Peltier lab devices

[PolytheneSam]

I found some patents relating to the use of peltier (and magnetocaloric) based hot/cold plates and related things..

Patent US3254494

peltier, lab

Patent US3986337

cold plate

Patent US4364234

cooler

Patent US4384512

beverage cooler

Patent US4785636

magnetocaloric

Patent US5842353

hot/cold plate for drinks

Patent US6338570

cold stirrer for drinks

Alternative to Espacenet:

http://patft.uspto.gov/netahtml/srchnum.htm

http://www.geocities.com/dritte123/PSPF.html
The hardest thing to explain is the obvious

[Elementary]

I've looked into using Peltier devices for cooling and heating applications in the lab. The only problem is that they are so expensive !
Nobodys home

[notfman]

Used and overstocked Peltier devices can be found online through discount electronic vendors.

http://www.allelectronics.com/cgi-bin/category.cgi?category=775&type=store

http://sales.goldmine-elec.com/prodinfo.asp?prodid=3571

etc
¿Qué te parece? so...waddaya think?

[terbium]

How cold will they get? It would be neat if one could use them for the coolant in cold-traps in vacuum systems.

[notfman]

How cold will they get?

Depends. Current applied to the device will produce heat on one side and cold on the other side, from 30 to 100° C  difference between the two sides, or even more depending on the device and how it's set up. A good heat sink is recommended. Modules can be mounted in parallel to increase the heat transfer effect or can be stacked to achieve high differential temperatures.

n

¿Qué te parece? so...waddaya think?

[Leviathan]

The  temperature of the peliter is achieved by a thermoelectric assembly can be estimated by taking the Delta-T across the module. Delta-T is the difference in temperature between the cold side Tc from the temperature of the hot side Th. The Delta-T assumes no heat load, and Th=300K. The cooler the hot side of the module, the cooler the cold side will be. As soon as power is applied to the module the hot side of the module will begin ejecting this as heat to the heat sink causing it to rise in temperature. The ability of the heat sink to dissipate this heat as well as the heat being pumped through the cold side will determine the actual operating temperature of the hot side thus, the cold side.

Thermoelectric modules are operated from a DC power source rather than AC. The best tradeoff in power vs. performance (Q) is at about 75% of maximum.  Beyond that point, you are applying more power and not getting much increase in return.  If you exceed by 25%, you are putting in a great deal more power, and getting the same performance as you would at 75% of Vmax(volts).  For instance, a 127-couple module has a Vmax of approximately 16v, and can be powered efficiently with a  12vdc power supply.  When heating is desired in addition to cooling a bipolar power supply is required. The power supply will need to provide the current proportional to the modules Imax (amps). If you need to regulate the temperature, you will need a temperature controller,

here's a page with all the formula you need

(http://www.melcor.com/formula.htm) to calculate what kind of peliter you need ... oh, and a 226 watt peltier can be purchased for about 38 bucks american and the dimensions are 50mm X 50mm X 3.10mm (I know its small but its good for the smaller end groups.

Leviathan
Better Living through CH₃emistry

[Leviathan]

Modules can be mounted in parallel to increase the heat transfer effect or can be stacked to achieve high differential temperatures.

sorry for the double post but I've always heard stacking TEC's dosn't give any benifit at all and its pretty useless ... I'm not 100% sure though but I know I've heard it somewhere

Leviathan
Better Living through CH₃emistry

[mnkyboy77]

SWIM has seen them at his work cool equipment downwards of -30 C, (Thats also with a 8 A power supply)...One major problem with them is they ain't worth a broke dick if the room temp is warm - hot.  (A cooler room helps them alot).


The MAN lives next Door, So SHHHHH!

[Elementary]

If you used a ice water filled aluminuim box for the heatsink, you would be able to achieve temperatures cool enough to liquify anyhydrous ammonia ? For the sake of a bit of wasted electricity !
Nobodys home

[Leviathan]

If you used a ice water filled aluminuim box for the heatsink, you would be able to achieve temperatures cool enough to liquify anyhydrous ammonia ? For the sake of a bit of wasted electricity !

If you have a "Potted" peltier it seems possible (potting protects the electrics inside the peltier) but anhydros NH3 only has to be colled to -33°c correct? you can buy peltiers with enough DeltaT to achieve that no problems.

Also don't forget that one side is HOT and the other COLD so by placing it in a bath of ice water, you ARE cooling it by however many degrees on one side but the HOT side is the same temp, just opposite (eg, -30 on one side, +30 on the other) so that might defeat the purpose.

I'm only 95% sure on this however, so if someone has some experience with it, feedback would be greatly appriciated.

