Thermodynamics HW Solutions 617

Thermodynamics HW Solutions 617 - Chapter 7 External Forced...

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Chapter 7 External Forced Convection 7-87E Steam is flowing through an insulated steel pipe, and it is proposed to add another 1-in thick layer of fiberglass insulation on top of the existing one to reduce the heat losses further and to save energy and money. It is to be determined if the new insulation will pay for itself within 2 years. Assumptions 1 Heat transfer is steady since there is no indication of any change with time. 2 Heat transfer is one-dimensional since there is thermal symmetry about the centerline and no variation in the axial direction. 3 Thermal properties are constant. 4 The heat transfer coefficients remain constant. 5 The thermal contact resistance at the interface is negligible. Properties The thermal conductivities are given to be k = 8.7 Btu/h ft °F for steel pipe and k = 0.020 Btu/h ft °F for fiberglass insulation. Analysis The inner radius of the pipe is r 1 = 1.75 in, the outer radius of the pipe is r 2 = 2 in, and the outer
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