ArduinoTheOOWay.html

yv1hx

Marco-Luis
Researcher & Telecom Specialist at  virtual Meteorology Center and  CIDETIU

tkbyd

other factor is going to be the nature of the surface from which the evaporation is taking place. A beach of pebbles, with water "under" them will lose water more slowly than a well plowed field with no plant life. And if you want to know how much water is being lost per horizontal square meter of surface, you will ALSO need to know what is growing there. Take the pebble beach: No plants, one rate of evaporation. Tall grasses: Very different.

Probably unknowable, in the end. But if the question is "when do I need to water", then other apporoaches may be valid.

OR, monitoring some of the things discussed above, and knowing that others aren't changing much (e.g. plant cover) can help you know when "more water" or "less water" will be right... even if you don't have an absolute "rate of evaporation" to use.

Just some random ideas.

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