Answer to Question #183121 in Mechanical Engineering for luke

Question

A bakelite coating is to be used with a 10mm diameter conducting rod whose surface is maintained at 200C by passage of an electrical current. The rod is in a fluid at 25C and the convection coefficient is 140W/m2-K. What is the critical radius associated with the coating? (millimeters) *

Answer 1

conducting rod diameter, D₁ = 10mm

conducting road surface maintained at T_i = 200°C

rod subjected to a fluid T_∞ = 25°C, h = 140 W/m²K

bakelite thermal conductivity, k = 1.4 W/m²K

Since the radii of the bare and insulated rod are assumed equal, critical radius can be found as;

r_critical = $\dfrac{k}h$ = $\dfrac{1.4}{140}$ = 0.01m