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!!

 

[IRstuff]

yah, 2 min is a bit more than 60 s

Shouldn't it be ~249 W since it's going to be over 2 minutes
> That sounds familiar! ;-) You need to have remember that specific heat is in joules, and the 2 minute time element is what gets you watts.

TTFN

FAQ731-376
Chinese prisoner wins Nobel Peace Prize

 

[Vig16]

LOL, so did I forget to convert something in the way I arrived to 249 W?

 

[IRstuff]

Ione's calculation, using 120 s, instead of 60 s, is the correct calculation. You didn't divide by time, at all, even though you mentioned watt = joule/s

TTFN

FAQ731-376
Chinese prisoner wins Nobel Peace Prize

 

[IRstuff]

Ohh, and YMMV, i.e., your mileage may vary. Since the TEC does not do much pumping when deltaT is either zero, or max, the 250W is a ballpark estimate. Ione's 500W might be closer to what might be actually needed, particularly in light of the fact that my TEC selection was two 400 W,max TECs.

TTFN

FAQ731-376
Chinese prisoner wins Nobel Peace Prize

 

[Vig16]

Oh, OK...thanks!

 

[Vig16]

IR - am I able to take the TEC's apart for do my own configurations for the labyrinth? Or is there a different way I should do that?

 

[Compositepro]

Cooling could be done simply by running your hot water through a copper tube coiled in a water bath. 38C is far above room temp. so the water bath will cool naturally.
You could even use a tube-in-tube heat exchanger where cold water flows through a copper tube into a heated metal block, gets hot, and then flows out of the block through a tube that surrounds the the copper tube with the water coming-in (a counter-flow heat exchanger).

 

[IRstuff]

No, TECs must be treated as blackboxes that should never see the light of day. I would think that a serpentine would be adequate.

TTFN

FAQ731-376
Chinese prisoner wins Nobel Peace Prize

 

[macmet]

Composite pro is on to something. But I would suggest that you consider cooling the cold fluid to a low temperature (i.e. below 0). When I did it I used propylene glycol so I could cool it with minimal concern of ice.

I used TEC's to cool the propylene glycol.

 

[Vig16]

IR - Since I can't open the TEC, how would I go about getting the serpentine path to touch the cold face of the TEC?

Compositepro and macmet - I like those ideas too, so I'm going to give yours and IR's a shot to see which is best for my application! Thanks!

 

[IRstuff]

My starting point might be a copper block attached to the TEC with high thermal conductivity adhesive. A copper pipe serpentine would be soldered, brazed, or whatever, to the copper block. The thermal mass of the copper pipe and block would help with the thermal efficiency, assuming you're allowed to precool the serpentine.

The precool temperature should be as low as practical, since thermal transfer is proportional deltaT. The colder the serpentine, the faster it cools, provided you don't get freezing or other annoying side effects of cold objects.

TTFN

FAQ731-376
Chinese prisoner wins Nobel Peace Prize

 

[Compositepro]

Those who brew beer at home must cool 5 gallons of boiling wort to less than 100F for fermentation. This is done in a few minutes by siphoning the hot wort through a copper tube coiled in a sink full of water. The top layer of water in the sink will become quite warm while the bottom stays cool. Keep it simple.

 

[bithkits]

Be careful with TEC's. How will you cool the hot sides? Something to think about. If the hot side is not adequately cooled the TEC will actually *HEAT* up the cold side and put more heat into the system.

Stacking/staging doesn't work for larger heat loads - each layer has to remove the heat from the previous TEC as well as the electrical power supplied to that previous TEC.

This is important - a 200W TEC puts out way more than 200W of heat on the hot side and only removes 200W of heat on the cold side for large delta T.

People also tend to underestimate the electrical power supply for TEC's - they can really eat up the amps.

On the other hand, reverse the polarity and the TEC's become heaters so you could use the same TEC's to heat and then cool the fluid.

I don't quite follow why you would want to open/dismantle the TEC's? Are we talking about the same thing here - thermo-electric coolers, also known as Peltier coolers...

See this site for more info (albeit for computer cooling):

http://www.overclockers.com/forums/showthread.php?t=309722

Adriaan.
I am a Mechatronics Engineer from South Africa.

http://www.martin-electronics.co.za

 

[Vig16]

Compositepro - I like that idea, but how long does it take to cool the water for that volume?

bithkits - I heard the same thing from one of the other engineers here yesterday, which kind of gave me second thoughts about that. Also, it seems to be a little more expensive than what we were looking to spend.

 

[IRstuff]

We're not talking about stacking though, just talking about making the cooled area longer than it is wide.

TTFN

FAQ731-376
Chinese prisoner wins Nobel Peace Prize

 

[Vig16]

I was just thinking of something else with cooling the water. What if I used air, such as a fan, to be blown through the water? What calculations do you think would be necessary to see how much air I'd need to get the to cool the water?

 

[Vig16]

Sorry to bring up this old thread again, but I just came up with another idea. What if I used a Phase Change Material (PCM)? I found this material (

http://microteklabs.com/pdfs/MPCM-37D Product Data Sheet.pdf)

which would put me right in the 35-38°C range and used 1.25g of the PCM (since 1g would dissipate ~200 J and I need to dissipate ~250 J).

My plan for this is:

1. Have the 70°C water running through the Silicone tubing that I have

2. Insulate the Silicone tubing with the PCM which would be encapsulated with a copper tube.

Does this look like something that would work or am I misunderstanding PCM's?

 

[Compositepro]

Great idea! One of the more common PCM's is called "ice".

 

[IRstuff]

The issue is rarely the material, the question is how to get access to the actual properties of the material in the timeframe alloted, without any ancillary side-effects.

You'd need to come up with some sort of flow-through sieve-like structure that won't contaminate your samples with itty-bitty balls of PCM. Then you need to bring the PCM back down below its melting point, which requires some sort a cooling system.

TTFN

FAQ731-376
Chinese prisoner wins Nobel Peace Prize

 

[Vig16]

Would I actually have to have the PCM's "in" the liquid? Couldn't the PCM just be outside of the thin-walled Silicone tubing that the hot water is running through?