Peltier Cooler Temperature

[Warpspeed]

When using peltier Devices, you always get the best cooling when operating at Full current.

That has not been my experience.

And the curves in the data sheet for that actual device suggest otherwise as well.

 

[chemelec]

That has not been my experience.

And the curves in the data sheet for that actual device suggest otherwise as well.

View attachment 137272

Based on what your saying, Go to Zero Volts and you will get the Best cooling.
I DOUBT IT!

 

[Warpspeed]

Thanks, a lot Chemelec.

Those curves do not show maximum cooling capacity at zero volts, you are being sarcastic. Try to help people, and getting stomped on is why I come to this Forum less and less these days.

But those curves do show a definite peak well below maximum rated input power. Those curves are manufacturers curves for the actual device being discussed here.

 

[gauravkothari23]

30 Degrees Air Temperature is Hot.
So your heat sink or hot side of the peltier will probably be more like 40 to 45 degrees.

It is Unlikely you will get this to go down to even 5 Degrees.

There are STACKED Peltiers that have a Greater Cooling, but there More Expensive.

the one i am using is TEC-12706 which is 12v 6Amps 92 watts Peltier module
but instead of that can i use TEC-12715 which is 12v 15 Amps 164 watts for better and fast cooling...??

 

[c_mitra]

the one i am using is TEC-12706 which is 12v 6Amps 92 watts Peltier module but instead of that can i use TEC-12715 which is 12v 15 Amps 164 watts for better and fast cooling...??

The Peltier module is basically a heat pump; it is a Carnot cycle running in reverse. Only problem is that is far from ideal.

Let us say one side temp is T1 and the other side is T2. You are pumping heat (heat and temp are different beasts altogether) from the colder side and putting it out on the hotter side.

The amount of energy being supplied (yes, you need to do work on the system) is used to take some heat from the cold side, raise the temp to the hot level and push it out.

For an ideal refrigerator, you can put more and more energy and reduce the temp of the cold side as much as you want (you can go close to the abs zero).

For a real refrigerator, there is some degree of irreversibility; in this case here it is the heat leakage from the hot to the cold side by conduction AND the part of the energy input getting converted into heat (joule heat).

As the temp diff increases, the heat leakage increases. As the input power increases, the joule heat increases. Therefore you cannot get more than (some value) a given amount of temp difference depending on the Peltier module.

Getting a temp difference of 20-30C between the two ends may be considered a good value.

 

[dick_freebird]

The COP curves show what I was alluding to earlier in
suggesting you map out (with some granularity) the
achieved delta-T vs input power. Bearing in mind that
coefficient of performance is not the same as ultimate
temperature differential, still it might well be that a
stack-of-two operated at peak efficiency does better
than a single element pushed to its power limit.

Once you have gotten a grasp of your assembly's
performance and dependencies relative to what the
element's applications materials indicate, you'll know
whether to work more on the bench or step back to
a more analytical trades-study of that sort. Until then
there isn't much point to getting more theoretical.

 

[chemelec]

Here is the data Sheet for the 2-Stage Peltier's I have.
I see a price on the internet of about 158 British Pounds.
I Bought these Years ago, for a LOT LESS than that.



- - - Updated - - -

Here is the 6 Amp, 14.5 Volt Single version

 

[c_mitra]

... Bearing in mind that coefficient of performance is not the same as ultimate temperature differential, still it might well be that a...

1. Refrigerators are evaluated by the amount of heat pumped; max amount of heat pumped will be when \Delta T is zero;
2. There will be a max \Delta T when the amount of heat pumped will be zero;
3. Multiple engines (refrigerators) in series is always equivalent to a single engine (but for the leakage);
4. For real engines, max \Delta T can only be increased by series connection (stepped up heat pumping);
5. COP is basically heat pumped at a given \Delta T; the power used is mostly appears at the heat on the sink side.

