Sciencemadness Discussion Board - Cool electronic devices you can make for thr lab but are uncommon.

Cool electronic devices you can make for thr lab but are uncommon.

coppercone - 10-5-2018 at 08:05

So, other then
-hotplates/stirrers
-tube furnaces
-kiln furnaces

What are some fun electrochemical design projects?

I thought
1) mechanical stirrer
2) ball mill. Interesting project due to the fact that you need to change velocity depending on container size
3) aspirator pump: mechanical pump to cycle fluid to an aspirator, vacuum gauge monitoring connected to a very damp pid, cooling system to keep the water at 4c or so
4)coolant cycle pump (common but a good one would use peltiers in a pid to do 0 01c resolution at 1kW cooling capacity. Expect approx 2k cost
5) melting point tester. Started towork on this may detail project

SWIM - 10-5-2018 at 08:33

Aspirator pumps and ball mills are actually pretty common on here.

Mechanical stirrers and condenser coolers less so, but there's been work on those recently by Jjay and Melgar respectively, and several others.

Might be good to review the threads on those items and see what others have tried, and what problems still need to be whipped.

I would be interested to hear of an example where a 0.01C accuracy on the cooling water flow would be useful.

Ubya - 10-5-2018 at 10:21

1kW of cooling power using peltiers, that will be fun (considering inefficiencies $ 2k thrown away)

DavidJR - 10-5-2018 at 10:24

Melting point apparatus would be good.

coppercone - 10-5-2018 at 15:41

Quote: Originally posted by Ubya

1kW of cooling power using peltiers, that will be fun (considering inefficiencies $ 2k thrown away)

It's actually not that bad. 2k$ would be really high end with swagelok parts and stuff. Peltiers have a bad rep but they are actually really nice for stability, and you would be surprised how usable and convenient something in the 1kW region is in the laboratory. Once you use a machine that you can adjust the PID loops of to your process you will probably not wanna go back to clunky compressors lol, or you will want a dual stage system with the compressors cooling the peltiers.

I was thinking that high temperature stability of the coolant water would mean a better vacuum stability for the pump at its maximum low pressure.

[Edited on 10-5-2018 by coppercone]

VSEPR_VOID - 11-5-2018 at 01:59

Centrifuge would be a nice touch and drying oven/desiccator is useful

Sulaiman - 11-5-2018 at 03:08

Quote: Originally posted by coppercone

1) mechanical stirrer
2) ball mill. Interesting project due to the fact that you need to change velocity depending on container size
3) aspirator pump: mechanical pump to cycle fluid to an aspirator, vacuum gauge monitoring connected to a very damp pid, cooling system to keep the water at 4c or so
4)coolant cycle pump (common but a good one would use peltiers in a pid to do 0 01c resolution at 1kW cooling capacity. Expect approx 2k cost
5) melting point tester. Started towork on this may detail project

The electronics for 1,2,3 & 4 are mostly motor speed controllers,
readily available as cheap ready made modules via eBay etc.
#5 can be done with a phase controller (triac light dimmer) module + thermometer
or a REX-C100 with thermocouple.
so
the 'hard' parts for all of the suggestions are actually the mechanical parts.

Each of the suggestions is already commercially available,
so the main motivation for d.i.y. is cost
- using whatever is 'in stock' or available regionally will be used.

So each of us will come up with a slightly different implementation.
The important thing is to give enough general information for others to recreate their own version based on their availability of parts.
=============================================
I made a small dual TEC-based water cooler
- on its own suitable for 50 to 100 Watts cooling power, nearer to 50 than 100

A useful device by itself for small scale (10/14) distillations etc.
With the addition of a hot water 'radiator' suitable for larger scale (24/29).

IF I wanted more cooling power
(1 kW is quite a large still ... 1.8l water or 4.3l ether per hour)
I would first investigate passive coolng - large air-cooled surfaces,
if active cooling is required the a commercial/domestic water chiller or refrigeration unit would be MUCH cheaper and efficient.

If you search SM you will find attempts at all of your ideas.

