Theory for pyrolysis in FDS Verification Guide

[lihy213]

Dear contributors,

In the FDS Verification Guide, page 171, it shows that "For cylindrical surfaces, the volume per unit surface area is r/2", if it means the top and bottom surface of a cylinder are not included, or the result should be $\pi r^2h\over {2\pi r^2+2\pi rh}$, h is the height of the cylinder.

Kind regards,
LI

[drjfloyd]

Ends are not included
V = pi r^2 h
A = 2 pi r h
V/A = r/2

[lihy213]

Thanks! But, could you please explain it? 😄

[mcgratta]

Two reasons -- first, the area of the ends is usually much smaller than the area of the side. Second, the assumptions about radiative and convective heat transfer are based on the assumption that the length is significantly longer than the diameter. If that assumption is not appropriate for you, you may want to model the particle as a sphere.

[lihy213]

Thanks for your kind reply! Now it becomes clear. 😄