How Do You Calculate Airflow and Pressure Changes in a Duct System?

[zakf355]

fluid mechanics question help!?

Homework Statement

Air flows through a horizontal duct of dimensions 300 x 300 mm with a velocity of 15 m/s. At position (1) in the duct a water gauge (water manometer) registers a hieght of 215mm. The duct bends downwards and reduces in size to 240 x 240 mm, dropping a distance of 12 m to position (2). the specific volume of the air is 0.85 m^3 / kg and this may be taken as constant. Determine:

a) volume flow rate and mass flow rate.
b) pressure at (1) in kPa
c) The Velocity at (2)
d) pressure at (2) in kPa (guage) and mm water gauge if losses are neglected.
e) pressure at (2) in kPa (gauge and mm water gauge if losses are 10% of the total head at (1) and elevation (2) is used as datum

Homework Equations

Bernoulli's Equation

mass flow rate = v A relative density

The Attempt at a Solution

im struggling guys

Homework Statement

Homework Equations

The Attempt at a Solution

 

[SteamKing]

I'm not surprised that you're struggling. Are you sure that the water gauge at point 1 reads 215 m? That's a pretty large water gauge, equal to the height of a 70 story building. BTW, atmospheric pressure is about 10 m W.G.

 

[zakf355]

haha its mm. silly me :/

 

[SteamKing]

You've got to show some effort to get help from PFers. That's the rules. "I'm struggling" isn't good enough.