al power plant, at 80°C enters a 15-cm-diameter a ations assume a pipe at a rate

Question

al power plant, at 80°C enters a 15-cm-diameter a ations assume a pipe at a rate of 8.5 kg/s and leaves alua rof 35 C. Is this a good assumption jected back to the ground. Windy air pipe. Disregarding radiation, determis inders and Spheres laminar flow of air across a hot circular Considd int on the cylinder will the heat transfer ould your answer be if the flow were tur- What diameter steam pipe whose external T-15-C omg 90 C passes through some open area e against the winds. Determine the rate of rom the pipe per unit of its length when the air is A long and 7 C and the wind is blowing across the FIGURE P19-46 Using an appropriate cal convecti of 50 km/h. placed in a cross ·A, at 20°C (1 atm) with velocity of io m/s. The rod 19-47 A 6-mm-diameter electri an electric current of 50 A and has f 5 mm and its surface has an emissivity of length. Determine the surface ten a windy day when the air tempera 1611 sted from the rod is 16000 whn, determine the blowing across the transmission li heated long cylindrical rod is ture, andor eature, a e upper surface of a f of the plate length 4 ocal convelondiamie surrounding temperature is 20°C and the heat ture of the rod. Evaluate the air properties person extends his uncovered arms into the he 10 C A pede at 54F and 20 mph in order to feel nature outside at 54°F and 20 mph in order to feel nature Initially, the skin temperature of the arm is 86°F urface temperature is a free sted to . osc treamag the arm as a 2-ft-long and 3-in-diameter cylinder. r has a free 10°C, respectively sfer coefficients at luate the air prop- e film temperature Ively.rmine the rate of heat loss from the arm. lines 54 F, 20 mph FIGURE P19-47 86 F Reconsider Prob. software, investig 19-48 velocity on the surface temperat velocity vary from 10 km/h to 8 perature as a function of wi results. convection heat erature, and the ing the location ocal convection 19-49 A long aluminum wire at a temperature of 280°C. The flow at 20°C at a velocity of heat transfer from the wire to t is first exposed to the air. FIGURE P19-44E

Explanation / Answer

19-44

Assumptions

1 Steady operating conditions exist.

2 Radiation effects are negligible.

3 Air is an ideal gas with constant properties.

4 The arm is treated as a 2-ft-long and 3-in-diameter cylinder with insulated ends.

5 The local atmospheric pressure is 1 atm. Properties

The properties of air at 1 atm and the film temperature of (Ts + T)/2 = (86+54)/2 = 70F are

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