Fantasma4500
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Electric cooling!!
looking around on the internets i see little to no effort done in making compact cooling devices
as i grasp the concept -- you create cold, on the terms of creationg more heat, the heat is lead away from the cooling spot (as seen with fridges
being hot on the back)
have there been any effort to create a compact cooling device for chemistry use? i see the limitations of an such device would be disposing of the
then formed heat on the hot end, this should be disposable of by spraying a fine mist of water onto the hot part, as well as blowing air at it, or
sucking the air off, taking advantage of the evaporative cooling effect
-70*C which can be reached would def prove very useful for chemistry applications, im sure a very effective device is doable, how much this device
were to fill should be second prority. consider liquifying of chlorine gas without having to use dry ice or even worse than that, why is this not a
thing yet??
hotplates used far and wide, where is the duality paralel market??
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Sulaiman
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I have had a little play with peltier coolers,
roughly, the more heat pumped the lower the temperature difference, and each 'pump' consumes a lot of power.
There are many consumer devices that use peltier coolers, few that freeze water.
If you want to play, I suggest that you get 5 pieces
e.g. http://www.ebay.co.uk/itm/5Pcs-TEC1-12706-Thermoelectric-Coo...
one mounted on four in parallel mounted on a large forced air or water cooled heatsink.
Four for the second layer to remove the heat pumped and generated by the first.
The junction of the four with one gets down to near 0C, allowing maybe -50 to -70 at the surface of the one.
Each peltier element consumes about 70W,
so the heatsink needs to dissipate 350W plus heat pumped from cold end,
with minimal temperature rise above ambient.
So you need a minimum of;
5x peltier element
1x metal block to connect one peltier to four peltiers
1x VERY efficient heatsink (< 0.1 C/W)
1x 12V 20A power source
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Fantasma4500
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an computer aluminium heatsink should be possible to electroplate with silver, which isnt as expensive as you would think, this should help with heat
conductivity, again im stressing the idea of using evaporative cooling, for individual experimental purposes you can try getting infront of a fan and
then running a wet rag over your arm, it may reach down to 0*C
what i think is very required is to effectively transfer the formed heat away from the cooling surface, as far and as efficient as possible
they have made -70*C freezers, do they depend almost entirely on having a large heat-dispersion area?? they do open these freezers up every here and
now, so it cannot be taking that long for the freezers to reach -70*C
i dont think 0*C at most is acceptable, barely useful, a novelty - take no offense
as chemists, solutions we must purpose, although this is more in the department of physics
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Sulaiman
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Silver plating will not significantly increase the thermal conductivity of a heatsink as it is so thin,
better to use solid copper, or more practical, a copper block heat spreader on an aluminium heatsink.
Why do you assume 0 C ?
you mentioned -70 and I mentioned -50 to -70 (0 C is between the stages)
[Edited on 22-7-2016 by Sulaiman]
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RogueRose
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I've contemplated many ideas for cooling (and heating - both used to do the opposite of their "ability" - meaning use heat to cool and cool to heat -
the last was difficult to come up with any methods outside blackholes..)
I was wondering how effective concrete is in absorbing heat from a fluid (mainly hot water). Many people have large slabs of concrete, many is a cool
basement, garage, etc. If an area, 4' x 12', were used to pass water from one corner to the opposite corner at a depth of maybe 1/4"-1/2" (filling
the entire 48 sq ft so added water mixes slowly and cools by the time it gets to the opposite corner). How much heat could be transferred to the
concrete and how fast would the concrete transfer that to the ground?
Basically using the concrete as a heat sink and building a platform over it to contain the water and keep things/people off it.
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Fantasma4500
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assuming you mean 0*C in relation to evaporative cooling of water -- the lower the temperature of the water is, the less efficient it will evaporate,
thus cool, when the water becomes frozen it cannot volatize anymore and thus the cooling effect goes to zero, doubtful that waters evaporative cooling
alone can make the water itself freeze, regardless it depends on a very thin layer of water for high efficiency.
i see the link you gave me suggest they can reach down to -30*C, proof of concept we have right here. now we just need to build these tiny little
things bigger and meaner
hm hm, i would suggest the ground has a limit of cooling down to 6*C, i would suggest tossing a rod of copper or aluminium (for cheapness) into the
ground and then somehow hooking this up to more aluminium
i still stick very much to the idea of evaporative cooling, you could splash some acetone onto your hands to really feel the concept of evaporative
cooling, but solvents we would refrain from as its a lot more expensive and adds a fire hazard and more than that.
water is very good at conducting heat, there is however people who totally immerse their computer hardware in oil that then has a very large ability
to absorb heat as were talking 10L of oil that can absorb heat -- and then comes the surface area in which the heat can radiate out of, the trick is
that oil wont shortcut electronics
maybe copper powder (which is very easy to produce) paired with concrete or other similar binder could work? copper could also just be melted and
poured into sand-styrofoam mold to create whatever piece of metal you desire
i wouldnt bet my money on concrete as being good at heat conductivity, but i see your point, i think basements are cold mainly because they dont have
a lot of light coming in through windows and into the room itself to thereafter radiate heat, they are also constantly in touch with the approx 6*C
temperature (relatively to 20*C room temperature this is cold)
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wg48
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Quote: Originally posted by Sulaiman  | I have had a little play with peltier coolers,
roughly, the more heat pumped the lower the temperature difference, and each 'pump' consumes a lot of power.
