Question

Part 1 How fast do small water droplets of 0.23 um (23 x 108 m) diameter fall through the air under standard sea-level conditions? Assume the drops do not evaporate. Repeat the problem for standard conditions at 5000-m altitude. (a) For the condition that the droplets are falling at a constant velocity, what is the relation between the weight ofa drop W, the buoyancy force Fe, and the drag force F? (b) What is the expression for the weight of the droplet in terms of the specific weight of water y and the diameter of the droplet D? (c) What is the expression for the drag force Fin terms of the drag coefficient C, frontal area A, air density p, and velocity U? (d) The droplets are very small and fall very slowly. Assuming that the Reynolds number is small, the drag can be given by the relation CD = 24/Re, where Re = UpDw. Substitute into the relation for F the expression for drag coefficient and the area in terms of diameter. What is the expression for the drag force? (a) F Click here to enter or edit vour answer 2 Click here to enter or edit your answer (c) F- Click here to enter or edit your answer (d) F- Click here to enter or edit vour answer 2 Part 2 (a) Equate the expression for the drag force to that for the weight and solve for the velocity. What is the expression for the velocity of the drop? For sea level conditions: (b) What is the value of y? (c) what is the value of μ? (d) What is the velocity of the droplet U? (a) U N/m3 N-s/m2 m/s (c) μ ▼ Part 3 (a) What is the viscosity at 5000 m? (b) What is the droplet velocity at 5000 m? N-s/m (a) u (b) V = m/s LINK TO TEXT Attempts: 0 of 6 used SAVE FOR LATER SUBMIT ANSWER Part 4 (a) The Reynolds number needs to be determined to be certain that the correct expression for the drag was used. What is the density of air at sea level? (b) What is the Reynolds number at sea level? (c) Is the Reynolds number low enough to use the expression for drag? kg/m3 (b) Re-

Answer 1

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