If we have two specific amounts of water, Q1 and Q2
If Q1=Q2,
Q1 is placed steadily at a conduit with exposed area A, while
Q2 is pumped in closed loop, but through the loop we have an exposed area A too.
If the environmental conditions are the same,
Which amount of water will evaporate faster, Q1 or Q2?
Velocity of the surface will affect the drag forces of the air and disturb the boundary layer. More detail is needed to make a conclusion if non-equilibrium conditions exist. A high velocity surface will have important edge effects with any opening. The question did not specify flow rates or opening size. My remarks pertain to equilibrium conditions and low flow rates.
High velocity flows will not increase evaporation if the opening is constrained to stabilize air mixing and boundary layers. Nevertheless, it is difficult to achieve stable conditions with a high velocity flow. The surface and edge effects will contribute to droplet production, greatly disturbing stable and equilibrium conditions.
The questioner should provide more information in order to describe and consider limiting conditions. We could speculate endlessly and find conditions that will exceed any claim.
Dear @Mohammad, I think that under the same conditions, the moving amount of water Q2 will evaporate faster than the steady amount of water Q1 because the moving helps molecules to evaporate.
Yes My dear Mohammad N. Elnesr; I also go with @Abedallah M Rababah, moving water will evaporate faster than standing water. Regards.
Couple of things to consider would be the temperature gradients and the nature of the boundary layer between the water and the atmosphere.
Given other the same, Q2 will evaporate faster - It would be useful to perform an experiment though. I've started with experimenting ( http://db.tt/Z1pXwH2z ) but had to stop due to the resource cuts.
Q1 would be expected to have lower evaporation on account of a boundary layer of water vapor building up over the water surface. Q2 would be expected to have higher evaporation on account of a smaller boundary layer effect. In addition, as others mention, the turbulence in flow implies that molecules have higher energy, which can allow them to surmount the evaporation energy threshold faster.
It seems we can do simple experiment.
1. Motion without any acseleration in atmosphere (dry air). The same case water under ventilator. We well know that water will evaporate faster under ventilator.
2. Motion without any acseleration in vacuum. No motion or motion are two case. In second we can use moving reference frame and have no deference.
If conditions more complex then above we must see.
The moving water should because of loss of kinetic energy 1/2mv^2,m=mass of water,v=velocity of movement of water.
Linus
Okafor Linus
I do not undestand You answer.
For example in vacuum without acseleration the center of mass (water + steam) will move with the same velosity so kinetic energy will be the same as in initial state.
Standing or steady water has higher evaporation than moving or dynamic water
There will be no difference if the temperature and the surface area are the same. It might appear that the energy of the moving water is higher, but not if measured by temperature. If the temperature is the same, then the average energy of the molecules is the same. One can argue that turbulence will increase evaporation. The energy argument is the same. Nevertheless, a turbulent surface will have more area if the surface is rippled. For the same open area, the evaporation will be higher for the rippled surface. If the total surface area of the rippled surface is the same as the total surface area of the smooth surface (open areas have difference sizes) the evaporation will be the same.
I think Amartya K Saha right. The partial pressure of vapor near boundary grouse but in moving case the boundary lyaer can go away.
The boundary layer will not flow away with the moving water. The moving water will move below the boundary layer.
Joseph L Alvarez
You are right, but the exchange beetween boundary layer and external flow depend from velosity of external flow. So, flux of vapor away more if velosity of external flow more. Situation more comlex (laminar or turbulent regime ets), but in general the flux depend from velosity.
Velocity of the surface will affect the drag forces of the air and disturb the boundary layer. More detail is needed to make a conclusion if non-equilibrium conditions exist. A high velocity surface will have important edge effects with any opening. The question did not specify flow rates or opening size. My remarks pertain to equilibrium conditions and low flow rates.
High velocity flows will not increase evaporation if the opening is constrained to stabilize air mixing and boundary layers. Nevertheless, it is difficult to achieve stable conditions with a high velocity flow. The surface and edge effects will contribute to droplet production, greatly disturbing stable and equilibrium conditions.
The questioner should provide more information in order to describe and consider limiting conditions. We could speculate endlessly and find conditions that will exceed any claim.
Evaporation is a function of concentration of the substance evaporating in the air, Concentration of other substances in the air, Flow rate of air, Inter-molecular forces, Pressure, Surface area,Temperature of the substance.
For the case stipulated, all other factors being considered constant except the surface area.
Since effective surface area of moving water will by far greater than that possessed by still water, rate of evaporation will be more in case of moving water.
The moving water will possess kinetic energy to make it cooler than the standing water and more evaporation than the standing water
Linus
Dear @Joseph L Alvarez, and @Konstantin V Koshel
Regarding the information you requested,
I assume the steady pond of a reasonable area, (say 10m diameter), and the other pond of the same size but the water flows through it almost similar to the attached simple illustration.
Thank you for your contributions...
Would like to know if "conduit" and "closed loop" are two terms used for the same system that Q1 and Q2 are enclosed in?
My question is about a dynamic medium, an open system with a lot of dissolved salts NaCl in particular and instead of mixing by a force, by a mechanical impeller, ebb and flow if tides. How about this case which in unsteady, non-equilibrium also?
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