Paradichlorobenzene melts at 53°C, while orthodichlorobenzene melts at 17.6°C. They form a eutectic of 87.5 wt% of the ortho isomer at 23°C. The normal boiling points of these two isomers differ by about 5°C. A mixture of 80 wt% of the para isomer at the saturation temperature of 43°C is fed to the top of a falling-film crystallizer, where coolant enters at 15°C. If 8-cm i.d. tubes are used, determine the time for the crystal-layer thickness at the top of the tube to reach 2 cm. Which isomer will crystallize? From Perry’s Chemical Engineers’ Handbook, ρc = 1:458 g/cm² and ΔH_f = 29:67 cal/g. Crystal thermal conductivity is 0.15 Btu/h-ft-°F for either isomer.