×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

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

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

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

(OP)
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.

RE: Amount of Watts to lower temperature of a volume of air?

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.    

RE: Amount of Watts to lower temperature of a volume of air?

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

RE: Amount of Watts to lower temperature of a volume of air?

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
www.KleinfeldTechnical.com

RE: Amount of Watts to lower temperature of a volume of air?

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

RE: Amount of Watts to lower temperature of a volume of air?

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

RE: Amount of Watts to lower temperature of a volume of air?

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

RE: Amount of Watts to lower temperature of a volume of air?

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.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources