Heat and Mass Transfer: Fundamentals and Applications
5th Edition
ISBN: 9780073398181
Author: Yunus A. Cengel Dr., Afshin J. Ghajar
Publisher: McGraw-Hill Education
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Textbook Question
Chapter 8, Problem 67P
Air at
(1atm) enters into a 5-mm-diameter and 10-cm-long circular tube at an average velocity of 5 m/s. The tube wall is maintained at a constant surface temperature of
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Determine the convection heat transfer coefficient for the flow of (a) air and (b) water at a velocity of 2 m/s in an 8-cm-diameter and 7-m-long tube when the tube is subjected to uniform heat flux from all surfaces. Use fluid properties at 25°C.
Air (1 atm) enters into a 5-cm-diameter circular tube at 20°C with an average velocity of 5 m/s. The tube wall is maintained at a constant surface temperature of 160°C, and the outlet mean temperature is 80°C. Estimate the length of the tube.
Water flows at 1 kg/s in a 10 mm diameter tube and is to be heated from 25 to 75 ° C. The
tube surface temperature is maintained at 100 °C.
Using the following properties for the water:
p= 998 kg/m?, Cp = 4171 J/kg K, k = 0.651 W/m K, µs = 4.71 x 104 kg/m s,
Hw = 2.82 x 104 kg/m s and Pr = 3.02.
a) What is the required tube length for these conditions?
b) To design a water heating system, consider using tube diameters in the range from
10 to 30 mm. What are the required tube lengths for water flow rate of 1 kg/s? Plot
the tube length as a function of tube diameter.
c)
Plot the pressure gradient as a function of the tube diameter for the given water flow
rate of 1 kg/s. Assume tube wall is smooth.
Chapter 8 Solutions
Heat and Mass Transfer: Fundamentals and Applications
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- 7.43 Liquid sodium is to be heated from 500 K to 600 K by passing it at a flow rate of 5.0 kg/s through a 5-cmID tube whose surface is maintained at 620 K. What length of tube is required?arrow_forward6.1 Determine the heat transfer coefficient at the stagnation point and the average value of the heat transfer coefficient for a single 5-cm-OD, 60-cm-long tube in cross-flow. The temperature of the tube surface is , the velocity of the fluid flowing perpendicular to the tube axis is 6 m/s, and the temperature of the fluid is . Consider the following fluids: (a) air, (b) hydrogen, and (c) water.arrow_forwardAir enters a 25-cm-diameter 12-m-long underwater duct at 50°C and 1 atm at a mean velocity of 7 m/s, and is cooled by the water outside. If the average heat transfer coefficient is 85 W/m2?K and the tube temperature is nearly equal to the water temperature of 10°C, determine the exit temperature of air and the rate of heat transfer. Evaluate air properties at a bulk mean temperature of 30°C. Is this a good assumption?arrow_forward
- Water flows at 1 kg/s in a 10 mm diameter tube and is to be heated from 25 to 75 ° C. The tube surface temperature is maintained at 100 °C. Using the following properties for the water: p= 998 kg/m?, Cp = 4171 J/kg K, k = 0.651 W/m K, µs = 4.71 x 104 kg/m s, Uw = 2.82 x 104 kg/m s and Pr= 3.02. a) What is the required tube length for these conditions? b) To design a water heating system, consider using tube diameters in the range from 10 to 30 mm. What are the required tube lengths for water flow rate of 1 kg/s? Plot the tube length as a function of tube diameter.arrow_forwardAir (1 atm) entered into a 5-mm-diameter circular tube at an average velocity of 5 m/s. The tube wall is maintained at a constant surface temperature. Determine the convection heat transfer coefficient for (a) a 10-cm-long tube and (b) a 50-cm-long tube. Evaluate the air properties at 50°C.arrow_forwardConsider a 50-mm-diameter and 25-m-long smooth tube that is maintained at a constant surface temperature. Fluids enter the tube at 30°C with a mass flow rate of 0.02 kg/s. Determine the tube surface temperatures necessary to heat water, engine oil, and liquid mercury to the desired outlet tem-perature of 170°C.arrow_forward
- Consider a 10-m-long smooth rectangular tube, with a = 50 mm and b= 25 mm, that is maintained at a constant surface temperature. Liquid water enters the tube at 20°C with a mass flow rate of 0.027 kg/s. Determine the tube surface temperature necessary to heat the water to the desired outlet temperature of 80°C. (Nu = 3.39) "Carrow_forwardHot air at atmospheric pressure and 85°C enters a 10-m-long uninsulated square duct of cross section 0.15 m * 0.15 m that passes through the attic of a house at a rate of 0.1 m3/s. The duct is observed to be nearly isothermal at 70°C. Determine the exit temperature of the air and the rate of heat loss from the duct to the air space in the attic. Evaluate air properties at a bulk mean temperature of 75°C. Is this a good assumption?arrow_forwardWater at 15ºC is to be heated to 65ºC by passing it over a bundle of 4-m-long 1-cm-diameter resistance heater rods maintained at 90ºC. Water approaches the heater rod bundle in normal direction at a mean velocity of 0.8 m/s. The rods arc arranged in-line with longitudinal and transverse pitches of SL 4 cm and ST 3 cm. Determine the number of tube rows NL in the flow direction needed to achieve the indicated temperature rise.arrow_forward
- Air at atmospheric pressure and 27°C enters a 12-m-long, 1.5-cm-ID tube with a mass flow rateof 0.1 kg/s. The tube surface is maintained at a uniform temperature of 90°C. Calculate the average heattransfer coefficient and the rate of heat transfer to the air.arrow_forwardEvaluate the convection heat transfer coefficient for the flow of (a) air and (b) water at a velocity of 5 m/s in an 8-cm-diameter and 10-m-long tube when the tube is subjected to uniform heat flux from all surfaces. Use fluid properties at 25° C and assume fully developed turbulent flow in the entire duct.arrow_forwardWater is flowing through a 25-mm diameter and 10-m long tube. The water enters the tube at 20\deg C with a mass flow rate of 0.2 kg/s. The outlet mean temperature is 60\deg C, and the tube surface temperature is maintained constant. Determine the hydrodynamic and thermal entry.lengths. Is the flow fully developed? What is the convective heat transfer coefficient inside the pipe?arrow_forward
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