# IF YOU CANNOT SOLVE THEM ALL THEN PLEASE DONT SOLVE ANY. A hollow aluminum sphere, with…

IF YOU CANNOT SOLVE THEM ALL THEN PLEASE DONT SOLVE ANY.

A hollow aluminum sphere, with an electrical heater in the center, is used in tests to determine the thermal conductivity of insulating materials. The inner and outer radii of the sphere are 0.15 and 0.18 m, respectively, and testing is done under steady-state conditions with the inner surface of the aluminum maintained at 250°C. In a particular test, a spherical shell of insulation is cast on the outer surface of the sphere to a thickness of 0.12 m. The system is in a room for which the air temperature is 20°C and the convection coefficient at the outer surface of the insulation is 30 W/m2.K. If 75W are dissipated by the heater under steady-state conditions, what is the thermal conductivity of the insulation? k; = i W/m-K Physical Properties Mathematical Functions Question 9 View Policies Current Attempt in Progress A stainless steel (AISI 304) tube used to transport a chilled pharmaceutical has an inner diameter of 36 mm and a wall thickness of 2mm. The pharmaceutical and ambient air are at temperatures of 10°C and 23°C, respectively, while the corresponding inner and outer convection coefficients are 400 W/m2K and 8 W/m².K, respectively. Evaluate the properties of the stainless steel at T = 280K (a) What is the heat gain per unit tube length? 9 uninsulated W/m 0.05 W/m-K) is applied to the tube? (b) What is the heat gain per unit length if a 10-mm-thick layer of calcium silicate insulation (ins 9’insulated = W/m Physical Properties Mathematical Functions Question 10 View Policies Current Attempt in Progress A2-mm-thick insulating coating ik 0.13 W/m-K) covers a 2-mm diameter electrical wire. The thermal contact resistance between them is R” 6x 104 m² K/W. The ambient air is at 25°C and has a convective heat transfer coefficient of 7 W/ mK. If the temperature of the insulation cannot exceed 55°C, what is the maximum electric power that can be dissipated per unit length, in W/m? Find the corresponding surface temperature of the wire, in °C. W/m T, = Question 13 View Policies Current Attempt in Progress Large, cylindrical bales of hay used to feed livestock in the winter months are D = 2 m in diameter and are stored end-to-end in long rows. Microbial energy generation occurs in the hay and can be excessive if the farmer bales the hay in a too wet condition. Assuming the thermal conductivity of baled by to be k = 0.04 W/m-K, determine the maximum steady-state hay temperature for (a) dry hay 1 W/m”). (b) moist hay q = 10 W/m?), and (c) wet hay (= 75 W/m² ). Ambient conditions are T, = 0°C and h = 25 W/m².K. (a) Triax.dry = (b) Tmax moist = 8 (c) Tmax, wet = Physical Properties Mathematical Functions