Timeline for Why does water get significantly colder while falling through the air?
Current License: CC BY-SA 3.0
9 events
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| Nov 18, 2016 at 22:16 | vote | accept | jheindel | ||
| Sep 7, 2015 at 16:38 | comment | added | David Hammen | Another factor is that they are little droplets. Temperature drop by Newtonian cooling is proportional to surface area and temperature, but inversely proportional to mass. The ratio of surface area to mass for a spherical droplet is $3/(\rho r)$, where $\rho$ is density and $r$ is droplet radius. Decreasing droplet size increases Newtonian cooling (and also evaporative cooling as well). Some shower heads let you control whether the water is a fine mist or larger drops. The effect is much reduced when you use larger drops. | |
| Sep 7, 2015 at 14:44 | history | edited | Gert | CC BY-SA 3.0 |
Clarification added, re. friction.
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| Sep 7, 2015 at 2:43 | comment | added | Gert | @jheindel: I'll work out the work done by a droplet travelling through air tomorrow. | |
| Sep 7, 2015 at 2:32 | comment | added | Gert | @jheindel: hi. If anything, drag forces (i.e. friction) generate heat, just rub your hands together. Friction has negligible effects here though: the work done is mostly an increase in kinetic energy of the air in the wake of the droplet (turbulent flow). To measure temperature of the water use a styrofoam cup (fill it up and empty it several times, so the cup is at the same temperature as the water) and a decent domestic thermocouple based thermometer. Repeat all measurements a few times (noting all readings), then compare top and bottom water temperatures. Hope this helps. | |
| Sep 7, 2015 at 2:24 | comment | added | jheindel | I totally agree that evaporation must be a major contributor, but I think it's undeniable that the water must exert work on the atmosphere in order to pass through it. It just seems like that energy would be dissipated by lowering of temperature. And yes I agree that using actual data would be much better. I would particularly like some experiment to test if the work the water does on the atmosphere changes its temperature. Any suggestions on that? | |
| Sep 7, 2015 at 0:59 | history | edited | Gert | CC BY-SA 3.0 |
Addition
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| Sep 7, 2015 at 0:52 | history | edited | Gert | CC BY-SA 3.0 |
Emph. added.
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| Sep 7, 2015 at 0:47 | history | answered | Gert | CC BY-SA 3.0 |