Peltier devices

[illitirate.is.me]

hmm, the bulkyness is undesirible.
hence the reason i was wanting to use the Peltier rather then a standard compressor.
The liquid idea was another thought, feron or possibly just metho could run through tht etubes, and thus conduct the heat better.
The problem then is how to pump it on such a small scale, the tubes couldnt be any smaller then half a CM or a tad bigger, and the flow would have to be slow.
i really wanna make this work guys.
instead of a trapdoor, what about one of those folding fans, they fold completely flat when no power is applied.
I like the idea of the temp switch on the actual heat sink.
i think i am going to purchase some modules to play around with.
any more ideas.

 

[chemelec]

hmm, the bulkyness is undesirible.
hence the reason i was wanting to use the Peltier rather then a standard compressor.
The liquid idea was another thought, feron or possibly just metho could run through tht etubes, and thus conduct the heat better.
The problem then is how to pump it on such a small scale, the tubes couldnt be any smaller then half a CM or a tad bigger, and the flow would have to be slow.
i really wanna make this work guys.
instead of a trapdoor, what about one of those folding fans, they fold completely flat when no power is applied.
I like the idea of the temp switch on the actual heat sink.
i think i am going to purchase some modules to play around with.
any more ideas.

Liquid Cooling gets even more complicated, and you still need a Good Radiator to dispurse the heat to the air. And at 80 Degrees, your lucky if you can keep the heat sink on the hot side lower than 90 Degrees, no matter which system you use.

Also Available are Multstage Peltier devices. More Expensive but they do achieve Higher Temperature Differentials.
I believe I show aTwo Stage one on my website.
(They also come in 3 Stages, maybe higher now)

However, The heat pumping capacity, along with the Insulation factor and the refigerator volume will determine how cold it gets.

No Matter what else, One Inch of Insulation is NOT Enough for a fridge, unless you only want 40 to 45 degrees with an outside ambient temperature of 80 degrees.

Than there is the Battery Consideration. Drawing 5 or 10 Amps for even relatively short periods of time can deplete a battery Pretty Quick.

I have been using these devices for over 30 years and there are No Simple shortcuts.

Cooling a Slide on a Microscope to freezing is Quite Simple because of the Small Size, but a Fridge is another thing.

 

[illitirate.is.me]

Hmm, what about water cooling then??
Say i have a body of water, 1000L in excess to which stays a constant 26-27 degrees (78-80) to which i could continually pump around the hot side of the peltier. And get a peltier to which has a 'pulldown' greater then that 26-27 degrees. Say 30-35 degrees.
Then wouldn't the cold side of the peltier keep a stable temperature of that amount (the 30-35 degrees) below the temperature of the hot side (the temperature of the water) and thus keep a stable temperature below zero??

Also; When looking at a rating for peltier devices; that have the temperature differential of 40 degrees; is this celcius or Fahrenheit??

And how can one inch of rubber around the whole outside of this thing not be enough insulation; i doubt they have that much in a fridge.
what type of insulation would you recommend.
As you can see; i am really trying ot get this to work

 

[Oznog]

You missed the point on PWM. On-off modulation is just as bad, or actually worse, than PWM. It's not so bad for high duty cycles, but it's terrible for trying to work with a higher voltage than you want by doing on-off or PWM.

Your goal is basically unrealistic. The pumping ability of a Peltier is VERY low at a 80F temp differential. It may even be less than zero- meaning if you have a fridge already cooled down to a 80F temp differential with ice or whatever and turn this thing on, the Peltier will start warming things up, not cooling it down.

And I should mention this is already assuming excellent hot/cold sinks. That's very difficult to achieve. If you've got a Peltier running at 20W, the heat sink could easily leave the hot side of the Peltier itself 20F above ambient. So now your Peltier is actually trying to pump a 100F differential, not 80F. Well, no Peltier I know of is going to do this! You can stack 2 together but the heat from the cascade makes the pumping ability very, very low. Good to cool a sensor with very low thermal mass, no good for a fridge.

There's a reason people haven't made Peltier freezers- the technology makes it impractical. Sadly, no clever manipulation will change the basic device efficiency and it's been WELL researched. The world waits for a better Peltier device.

Switching from 1" insulation to 4" only has a limited effect- because the Peltier itself is a huge leakage, more than anything else here. Almost like leaving the door open.

There are small cooling systems that aren't too big. Danfoss makes some dorm fridge-sized R134a devices. There's also the ammonia-hydrogen adsorption "Servel" cycle, which was the first type of refrigerator.