EDIT: I re-read my post and it seems rather negative/de-motivating - sorry.
Each of us that attempts any of the above, and reports their results, adds to a general body of knowledge.
Even failures - preferably with reasons - is useful knowledge.
So, ignore the tone of my grumpy mood post and go full steam ahead.
BUT, please see what others have done first

[Edited on 11-5-2018 by Sulaiman]

coppercone - 11-5-2018 at 06:02

A good melting point tester will use a four wire rtd and have very well controlled temperature change rates so the rtd doesnot permamently drift. The electronics also have to be low noise and temperature stable.

You will find the sensor and sensor interface electronics (even supposedly good ones like from honeywell) have fairly shitty specifications.

I would shoot for stability of better then 100 parts per million per degree celcius, 100ppm repeatability and 500ppm accuracy. (calibration is difficult and would actually require many samples from test sources to be linear hence the loose 500ppm specification.

You would actually want two melting point testers, i would limit coil rtds to controlled ramp rates at 150c or so and a seperate tester tester meant for higher temperature operation that uses a rtd which takes a beating and is less accurate or a less accurate thermocouple.

There is also the issue of oxidation and the thermal emissivity changing with temp. The higher temp one would desire an argon blanket. I experimented with aluminum that had a heating cartiridge in it with a groove for the heater and i was not impressed.

I guess the nice thing about thermal electronics is that you can get away with relative butchery on the power electronics side (i.e. a triac) so long you have good control and sensor electronics.

Good peltier control is kinda difficult too because you need to ramp them slowly and provide a somewhat filtered signal to prevent thermal stress damage .

coppercone - 11-5-2018 at 07:04

And if you want a defacto way to catagorize a tec, you basically make a heat load, which is a well insulated coldplate that has either heater strips stuck onto it or heating cartriges.. Then you cyxle water between the tec chiller and the heat load.

You put a fixed wattage on the heat load and measure the temperature of whats dissipating your tec power (probobly air but you can use a water or freon heat echanger) and the temperature of your water.

Then you say the tec system is capable of some particular temperature differential at some particular flow with some number of watts heating the system.

This is how the high end ones are catagorized. You want heavy insulation on the whole system and decent amount of turbulance in your two heat exchangers.

Then you can do further catagorizations like changing the heatload power to see the responce characteristic.

coppercone - 11-5-2018 at 08:05

I also think that using precisely chilled water would benefit fractioning with active cooling, but maybe the scale required for this to be useful is too large, to keep the number of theoretical plates consistant during the whole process.

I dont think it would be too useful for distilation condensation control though.. Am i wrong?

Of course you could make a device that attaches to the distiller to eliminate the need for water flow, or to control reflux.. But i feel that a useful water less system is toodifficult for a research chemist because we have a variety of different condesners we like touse for reflux depending on whats going on.. I think this is more suited for a known process.

If you have excellent lab scafolding to support a heavy object in odd positions then having some standard reflux column might be an aleight option.. You can even use the same sensors used to detect water on car windsheilds to maintain the position of your reflux line by gently varying the cooling power..

And maybe you can make thermal transfer bushing sets to accomodate different glassware sizes..

But, i do have trouble imagining a simple device that can matcha reflux condenser without coolant moving through the interior coil. It would need to be long. Dont feel something useful is practical to make by yourself without serious effort unless yku like small scales.

Biggest benefit is that you dont have to worry about a water leam destroying/stressing your setup or causing an explosion, erruption etc.

But it would be suceptible to corrosion and damage from leaks and when you disassemble glassware with solvents in it.

Guess you can calculate the interior area of a fredrich column or reflux condesner and guesstimate how long a linear condesner cooled by tecs you would need for the same cooling area. And thermally coupling tecs mounted to a heatsink to a piece of glass without a prohibitively thick interface medium like grease is a serious pain in the ass. You can use special low melting point solders to mate certain metals with glass but i believe you would get stress build up on a decent surface area that would be close or exceede the capacity of glass.

I would like to design these kinds of things towards 24/40 setup sizes, i feel that they are practical and fun.

I think you enter a whole different ball game with microchemistry like 14/20 though when there are not alot of watts to deal with.

Another device i had a bone to pick with for a long time is a kugelrohr. I feel that they are ridiculosuly overpriced.

