Yes, just to add a bit more on the # particles / sec:
From the injection panel I see you have a surface injection. Fluent injects 1 parcel per time-step per cell face. So from what I remember, it'd be as follows:

Let's say your surface is composed of 500 cell faces, and that you have 10 diameters in the RR distribution. Imagine your particle injection time-step is 1ms.
Then # particles / sec = 500 * 10 / 0.001 s = 5e6 [s^-1]
Particle mass = pi / 6 * rho_p *d_p^3 [kg]

So based on m_dot [kg/s] , different d_p (based on RR distribution) will be injected to satisfy the mass flow rate. You see you still need to provide particle velocity [m/s] ? That's why you need it as independent input.

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