"Piggy-backing" Peltier Modules..

[Syncro5]

Has anyone had any success with mounting two Peltier modules together in order to achieve higher temperatures on the hot side and lower temperatures on the cold?

I'm currently designing a combined heating and cooling system which will ultimately be used for a batch pasteurisation process. The Peltiers I'm using have a temperature difference of 70°C meaning if I opperate from an ambient temperature of 20°C I should achieve around 55°C on the hot side and around -15°C on the cool side (roughly). However I need at least 70°C on the hot side! In order to achieve the higher temperature I bonded two of the modules together in the hope that the hot side of the first would increase the temperature of the cool side of the second meaning that the temperature difference sets from a higher higher point.

The result was that the hot side of the second Peltier module did increase. However, the cold side of the first module also increase (where I thought it would decrease). Could anyone with a better understanding of Peltier modules (not hard I know) shed any light on the matter?

Thanks,

Joe.

 

[LionelHutz]

It sounds like it didn't work and instead you basically increased the heatsinking on the cold side which raised the cold and hot temperatures.

What happened in the middle junction?

 

[MagicSmoker]

syncross: You can stack Peltier modules to get a higher delta T, but this is usually done to achieve a colder temperature on the cold side (it is, for example, commonly used to cool down infrared imaging sensors), not a hotter temperature on the hot side. Note that the module with the cold side exposed needs to have a smaller area than the module with the hot side exposed. If you use two modules with the same area you probably won't gain much delta T.

See this website for a good overview of how Peltier modules work:

http://www.tellurex.com/technology/peltier-faq.php

 

[IRstuff]

Note that the TEC that's closest to the ambient temperature interface must pump not only the what you're trying to heat/cool, but also the heat of the second TEC. As a general rule, therefore, a TEC stack's heat pumping performance is severely deprecated from the datasheet value. I suggest you look at some off-the-shelf stacked TECs to see how poor the performance actually is. It's very likely that your second TEC's heat load is already overwhelming your anchor TEC's capacity.

TTFN
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[Syncro5]

Thanks for the help! I've found that the cooling power of the Peltier modules is enough with out the need to stack them.

This just leaves the heating.. I need 550W of heating power constantly over 15 minutes with out going over 65°C / 66°C. I've been looking at heating cable which is used for preventing ice forming on pipes and also under-floor heating cable which would both seem to do (although I'll need a lot of it in order to get the 550W).

Does anyone have any thoughts / concerns with using this type of heating wire for this application? Are there any alternatives?

Cheers,

Joe.

 

[IRstuff]

?? 500W is a lot for something that can be cooled by a TEC. Have you looked at:

http://www.minco.com/~/media/

http://WWW/Resource Library/Heaters/Silicone Rubber Thermofoil Heater Tech Spec.ashx

TTFN
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