Leviathan
Better Living through CH₃emistry

[uemura]

OK. Uemura also played around with these Peltier elements. He wanted to get rid of the ice-cube cooling normally used (he doesn't live in the states, so there is now ice machine in the fridge   )

He first started to cool down the warm side of the element with one of the 12V computer fans ( =Micky Mouse Fans ) and the only thing that happened was the warm up of the cool side as well. Lesson 1: ignore any Micky Mouse Fans

Then he bought an expensive high-tec (still air however) 2GHz CPU cooler with two high-speed fans and was able to achieve at least a temperatue difference like 30-35DegC. This is still 50% less than the achievable difference which is said to be 70DegC. Cooling down a waterbath (500ml H2O) from rt to 0 DegC took 30mins. Lesson 2: don't consider Peltier elements as fast devices

At least this would allow a rxn (say epoxidation at 0 DegC) to run overnight without interuppting nice dreams to add ice cubes.


The way to go is indeed using a water cooled heat sink. In the net there are around nice sites from computer freaks refurnishing there PC into a chemical plant with pipes and cooling towers (you can get good ideas from there, use 'peltier' and 'cooling tower' for a google search).

Problem even with water cooled heat sinks is of course the water warms up and after some time its cooling capacity goes down. Here comes the cooling tower into place, where in a long plastic tube water is sprinkled from top to down to cool it (with the additional aid of another fan blowing air into the cooling tower) and in the end the whole system looks like a nuclear plant.

Lesson 3: Nice project, looks like a lot of fun, but not easily setup for keeping ammoniak liquid

added later:

http://www.dansdata.com/peltprac.htm

Carpe Diem

[uemura]

Uemura hates the new geocity philosophy for dummies, you have to use the stupid upload wizard to put a 22kb jpg in a folder. Whats wrong with ftp? Anyway, here is a pic of a simple and improvised Peltier water bath cooler.


Carpe Diem

[Organikum]

As I like to play around with teknical devices I was fascinated by peltier elements too. Started with a plan for CPU cooling - wanted a silent high performance machine.
To make a long story short: If not manufactured by specialists and priced for military use then these  peltiers are plain shit. I would not trust them for 10 minutes if running on more than 50% performance. The reachable temperature difference maybe 40°C if you stage them you soon will need ya own power plant to feed and a little river to cool them. As UEMURA said: the machinery needed to make them work only a little bit is enourmous and will fail by Murphy´s law.

A nice idea - but no way. Forget it.
The magnetic cooling is just the same.

New/old ways that work are: for cooling down to -70°C and if you have an supply of pressured air: the "Wirbelrohr", aka "vortex tube" aka "Ranque-Hilsch Resonator". Quite noisy if not properly insulated, but ya need only an compressor. No moving parts at all. How it works? Answer the question and get the Nobel-Price..... (this is no joke!)
The "Stirling-Engine" is perhaps the best cooling/heating device known. Reachable temperatures are at 2,5°K if staged. Used in gas liquidification by industry and science. Not quite cheap but if you count all costs of peltiers this might be cheaper. Stirlings are the HIT! One side cold the other hot, I believe a well buildt midrange Stirling would satisfy all laboratory needs and more. Like ice for your cocktails.


Peltier - an expensive way for loosing faith in HighTek
ORGY
"I hope I'm becoming more eccentric. More room, you know.
 More room in the brain."

[lugh]

New/old ways that work are: for cooling down to -70°C and if you have an supply of pressured air: the "Wirbelrohr", aka "vortex tube" aka "Ranque-Hilsch Resonator". Quite noisy if not properly insulated, but ya need only an compressor. No moving parts at all. How it works? Answer the question and get the Nobel-Price..... (this is no joke!)

Funny thing about that statement, Mr. Smith didn't get a Nobel prize for writing this in Scientific American, his explanation makes perfect sense to SWIL  



