Silly question about TECs.

[Daniel Pitts]

Lets say I have two Thermoelectric coolers, each of which can create a
∆t of 60°c. Now, lets say I'm a mad scientist and decide to layer them
together, so that the cooling side of one is on the heating side of the
other. Have I in effect made a 120°c TEC, or did I just melt my carpet?
Or is it somewhere in-between 60° and 120°? (which is more like what I'd
expect). Or, is it just that it moves 60° twice as far?

If it actually does improve the cooling capacity, I'd expect diminishing
returns (since otherwise absolute 0k would be way too easy to achieve).
Is there a formula for this? I'd actually love to liquify air, just to
play around with (knowing of course how dangerous it can be without the
proper safety gear).

Thanks,
Daniel.

P.S. If the unicode doesn't come through as it should in your reader,
and you see some strange "junk" in my first paragraph: "∆" is "Delta",
and "°" is Degree.

 

[Jasen Betts]

On 2012-06-04, Daniel Pitts <newsgroup.nospam@virtualinfinity.net> wrote:

Lets say I have two Thermoelectric coolers, each of which can create a
∆t of 60°c. Now, lets say I'm a mad scientist and decide to layer them
together, so that the cooling side of one is on the heating side of the
other. Have I in effect made a 120°c TEC, or did I just melt my carpet?
Or is it somewhere in-between 60° and 120°? (which is more like what I'd
expect). Or, is it just that it moves 60° twice as far?

one of the above, the cooler one puts out more heat than it takes in
so the hotter one has more work to do. if you're moving only a small
amount of heat at the cold end the hot end can probably keep up

If it actually does improve the cooling capacity, I'd expect diminishing
returns (since otherwise absolute 0k would be way too easy to achieve).
Is there a formula for this? I'd actually love to liquify air, just to
play around with (knowing of course how dangerous it can be without the
proper safety gear).

apparently you can do that with just dewar vessel and a compressor,
I don't know if you can do it with one from a hardware shop.
and yeah, liquid oxygen looks pretty dangerous.

--
⚂⚃ 100% natural

--- Posted via news://freenews.netfront.net/ - Complaints to news@netfront.net ---

 

On Sun, 03 Jun 2012 19:14:26 -0700, Daniel Pitts
<newsgroup.nospam@virtualinfinity.net> wrote:

Lets say I have two Thermoelectric coolers, each of which can create a
?t of 60°c. Now, lets say I'm a mad scientist and decide to layer them
together, so that the cooling side of one is on the heating side of the
other. Have I in effect made a 120°c TEC, or did I just melt my carpet?
Or is it somewhere in-between 60° and 120°? (which is more like what I'd
expect). Or, is it just that it moves 60° twice as far?

If it actually does improve the cooling capacity, I'd expect diminishing
returns (since otherwise absolute 0k would be way too easy to achieve).
Is there a formula for this? I'd actually love to liquify air, just to
play around with (knowing of course how dangerous it can be without the
proper safety gear).

Thanks,
Daniel.

P.S. If the unicode doesn't come through as it should in your reader,
and you see some strange "junk" in my first paragraph: "?" is "Delta",
and "°" is Degree.
Yes. You can stack TECs to get a higher temperature differential. The

problem is low effiency though. Because the TEC device produces heat
as it moves heat the subsequent TECs need to remove more heat than the
previous ones. So you either need to use bigger TECs as the stack
increases or reduce the amount of heat moved.

 

[Tim Wescott]

On Mon, 04 Jun 2012 08:05:36 -0700, George Herold wrote:

On Jun 4, 10:39 am, e...@whidbey.com wrote:
On Sun, 03 Jun 2012 19:14:26 -0700, Daniel Pitts





newsgroup.nos...@virtualinfinity.net> wrote:
Lets say I have two Thermoelectric coolers, each of which can create a
?t of 60°c.  Now, lets say I'm a mad scientist and decide to layer
them together, so that the cooling side of one is on the heating side
of the other.  Have I in effect made a 120°c TEC, or did I just melt
my carpet? Or is it somewhere in-between 60° and 120°? (which is more
like what I'd expect). Or, is it just that it moves 60° twice as far?

If it actually does improve the cooling capacity, I'd expect
diminishing returns (since otherwise absolute 0k would be way too easy
to achieve). Is there a formula for this? I'd actually love to liquify
air, just to play around with (knowing of course how dangerous it can
be without the proper safety gear).

Thanks,
Daniel.

P.S. If the unicode doesn't come through as it should in your reader,
and you see some strange "junk" in my first paragraph: "?" is "Delta",
and "°" is Degree.

