Heat Transfer of Gas Flow in Tubular Furnace

[urbanos]

Hello,

its the first project I have as chemical engineer and since my transport phenomena courses has been quite a while, so I am having a hard time findind the solution to that phenomenically simple problem.

I have a quartz tube inside an electrical furnace. I want my gases to reach a certain temperature (800 oC). What is the necessary length in order for the gas to reach that temperature. Assuming that I know all the physical properties, flow rate, Inlet Temperature etc. Whats the formulas I have to use??? I dont write any number to keep it simple.

from the research that I have done:
from Perrys Handbook I used these 2 formulas shown in the picture.

but the numbers I am getting are wrong!!!

Please any help would be appreciated!

 

[Tauwen]

For some reason I can't see the picture with the used formulas, so some guidelines in general for solving it with minimal software background:
- You need to calculate the heat transfer properties (e.g.: h.t.coef.)
- choose a small length fraction and calculate heat transfer assuming that the gas temp is constant in this segment and the its temp only increases on the exit point
- with the exit temp calculate the next segment and so on... the smaller the chosen length the more accurate result you get. (Obviously use so much segments as needed to get the 800°C on the end.)

I know its not the most elegant solution, but it simple and can be done with the "most commonly used spreadsheet application" (I'm trying not to promote...)

 

[Tauwen]

ahh... I forgot: if the inlet - outlet temperature difference of the tubular furnace is significant than you must recalculate the temp dependent properties of the gas and everything depending on them for the segments.

 

[25362]

May be you can extract some info from the following links:

http://www.watlow.com/downloads/en/specsheets/hanhtt0813.pdf

http://www.watlow.com/downloads/en/catalogs/heaters.pdf

http://www.sciencedirect.com/science/article/pii/001793106290087X