[Edited on 11-5-2018 by coppercone]

[Edited on 11-5-2018 by coppercone]

Twospoons - 11-5-2018 at 12:35

Quote: Originally posted by coppercone

Quote: Originally posted by Ubya

1kW of cooling power using peltiers, that will be fun (considering inefficiencies $ 2k thrown away)

There are other ways to achieve accurate control at those power levels, using a compressor driven heat pump. Look up "hot gas bypass". This is a system which uses a bypass valve to feed some of the hot condenser side gas into the evaporator coil. I built a controller for a system like this for refrigerated shipping containers - it would happily hold a container at 1C with 0.1C accuracy using a 7kW refrigeration compressor capable of -25C.
The other method is to have a reservoir of very cold fluid (water or brine), chilled by compressor, and using a mixing valve to control the cooling loop temperature.
These methods seem far more practical than setting up 1kW of peltiers with their terrible COP.

coppercone - 11-5-2018 at 13:10

if you use water cooling and a cooling tower a 1kW chiller is a rackmount piece of equipment that fits in a 19 inch rack and is about 5 inches tall and 1.5 feet deep. this is with the pump, power supply, control electronics, internal reservoir tank, plumbing etc

Otherwise,. for air cooling, you are looking at something like two 10x10x4 inch heat sinks with decent fans (might want to break it up into 2 separate modules so you don't get the pressure drop along the fins, plus the before mentioned items

hs -> peltier -> heat exchanger (with plumbing for coolant loop)-> peltier -> hs
with the sideway view being like

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The idea is that heat is being removed from the top and bottom to the air, or to liquid cooled plates (rather then heat sinks).. you can push air through the whole thing if you put it in a box with the channels formed by the heat sink fins facing the face of the fan. Otherwise you need two fans and alot of room around the thing (Unless you need real uniformity, which is kinda pointless given that your cooling a fluid stream, its retarded to do it this way, just because mounting it mechanically would be ridiculous.. would be really complicated vent arrangement. This method is extremely compact. With the method I described, you can also put two fans, one sucking one blowing, on both ends of the channel, to account for pressure drop without needing super fans or complicated duct system/.

You don't want to design something that has air intake on the back and the side and blows out air both sides unless its really necessary.......

If your fluid stream going through the main exchanger is really slow, the temperature differential MIGHT have some kind of effect.

These can do 0.01c control easily. 0.001c with very good insulation. And if you make it with the right parts, the coolant cycle pump and heat sink fans will ware out several times before there is any ware on the main heat exchange unit.

How fast is the response of a hot gas bypass unit? Like what kind of thermal time constants can it deal with? And how is the longevity of the mixing valve / etc with repeated temperature oscillations (like from temperature cycling).. thats where these guys excel at. Shipping container is a very static load..

but I don't want this thread to get derailed by peltiers. I will be honest though I don't really like mechanical compressors they just fucking annoy me for whatever reason. And they sound like shit. I would like to hear about them though, I was always curious about higher end laboratory refrigeration systems.

[Edited on 11-5-2018 by coppercone]

[Edited on 11-5-2018 by coppercone]

diddi - 11-5-2018 at 17:33

i am tinkering with a recirculating peltier cooling system atm. just need a couple of days on the mill to get it how i want. if it works i will post more info

wg48 - 12-5-2018 at 03:54

Below is what you need for a 1kW @ 30C delta. You would also need a 2kW DC supply and somthing to put it all in. It would keep a small lab cosy in winter. A 100W system would be more practical.
thermo2.jpg - 28kB

Panache - 12-5-2018 at 05:26

For a water chiller just pickup a water cooler from the side of the road and jerry it into a recirculating water chiller. i have a few of these, a small pump easily fits inside them as they have excess space in the middle so they are tall enough. i also converted one into a water bowl for my dog, keeps her water at 4C, which likely is completely unesseccaery as she is happy as hell to use the toilet but i choose to believe in summer she feels extra love because of my efforts.

coppercone - 12-5-2018 at 06:38

You want two heatsinks, to make a sandwich on your heat exchanger. You won't get terrible better performance using an all copper expensive to braze heatsink...

That heat exchanger you listed looks kinda odd, you want something like this

http://www.lytron.com/Cold-Plates
https://www.amstechnologies-webshop.com/cp15g05-aluminum-col...

For the power supplies, its a good idea to find arrangements of your peltiers that can use something like a telecom 48V power supply made by lambda, meanwell, etc. Then you control it with a H bridge.

