Help with Peltier modules
Help with Peltier modules
(OP)
Hi all,
I'm somewhat of a novice with electronics but I am currently designing a system which needs to heat 2l of liquid up to 64°C for a short time (around 2 min) and then quickly cool it to below 7°C.
Is it possibe to use peltier modules for both aspects of the system, heating first and then reversing the current to immediately cool?
If so say we are opperating from an ambient temperature of 20°C. Would a Peltier module with a Delta T of 90°C mean the hot side increases to 65°C (ambient of 20 + 45) and the cold side decreases to -25°C (ambient of 20 - 45).
Any info on the matter would be greatly appreciated!
Thanks,
Joe.
I'm somewhat of a novice with electronics but I am currently designing a system which needs to heat 2l of liquid up to 64°C for a short time (around 2 min) and then quickly cool it to below 7°C.
Is it possibe to use peltier modules for both aspects of the system, heating first and then reversing the current to immediately cool?
If so say we are opperating from an ambient temperature of 20°C. Would a Peltier module with a Delta T of 90°C mean the hot side increases to 65°C (ambient of 20 + 45) and the cold side decreases to -25°C (ambient of 20 - 45).
Any info on the matter would be greatly appreciated!
Thanks,
Joe.





RE: Help with Peltier modules
No.
2 grams? Yes.
You should consider reservoirs of heat and cool.
Keith Cress
kcress - http://www.flaminsystems.com
RE: Help with Peltier modules
It's a Physics 101 problem. Refer to Thermal Mass (a.k.a Heat Capacity)
Think how long it takes for an electric kettle (~1500 watts !!!) to raise a litre or two of water to ~100°C. A typical TEC will be many, many, many times less powerful (in either direction) and would thus take far longer than indicated by your choice of temporal domain adjectives.
RE: Help with Peltier modules
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Help with Peltier modules
Keith Cress
kcress - http://www.flaminsystems.com
RE: Help with Peltier modules
If you want to change temperature fast, you need a lot of surface area. Think a heat exchanger with a lot of tubes, or a chamber, thin in one dimension and large in the other two, or maybe a large tall thin annulus. Selection depends on the nature of the process fluid you wish to heat and cool.
As mentioned, you would surround the process fluid with hot fluid from a hot reservoir, then quickly drain the hot fluid and pump in some cold fluid from a cold reservoir, then drain that to repeat the cycle. It's possible to use one heat transfer fluid and heat and cool it dynamically, as in a reversible heat pump, but it's simpler to use the separately heated and cooled reservoirs.
Mike Halloran
Pembroke Pines, FL, USA
RE: Help with Peltier modules
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Help with Peltier modules
TTFN
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RE: Help with Peltier modules
The OP didn't actually give any rate of change values. The only absolute time reference "around 2 min" could be interpreted to be the time spent at a steady +64°C. The only information about the rate of change are the undefined adjectives quickly and immediately.
RE: Help with Peltier modules
TTFN
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RE: Help with Peltier modules
In all seriousness, there are many polymeraze chain reaction (PCR) reactors (for genetic research) on the market using Pletier devices operating through temperatures similar to the OP's temperature range. One problem that develops is that thermal cycling develops thermal expansion stresses where the thermoelectric chips (typically BiTe) bond to the ceramic face plates. This set up fatigue stresses with each cycle. There is a Russian company that makes Peltier devices but with a compliant bonding layer between the BiTe chips and the ceramic faceplates; the compliant layer helps relieve the thermal expansion strains. In testing I did for a Peltier chiller, these devices withstood better than a factor of 100 more cycles than the more traditional solder/braze bonded peltier devices. A quick google reminded me of that company name, it's website is http://sctbnord.com/article_157.html
RE: Help with Peltier modules
Just to clarify the 2 min is the time in which the liquid must remain at 64°C. Getting there shouldn't take any longer than 10 - 15 minutes though and likewise with the cooling would be around 15 minutes also. There will be a system in place keeping the mixture homogenised so it can be heated uniformly.
Another point I really should have mentioned is that the liquid being heated will change properties above 70°C so the heat source needs to remain below that temp to stop the properties of the liquid changing local to the heat source. So yes.. a big surface area to volume is key.
Is the general consensus here that using a separate heating and cooling system to generate hot and cool reservoirs would be more cost-effective than using the Peltier modules?
I am aware this is starting to stray a little from electrical to thermal dynamics so I'll repost in a separate forum when I progress from the initial "is it possible" stage.
RE: Help with Peltier modules
Luxury. The project just became perfectly feasible in any number of ways.
RE: Help with Peltier modules
Will, or can, the fluid be agitated for better thermal conduction?
TTFN
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RE: Help with Peltier modules
- Yes it will have. Something like a rotating mixer in the centre of the container and baffle plates around the outside (which could also be used for increasing the SA for heat transfer).
So this option may be feasible! To relate back to the original post, does the Delta T of the Peltier module split equally either side of the ambient operating temp? (i.e. when using a module with a Delta T of 90°C, operating in a 20°C environment, does the hot side raise to +65°C and the cold side drop to -25°C). I'm sure it won't be quite as easy as that but for a there or there about rule?
RE: Help with Peltier modules
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RE: Help with Peltier modules
I really appreciate all the help, I think I have enough support here to buy some peltier modules and start prototyping!
Thanks again,
Joe.
RE: Help with Peltier modules
RE: Help with Peltier modules
Use a mechanical heat pump. Use the reservoir scheme. Use the mechanical to heat one reservoir and cool the other. Make the heat exchange fluid something that works at both temps. Glycol of some sort perhaps. Then just alternately flood the cooling chamber from the appropriate reservoir.
Keith Cress
kcress - http://www.flaminsystems.com
RE: Help with Peltier modules
I wasn't sure what you meant by "mechanical heat pump" so did a quick google search and all I can find are vapour compression refrigeration systems.. is that what you had in mind? Heat one reservoir of exchange fluid using the condenser coils and cool another using the evapourator coils? That option still seems, to me, like a more expensive option but you are the experts! I'll get in touch with some refrigeration companies too.
Thanks again!
Joe.
RE: Help with Peltier modules
RE: Help with Peltier modules
A Peltier can have some tough issues associated with them. Peltiers have strict physical demands that make them hard to use. They also work via electrons directly transporting the heat. Hence, the systems depend directly on the quantity of electrons. That means large currents, which in turn, means small voltages. The power supplies that are required to supply low voltage large currents are inefficient and expensive.
Keith Cress
kcress - http://www.flaminsystems.com