How to cool water fast! 1

[Vig16]

OK, so I've been working on a few different things lately and one that I've been fumbling around with is being able to heat up water to about 70 deg C, then back down to about 38 deg C...all in less than 2 minutes too lol.

I can't really think of a way to get the water down to almost half the temperature of what it was in that short of a timespan. I'm sure by having a fan at one end of the tube of passage and having that moving quickly I could do it, but I haven't had much luck with that theory...

Any ideas would be GREATLY valued!

Thanks so much!!

 

[MintJulep]

How about just not heating it up in the first place?

 

[ione]

You've apparently forgotten to specify the amount of water to be cooled (not a trivial detail)

 

[Vig16]

Mint - I heat it up to kill some contaminants in whatever I'm trying to heat up.

ione - I'm not trying to do it to a big volume of water, ~8 ounces.

 

[amorrison]

I would look for some type of solid copper spheres (the size of bb's or shotgun shot). Have one "cup" of hot spheres for the heating that are added to the water then the water is poured out into a cold "cup" filled with chilled copper spheres.

Calculations NOT to follow<)).

 

[IRstuff]

TE coolers might do the job, with adequate heat sinking. The standard polymerase chain reaction (PCR) system heats to ~98ºC and cools down to around 20ºC within seconds, albeit with rather tiny volumes.

Your nominal conditions will require about 253 W of cooling. Can you physically move the container from the heater to a cooler in a aluminum container? What kinds of container can you use, i.e., something with lots of fins in it?

TTFN

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[ione]

3 kg of ice might do this job

 

[Vig16]

Thanks for all the replies again, guys!

IRstuff - are TE coolers what's used in PCR to get the temperature to drop so quickly? I read about PCR, but didn't see anything relating to TE cooler.

And the container cannot be moved from under the nozzle to a cooler in an alumininum container. I can use any container that would allow me to pass the 70 deg C water through for a short period of time (even just a pulse), then I'd have to introduce some way of cooling that initial "pulse" down to about 38dC.

ione - the ice would definitely do the trick, but I wanted to avoid ice to reduce the temp, sorry for not including that in my description.

 

[IRstuff]

The TECs are built in to the hardware, which consists of a thermal plate with wells for the ampules, and underneath the plate is a TEC that does both the heating and cooling. PCR is relatively mindless; you simply load up the ampule with the DNA strands to be replicated, add in the reagents, and run the temperature cycle about 20 times or so. The high temp step breaks up the replicated strands and the low temp step starts the replication process over again.

The thermal conductivity of ice is quite low, relative to water, but, lots of really cold water, say 5ºC, with lots of flow and lots of contact area is certainly a possibility. Hypothetically, a 32ºC reduction in 8 oz of water can be accomplished by raising 7 cups of 5ºC water to 10ºC.

How often do you need to do this, as this would scope the overall cooling capacity needed. If it's one cup per day, that's quite different than one cup every 2 minutes.

TTFN

FAQ731-376
Chinese prisoner wins Nobel Peace Prize

 

[Vig16]

Well, I think it would probably be needed once every 2-3 hours. I don't have a problem with getting the heat up to 70dC, I just need to find a way to get the end product down to 38dC.

Would a TEC do this for me?

 

[vpl]

Are you thinking about something like this?

http://www.avantiproducts.com/products/id/273

It looks like they keep the water hot. If you want the final product cooler, you add a bit of cold water from the cold water dispenser.

(By the way, there is pdf of the parts manual on the link. You might get some ideas from looking at what they use.)

Patricia Lougheed

******

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[Vig16]

vpl - that works too, but I'm looking to have it all done at once, so the final product will have 38dC water when you take the cup/bottle/container away.

 

[IRstuff]

OK, so two of these guys:

http://customthermoelectric.com/tecs/pdf/19911-5M31-28CZ_spec_sht.pdf

face-to-face, with serious heatsinks on the outsides, and a thermally conductive labyrinth between the faces for the water to flow through. Assuming you can throttle the flow down to 0.066 oz/s, there should be sufficient cooling capacity to get the temperature down 32ºC. That works out to be about 38 drops/s ;-)

TTFN

FAQ731-376
Chinese prisoner wins Nobel Peace Prize

 

[Vig16]

So when you say face-to-face, should the hot side of one TEC face the cold side of the other TEC while the water tube runs through a "maze" of some sort and just have the TEC's programmed to have the hot side that contacts the water tube activated to heat the initial flow of water that's going through, then have that TEC shut off and activate the cold side of the other TEC as the water is passing through?

 

[IRstuff]

No, both cold faces facing each other, since you need a minimum of 250W of cooling, and the TECs cited only provide about 200 W each at 30ºC deltas. Now that I relook at that it might be better to put both of them in series rather than face-to-face, since you're not going to get much cooling at the start of the maze.

TTFN

FAQ731-376
Chinese prisoner wins Nobel Peace Prize

 

[macmet]

I've used TEC's and they work fairly well. I was using them in an application where size was critical and I found I had trouble cooling the hot side. Depending on your system, this may not be an issue for you.

Have you thought about adding dry ice? I used to use that to kick start the process.

 

[Vig16]

IR - Thanks for your advice! I totally understand what you mean about running them in series as there won't be much cooling at the start of the maze. I have enough wiggle room to try both configurations, but I'll give the series configuration a shot first...thanks again for all your help!!

macmet - I thought about dry ice, but I'd like to refrain from using ice to do this as I want as little operator assistance during use. Thanks for the input though!!

 

[Vig16]

IR - I had one question about your amount of energy it takes to cool the water 32 degrees C. You said it takes 253 W to do so; however, when I do the calculations, I only get ~134 Watts.

Since 4.186 J is needed to drop water by 1dC, I did 4.186*32=133.952. And since 1 watt=1 Joule/1 sec, I don't see where you got the 253.

I probably calculated it wrong, but if so, where did I go wrong in my calculations?

 

[ione]

Mass = 8 ounces = 0.223 kg (approx)

Specific heat of water = 4187 J/kgK

Temperature decrease = 32 °C

Time = 2 mins = 60 seconds

Power = 4187 * 0,223 * 32 /60 = 498 W (approx). Obviously if time available for cooling process decreases power will increase

 

[Vig16]

ione - Shouldn't it be ~249 W since it's going to be over 2 minutes?