The new hotness is the Stirling cycle refrigerator. There's actually at least one commercial product out there as a small Stirling fridge.

 

[chemelec]

Hmm, what about water cooling then??
Say i have a body of water, 1000L in excess to which stays a constant 26-27 degrees (78-80) to which i could continually pump around the hot side of the peltier. And get a peltier to which has a 'pulldown' greater then that 26-27 degrees. Say 30-35 degrees.
Then wouldn't the cold side of the peltier keep a stable temperature of that amount (the 30-35 degrees) below the temperature of the hot side (the temperature of the water) and thus keep a stable temperature below zero??

Also; When looking at a rating for peltier devices; that have the temperature differential of 40 degrees; is this celcius or Fahrenheit??

And how can one inch of rubber around the whole outside of this thing not be enough insulation; i doubt they have that much in a fridge.
what type of insulation would you recommend.
As you can see; i am really trying ot get this to work

The 1000 Liters of water would help, But you now need to Pump it. Besides being somewhat difficult, That draws more power.
You will also need to build an efficient transfer plate to get the water to cool the TE Module.

As to that Rubber, it is unlikely any better than foam. And One Inch Thickness is Still NOT Enough.

And as Said by me and others, there is the Reverse Loss through the TE Module. You really need to consider this Loss or create a double chamber with fans and a door to Reduce this effect.

But if your so Determined, Go ahead and experiment.

 

[illitirate.is.me]

lol; im like a mule lol stubborn
i just cant get over the size; its just too convenient. as for all the hassles, we shall work them out eventually.
I was looking on the 'supercool' website (manufactures of peltier devices) who claim to have peltiers with a potential differential of over 100 degrees celcius, well above the 40 degrees needed. I think these shall help, and more investigation shall be going that way.

as for insulation; can anyone tell me what insulation is inside a refrigerator/freezer.
the only ones we have are currently in use and i do not wish to pull one apart, i googled some things, trying to find a cross section but i came up with nothing; so i ask someone here. ??

 

[chemelec]

lol; im like a mule lol stubborn
i just cant get over the size; its just too convenient. as for all the hassles, we shall work them out eventually.
I was looking on the 'supercool' website (manufactures of peltier devices) who claim to have peltiers with a potential differential of over 100 degrees celcius, well above the 40 degrees needed. I think these shall help, and more investigation shall be going that way.

as for insulation; can anyone tell me what insulation is inside a refrigerator/freezer.
the only ones we have are currently in use and i do not wish to pull one apart, i googled some things, trying to find a cross section but i came up with nothing; so i ask someone here. ??

Most Refigerators just use a Foam insulation, 1 to 2 inches thick.
But Unlike Peltier devices, they use Brute Force Cooling with compressors.

And with Peltier Devices, It is NOT Just the Temperature Differential, that needs consideration, It is also the "Heat Pumping Capacity".

You should also be aware, that as the temperature goes lower on the cold side, so does the efficiency on peltier devices.

This is also True for the Hot Side. For Example:
If the hot side is at 30 degrees, the cold side MIGHT Reach -30.
"A 40 degree difference".
However if the Hot side is at Zero, the cold side will Never reach -40.
Maybe not even -20.

You need to Really look at, Read and Understand the Technical Data on these Peltier devices.

 

[Oznog]

Yeah look at what the data is telling you.
OK, at MOST it's 100C (180F). At this point, there is 0 watts pumping capacity. This is a region where there is no useful output. (BTW, most I saw there were more like 75C).

So you want to have a box 80F below the outside temp. Now let's throw some figures out here.

Under loading, the heat sink might only be able to cool the hot side of the device to within 20F of ambient. You might have it where the end of the furthest cooling fins is only 5F warmer, the aluminum next to the device might be 15F warmer and the device itself is 20F warmer. The cold side might end up being 20F colder than the box. The cooling side doesn't deal with as much thermal flow but probably can't have a fan due to freezing concerns- ice on the shaft and blades.

So, now we need to span 120F. Technically possible. But the pumping capacity is only 33% of the 0F rating on that 100C differential device. That's fairly low. For the 75C differential device, you're at like 11%.

Excellent sinks will substantially improve this situation. Again ice is a limiting factor on that cold sink. However, as sinks get huge, then the size difference between this and the HCFC compressor system is reduced.

Also understand that Peltiers are FAR less efficient, even with ideal heat/cold sinks. This is completely impractical to run on batteries for example.

 

[avinaik]

Air compressor.

when we run 500 CFM comporress ,we uses water cooling system. how much minimum tempreture can be use for cooling compressor body?