Chapter 13, Problem 13.137P

A grain dryer consists of a long semicircular duct of radius $R=1\text{m}$ . One-half of the base surface consists of an electrically heated plate of emissivity ${\epsilon }_p=0.8$ , while the other half supports the grain to be dried, which has an emissivity of ${\epsilon }_g=0.9$ . In a batch drying process for which the temperature of the grain is
$T_g=330\text{K}$ , 2.50 kg of Water are to be removed per meter of duct length over a 1-h period.

(a) Neglecting convection heat transfer, determine the required temperature T_pof the heater plate.
(b) If the water vapor is swept from the duct by the flow of dry air, what convection mass transfer coefficient h_mmust be maintained by the flow?
(c) If the air is at 300 K, is the assumption of negligible convection justified?