1-mm-diameter cylindrical resistor, insulated with a sheath of thermal conductivity, k, of 0.12 W/m-K, is located in an evacuated enclosure. The surface emissivity of the sheath is 0.85. The resistor is maintained at 450 K and the enclosure is at 300 K. What is the radius of the sheath that maximises the rate of heat loss from the resistor? Evaluate the corresponding maximum heat rate per unit length of the resistor and the sheath surface temperature. Determine the value of the parameter hirerlk where h, is the linearised radiation heat transfer coefficient at the critical radius, rer. Comment on your results. State all assumptions made. What is the rate of heat loss per unit length from the uninsulated resistor if its surface emissivity is the same as the sheath surface of the insulated resistor?

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Conduction and Convection

When energy travels from one object to another it is said to have undergone heat transfer. Heat transfer is nothing but the transfer of thermal energy or internal energy from one thing to another, like e.g., when a vessel with water, kept on top of a burner, heats up because of the flame underneath it.