Peltier Assembly

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leiouzhang
 
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Peltier Assembly

Post by leiouzhang »

Hi,

I am doing the thermal conductivity test and using Peltier Assembly to create temperature difference, now having two questions about using the Peltier Assembly.

1. I need to find the heat transfer rate, and try to find the rate of heat transfer by using power W =I*V, when the Peltier assembly is powered up and temperature of the aluminum plate surface area reach to a constant temperature, does the heat absorbed from the another side (fan side) = the heat release from the aluminum side? Thanks

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adafruit_support_bill
 
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Re: Peltier Assembly

Post by adafruit_support_bill »

Peltier junctions are not 100% efficient. There is extra heat created in the process of pumping heat from one side to the other.

If you are powering the device with 12v @ 5A, that is 60 watts of extra energy that is being put into the system and it has to come out as heat.

leiouzhang
 
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Re: Peltier Assembly

Post by leiouzhang »

Hi Bill,

Thanks for that, I don't quite understand about the 'extra energy' is there any 'original energy' going through the system? and I forgot put my 2nd question, Do I need a separate power supply for power up the fan itself? I was using one power supply for the fan and Peltier plate, only the peltier plate worked, the fan wasn't working. Thanks

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adafruit_support_bill
 
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Re: Peltier Assembly

Post by adafruit_support_bill »

Heat is a form of energy and the peltier junction pumps the heat from one side of the junction to the other. The heat energy that comes out of the hot-side is the combination of the heat absorbed from the cold side plus the electrical energy that drives the device.

You should be able to power the peltier and the fan from the same supply. Does the fan work if you power it separately?

leiouzhang
 
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Re: Peltier Assembly

Post by leiouzhang »

Hi Bill,

Anyway you could help me to find the heat absorbed from the cold side for this Peltier cooler? Thanks

Yes, the fan works if I connect the poser separately.

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adafruit_support_bill
 
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Re: Peltier Assembly

Post by adafruit_support_bill »

Efficiency depends on the temperature differential, but in any case it is fairly low (10-15%). http://en.wikipedia.org/wiki/Thermoelectric_cooling
Probably the best way to measure this is to cool a known volume of liquid and see how much the temperature changes in a specific period of time.

leiouzhang
 
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Re: Peltier Assembly

Post by leiouzhang »

Hi Bill,

Thanks for that, In this case, can I understand that the W(total) is actually = (V*I) which is the electrical energy + (P*I*t) and the P is in between 0.1-0.15?

The way I was thinking of to measure the Q is using 1 Peltier assembly as heat pump, and use the surface of aluminum plate (A) to contact the aluminum plate (B) and oversee the temperature change of the aluminum plate (B) and using Q=mc(T1-T2) to find the heat transfer rate.

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adafruit_support_bill
 
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Re: Peltier Assembly

Post by adafruit_support_bill »

That sounds like a good plan. I'd recommend using some thermal grease between the aluminum plates to improve the thermal conductivity of that interface.

thefatmoop
 
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Re: Peltier Assembly

Post by thefatmoop »

might also be worth mentioning that a peltier's efficiency is a function of the temperature difference across the peltier junction ;p That won't be too hard to get a characterization equation

leiouzhang
 
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Re: Peltier Assembly

Post by leiouzhang »

thanks for the advice.

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