If you want 2kW of power, and you have two sides, you can independantly power the two different peltier sides, if you want redundancy incase of a short circuit.

Using air for above 500W is a little crazy. I have not seen it done. Traditionally this seems to be done by using water to cool the peltiers and directing said water to a cooling tower or large radiator outside the building (this is typically part of facilties infrastructure for certain labs).

http://www.meanwell.com/meanwell_products.html

Those will be OK since you don't have some kinda crazy reactive load or whatever. Then you just chop them with a simple H bridge circuit.

[Edited on 12-5-2018 by coppercone]

[Edited on 12-5-2018 by coppercone]

coppercone - 12-5-2018 at 06:47

Quote: Originally posted by Panache

For a water chiller just pickup a water cooler from the side of the road and jerry it into a recirculating water chiller. i have a few of these, a small pump easily fits inside them as they have excess space in the middle so they are tall enough. i also converted one into a water bowl for my dog, keeps her water at 4C, which likely is completely unesseccaery as she is happy as hell to use the toilet but i choose to believe in summer she feels extra love because of my efforts.

What kind of heat exchanger do you use for a corrosive system?

I have a nice lytron one, that I can hook up into the freon line of a compressor, but I doubt it would like cooling whatever corrosive trash is sucked in through an aspirator, so I would need to make a secondary loop regardless of what the primary loop is cooled by, and a secondary recirculation pump.

Glass coils?

How hard is it to wind a glass coil without a glass lathe? I have oxy or air / hydrogen or acetylene torches

Easiest would be to use stainless tubing
https://www.grainger.com/product/3ACU2?cm_mmc=PPC:+Google+PL...

I have my doubts about using copper. With all the effort that goes into building this thing, I would hate to have to look at nasty gross ass chemically damaged copper. I would like it to be spotless like a nuclear reactor even if its in a old 5 gallon cat litter bucket.

Are there any common lab particulars you can think of that stainless steel 316 will react with?

Br2, Cl2, HCl, HNO3 come to mind quickly.

Also, I have a nice motor drive that uses 90V and has a field winding. It's actually meant for pumps.

Can you suggest a pump that would work well for a lab aspirator ?(my focus is solid state devices and precision instrumentation I don't know much about driving pumps, specifying them, motor drivers, etc)

I would like to setup a loop to control the vacuum via feedback of vacuum pressure.

I would also like to know how much heat in a pump is generated by the pump assembly, and how much by the electric motor, and if the heat conducted to the fluid can be reduced by separating the two by a long shaft or belt drive.

https://www.ebay.com/itm/316-Stainless-Steel-Round-Tube-OD-1...

[Edited on 12-5-2018 by coppercone]

Sulaiman - 12-5-2018 at 07:10

I hope that you do make a cost effective water cooler,
and contribute some more information,
there have been a few TEC-based discussions,
latest: http://www.sciencemadness.org/talk/viewthread.php?tid=80597
and I'm having a dabble myself: http://www.sciencemadness.org/talk/viewthread.php?tid=64759&...

coppercone - 12-5-2018 at 07:14

another biggie for those peltiers is to provide proper torque to mate them with the heat sink for the thermal compound to work well.

coppercone - 12-5-2018 at 07:26

But for 316 stainless, I looked at the list:

Potential problems include:
Aluminum Fluoride D
Aluminum Hydroxide
Ammonium Phosphate, Dibasic
Aluminum Chloride
Aluminum Salts
Ammonium Fluoride
Aniline Hydrochloride
Antimony Trichloride
Aqua Regia (80% HCL, 20% HNO
Aromatic Hydrocarbons ?????????
Bleach (chlorine, 12.5%)
Bromine
Calcium Hypochlorite, 30%
Chloric Acid
Chlorine Dioxide
Chlorine Water
Chlorine, anhydrous liquid
Clorox® bleach (sodium hypochlorite, 5.25%)
Copper Chloride
Copper Fluoborate
Ethyl Sulfate
Ferric Chloride
Ferrous Chloride
Fluorosilicic Acid
Hydrobromic Acid (including dilute)
Hydrofluoric Acid (Unsure of minimum concentration)
Hydrogen Cyanide
Hydrogen Sulfide
Hypochlorous Acid
Iodine
Iodine Solution
Lead Sulfamate
Magnesium Chloride
Melamine
Mercuric Chloride, dilute
HCl
Nickle Chloride
Ginger Oil (?????)
Concentrated Oxyalic Acid
Phosgene
Phosphoric Acid Concentrated
Phosphorus Oxychloride
Resorcinal
Silver Bromide
Silver Chloride
Sodium Benzoate
Sodium Bisulfate, 10%
Sodium Bromide
Sodium Cyanate
Sodium Sulfide
Stannic Chloride
Stannic Chloride
Sulfur Chloride
Sulfuryl Chloride
Tartaric Acid
Tetraphosphoric Acid
Tin Ammonium Chloride
Tin Salts
Trichloroacetic Acid

