A stream of air enters an 850 cm ID pipe at a velocity of 70

A stream of air enters an 8.50 cm ID pipe at a velocity of 70.2 m/s at 25ºC and 2.10 bar (gauge). At some point downstream, the pipe ID changes, and the air flows through a 4.50 cm ID pipe at 80ºC and 5.20 bar. a. Determine whether or not the air can be assumed to be an ideal gas. b. Determine the molar flow rate (mol/s). c. Determine the air velocity in the 4.50 cm ID pipe.

Solution

a) The air can be considered as ideal gas as the pressure is sufficiently low and temp high.

b) Molar flow rate

Volume flowing per secondd = Speed * Area = 70.2 * pi * .0425*0.0425 = 398 liters/s

Now using the ideal gas equation

n\' = PV\'/RT = (2.1+1.1)398/8.314*298 = 0.51 mol/s

c) V\' = n\'RT/P = 0.51*8.314*350/6.3 (5.2 bar is the guage pressure)

V\' = 237.5 lit/s

Hence the velocity will be

Velocity = V\'/Area = 237.5 = 149.5 ms-1