A 2-m * 1.5-m section of wall of an industrial furnaceburning natural gas is not insulated, and the temperatureat the outer surface of this section is measured to be 80°C.The temperature of the furnace room is 30°C, and the combinedconvection and radiation heat transfer coefficient at thesurface of the outer furnace is 10 W/m2·K. It is proposed toinsulate this section of the furnace wall with glass wool insulation(k = 0.038 W/m·K) in order to reduce the heat lossby 90 percent. Assuming the outer surface temperature ofthe metal section still remains at about 110°C, determine thethickness of the insulation that needs to be used.The furnace operates continuously and has an efficiency of78 percent. The price of the natural gas is $1.10/therm (1 therm =105,500 kJ of energy content). If the installation of the insulationwill cost $250 for materials and labor, determine how long it willtake for the insulation to pay for itself from the energy it saves.

A 2-m * 1.5-m section of wall of an industrial furnaceburning natural gas is not insulated, and the temperatureat the outer surface of this section is measured to be 80°C.The temperature of the furnace room is 30°C, and the combinedconvection and radiation heat transfer coefficient at thesurface of the outer furnace is 10 W/m2·K. It is proposed toinsulate this section of the furnace wall with glass wool insulation(k = 0.038 W/m·K) in order to reduce the heat lossby 90 percent. Assuming the outer surface temperature ofthe metal section still remains at about 110°C, determine thethickness of the insulation that needs to be used.The furnace operates continuously and has an efficiency of78 percent. The price of the natural gas is $1.10/therm (1 therm =105,500 kJ of energy content). If the installation of the insulationwill cost $250 for materials and labor, determine how long it willtake for the insulation to pay for itself from the energy it saves.

Physics for Scientists and Engineers: Foundations and Connections

1st Edition

ISBN:9781133939146

Author:Katz, Debora M.

Publisher:Katz, Debora M.

Chapter21: Heat And The First Law Of Thermodynamics

Section: Chapter Questions

Problem 61PQ

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