A_PIPE_OF_OUTSIDE_DIAMETER_20_MM_IS_TO_BE_INSULATED_WITH_ASBESTOS_WHICH_HAS_A_MEAN_THERMAL_CONDUCTIVITY_OF_0.1_W/M_DEGREE._THE_LOCAL_COEFFICIENT_OF_CONVECTIVE_HEAT_TO_THE_SURROUNDINGS_IS_5_W/SQUARE_METER_DEGREE._FIND_THE_CRITICAL_RADIUS_OF_INSULATION_FOR_OPTIMUM_HEAT_TRANSFER_FROM_A_PIPE??$

• A. 10 mm
• B. 20 mm
• C. 30 mm
• D. 40 mm