Wet pharmaceutical tablets are processed in an infrared dryer consisting of a cylindrical drum (left(D_{d}=0.5 mathrm{~m} ight))

Question:

Wet pharmaceutical tablets are processed in an infrared dryer consisting of a cylindrical drum \(\left(D_{d}=0.5 \mathrm{~m}\right)\) that rotates slowly about a stationary cylindrical infrared heater \(\left(D_{h}=0.1 \mathrm{~m}\right)\). The outside of the drum is wellinsulated. Moisture from the tablets is transferred to nitrogen that flows axially through the dryer. As the drum rotates, the tablets tumble due to the combined effects of rotational and gravitational acceleration, forming a thin layer of pharmaceutical product that covers half of the drum's lower interior surface. Consider tablets of temperature \(T_{p}=320 \mathrm{~K}\) and an emissivity of \(\varepsilon_{p}=0.95\). If the flow of nitrogen maintains a convection mass transfer coefficient of \(0.025 \mathrm{~m} / \mathrm{s}\) on the surface of the tablets, what is the evaporation rate per unit drum length? Neglecting convection heat transfer, determine the heater temperature, \(T_{h}\), that must be maintained to drive the evaporation. What is the temperature of the inner drum surface not covered with tablets? The infrared heater has an emissivity \(\varepsilon_{h}=0.85\). The view factor of a long half-cylinder of diameter \(D_{d}\) to itself, in the presence of a concentric coaxial cylinder of diameter \(D_{h}\), may be expressed as

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