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