Thermal Processing and Kinetics

In an HTST milk pasteurizer, milk flows through a holding tube of inside diameter $d = 0.05\text{ m}$ (cross-sectional area $A = \frac{\pi}{4}(0.05)^2 \approx 0.0019635\text{ m}^2$) at volumetric flow rate $Q = 0.0019635\text{ m}^3/\text{s}$ (velocity $v = Q/A = 1.0\text{ m/s}$). For minimum holding time $t = 15\text{ seconds}$, the minimum required holding tube length in meters is: