A gravity settling chamber consists of a horizontal rectangular duct that is $6 \mathrm{~m}$ long, $3.6 \mathrm{~m}$ wide, and $3 \mathrm{~m}$ high. The chamber is used to trap sulfuric acid mist droplets entrained in an air stream. The droplets settle out as the air passes through the duct and may be assumed to behave as rigid spheres. If the air stream has a flow rate of $6.5 \mathrm{~m}^{3} / \mathrm{s}$, what is the diameter of the largest particle that will not be trapped in the duct?

$\left(ho_{\text {acid }}=1.74 \mathrm{~g} / \mathrm{cm}^{3} ; ho_{\text {air }}=0.01 \mathrm{~g} / \mathrm{cm}^{3} ; \mu_{\text {air }}=0.02 \mathrm{cP} ; \mu_{\text {acid }}=2 \mathrm{cP}\right)$