There are many consumer devices that use peltier coolers, few that freeze water.
If you want to play, I suggest that you get 5 pieces
e.g. http://www.ebay.co.uk/itm/5Pcs-TEC1-12706-Thermoelectric-Coo...
one mounted on four in parallel mounted on a large forced air or water cooled heatsink.
Four for the second layer to remove the heat pumped and generated by the first.
The junction of the four with one gets down to near 0C, allowing maybe -50 to -70 at the surface of the one.
Each peltier element consumes about 70W,
so the heatsink needs to dissipate 350W plus heat pumped from cold end,
with minimal temperature rise above ambient.
So you need a minimum of;
5x peltier element
1x metal block to connect one peltier to four peltiers
1x VERY efficient heatsink (< 0.1 C/W)
1x 12V 20A power source |
I think power current is closer to 30A
A 0.1 C/W heatsink would have temperature rise 35C (not counting the small effect of the heat pumped from the first cold face). Hence reducing the
minimum temperature achievable by that amount.
A 0.02 C/W air cooled heat sink (7C raise) would be huge say four of 125mm x125mm x 300mm aluminium heatsinks plus a spreader plus fans for 5m/s air.
More stages with smaller temperature difference is more efficient. For example a four stage device TEC4-24603, 45W to pump approximately 3.4W across
54C
see http://uk.dhgate.com/product/peltier-4-stage-tec4-24603-3a-1...
PS: Evaporative cooling only cools down to the dew point which typically is only 10C below the air temperature depending on the relative humidity. See
the graph I posted in the hot day cold acid thread.
PSS With only a round 10W of cooling capacity at 50C temperature difference, a reasonably sized peltier cooler is not suitable for cooling a typical
sized condenser.
[Edited on 22-7-2016 by wg48]
[Edited on 22-7-2016 by wg48]
[Edited on 22-7-2016 by wg48]
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Sulaiman
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oops! well caught, of course it should be 30A and not 20A ... slipped !
That 4-stage TEC is nice, but not much heat pumping ability.
I had originally planned to use several TECs of increasing capacity in series,
but I was too cheap and just made a 2-stage cooler. 
(the heatsink that I used was also insufficient ... Mk.II maybe one day ....)
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wg48
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| Quote: Originally posted by Sulaiman | oops! well caught, of course it should be 30A and not 20A ... slipped !
That 4-stage TEC is nice, but not much heat pumping ability.
I had originally planned to use several TECs of increasing capacity in series,
but I was too cheap and just made a 2-stage cooler.
(the heatsink that I used was also insufficient ... Mk.II maybe one day ....)
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On my approximation your two stage has a slightly better coefficient of performance (cop) than the four stage device
ie 30/(350+30)= 0.079 versus 3.4/(43.8+3.4)=0.072
The correct stacking ratios and performance needs to be derived from more accurate equations. I only estimated the pumping capacity at half the
maximum temperature difference.
If you look at fig 2 of this link http://science.unitn.it/~semicon/members/pavesi/Application%...
you can see how the cop increases with lower temperature difference (hence more stages are better up to a point) and peaks at a lower than maximum
current.
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PHILOU Zrealone
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| Quote: Originally posted by Antiswat | | when the water becomes frozen it cannot volatize anymore and thus the cooling effect goes to zero, doubtful that waters evaporative cooling alone can
make the water itself freeze |
Frozen water CAN vapourize...this is called sublimation, it occurs into specific regios of the pressure-temperature-volume diagram.
In principle, if you have a strong enough vaccuum pump,a large enough water quantity and insulation ... you could make water freeze from lowering of
the pressure and long enough working...of course most of the water will be vapourized before it happens.
To reach -70°C or lower usually the engineers use a cascade of fridges....with different cooling fluids...
A normal fridge takes the heat from the food and drinks into an insulated recipient and transfer it to a fluid that is pumped into a
dillatation-compression cyclus...the expansion cools down the fluid what takes the heat from the insulated compartiment...the compression heats up the
fluid that is run into a heat exchanger to dissipate the heat into the surrounding...this is the reason why encasted fridges needs good
aeration/venting behind to ensure external cooling.
In summary:
Insulated compartiment = inner heat source that transfers heat to the cool source into the fridge = fluid that expands.
The "hot" expanded fluid is compressed and becomes hotter and an external heat source that transfers heat to the surrounding cool source (universe is
an infinite cool source...how cool is that  ).
So if you have a second fridge itself insulated Inside the first fridge...its inner hot source can transfers its heat to the external fridge via
another cooling fluid and becomes cooler.
