radioman Posted November 4, 2011 Report Share Posted November 4, 2011 It seems that the rains have abated for now and maybe for a few months if we are lucky. The sun is out and heating the flood waters which makes me wonder how much evaporation is taking place and, given the area exposed to sunlight, is this likely to be significant in reducing the level of flooding, or will it be a mere drop compared to the seemingly already small amount that is actually being drained? Link to comment Share on other sites More sharing options...
cavanami Posted November 4, 2011 Report Share Posted November 4, 2011 IMO, a mere drop Link to comment Share on other sites More sharing options...
Vintage_Kwai Posted November 4, 2011 Report Share Posted November 4, 2011 Took a minibus back to Bangkok on the just-opened section of the Asian Highway on Wednesday. It looks like a sea from Lopburi/ Singburi all the way to either horizon; water is still fast flowing too. There is a lot that is not being said about the amount of water yet to come. At least the highway is now passable so a sign of some abatement... Link to comment Share on other sites More sharing options...
Mekong Posted November 4, 2011 Report Share Posted November 4, 2011 It seems that the rains have abated for now and maybe for a few months if we are lucky. The sun is out and heating the flood waters which makes me wonder how much evaporation is taking place and, given the area exposed to sunlight, is this likely to be significant in reducing the level of flooding, or will it be a mere drop compared to the seemingly already small amount that is actually being drained? Many factors have an effect on evaporation rates. Concentration of the substance evaporating in the air If the air already has a high concentration of the substance evaporating, then the given substance will evaporate more slowly. Concentration of other substances in the air If the air is already saturated with other substances, it can have a lower capacity for the substance evaporating. Concentration of other substances in the liquid (impurities) If the liquid contains other substances, it will have a lower capacity for evaporation. Flow rate of air This is in part related to the concentration points above. If fresh air is moving over the substance all the time, then the concentration of the substance in the air is less likely to go up with time, thus encouraging faster evaporation. This is the result of the boundary layer at the evaporation surface decreasing with flow velocity, decreasing the diffusion distance in the stagnant layer. Inter-molecular forces The stronger the forces keeping the molecules together in the liquid state, the more energy one must get to escape. This is characterized by the enthalpy of vaporization. Pressure Evaporation happens faster if there is less exertion on the surface keeping the molecules from launching themselves. Surface area A substance that has a larger surface area will evaporate faster, as there are more surface molecules that are able to escape. Temperature of the substance If the substance is hotter, then its molecules have a higher average kinetic energy, and evaporation will be faster. Density The higher the density the slower a liquid evaporates. These factors can be observed daily without many people realizing it, Petrol (Gasoline) in an open vessel will evaporate where as in a sealed vessel (gas tank) it won't due to the vapor area being 100% saturated with the substance evaporating in air. Petrol will evaporate faster than water due to the differences in density also referred to as "Latent Heat of Evaporation" . Washing will dry faster on a windy day due to the airflow reducing the concentration of substance evaporating in the air not because the wind blows the water off, it will also dry faster if stretched out rather than crumpled up due to increase of the surface area exposed to evaporation, etc etc. As for the floodwaters, the factors affecting evaporation are Temperature, Wind Speed, Relative Humidity and Atmospheric Pressure, so evaporation will occur quicker on a hot windy day with low humidity and atmospheric pressure than it will do on still day with high humidity. The end of todays Science lesson Link to comment Share on other sites More sharing options...
radioman Posted November 4, 2011 Author Report Share Posted November 4, 2011 Ah good stuff. I knows a bit about how to make them electron thingy's move about in the air but all this liquid stuff has me at all sea, ha ha! All very obvious stuff with some thought. Link to comment Share on other sites More sharing options...
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