Question:-
It is desired to increase the heat dissipation rate over the surface of the an electronic device of spherical of 5 mm radius exposed to convection with h = 10w/m2 k by encasing it in a spherical sheath of conductivity 0.04 w/mk. For maximum heat flow the diameter of the should be
Option (A)
18 mm
Option (B)
16 mm
Option(C)
12 mm
Option(D)
8 mm
Correct Option:
(B)
Question Solution:
Critical radius for sphere
Rc = (2k/h) = (2 x 0.04)/10 = 0.008m
\ diameter – 2rc = 16mm
question-answer-faq-2786