But I mean, so long you use a trap condenser,. and dispose of the old water after your done, can the stuff listed as corrosive harm the steel in the concentrations that would form from lab scale vacuum use?

Panache - 13-5-2018 at 00:20

Coppercone ive pm'ed you however if you are wanting to loop back for pressure regulation I've had vac pumps (graphite vane-types) controlled via a VSD, this however is for systems that are producing some non-condensable gases, otherwise you need a finely controllable atmospheric bleed still somewhere between system and pump, like a needle valve.
Once running you could program the vsd but obviously its not going to adjust your needle valve.

Standard on all vacuum systems is a cold trap, basically a large bore U-tube sitting in either liquid nitrogen or dry ice, but no-one ever uses these in a lab or home environment. Cheaper using wash bottles specific to your needs (ie caustic for acid non- condensable etc).

And im surprised the list is so short for 316.

btw that lytron site is quite good

[Edited on 13-5-2018 by Panache]

[Edited on 13-5-2018 by Panache]

[Edited on 13-5-2018 by Panache]

Sulaiman - 13-5-2018 at 00:59

Quote: Originally posted by coppercone

another biggie for those peltiers is to provide proper torque to mate them with the heat sink for the thermal compound to work well.

I just glued heatsink:TEC:WaterBlock:TEC:Heatsink with araldite epoxy resin

Because the temperature changes and differentials of temperature at each boundary are quite small.
If the araldite fails I'll report back here a.s.a.p. but it seems OK so far.
============================================
The most obvious heat exchangers:
https://www.ebay.co.uk/itm/230mm-Graham-Condenser-24-29-Join...
https://www.ebay.co.uk/itm/410mm-24-40-Graham-Condenser-Join...
and I got one of these from my secret santa, it is efficient,
https://www.ebay.co.uk/itm/200mm-24-29-Glass-Reflux-Graham-C...
then route the hot water output via an old/used or cheap central heating radiator to remove most of the heat,
for higher efficiency add axial fans to force air through the radiator.
Then use your active cooling, reservoir and pump.

Why pump 100's Watts via TECs when only 10's Watts are required ?
Not very compact but cheap, reliable and efficient.

ANY large surface area water container can be used to passively cool the hot water from the glassware; copper tubing, automobile radiator, air-con radiators etc.
The radiator can be distant from your glassware, or, outside your lab.

EDIT: I have only had one lash-up test during winter so far,
I hope to start measurements on this arrangement in a few months from now during summer, because as ambient temperature increases, the radiator becomes less effective... T.B.D.

[Edited on 13-5-2018 by Sulaiman]

Panache - 13-5-2018 at 01:19

Graham or linear condensers are best for vacuum distillations because they provide no back pressure (actually never really thought about it but in vacuum systems technically would this be referred to as forward pressure?)), however they are horribly inefficient and are susceptible to 'walling'; where a fluid flow down the centre of the tube escapes heat exchange. Adding something that disrupts this flow is the same as using a nonlinear condensor.

coppercone - 13-5-2018 at 06:09

Quote: Originally posted by Sulaiman

Quote: Originally posted by coppercone

another biggie for those peltiers is to provide proper torque to mate them with the heat sink for the thermal compound to work well.

I just glued heatsink:TEC:WaterBlock:TEC:Heatsink with araldite epoxy resin

The problem with epoxy is that the thermocoefficent of expansion of the aluminum or other heat sink material is different then the ceramic of the tile so it turns into a reliability problem with cracked tiles and open circuits. It may take a while.

You also want to cycle the temperature slowly, its gonna depend on thermal time constants, but I don't remember what is considered reliable rate of change.

