A consulting firm has designed a steam system for a new process unit at your plant. Super heated steam is delivered to the unit via a 3-in. steel pipe that has an ID of 3.068 in. and an OD of 3.5 in. The steam is at 800F with a heat-transfer coefficient of 100 Btu/ h*ft^2*F. The pipe is covered with a 0.5-in. thick layer of Type I insulation having an R-value of 1, followed by a 1-in. thick layer of Type II insulation having an R-value of 4. The steam line will be exposed to ambient air at 80F with a heat-transfer coefficient of 5 Btu/ h*ft^2*F. Design specifications call for the external surface temperature of the insulation to be no greater than 110F and the manufacturer’s literature states that Type I insulation is suitable for temperatures up to 1200F while Type II insulation is suitable for temperatures up to 500F. Your job is to evaluate the consulting firm’s design. Proceed as follows: (a) Calculate the rate of heat loss from the steam line per foot of pipe length that will actually occur if the consulting firm’s design is implemented. (b) Calculate the appropriate temperatures needed to determine whether or not all design and material specifications have been met. (c) State whether or not the consulting firm’s design is acceptable and the reason(s) for your conclusion. In these calculations, neglect the thermal resistance of the pipe wall, contact resistances, and radiation effects.
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A consulting firm has designed a steam system for a new process unit at your plant. Super heated steam is delivered to the unit via a 3-in. steel pipe that has an ID of 3.068 in. and an OD of 3.5 in. The steam is at 800F with a heat-transfer coefficient of 100 Btu/ h*ft^2*F. The pipe is covered with a 0.5-in. thick layer of Type I insulation having an R-value of 1, followed by a 1-in. thick layer of Type II insulation having an R-value of 4. The steam line will be exposed to ambient air at 80F with a heat-transfer coefficient of 5 Btu/ h*ft^2*F. Design specifications call for the external surface temperature of the insulation to be no greater than 110F and the manufacturer’s literature states that Type I insulation is suitable for temperatures up to 1200F while Type II insulation is suitable for temperatures up to 500F. Your job is to evaluate the consulting firm’s design. Proceed as follows:
(a) Calculate the rate of heat loss from the steam line per foot of pipe length that will actually occur if the consulting firm’s design is implemented.
(b) Calculate the appropriate temperatures needed to determine whether or not all design and material specifications have been met.
(c) State whether or not the consulting firm’s design is acceptable and the reason(s) for your conclusion. In these calculations, neglect the thermal resistance of the pipe wall, contact resistances, and radiation effects.
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