Amount of Watts to lower temperature of a volume of air? 1

[aalfabob]

I am trying to figure out how many watts of power (from a peltier) are needed to cool a certain amount of air (About 162 CFM) 1 degree C. Any information about how to solve this would be helpful.

 

[chicopee]

use equation q=(dM/dt)*cp*dT
where dM/dt= dV/dt*rho
dV/dt= air flow
cp = specific heat of air
dT= change in temp
when cp,dT,dV/dt and rho are in metric uniys, your answer s/b in watts.

 

[imok2]

Also: BTUH = CFM x 1.8*F x 1.08; Then devide by 3.412 = Watts. 1.8*F = 1*C

 

[JKEngineer]

The equation presented by chicopee is the watts of heat removal from the air. Air mass/time * heat capacity * change in temperature.

Depending on how the peltier cooler is specified, watts removed or watts to power, you will have to adjust the value by the performance coefficient of the cooler.

If there is heat transfer from the surroundings, such as pipe wall, computer case, hot chips, etc., you will have to adjust the watts to be removed by that as well. In other words, as you are cooling the air, is something else heating it up? If so, you need to be concerned about it as well.

Jack

Jack M. Kleinfeld, P.E. Kleinfeld Technical Services, Inc.
Infrared Thermography, Finite Element Analysis, Process Engineering

http://www.KleinfeldTechnical.com

 

[aalfabob]

Thanks for the help, im getting around 148 watts per degree C.

 

[IRstuff]

Note also, the calculations do not consider the heat transfer efficiency between the air and your cooler.

162 cfm is a sizable amount of air and you'll need to figure out how to get your watts to every cfm of that air.

TTFN

 

[friartuck]

162cfm = 0.07645m3/sec

Rho=M/Vol

Mass flow =vol x density

M=0.07645x1.205(density of air)=0.0921kg/sec of airflow

Q=mc DT

m=0.0921
c=1.01kJ/kG C
Dt=1 degree

= 0.0921x1.01x1
=0.093kW or 93Watts to cool air 1 degree (Excluding HX plate effectiveness etc)



Friar Tuck of Sherwood

 

[Istre]

Also, something to think about when using a Peltier device for cooling is that it doesn't magically produce a cold temperature on the cold side of the device. Like any cooling system, it can only wick away a certain amount of heat per second, so the cold side temperature is completely dependant on the hot side temperature. If the hot side is too hot, the Peltier device would be ineffective at best, and at worst could possibly end up operating hotter than what you're trying to cool.

Also, the Peltier is itself a relatively large heat dump, so care must be taken to provide enough airflow to ensure that the heat the Peltier draws out of the device you're cooling and the additional heat the Peltier adds does not collect in the space it's enclosed in. Peltier devices can quickly fry electronics if the cooling fans fail to provide enough airflow because the additional heat they produce tends to stagnate at the hot side of the Peltier, driving hot side ambient temperature up, and thus driving the cold side temperature through the roof. Heat flow into the Peltier is then impeded by the shrinking temperature differential between the Peltier and the cooled device, and as the Peltier continues to heat, the Peltier insulates itself more and more, eventually frying whatever you were trying to cool.

In a nutshell, a properly sized Peltier and airflow system should cool better than ambient airflow alone, but in the event the airflow fails, the chip (I'm assuming electronics here) will fry in a heartbeat. They're good devices if used correctly, just take care.