×
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

Modeling Convection Oven Flow

Modeling Convection Oven Flow

Modeling Convection Oven Flow

(OP)
This may be a double post...sorry if it is.  

Im trying to predict the amount of time to heat a sample to a certain temperature using a forced convection oven.  
Its a small sample sitting in the oven.  Can i neglect internal energy of the sample and set the Heat input via Conv and Cond equal to the work supplied by the oven?

I contacted the manufacturer of the oven and they gave me a wattage value supplied to the heating element (3kW)  Typically how much of this is actually supplied to the oven?  Also, can i assume this input is constant?

Thanks,
This is a pretty stupid question, but im just starting out my engineering career and i've got lots to learn.

RE: Modeling Convection Oven Flow

A good heat transfer reference is "A Heat Transfer Textbook" by Lienhard and Lienhard. You can download the textbook for free, just google the title.

For heating, a lumped capacitance method (i.e. Biot Number<<1):

T-T_infinity =( T_initial-T_infinity)*e^(-time/(R*C))]

Where
C: is thermal capacitance it is equal to:  Density*Volume*Specific Heat of material
R: is thermal resistance and it is equal to heat transfer coefficient * Area exposed to heat transfer

Determing the Heat Transfer Coefficient is not a simple task, but you can find some ways to estimates it in a heat transfer textbook. It may be simpler to calibrate and use a thermal couple and determine the time to heat your material experimentally.  


By the way, Your problem is not a super simple problem at all and its never a sign of stupidity to ask a question.

RE: Modeling Convection Oven Flow

A convection oven is usually not very well insulated, so there's a bit of heat loss.  You can probably assume a worst-case of the oven's outer surface being at 60ÂșC, which can cause skin burns with prolonged contact.

A lumped model will be pretty close, so long as the sample is relatively small and relatively thermally conductive.

TTFN

FAQ731-376: Eng-Tips.com Forum Policies

RE: Modeling Convection Oven Flow

Quote:

can i assume this input is constant?

Probably not.

Assuming that the controls work to maintain a (near) constant temperature, once the contents of the oven reach near steady state the power input has to equal the box losses.  The controls with cycle or modulate the power to do that.

RE: Modeling Convection Oven Flow

(OP)
Thanks for all the suggestions.
-Nick

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