[Edited on 13-5-2018 by coppercone]

DavidJR - 14-5-2018 at 12:14

Quote: Originally posted by coppercone

Indeed - you can get special thermally conductive adhesives which are designed for sticking heatsinks onto chips etc, which I think are silicone based as they feel rubbery when cured. That would allow for a little bit of movement so I would expect that to be more reliable than epoxy resin. Also, obviously araldite isn't specifically designed to be thermally conductive, so thermal performance is probably worse, but considering how thin the layer is, that may not be a problem.

Twospoons - 14-5-2018 at 13:17

And epoxy has a higher expansion coefficient than either aluminium or ceramic, by a factor of two.
Graphite powder would probably make a good thermal interface material in this case - its lubricating, highly conductive,, and already dry so it wont thicken over time or with low temps.
And as with all thermal compounds, thinner is better. In some cases using a thicker layer is worse than using none at all.

coppercone - 14-5-2018 at 15:38

Unless you have sealed modules (they are sold but significantly more expensive), or seal the modules yourself with a electronics grade silicone, I would highly advise not to use anything electrically conductive as your thermal compound.

What happens is, as the heat ex changer cools and heats up, the peltier plate start rotating/walking, then you get exposed thermal interface materials.

Your best bet is the silpad, which is expensive, but has a higher performance then grease, typically, because it won't dry out.

You also want to join the module strings together with flexible wire so there is some slack so they can rotate and move around a bit over the years, otherwise they will get tension on the solder joints and either open circuit or short out the power supply to the heat sink. For this reason sealed modules are better, because typically the seal will hold on to the wire, so even if the pad is ripped off, the wire will stay in the sealed area so it can't take out your power supply with a short circuit (though you should have short circuit protection).

The other reason for sealed modules is because of condensation, the thing gets hot and cold and its difficult to prevent moisture condensation from occurring, which can short things out.

The sealing process typically requires temperature controlled curing ovens.

What I recommend doing is either making (with silicone) or getting presealed modules, then sealing up the entire heat exchanger with a secondary moisture seal.

The best way to do this is to get a gasket that fits between your heat exchanger and the heat sink, with a small cut away for wires, and to seal with quality adhesive here.

You will want to use robust wires. Be sure to calculate how much wire you have inside of your heat exchanger, know its gauge, and calculate the thermal dissipation that occurs in the wire. If you wire the peltier strings up for high current , the thicker wire you use the less thermal losses there will be in the wire, this way your peltiers are not fighting the wire dissipation.

I would actually recommend high gauge high strand count silicone wire to connect the peltier modules together, as it is rather flexible, higher gauge wires with other types of insulation may pull considerable tension on the pads of your peltiers, which can rip off rather easily.

If the sealing compound has difficulty adhering to your wire, simply place a sticky glue heat shrink (3M makes it) over the wire at the point where it will be glued, the surface of the heat shrink material will be more adherant to the glue then certain wire insulation types.

CouchHatter - 15-5-2018 at 08:10

As far as projects go, there are a few that haven't been mentioned that I would find useful. Not all strictly electronic. I found a bunch of these on somebody's sig, can't remember...

UV lamp for TLC visualization
http://www.sciencemadness.org/talk/viewthread.php?tid=29250#...
Gas scrubber by BromicAcid
http://www.sciencemadness.org/talk/viewthread.php?tid=70003
Rotary evaporator
http://www.sciencemadness.org/talk/viewthread.php?tid=23139
Syringe pump
http://www.sciencemadness.org/talk/viewthread.php?tid=22713#...

coppercone - 15-5-2018 at 08:39

Another idea similar to the syringe pump is a powder auger, though these are both motor controller projects..

DavidJR - 15-5-2018 at 13:33

Quote: Originally posted by coppercone

The other reason for sealed modules is because of condensation, the thing gets hot and cold and its difficult to prevent moisture condensation from occurring, which can short things out.

I have also heard of TECs being damaged by condensation freezing inside and cracking the ceramic plates.

coppercone - 16-5-2018 at 05:51

This can most derinatly happen frozen water has immense force

Btw if you like peltiers a hack i figured out i think to save you money on custom components.

If you are handy with a dremel diamond saw and a soldering iron you can probobly cut yourself out a peltier zigaraut to make something like a tiny multistage peltier without having to buy anything special.

You will have higher thermal resistance then a commercial one because the ceramic will be thicker since the joints will be twice as thick. Might be good for prototyping though since you can make whatever you want. Keep in mind the peltiers are provobly lapped you need to maintain even tension on the semiconductor doped bits

This is more useful for electronics... But you can make a multi stage peltier heat exchanger like described before to do something like chill alcohol or maybe something else so long you got a gear pump to move dense fluid.. Ithink you can get like -20c but you will need to move alot of heat. I dont think it will be practical to do more then like 100w without a liquid heat exchanger and a big radiator to dissipate heat from a water coolant loop.

But i suspect that if you use a decent heatsink, like the ones meant for cpu, and make a small diamond cut multistage peltier, and get your self quality insulation, you can make a decent freezing point tester.

Things i can think about it:
See if glyoxylic acid you made is ready to solidify
Determine freezing point of p-xylene to see isometric purity..

[Edited on 16-5-2018 by coppercone]

[Edited on 16-5-2018 by coppercone]

stamasd - 25-5-2018 at 06:09

Let me chime in with a couple of projects I've had on the backburner for a while now. One day though...
1. peristaltic pump with MCU control - useful for those reactions with variable addition rates over time
2. induction oven

Melgar - 26-5-2018 at 04:32

Quote: Originally posted by coppercone

another biggie for those peltiers is to provide proper torque to mate them with the heat sink for the thermal compound to work well.

I actually used an obsolete CPU fan for the one I made. It would easily scale up to multiple CPU fans, and the one I used could fit two 40x40mm ones under it. If you need more cooling though, much higher than 60W will generate so much heat you won't be able to get any actual cooling.

Anyway, I used the spring mechanism from the clamp that would normally hold the fan onto a CPU. Then I used my Dremel to notch the underside of a screw head, such that I could put a screw into either side of the fan, fit the two sides of the spring into the notch, then push down the lever to apply pressure. The stuff between them was just regular heatsink silicone grease:

http://www.sciencemadness.org/talk/viewthread.php?tid=80597

It works well enough for 14/20 distillations of solvents that are liquid at room temperature. When you're running it, the coolant will eventually reach approximately the boiling point of your solvent anyway, then the TECs will drop it below that somewhat. If running it in a loop with nothing actually being cooled, condensation will form on the tubing.

coppercone - 26-5-2018 at 07:51

Yes but just technically if you look at the data sheet for your thermal grease, if its a decent thermal grease, not some fly by night chinese one, you will have a specification that shows you thermal transfer vs surface pressure.

If you put bolts around the thing, you can ensure good surface pressure by using the correct torque on the bolts and calculate it. Tighten it like a car rim.

The thing is though, sometimes its rather high, and if you have a large heatsink, you can actually cause deflection/bending in the heat sink, so you might need to add special thick steel plates or such to prevent bowing.. if it bows you can crack the modules and thermal dissipation is uneven. Easy to do if you are bonding water heat exchangers together, not sure how you would do it for air cooled heat sinks (I would recommend just making the heat sink modules small enough that you can rely on bolts around the 4 corners providing adequate pressure without needing to reinforce things like copper/aluminum.

I am actually working on an induction heater but the control system is a pain in the ass, the big problem is basically, even if you want to use a external thermocouple or pyrometer to control it with really slow ramp rates (to eliminate difficult programming and tuning), you still need to make some kind of fucking phased locked loop to detune it.. basically what can happen is if you put a metal of different conductivity into one, the induction coil begins to look like it has shorted turns (i.e. aluminum), so then you are running the tank circuit at a higher frequency then the resonance, so it can cause your transistors to explode violently (i have seen this on a induction stove when I put an aluminum pot on it by accident, with a steel thing in it, pressure cooker while trying to make a pastrami)

so then you need electrical feedback from the isolated (i made a transformer for mine) side, to measure phase, so I need to figure out how to do that reliably, I think a silicon laboratories isolator will do the trick but it basically put an annoying electrical feedback requirement on it. I did not want to make a damn feedback circuit for something water cooled running at hundreds of amps, I was hoping I could just aim a pyrometer/IR sensor at the pot and link em together to make a good high temperature solution with some analog electronics.

[Edited on 26-5-2018 by coppercone]