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In: Mechanical Engineering

A thin-walled tube with a diameter of 6 mm and length of 20 m is used...

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 0.005 kg/s. Autumn winds at a temperature of 15°C blow directly across the tube at a velocity of 5 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.)

1.What is the value for the Nusselt number on the inside of the tube?

2.What is the average inside heat transfer coefficient, in W/m2·K?

3.What is the value of the Nusselt number on the outside of the tube?

4.What is the average outside heat transfer coefficient, in W/m2·K?

5.What is the overall heat transfer coefficient, U, in W/m2·K?

6.What is the temperature of the gas at the outlet of the tube, in °C?

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