Compare heat transfer at the same wire-surface temperature and ambient temperature before and after covering. A plastic sleeve of outer radius r0 = 1 mm covers a wire (radius r = 0.5 mm) carrying electric current. Thermal conductivity of the plastic is 0.15 W/m-K. The heat transfer coefficient on the outer surface of the sleeve exposed to air is 25 W/m2-K. Due to the addition of the plastic cover, the heat transfer from the wire to the ambient will
increase
For cylindrical insulation, critical radius is \(r_c=k/h=0.15/25=0.006\ \mathrm m=6\ \mathrm{mm}\). Increasing outer radius from 0.5 to 1 mm remains below rᶜ, reducing total thermal resistance. At fixed wire and ambient temperatures, heat transfer therefore increases.
Important Questions from Critical Thickness of Insulation
Two insulating materials of thermal conductivity K and 2K are available for lagging a pipe carrying a hot fluid. If the radial thickness of each material is the same.
For pipes, the radius of the pipe is taken higher than the critical radius, so that any insulation added will ______.
The insulating ability of an insulator with the presence of moisture would
A steam pipe is to be insulated by 2 insulating materials put over each other. For best results
The critical radius of insulation signifies
