Thick fluids such as asphalt and waxes and the pipes in which they flow are often heated in order to reduce the viscosity of the fluids and thus to reduce the pumping costs. Consider the flow of such a fluid through a 100-m-long pipe of outer diameter 30 cm in calm ambient air at 0oC. The pipe is heated electrically, and a thermostat keeps the outer surface temperature of the pipe constant at 25oC. The emissivity of the outer surface of the pipe is 0.8, and the effective sky temperature is −30oC. Determine the power rating of the electric resistance heater, in kW, that needs to be used. Also, determine the cost of electricity associated with heating the pipe during a 10-h period under the above conditions if the price of electricity is $0.09/kWh. Properties The properties of air at 1 atm and the film temperature of (Ts+T∞)/2 = (25+0)/2 = 12.5°C are: k = 0.02458 W/m.oC, ν = 1.448x10-5 m2/s, Pr = 0.7330
Thick fluids such as asphalt and waxes and the pipes in which they flow are often heated in order to reduce the viscosity of the fluids and thus to reduce the pumping costs. Consider the flow of such a fluid through a 100-m-long pipe of outer diameter 30 cm in calm ambient air at 0oC. The pipe is heated electrically, and a thermostat keeps the outer surface temperature of the pipe constant at 25oC. The emissivity of the outer surface of the pipe is 0.8, and the effective sky temperature is −30oC. Determine the power rating of the electric resistance heater, in kW, that needs to be used. Also, determine the cost of electricity associated with heating the pipe during a 10-h period under the above conditions if the price of electricity is $0.09/kWh. Properties The properties of air at 1 atm and the film temperature of (Ts+T∞)/2 = (25+0)/2 = 12.5°C are: k = 0.02458 W/m.oC, ν = 1.448x10-5 m2/s, Pr = 0.7330
Elements Of Electromagnetics
7th Edition
ISBN:9780190698614
Author:Sadiku, Matthew N. O.
Publisher:Sadiku, Matthew N. O.
ChapterMA: Math Assessment
Section: Chapter Questions
Problem 1.1MA
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Thick fluids such as asphalt and waxes and the pipes in which they flow are often heated in order to reduce the viscosity of the fluids and thus to reduce the pumping costs. Consider the flow of such a fluid through a 100-m-long pipe of outer diameter 30 cm in calm ambient air at 0oC. The pipe is heated electrically, and a thermostat keeps the outer surface temperature of the pipe constant at 25oC. The emissivity of the outer surface of the pipe is 0.8, and the effective sky temperature is −30oC. Determine the power rating of the electric resistance heater, in kW, that needs to be used. Also, determine the cost of electricity associated with heating the pipe during a 10-h period under the above conditions if the price of electricity is $0.09/kWh.
Properties The properties of air at 1 atm and the film temperature of (Ts+T∞)/2 = (25+0)/2 = 12.5°C are:
k = 0.02458 W/m.oC, ν = 1.448x10-5 m2/s, Pr = 0.7330
Transcribed Image Text:Tsky = -30°C
T3 = 25°C
ɛ = 0.8
T = 0°C
Asphalf
D=30 cm
L = 100 m
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