A long pyroceram rod of diameter 20 mm is clad with a very thin metallic tube for mechanical protection. The bonding between the rod and the tube has a thermal contact resistance of R_t.c = 0.12 m ∙ K/W.

(a) If the rod is initially at a uniform temperature of 900 K and is suddenly cooled by exposure to an airstream for which T_∞ = 300 K and h = 100 W/m² ∙ K, at which time will the centerline reach 600 K?

(b) Cooling may be accelerated by increasing the airspeed and hence the convection coefficient. For values of h = 100, 500, and 1000 W/m² ∙ K, compute and plot the centerline and surface temperatures of the pyroceram as a function of time for o < t < 300 s. Comment on the implications of achieving enhanced cooling solely by increasing h.

Transcribed Image Text:

Thin metallic tube Ceramic rod -Bonding interface D = 20 mm