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7. Given a 55-foot long pipe carrying liquid nitrogen through a chemical plant (T = -321 °F) is constructed of iron and insulated by a layer of foamed polyurethane. The

pipe has an inner diameter of 2.5 inches, and the iron has a thickness of ¼ inch. The foam layer is 1.5 inches thick, and the room air outside the foam layer is 75 °F. A. Draw a sketch of the problem including a thermal resistance diagram for heat transfer between the liquid nitrogen and the air. Label each resistance as conduction or convection. B. What is the thermal resistance of the iron pipe? (answer in h-°F/Btu) C. What is the rate of heat transfer (q)? Include a direction. D. What is the surface heat flux, q", at the foam/air interface?

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