That way with the play of Russian dolls, via-via, you can pump the heat from the innerst fridge to the surrounding and into each fridge you get
cooling of the external heat source of the inner fridge and transfer of the heat to the external fridge.
PH Z (PHILOU Zrealone)
"Physic is all what never works; Chemistry is all what stinks and explodes!"-"Life that deadly disease, sexually transmitted."(W.Allen)
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Varmint
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I would be exceedingly careful if you decide to order any peltier coolers off ebay or amazon.
The incredible deals on high count bundle packaging is an illusion. We ones I bought (all of them in two separate lots/suppliers) are factory seconds
and outright total failures.
The rule seems to be, if there is physical damage (cracks or chips in the ceramic faces), they will perform quite well. If they are cosmetically
perfect, these tend to be very low spec temp transport wise, or stone cold dead.
As far as water ice sublimation, before ice makers became common in freezers, we all used to make ice cubes in trays. Many people would stack trays
atop one another, and many time the bottom tray might not be used for months, at which time the cubes could be 1/2 or 1/3 the normal size.
Ergo, it needs no particular sweet spot, it occurs at all temperatures above abs 0.
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RogueRose
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I thought I would test a concrete slab for how fast it absorbs heat from water.
I placed about 2 gallons of water in a plastic kitchen trash bag (very thin, probably .5 to 1 mil) and set it on the concrete. The water was about
1.5" deep as the bag spread out. The slab was 70F and water was 120F. The water reached 83F in about 35-40 mins and the slab rose to 83F. The temp
of the slab within 1" of the bag was still 70F so the heat doesn't migrate very far or it radiates well.
After removing the bag, the concrete reached 70F in about 7 mins.
I also found that the ambient temp plays a large role in the temp of the concrete. As the temp dropped at dusk, the temp of the concrete fell with
the air temp. This slab is fully explodes to outside weather except for an over-head covering.
I do have a feeling that were I to do the same experiment in a covered basement (I have one that stays at ~60F year round) the heat would be absorbed
by both surrounding air and slab, but the absorption would be faster.
If looking to cool a computer CPU, I would think concrete with ground contact (especially in a basement setting) would do well as at least a first
stage cooling. Getting the temp from 60-70 down to freezing point is much less work that starting at 120-140 coming off a CPU. I have seen some
setups that use 1/8 or 1/4" vinyl hose and an aquarium pump to circulate the water. A setup like this could be made for $25-40 that would do a better
job cooling than $200 commercial setups with a radiator.
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subsecret
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Computer component cooling blocks would be fantastic for this application. Put blocks on each side of the Peltier units. I'd connect the cold side in
series and the hot side in parallel. You could even put coolers on both sides of the cold blocks for more cooling power.
Fear is what you get when caution wasn't enough.
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XeonTheMGPony
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peltiers are an immediate fail very poor performance thermally.
Carnot cycle will blow them out of the water, easy to make based off a water cooler.
-70c will NOT ever happen with out a cascade or auto cascade system.
A single peltier chip could be use full for a heat driven vacuum desiccator.
As for actual cooling my server was cooled North bridge cpu mosfets (Basicaly every thing) just with air, it never got much above ambient with proper
flow rate and large heat exchange surface area.
If you live in a dry environment look up evaporative cooling.
[Edited on 25-7-2016 by XeonTheMGPony]
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Fantasma4500
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yes evaporative coolings efficiency drops as humidty in air increases as the water evaporates slower
i still think most atmosphere maybe except for deep in rainforest would work to remove a large portion of the heat using a water mister and an air fan
maybe an attempt could be made to isolate a freezer with its electronic components and see how minimal an area the cooling could be directed to, this
may require the cooler room to be isolated and then a small bucket insert into the cooling room, the bucket of some heat transferring material, copper
aluminium silver etc, i know for a fact that fridges somehow depends on a slight vacuum, and freezers seems to do so as well, so the freezing chamber
would have to be closed from sorrounding atmosphere
maybe several cooling systems could be attached to one freezer box, or it could have some parts rebuilt for higher efficiency, larger pumps, larger
tubes and more coolant??
i really suck at physics so feel free to shoot down any of my ideas asap
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XeonTheMGPony
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a material boiling temp is dependent on the atmospheric pressure
at sea level propane (R-290) boils at -42c. If we further lower it it can boil cooler but efficiency drops off.
But to remove that heat we need to compress it to "squeeze" the heat out hence the need for the vapor pump (Compressor)
If you make your own evaporator it can be as big or small as you want, look up computer cooling via refrigeration.
With your skill level atm your best bet is to take apart a water cooler. this will give you a nice small cooling chamber lined in stainless steel
(Cheaper ones may use plastic)
they will remove 150 or so btu per hour, so longer running times will remove more heat.
Heat pumping rate is fixed, temp is controlled by insulation and run time. this is how all fridges freezers work.
As you learn you will find it is very easy to make a custom system with some basic tools.
Here is a cold plate I made in under an hour, it was for messing around with frost art, it is water cooled. to give you an idea of what can be don.
[Edited on 3-8-2016 by XeonTheMGPony]
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