# Transient Velocity for non spherical particles

Non-spherical particles can have spherical shapes or completely random and strange shapes that from now on are referred as non-spherical shapes. For axisymmetric shapes Gabitto and Tsouris finf it convient to use the aspect ratio,E , defined as the ratio of length projected on the axis of symmetry to the maximum diameter normal to the axis.

Wadell also proposed the degree of sphericity defined as

$Ø=\frac{A_V}{A_p}$

where $A_V$ is the surface of a sphere of the same volume as the non-spherical particle. This sphericity term is considered the best for isometrically shaped particles. Using this parameter, Haider and Levenspiel Presented a $C_D$ vs $R_e$ correlation. Which is as follows

$C_D=\frac{24}{R_e}[1+0.1118(R_eK_1K_2)^0.65657]+\frac{0.4305}{1+\frac{3305}{R_eK_1K_2}}$

Where the used $C_D$ and $R_e$ are based on the equal volume sphere diameter called volumetric diameter. $K_1$ and $K_2$ are shape factors applicable in sphericity for solids of spherical shape for non-shperical shpaes $K_1$ and $K_2$ are functions of the sphericity and particle orientation.

Chien, re-analysing pre-existing data in the petroleum engineering & processing literature proposed the following expression for the drag coeffiecient

$C_D=\frac{30}{R_e}+67.289exp(-5.03Ø)$

The later expression can be used to find a transient velocity profile. This together with the transient velocity method yields.

$\lambda_{non}=\frac{\lambda}{n_1}u_{max_{non}}=\frac{u_{max}}{n_1}$

$n_1=\frac{[1+0.1118(R_eK_1K_2)^0.65657]+\frac{0.4305}{1+\frac{3305}{R_eK_1K_2}}}{K_1K_2}$

For Drag coefficient by Ganser we have :

$\frac{du}{dt}=n_2-n_3u-n4u^2$

For the drag coefficient by chen, which by calculating the constans n_2,n_3 and n_4 would give a perfect fit.