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## Main Question or Discussion Point

Hello,

The particle Reynolds number makes me confused, and I hope someone can help me with this, please! Reynolds number is calculated by Re = ρ

Thank you in advance.

The particle Reynolds number makes me confused, and I hope someone can help me with this, please! Reynolds number is calculated by Re = ρ

_{f}UD/μ where U is particle velocity, D can be particle diameter, and ρ_{f}and μ are density and viscosity of the continuous fluid. How I can Reynolds number if the particle velocity U is unknow? Is it correct to calculate first the particle terminal velocity U_{t}= (gD^{2}(ρ_{p}-ρ_{f}))/(18μ) , (where ρ_{p}is the density of the particle), then to use the calculated U_{t}to calculate the Reynolds number? I need to calculate the particle's terminal velocity but stuck with the Re number.Thank you in advance.