# Calculation Methods - Packed Bed

Packed beds exhibit a pressure loss as the fluid flows through the bed. FluidFlow uses the Ergun equation to estimate the friction factor and pressure loss. The Ergun equation is commonly expressed as: ΔP = fp Hb ρ Vs 2 (ε 3/(1-ε) / Dp where fp is the friction factor and is defined by the equation: fp = 150/Rep + 1.75 and the Reynolds number is defined as: Rep = Dp Vs ρ / ((1-ε) μ)