$27.$ In a pneumatic conveying system with a diameter of $150$ mm$,$ if the air velocity is $20$ m$/$s and the solid particles conveyed have a density of $2500$ kg$/$m with a mass flow rate of $0\mathrm{.}1$ kg$/$s$,$ calculate the solid loading ratio and then the pressure drop over a $10$ m section.

$29.$ For a trickle bed reactor operating with a liquid superficial velocity of $0\mathrm{.}015$ m$/$s and gas superficial velocity of $1$ m$/$s in a column of $0\mathrm{.}5$ m diameter, first calculate the Reynolds number for the liquid phase. Then, estimate the pressure drop over a $5$ m bed height.