Why did my evap cooler do this?

[flyboy67109]

I made a homemade evap cooler for when I work in the garage. It's a real simple design made from a Styrofoam cooler with a hole in the top to place a small 5" fan and a hole on the side near the top for the air to exit. I put about two cups of water in the cooler and place a piece of burlap over the hole on the inside of the cooler making sure the burlap is wet. I put the lid on and point the fan into the box and turn it on. I works ok cooling the air about 20 degrees from the ambient air. It's far from perfect mainly because the burlap can't wick the water fast enough when the humidity is only around 10%. Usually, I place cold water with a few ice cubes to help cool things down even better. However, the other day I accidentally added hot water instead. Right after I did it, I wondered if it would still work. To my surprise, it did! I started blowing cold air right away. If that wasn't strange enough, when I went to re-soak the burlap after it started to dry out, I found that the water inside the cooler was actually cold. To give you some numbers to crunch, the ambient air was 105 F and the humidity was 11%. I was measuring 89 F for the air coming out the vent. The water I put is wasn't scalding but it was warm enough to wash with. I would guess a little over 100 F. I can understand how the warm water caused the evap cooler to still work because it works on the principle of heat being displaced by evaporation. But, why did the water inside the cool get cold? That was the weird thing to me.

[Cmdr. Arn1e]

due to evaporation, still - as the water is subject to the same laws of physics! (as the more 'excited' water molecules will leave before the less 'excited' water, you end up with cooler water than you started with...)

[Nuke]

things evaporate better if they are a little warm.

[Camacha]

Is this not the well know story of hot water freezing faster than cold water?

[Nuke]

no thats a myth as far as i can tell. i fill with hot water, not for any reason other than when i hold the tray with my right hand, the left hand turns the knob, and the hot knob is on the left side. i figure people in a similar predicament use all kinds of excuses to cover their blatant waste of energy (why heat water just to cool it down again).

[StrandedonEarth]

Boiling water will freeze faster than cold water. Temperature is an average of the speed the water molecules are bouncing around, some faster than others. The 'hotter' (faster) molecules evaporate first, leaving the colder molecules behind. At least, that's how I learned it. Then I googled it and found this

[xcorps]

'Does hot water freeze faster than cold water?'--the answer is 'Not usually, but possibly under certain conditions.' It takes 540 calories to vaporize one gram of water, whereas it takes 100 calories to bring one gram of liquid water from 0 degrees Celsius to 100 degrees C. When water is hotter than 80 degrees C, the rate of cooling by rapid vaporization is very high because each evaporating gram draws at least 540 calories from the water left behind. This is a very large amount of heat compared with the one calorie per Celsius degree that is drawn from each gram of water that cools by regular thermal conduction.

"It all depends on how fast the cooling occurs, and it turns out that hot water will not freeze before cold water but will freeze before lukewarm water. Water at 100 degrees C, for example, will freeze before water warmer than 60 degrees C but not before water cooler than 60 degrees C. This phenomenon is particularly evident when the surface area that cools by rapid evaporation is large compared with the amount of water involved, such as when you wash a car with hot water on a cold winter day. [For reference, look at Conceptual Physics, by Paul G. Hewitt (HarperCollins, 1993).]

"Another situation in which hot water may freeze faster is when a pan of cold water and a pan of hot water of equal mass are placed in a freezer compartment. There is the effect of evaporation mentioned above, and also the thermal contact with the freezer shelf will cool the bottom part of the body of water. If water is cold enough, close to four degrees C (the temperature at which water is densest), then near-freezing water at the bottom will rise to the top. Convection currents will continue until the entire body of water is 0 degrees C, at which point all the water finally freezes. If the water is initially hot, cooled water at the bottom is denser than the hot water at the top, so no convection will occur and the bottom part will start freezing while the top is still warm. This effect, combined with the evaporation effect, may make hot water freeze faster than cold water in some cases. In this case, of course, the freezer will have worked harder during the given amount of time, extracting more heat from hot water."

Scientific American, Takamasa Takahashi, a physicist at St. Norbert College in De Pere, Wis

[PakledHostage]

Another significant factor is the variation in water's vicosity vs. temperature. Water near 0°C is almost an order of magnitude more viscous than water near the normal boiling point.

My understanding is that hot water is used in Zamboni machines for this reason. The hot liquid forms a more uniform and thin layer that fills the skate marks in the ice effectively. The thin layer of warm water also freezes faster than a thicker layer of cold water would.