YouTube Spacelab-Physics experiment


Uploaded by Phelett on 11.12.2011

Transcript:
Hello! My name's Adam. I'm 17.
What I'm about to examine is evaporation rate of liquids such as water in a microgravity environment.
As we know evaporation takes place on the surface of the liquid at any temperature.
When the molecules manage to leave the liquid and enter the gas phase a mixture of water vapor and air is created.
Here you can see an equation which shows how the density of this mixture depends on the molar percent of water vapor.
Due to the the water molecules have a lower molar mass than dry air,
mixing them in any proportion results a gas with lower avarage molar mass and thus lower density than dry air.
This difference of densities triggers a convection which transports the molecules away from the surface preventing condensation.
The transportation process is similar to what happens on this simulation, I found on YouTube uploaded by "cfdnode", but in this case it's caused by temperature difference.
As the concentration of water vapor lowers the vapor-liquid equilibrium is shifted in the direction of evaporation,
thus the buoyancy speeds up the evaporation.
Since in a space-like environment there's no remarkable gravity,
the only motive force transporting molecules is diffusion.
It's the same because it's caused by thermal motion not by gravity.
On the ISS the change of rate could be calculated by measuring how a water drop's size changes over time,
and how the vapor surrounding the liquid absorbs light.
From the absorption we can deduce the concentration of water vapor at a given location at a given time.
It makes calculation easier if the container is spherical.
If I'm right that the absence of gravity (microgravity) makes evaporation slowlier(under the same conditions:pressure, temperature),
the difference of rates could have an effect on biological functions such as sweating ,
the process by which our body gets rid of excess heat.
The slowlier the evaporation is the slowlier the heat dissipation is.
To decide whether this difference is great enough to have such a significant effect or not,
the only way is to carry out this experiment in space.
Thank you.