In: Mechanical Engineering
A thin-walled tube with a diameter of 6 mm and length of 20 m is
used to carry exhaust gas from a smoke stack to the laboratory in a
nearby building for analysis. The gas enters the tube at 200°C and
with a mass flow rate of 0.001 kg/s. Autumn winds at a temperature
of 15°C blow directly across the tube at a velocity of 7 m/s.
Assume the thermophysical properties of the exhaust gas are those
of air.
(a) Estimate the average heat transfer coefficient for the exhaust
gas flowing inside the tube.
(b) Estimate the heat transfer coefficient for the airflowing
across the outside of the tube.
(c) Estimate the overall heat transfer coefficient U and the
temperature of the exhaust gas when it reaches the
laboratory.(Note: 90°C is a reasonable guess for the tube
temperature.)
What is the value for the Nusselt number on the inside of the tube? N ui =
What is the average inside heat transfer coefficient, in W/m2·K? h i =
What is the value of the Nusselt number on the outside of the tube? N u o =
What is the average outside heat transfer coefficient, in W/m2·K? h o =
What is the overall heat transfer coefficient, U , in W/m2·K? U =
What is the temperature of the gas at the outlet of the tube, in °C? T m, o =
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