Frequently Asked Questions and Problems for Practice
Q.1  What is the local Reynolds number? 
Q.2  What are the important dimensionless groups in heat transfer? Explain their physical significance. 
Q.3  What is the difference between Reynolds and Prandtl anologies? 
Q.4  Explain why there is more heat transfer in forced convection as compared to natural convection. 
Q.5  What is DittusBoelter equation and when is it applied? 
Q.6  Water is to be heated from 50^{o}C to 100^{o}C in a smooth hot pipe. The pipe is maintained at a constant temperature above 30^{o}C that of bulk water temperature under the condition of constant heat flux. Calculate the length of the pipe required for heating, if the tube diameter is 0.6 m and the Reynolds number of the water inside the pipe is 95000? 
Q.7  A tube bank having a square array of 100 tubes arranged in an inline position is at 100^{o}C. The diameter and length of the tubes are 15 mm and 100 cm, centre to centre tube spacing is 20 mm. Atmospheric air enters in the tube bank at 25^{o}C and at the free stream velocity of 5.5 m/s. Determine the total heat loss by the tubes. 
Q.8  Water at 15^{o}C flow past a sphere at the free stream velocity of 4 m/s. The diameter and temperature of the sphere are 30 mm and 70^{o}C, respectively. Calculate the heat loss by the sphere. 
Q.9  Atmospheric air flows at 10 m/s of free stream velocity in a rectangular duct having dimensions of 25 cm by 50 cm. The air and wall temperature of the duct are 25 ^{o}C and 50 ^{o}C, respectively. Calculate the mean exit temperature of the air per unit length of the duct. 
Q.10  Air at 25 ^{o}C flows in a 10 mm diameter tube at a Reynolds number of 50,000. If the length of the tube is 100 cm, estimate the average heat transfer coefficient for a constant heat flux at the wall. 
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