(i) Explain briefly the concept of critical thickness of insulation and state any two applications of the same.
The critical thickness of insulation refers to the minimum thickness of insulation required to prevent significant heat transfer through a material. It is the point at which the rate of heat transfer through the insulation is minimized.
Two applications of the critical thickness of insulation are:
1. Building insulation: In construction, the critical thickness of insulation is used to determine the appropriate thickness of insulation material to be used in walls, roofs, and floors. By ensuring that the insulation thickness exceeds the critical thickness, energy loss through heat transfer can be minimized, resulting in improved energy efficiency and reduced heating or cooling costs.
2. Industrial processes: In industrial settings, the critical thickness of insulation is important for equipment and pipelines that transport fluids or gases at different temperatures. By applying insulation with a thickness greater than the critical thickness, heat loss or gain can be minimized, improving the efficiency of the process and reducing energy consumption.
(ii) A 6 cm long copper rod (k = 300 W/mK) 6mm in diameter is exposed to an environment at 20°C. The base temperature of the rod is maintained at 160°C. The heat transfer coefficient is 20 W/m2K. Calculate the heat given by the rod and efficiency and effectiveness of the rod.