Three factors determine the performance of the Hilsch tube: the setting of the stopcock, the pressure at which air is admitted to the nozzle, and the size of the hole in the washer. For each value of air pressure and washer opening there is a setting of the stopcock which results in a maximum difference in the temperature of the hot and cold pipes. When the device is properly adjusted, the hot pipe will deliver air at about 100 degrees Fahrenheit and the cold pipe air at about -70 degrees (a temperature substantially below the freezing point of mercury and approaching that of "dry ice"). When the tube is adjusted for maximum temperature on the hot side, air is delivered at about 350 degrees F. It must be mentioned, however, that few amateurs have succeeded in achieving these performance extremes. Most report minimums on the order of -10 degrees and maximums of about +140 on the first try.
Despite its impressive performance, the efficiency of the Hilsch tube leaves much to be desired. Indeed, there is still disagreement as to how it works. According to one explanation, the compressed air shoots around the spiral and forms à high-velocity vortex of air. Molecules of air at the outside of the vortex are slowed by friction with the wall of the spiral. Because these slow-moving molecules are subject to the rules of centrifugal force, they tend to fall toward the center of the vortex.
The fast-moving molecules just inside the outer layer of the vortex transfer some of their energy to this layer by bombarding some of its slow-moving molecules and speeding them up, The net result of this process is the accumulation of slow-moving, low-energy molecules in the center of the whirling mass, and of high-energy, fast-moving molecules around the outside. In the thermodynamics of gases the terms "high energy" and "high velocity" mean "high temperature." So the vortex consists of a core of cold air surrounded by a rim of hot air.
The difference between the temperature of the core and that of the rim is increased by a secondary effect which takes advantage of the fact that the temperature of a given quantity of gas at a given level of thermal t energy is higher when the gas is confined in a small space than in a large one; accordingly when gas is allowed to expand, its temperature drops. In the case of the Hilsch tube the action of centrifugal force compresses the hot rim of gas into a compact mass which can escape only by flowing along the inner wall of the "hot" pipe in a compressed state, because its flow into the cold tube is blocked by the rim of the washer.

The Hilsch tube does make a great cold trap for oil pumps, all that talk about Maxwell's demon was hype  

[uemura]

To bring us all back to the classical cooling techniques, here is the deep temperature record achieveable absolutly OTC:

1.4 parts finely crashed ice +
2 parts Calciumchlorid-hexahydrat

Guess how deep is goes??




















-55 DegC !!!!!!!!!!!!!!!!!

[foxy2]

Only if your freezer goes down to -55C though!
How many home freezers get that cold?
Those who give up essential liberties for temporary safety deserve neither liberty nor safety

[terbium]

Only if your freezer goes down to -55C though!
No, just by mixing ice at 0C with calcium chloride.

[uemura]

Either Uemura doesn't get your point foxy or your are wrong. The above info is from a Merck publications on practical lab procedures. And it says:
Easy to prepared cooling mixtures....the cooling effect is based on the endothermal solution of the salt....important is to add solid salt to the ice...sorted by falling temp:
.
.
3 parts ice (finely crashed) + 1 parts NaCl        -21 DegC
1.2 parts ice (f.crashed)    + 2 parts CaCl2.6H2O  -39 DegC
1.4 parts ice (f.crashed)    + 2 parts CaCl2.6H2O  -55 DegC

You see, with the CaCl2 hexahydrat the proportions are important.
Carpe Diem

[Organikum]

For every difficult problem there will be found a simple, for everybody understandable solution. This solution is usually wrong.

I read this at an appendix to Murphy´s laws somewhere.

Mr Smith is wrong.
The only transfer from moving energy to heat is friction in his concept. The friction from the outer wall to the air in vortex. But a vortex has very low if any friction at all and anyway the friction will not generate enough calomeric energy for the phenomen. Also the cooling down below the level of temperature is not explained. Yes if I take the laws of thermodynamic it is understood that the outer vortex has to have a higher energy level than the inner, my dog explained that to me lately with ease. So a description is made but how the calometric differenciation happens, when do molecules decide to be "hot" or "cold" there is no answer. No explanaition is given. Please read again what Mr. Smith wrote, you will see that his friction idea is pure nonsense brought in the article to hide the lack of understanding. You have to start with air of homogenous temperature entering the tube.
Mr Smith (a pseudonym I´m shure) won´t get the Noble, he´ll end at the wall of shame.
Popular science magazines are well known for their will to explain everything to everybody. In cases like the "Wirbelrohr" and "quantum mechanics" they are fucked. Solution: make it up.

As you will not believe me and I will not start a discussion on something thats not to explain I say: everybody interested may use Google, for all others I declare:

Lugh is right! Mr Smith is right! Fluids cannot be compressed. The vortex tube is easy explained. Earth is the center of universe.

Lugh, if ya would have searched 5min. more you would know.


All Hail the MODs
ORGY

[Organikum]

function:






Cooling capacity 6 W @ 77 K @ 25°C
Cold end temperature 35 K
Input power less than 250 W
Operating voltage from 48 - 53 V DC
Cooldown time (from 23°C ambient) to 70 K < 10 minutes (30 g Cu mass)
Optimized compressor design for longlife operation (> 3 years)
No maintenance required
Small and compact design
Low weight (8 kg)
Low vibration
Low noise level
Ambient temperature range - 40°C to + 65°C


okay high ended, but look at

http://www.srimot.go.jp/eng/khirata/stirling/

and buy a cheaper one or build your own.


