15.13 A vacuum chamber, as used in sputtering electrically conducting thin films on microcircuits, is comprised of a baseplate maintained by an electrical heater at T s  = 300 K and a shroud within...

15.13
A vacuum chamber, as used in sputtering electrically conducting thin films on microcircuits, is comprised of a baseplate

maintained by an electrical heater at
T
s
 = 300 K and a shroud within the enclosure maintained at 77 K by a liquid-nitrogen (LN2) coolant loop. LN2 enters as a saturated liquid, experiences evaporation, and exits the loop as saturated vapor. The baseplate, insulated on the lower side, is 0.3 m in diameter and has an emissivity of å = 0.25.

(a)
How much electrical power
P
e
must be provided to the baseplate heater?

(b)
At what rate must liquid nitrogen be supplied to the shroud if its heat of vaporization (h
fg) is 125 kJ/kg?

(c)
To reduce the liquid-nitrogen consumption, it is proposed to bond a thin sheet of aluminum foil (å  =0.09) to the baseplate. Will this have the desired effect?