The heat loss from a boiler is to be held at a maximum of 900btu/h ft2 of wall area. what thickness of asbestos (k= 0.10 btu/h ft ℉) is required if the inner and outer surfaces of the insulation are to be 1600 and 500℉, respectively? now if a 3-in.-thick layer of kaolin brick (k= 0.07 btu/h ft ℉) is added to the outside of the asbestos, what heat flux will be result if the outside surface of the kaolin is 250℉? what will be the temperature at the interface between the asbestos and kaolin for this condition?

What is the function of the commutator in a dc motor? a. to spin the magnet b. to change direct current into alternating current c. to change alternating current into direct current d. to spin the wire coil

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Asheet of steel 1.5 mm thick has nitrogen atmospheres on both sides at 1200oc and is permitted to achieve a steady-state diffusion condition. the diffusion coefficient for nitrogen in steel at this temperature is 6 x 10- 11 m2 /s, and the diffusion flux is found to be 1.2 x 10-7 kg/m2 -s. also, it is known that the concentration of nitrogen in the steel at the high-pressure surface is 4 kg/m3 . how far into the sheet from this high-pressure side will the concentration be 2.0 kg/m3 ? assume a linear concentration profile.