 

[Vraj]

1)i will suggest you to remove the heatsink at cool side. this is having large surface area so it dissipate cold air.
2)provide more cooling at hot side. because the peltier is made for make temperature difference in two sides.
for different models, they have specific temperature difference .so if you provide cooling at hot side, you will get so lower temperature.
3)make the air flow with two fans in same direction.(helping each other).means 1 fan's out is input for 2nd fan.:thumbsup:

 

[chemelec]

Removing the Cold Sink will get the Temperature Lower, But Only on the Peltier Surface.
It will NOT increase Cooling inside a Cooler, It will actually Decrease it.

Two Fans connected as you state, will not increase cooling on the hot side.
If both fans operate at the same RPM, The volume of air flow will not change.

Just use a Fan with a HIGHER Air Flow.

 

[c_mitra]

Removing the Cold Sink will get the Temperature Lower, But Only on the Peltier Surface.
It will NOT increase Cooling inside a Cooler, It will actually Decrease it.

That depends on how you define "cooling". If you mean a greater amount of heat being pumped out per unit time, then perhaps your statement is wrong.

In the steady state, the heat flux will only depend on the temp difference across the device. But what you really want (i) a low temp and (ii) maintain that low temp.

Two Fans connected as you state, will not increase cooling on the hot side.
If both fans operate at the same RPM, The volume of air flow will not change.

Just use a Fan with a HIGHER Air Flow.

Two identical fans connected in series will actually increase the air flow because each fan will now have a lower pressure drop across it. Just like the case of two Peltier devices in series.

 

[dick_freebird]

Two inferior fans in series, however, may still not equal one
top-tier one. Scrounged 12VDC brushless fans that were
picked for quietness for example, will push less than 10%
of what you can get from a 110VAC ball bearing fan of
equal area. Check out Digi-Key's extensive and parametric-
selectable table of muffin fans, and see what yours might
be delivering. Although heat sink outer face vs ambient
temp tells youall you need to know about sufficiency of
airflow. And hot face vs heat sink outer face, about
adequacy of heat sink. Numbers. Get them.

- - - Updated - - -

Another note re fan performance in stacks - if airflow is not
straightened in between, the second fan sees already-
rotating air column and may impart little added thrust /
flow.

 

[c_mitra]

Two inferior fans in series, however, may still not equal one
top-tier one.

Agreed.

Another note re fan performance in stacks - if airflow is not
straightened in between, the second fan sees already-
rotating air column and may impart little added thrust /
flow.

Very true; centrifugal compressors (basically fans in series; also gas turbines that can be considered as heat engines) use stationary blades to correct for this. In the present case a small gap between the fans can induce sufficient turbulence to partly offset the flow pattern.

But I still "feel" that two fans working in series with the same RPM will deliver more air than one single fan (flow will be increased). I need to think more on that though.

 

[chemelec]

I Don't believe it will add More Speed, But it Will Add More FORCE.
So this will result in LESS SLOW DOWN, from Resistance against the Force of the Air.

(Sort-of like Adding More Horse Power.)

 

[c_mitra]

I Don't believe it will add More Speed, But it Will Add More FORCE.
So this will result in LESS SLOW DOWN, from Resistance against the Force of the Air.

(Sort-of like Adding More Horse Power.)

If you add more force but the speed (I assume you mean the speed of air) remains the same, them the mass of air moved must increase. Is there any other alternative?

But I do not understand how it could mean "LESS SLOW DOWN" but not increase the flow.

After all, the total energy input to the fan goes partly in friction (dissipation; no useful work done) and another part goes on imparting the velocity of the mass of air in a particular direction.

(Viscous drag of air is included in the friction)

It is reasonable to assume that if you input more power to the fan, the overall flow should increase. Household fans work on this principle.

 

[chemelec]

My thought is the Heat sink will try to block the air flow, probably slowing down the fan blades.
With the 2 fans, this is probably less likely.

 

[dick_freebird]

"May" and "probably" could be true, but engineering
wants quantitative performance and cost. Of course
the experiment is simple enough to try, if you have
the fans and the instrumentation. Then you can tell
us what happens.

You might experiment with pull vs push while you're
at it. Fans respond differently to being starved than
to being obstructed. And with ducting the heat sink
to ensure that the air is made to work, not let to
escape as it would like.

It's well past time to move from conjecture to
hardware and measurements.