Water at 40°F is to flow through a 1^1/2-in. schedule 40 steel pipe. The outside surface of the pipe is to be insulated with a 1-in.-thick layer of 85% magnesia and a 1-in.-thick layer of packed glass wool, k = 0.022 Btu/hft °F. The surrounding air is at 100°F.
a. Which material should be placed next to the pipe surface to produce the maximum insulating effect?

b. What will be the heat flux on the basis of the outside pipe surface area? The convective heat-transfer coefficients for the inner and outer surfaces are 100 and 5 Btu/h ft °F, respectively.