ORGY

[foxy2]

Too much pot tonight guys!!!

All right its all back in my brain.
The heat is sucked out to melt the ice and thus it gets that cold.  Fuck me, I'm a dumbass.  I've had 3 fucking thermo classes and I forget some of the most basic shit, thats depressing... 
I'll blame it all on the drugs, they made me do it  

Check these baths out!!

ethylether/CO2(s) = -100C

http://www.chem.ucla.edu/research/org/MERLIC_GROUP/c_links/cooling_baths.html

Those who give up essential liberties for temporary safety deserve neither liberty nor safety

[Osmium]

What most people seem to forget is that reaching a certain temperature isn't enough. Condensing a gas like NH3 is an exothermic process which will produce heat. , and that heat has to be removed by the cooling apparatus. Peltiers and the like are terribly inefficient, for an overnight cooling job I'd prefer a 5kg block of ice in an insulated bucket and a cheap circulating pump any day of the week.
I'm not fat just horizontally disproportionate.

[goiterjoe]

dry ice still provides really cheap low temperature cooling, and is available at your neighborhood livestock store.  It is used for freeze branding cattle.

[foxy2]

My local grocery store has dry ice
Those who give up essential liberties for temporary safety deserve neither liberty nor safety

[TrickEMethod]

Ditto on all the issues with getting high deltaT and high power output out of a peltier, but what you can get is easily implemented and reliable control of environmental temp against a dynamic endo/exo themic reaction.  That is not easily done using ice blocks and a bilge pump.

Here is what I have played with for low temperature control...

CO2 canister(donated by one of the faithful) which bleeds into a copper spiraled tube(ice maker hookup from home depot) which is inserted through two T connections (also from h-depot) the connections are dark grey plastic and compress down on the tube easily without leaks.  The opposite compression nut is removed and replace with a threaded pvc fitting that allows the connection of an external sheath of some type.  I often use a midium diameter tygon tube over a 1/2" threaded schedule 40 PVC 1" flange and a ring clamp to hold it tight.

                        ############################# 
    /----               %%%%%%%               %%%%%%%              ----\
   / ****===============****                     ****==============**** \
----------------------------------------------------------------------------
----------------------------------------------------------------------------
   \ ****=====|  |======****                     ****=====|  |=====**** /
    \----     |  |      %%%%%%%               %%%%%%%     |  |     ----/
                        #############################

##### outer sheath - ring clamp not shown

%%%%% flang or other adapter

***** threaded ends of T compression joints

/----
\---- compression nut

-----
----- inner copper or glass tube

====
=||=  T connector


What is being constructed (cheap and OTC) is a coaxial heat exchanger, that will cool a liquid flowing one direction on the outer tube using expanding CO2 gas from the canister on the inner tube flowing in the opposite direction.  Expanding co2 gas is way fucking cold as shit mucho bigtime!  I don't remember what terminal temp for CO2 is, but it hasn't frozen acetone at any flow rate that I have tested. 

I use an 12v oil pump for boat maint. to pump the acetone, but I don't know how long it will last given the noise it is making after about 12 hrs of use.  I am using a 12v solanoid valve from the high performance autoparts store intended for swithing nitrous on/off (120$) to blow bursts of co2 into the exchanger to implement gross temp control.  Lets say to the nearest 10-15deg C, but you won't get much better than that from such a crude control method.  Secondly, I have four speeds that I can drive the circulating pump, but only two are currently used: minimal maintnance flow and full cooling. 

Where the peltier comes in is at the junction between the reaction unit and the cooling setup.  By placing a peltier between the device to be cooled and the cooling system I can adjust with a very fine degree of control the amount of cooling delivered.  I can boost the cooling by running the peltier in the forward mode, or reduce the cooling by running the peltier in the reverse or heating mode.  If I am running the peltier in the reverse mode, I will also slow the coolant flow to minimal maintnance flow.  Peltiers can adjust the temp and direction very quickly, too quickly in fact.  If you don't implement a degree of deliberate histeresis to govern the temp swings, you can destroy the device through thermal stress.  Buy some extras and attach them using thermal lube and screw clamps instead of thermal glue witch requires a chisle for part replacement.

You will also need two temp sensors, one on the peltier and one in the reaction chamber.  By calculating the rate change and change of rate change factors you can quickly identify the dynamic "intentions" of the system.  The peltier sensor change values will freewheel as the coolant modulates and the reaction chamger sensor change values will freewheel as the reaction sinks or sources energy.

So just input it all into your computer and fuck around for a few months and it should all work out!

I have no life!

And on the eight day, God created Meth...
... and hasn't done much of anything usefull since!