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All Textbook Solutions for Principles of Heat Transfer (Activate Learning with these NEW titles from Engineering!)
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5.43 A refrigeration truck is traveling at 130 km/h on a desert highway where the air temperature is . The body of the truck is idealized as a rectangular box 3 m wide, 2.1 m high, and 6 m long, at a surface temperature . Assume that (1) the heat transfer from the front and back of the truck is neglected, (2) the stream does not separate from the surface, and (3) the boundary layer is turbulent over the whole surface. Calculate the required cooling rate of the refrigeration unit.
5.44PThe air-conditioning system in a Chevrolet van for use in desert climates is to be sized. The system is to maintain an interior temperature of 20C when the van travels at 100 km/h through dry air at 30C at night. If the top of the van is idealized as a flat plate 6 m long and 2 m wide and the sides as flat plates 3 m tall and 6 m long, estimate the rate at which heat must be removed from the interior to maintain the specified5.46P5.47P5.48P5.49P5.50P5.51P5.52P5.53P5.54P5.55PDetermine the rate of heat loss from the wall of a building resulting from a 16 km/h wind blowing parallel to its surface. The wall is 24 m long and 6 m high, its surface temperature is 27C, and the temperature of the ambient air is 4C.5.57P5.58P5.59P5.60P5.61P5.62P5.63P5.64P5.65P5.66P5.67P5.68P5.69P5.70P5.1DP5.2DP5.3DP6.1 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.
A mercury-in-glass thermometer at 40C(OD=1cm) is inserted through a duct wall into a 3 m/s airstream at 66C. This can be modelled as a cylinder in cross-flow, as shown in the figure. Estimate the heat transfer coefficient between the air and the thermometer.6.3 Steam at 100 kPa and is flowing across a 5-cm- OD tube at a velocity of 6 m/s. Estimate the Nusselt number, the heat transfer coefficient, and the rate of heat transfer per meter length of pipe if the pipe is at .
An electrical transmission line of 1.2-cm diameter carries a current of 200 amps and has a resistance of 310-4 ohm per meter of length. If the air around this line is at v, determine the surface temperature on a windy day, assuming a wind blows across the line at 33 km/h.6.5P6.6P6.7P6.8P6.9P6.10P6.11P6.12P6.13P6.14P6.15P6.16P6.17P6.18P6.19P6.20P6.21P6.22P6.23P6.24P6.25P6.26P6.27P6.28P6.29P6.30P6.31P6.32P6.33P6.34P6.35P6.36P6.37P6.38P6.39P6.40P6.41P6.42P6.43P6.44P6.45P6.46P6.47P6.48P6.49P6.50P6.51P6.52P6.53P6.54P6.55P6.1DP6.2DP6.3DP6.4DP7.1 To measure the mass flow rate of a fluid in a laminar flow through a circular pipe, a hot-wire-type velocity meter is placed in the center of the pipe. Assuming that the measuring station is far from the entrance of the pipe, the velocity distribution is parabolic:
where is the centerline velocity (r = 0), r is the radial distance from the pipe centerline, and D is the pipe diameter.
Derive an expression for the average fluid velocity at the cross section in terms of and D. (b) Obtain an expression for the mass flow rate. (c) If the fluid is mercury at , D = 10 cm, and the measured value of is 0.2 cm/s, calculate the mass flow rate from the measurement.
7.2P7.3P7.4P7.5P7.6P7.7P7.8P7.9P7.10P7.11P7.12P7.13P7.14P7.15P7.16PDetermine the rate of heat transfer per meter length to a light oil flowing through a 2.5-cm-ID, 60-cm-long copper tube at a velocity of 0.03 m/s. The oil enters the tube at 16C, and the tube is heated by steam condensing on its outer surface at atmospheric pressure with a heat transfer coefficient of 11.3 kW/m K. The properties of the oil at various temperatures are listed in the following table: Temperature, T(C) 15 30 40 65 100 (kg/m3) 912 912 896 880 864 c(kJ/kgK) 1.80 1.84 1.925 2.0 2.135 k(W/mK) 0.133 0.133 0.131 0.129 0.128 (kg/ms) 0.089 0.0414 0.023 0.00786 0.0033 Pr 1204 573 338 122 557.18P7.19P7.20P7.21P7.22P7.23P7.24P7.25P7.26P7.27P7.28P7.29P7.30P7.31P7.32P7.33P7.34P7.35P7.36P7.37P7.38P7.39P7.40P7.41P7.42P7.43 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?
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8.12 An electric room heater has been designed in the shape of a vertical cylinder 2 m tall and 30 cm in diameter. For safety, the heater surface cannot exceed . If the room air is at , find the power rating of the heater in watts.
8.13P8.14P8.15 A mercury bath at is to be heated by immersing cylindrical electric heating rods, each 20 cm tall and 2 cm in diameter. Calculate the maximum electric power rating of a typical rod if its maximum surface temperature is .
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10.1 In a heat exchanger, as shown in the accompanying figure, air flows over brass tubes of 1.8-cm 1D and 2.1-cm OD containing steam. The convection heat transfer coefficients on the air and steam sides of the tubes are , respectively. Calculate the overall heal transfer coefficient for the heal exchanger (a) based on the inner tube area and (b) based on the outer tube area.
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10.3 A light oil flows through a copper tube of 2.6-cm ID and 3.2-cm OD. Air flows perpendicular over the exterior of the tube as shown in the following sketch. The convection heat transfer coefficient for the oil is and for the air is . Calculate the overall heat transfer coefficient based
on the outside area of the tube (a) considering the thermal resistance of the tube and (b) neglecting the resistance of the tube.
10.4PWater flowing in a long, aluminum lube is to be heated by air flowing perpendicular to the exterior of the tube. The ID of the tube is 1.85 cm, and its OD is 2.3 cm. The mass flow rate of the water through the tube is 0.65kg/s, and the temperature of the water in the lube averages 30C. The free-stream velocity and ambient temperature of the air are 10m/sand120C, respectively. Estimate the overall heat transfer coefficient for the heat exchanger using appropriate correlations from previous chapters. State all your assumptions.Mot water is used to heat air in a double-pipe heat exchanger as shown in the following sketch. If the heat transfer coefficients on the water side and on the air side are 550W/m2Kand55W/m2K respectively, calculate the overall heat transfer coefficient based on the outer diameter. The heat exchanger pipe is 5-cm, schedule 40 steel (k=54W/mK) with water inside.10.7P
10.8 The heat transfer coefficient of a copper tube (1.9-cm II) and 2.3-em OD) is on the inside and on the outside, but a deposit with a fouling factor of (based on the tube outside diameter) has built up over time. Estimate the percentage increase in the overall heat transfer coefficient if the deposit were removed.
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