Yes. You can stack TECs to get a higher temperature differential. The
problem is low effiency though. Because the TEC device produces heat as
it moves heat the subsequent TECs need to remove more heat than the
previous ones. So you either need to use bigger TECs as the stack
increases or reduce the amount of heat moved.- Hide quoted text -

- Show quoted text -

I seem to recall stacks sold by the vendors (Melcor?), with something
like 120 deg C for a three (or four?) layer stack. And very small
amounts of power for the coldest element. I think the efficiency may
'crap out' at lower temperatures too (as 1/T?). You might guess that
the IR losses are roughly independent of T and the thermal energy
transported by each charge carrier goes as T.

So I'm afraid you can't liquify air with a stack. Which is too bad.

I've always wondered how much delta T I could get if I tied one end to a
liquid nitrogen bath.

George H.

Killjoy. You can liquify at itty-bitty bit of air.

For anything more, for the weight and size you're better off with that
compressor and dewar.

--
Tim Wescott
Control system and signal processing consulting
www.wescottdesign.com

 

[Tim Wescott]

On Mon, 04 Jun 2012 09:05:01 +0000, Jasen Betts wrote:

On 2012-06-04, Daniel Pitts <newsgroup.nospam@virtualinfinity.net
wrote:
Lets say I have two Thermoelectric coolers, each of which can create a
∆t of 60°c. Now, lets say I'm a mad scientist and decide to layer them
together, so that the cooling side of one is on the heating side of the
other. Have I in effect made a 120°c TEC, or did I just melt my
carpet? Or is it somewhere in-between 60° and 120°? (which is more like
what I'd expect). Or, is it just that it moves 60° twice as far?

one of the above, the cooler one puts out more heat than it takes in so
the hotter one has more work to do. if you're moving only a small amount
of heat at the cold end the hot end can probably keep up

I've seen ones designed to take IR imaging sensors down to cryogenic
temperatures -- it was a stack of over half a dozen coolers, each smaller
than the last. It looked like the roof of a Pagoda, with a cooler at the
end the size of a fingernail.

If it actually does improve the cooling capacity, I'd expect
diminishing returns (since otherwise absolute 0k would be way too easy
to achieve). Is there a formula for this? I'd actually love to liquify
air, just to play around with (knowing of course how dangerous it can
be without the proper safety gear).

apparently you can do that with just dewar vessel and a compressor, I
don't know if you can do it with one from a hardware shop. and yeah,
liquid oxygen looks pretty dangerous.

But dangerous in a very fun sort of way.

You probably don't want to play around with large volumes of the stuff,
though -- even a teaspoon poured on oil and set off will probably make a
pretty darn big bang.

--
Tim Wescott
Control system and signal processing consulting
www.wescottdesign.com

 

[George Herold]

On Jun 4, 10:39 am, e...@whidbey.com wrote:

On Sun, 03 Jun 2012 19:14:26 -0700, Daniel Pitts





newsgroup.nos...@virtualinfinity.net> wrote:
Lets say I have two Thermoelectric coolers, each of which can create a
?t of 60°c.  Now, lets say I'm a mad scientist and decide to layer them
together, so that the cooling side of one is on the heating side of the
other.  Have I in effect made a 120°c TEC, or did I just melt my carpet?
Or is it somewhere in-between 60° and 120°? (which is more like what I'd
expect). Or, is it just that it moves 60° twice as far?

If it actually does improve the cooling capacity, I'd expect diminishing
returns (since otherwise absolute 0k would be way too easy to achieve).
Is there a formula for this? I'd actually love to liquify air, just to
play around with (knowing of course how dangerous it can be without the
proper safety gear).

Thanks,
Daniel.

P.S. If the unicode doesn't come through as it should in your reader,
and you see some strange "junk" in my first paragraph: "?" is "Delta",
and "°" is Degree.

Yes. You can stack TECs to get a higher temperature differential. The
problem is low effiency though. Because the TEC device produces heat
as it moves heat the subsequent TECs need to remove more heat than the
previous ones. So you either need to use bigger TECs as the stack
increases or reduce the amount of heat moved.- Hide quoted text -

- Show quoted text -

I seem to recall stacks sold by the vendors (Melcor?), with something
like 120 deg C for a three (or four?) layer stack. And very small
amounts of power for the coldest element. I think the efficiency may
'crap out' at lower temperatures too (as 1/T?). You might guess that
the IR losses are roughly independent of T and the thermal energy
transported by each charge carrier goes as T.

So I'm afraid you can't liquify air with a stack. Which is too bad.

I've always wondered how much delta T I could get if I tied one end to
a liquid nitrogen bath.

George H.