Recent comments in /f/askscience

kilotesla t1_j3txubj wrote

That's possible but not certain. If you had a pile of ice cubes on a grate, such that water could drain away, and warm air could filter through accessing that full surface area, that might result in higher heat transfer than the same ice in a bucket full of melt water where the surface area accessible to the air is the surface of the bucket and the surface of the water, and is smaller than the total surface area of all of the cubes.

But if you froze the ice in the bucket to get a roughly cylindrical block of ice, and put that on the grate with the water draining away, the surface area would start out similar to that of the bucket, but would gradually decrease as the ice melted, whereas if you kept it in the bucket with the melt water, the surface area would stay constant.

Topics left as an exercise for the reader are consideration of heat transfer by radiation and the possibility of putting it in a bucket with a hole in it such that the water drains out. And then the challenge of how to fix a bucket with a hole in it without access to a working bucket, which might be important for getting water necessary to sharpen tools for carrying out the repair operation.

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BuildANavy t1_j3tneoc wrote

You're making a big assumption that there is a significant heat source transferring heat to the water other than through the air. Otherwise in both cases you still rely on heat transfer from the air, it's just that in one case it has to heat up the water first. In a typical experimental setup this might be from a bowl sat on a countertop at ambient temperature or something, but if the bowl had a very low thermal mass and was supported by very thin members then the draining setup could easily melt the ice quicker.

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CrateDane t1_j3ta6h4 wrote

>I found out today that ethanol reacts with organic fats (carboxylics only?) to form esters, which do not appear to act like ethanol in the body.

An alcohol can form an ester with a carboxylic acid, such as a fatty acid. Ethanol is obviously an alcohol, so that can happen under the right circumstances.

Thing is, when you're talking about fat, usually you're talking about triglycerides or maybe phospholipids etc. In those cases, the fatty acids have already formed an ester with an alcohol. It just isn't ethanol, but instead glycerol. So there's nowhere for ethanol to "attack".

In the process of digestion, those esters in dietary fat are actually broken down by enzymes, but those same enzymes would also immediately break any esters that ethanol might try to form.

In any case, the reaction conditions to form an ester aren't really there in the human body (except when aided by enzymes).

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Ambitious_Jelly8783 t1_j3t2qfn wrote

If you keep the water, all things equal, the water will protect the ice. The melted water will keep at 0*C, protecting the ice, where the air will be warmer, so if no water the air will apply a higher temp to the surface.

Water requires a lot of energy to change degrees. It is actually not a great conductor. Now if you have warm water, same reasonkng applies as it has lots of energy so it'll melt it very quickly.

Someone do the experiment and share it.

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djublonskopf t1_j3t04n9 wrote

Mounting any one immune response also requires a significant amount of energy...in studies on mice, older mice mounting an antibody response to an injected antigen aren't fully able to maintain their body temperature at the same time. So while I don't have hard numbers for humans, if you were taking dozens or hundreds of different vaccines in a short time you'd probably hit a point where the metabolic load was too much for the rest of the body....

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Burstar1 t1_j3sz9b6 wrote

Remember that the melt water is also interacting with the warm air as well. It's not the temperature difference that matters so much as the huge difference in the frequency of interactions between gases and liquids which is why water will outpace air here.

FTR I've done this experiment myself using a consumer cooler and blocks of ice. The portion of the ice that is exposed to the water visibly melts/shrinks faster than the exposed ice. A cube of ice sitting on a sheet of plastic mesh will last much longer than the same sized ice cube sitting on the bottom of the cooler (the little puddle it starts to form almost literally gobbles it up).

Want to cool a can of soda fast? Don't plop it in a pile of Ice alone. Add water to the ice and even though you've definitely added heat to the system the rate of the soda's temperature reduction will be vastly quicker.

Edit: and by cool in my previous statement I don't mean literal measurable change in temperature. If the ice is melting both it and the water are at 0deg C. It is the Heat of Fusion that is being transferred that I'm referring to.

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VT_Squire t1_j3syxzc wrote

>However, the water and air may not be at the same temperature, no?

That's exactly what I am getting at.

Thermal-conductivity is like a speed-limit, so to speak.

Degree for degree, you'd need roughly 11,000 times as much air exposure as you'd need water to melt both cubes in the same amount of time.

Double the temp of the air, you still need 5,500 times as much air... and so on.

At that point, it's not about what melts ice faster, it's about how much assistance you need to give the air to compensate for the fact that water is better at it.

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