Typical value free air convection heat transfer coefficient

[Askara]

whats would be typical value for free air convection heat transfer coefficient at high temperature of 1000 degree c?

let say i have a vertical cylinder of diameter 5 cm and 3 cm high. and i heat it to 1000 degree c. the room temperature is 20c . what would the convection heat transfer coefficient be?

 

[AlephZero]

Pick whatever formula you like best from http://en.wikipedia.org/wiki/Heat_transfer_coefficient

Or guess a number between 5 and 25 W/m^2.K, according to http://www.engineeringtoolbox.com/convective-heat-transfer-d_430.html

If you want an "accurate" value, you need to find a correlation based on measurements similar to your actual situation. For eaxmple your very short cylinder might be better approximated as a sphere than as a long cylinder ignoring end effects.

 

[russ_watters]

Note that at that temperature, radiation is probably a much bigger factor than convection, so you're going to want to calculate that.

 

[Askara]

the thing is engineering box say 5 and 25 W/m^2.K, i have seen some website say 5 and 50 W/m^2.K, and wikipedia 10-100 W/m^2.K so i don't really know what to chooese.

plus onvection heat transfer coefficient increase with temperature, it may be 25 W/m^2.K at 20-200 degree c but it will be higher at 1000 degree c.

 

[russ_watters]

It's a very difficult thing to estimate. I'd pick something conservative inside all three ranges. Like, 20.

What exactly the purpose of this question? Ie, how much accuracy is required? Can you measure instead of calculating? Use a controller?

 

[Askara]

russ_watters thanks, i alway just assumed radiation doesn't matter much but actually as you said, is it much bigger factor than convection. that's why the data i got doesn't match the result from convection