Tech. Book for Pyrolysis

[lihy213]

Dear team,
I am confused about the meaning of $\alpha^{\prime}$ in the following equations, which are from FDS6.9.1 Tech. Book Section 7.2.4. I can't find the implication of it from the context.

[rmcdermo]

It's just a dummy index for summation over tracked species.

[lihy213]

In the verification guide volume, section 12.4.2, the evaporation rate doesn't contain the term in the equation 7.42 but times a surface area $LW$. Why it should be this?

[drjfloyd]

7.42 is a generic equation for multiple component liquids. If you just have a pure liquid (one species) then B becomes (Y_sv - Y_g)/(1-Y_sv) so (Y_sv + (Y_sv - Y_g)/B) = (Y_sv + (Y_sv - Y_g) * (1-Y_sv)/(Y_sv-Y_g)) = Y_sv + (1-Y_sv) = 1

[lihy213]

So the 7.42 needs a term of area in the RHS of $\dot m_{\alpha}^{\prime\prime}$

[drjfloyd]

No. Double prime is a standard math convention for a per unit area quantity like having a dot is a standard convention for a rate quantity. So m dot double prime is mass rate per unit area. In 12.4.2 there is no double prime. It is just the rate. To go from rate per unit area to rate you must multiply by area.

[lihy213]

Since both of them are called evaporation rate in the Tech.Book, so it makes me confused. Now I understand.