  The mean radial component of relative velocity (MRV) between pairs of
inertial particles is studied, where the particles are advected by turbulent
flow and undergo collision-and-coagulation. A previously proposed
phenomenological model of MRV for low-inertia particles
\citep{saw2022intricate} is corrected (improved) and shown to produce better
predictions of the MRV as a function of particle separation distance $r$. Using
direct numerical simulation (DNS), the relationship between the MRV and
particle/turbulent parameters is studied. For particles with near-zero Stokes
numbers ($St$), the MRV is roughly independent of $St$. At larger $St$, the
magnitude of MRV increases with $St$, particularly when $St>0.2$. Assuming that
the relative particle velocities are derived from fluid velocity differences
associated with a nominal resonant length scale, an empirical relation between
$St$ is obtained: $d+\alpha St^{\beta}$, where $\beta\approx1.86$. Coupled with
this empirical result, the aforementioned MRV model could be extended to
predict MRV for any finite $St$, and we show that the predictions are accurate
against the DNS results. Our results also suggest that the extended model could
also accurately account for possible Reynolds number ($Re_{\lambda}$) effect by
simply allowing $\alpha$ and $\beta$ to be functions of $Re_{\lambda}$.
Additionally, when the particle diameter is smaller than the Kolmogorov length
scale, the MRV for particles with the same St is independent of the particle
diameter. The analysis under different Reynolds numbers
($Re_{\lambda}=84,124,189$) reveals that for particles with $St\ll1$, the MRV
is $Re_{\lambda}$-independent. For larger $St$, $Re_{\lambda}$ dependence is
observed such that the coefficients $\alpha$ and $\beta$ decrease with
$Re_{\lambda}.
