For Instructor Use Only Your score is: Full grade for this exam is 50 that will

Question

For Instructor Use Only Your score is: Full grade for this exam is 50 that will contribute 20 % towards your final grades and can be obtained by answering any two Questions, 5 extra points is possible if you attempt all three questions 1. Fluid Mechanics Lab #1: Flow Velocity Measurement In this experiment pitot static tube and water manometer were used to measure the air flow velocity Total 25 Points Tube-11 and tube-12 in the manometer measure the static pressure and total pressure respectively Note that water manometer we used in lab is inclined 30 degree. Suppose we measure wind velocity with hot wire anemometer as, V = 24 m/s. The static pressure measured by pitot tube is 150 mm of water (this is the length of water you actually been Air Density (@25 °C) 1.18 Kg/m3 Gravitational "g" 9.81 m/s2 Water Density (Manometer) 1000 Kg/m² a) What is the total pressure reading (in the unit of "mm" of water) that you will actually "see" in the manometer? (20 points) Iron Statile Pressure connection to U-tube Manometern Tube 11 b) What will be the dynamic pressure (in the unit of "mm" of water) of the air flowing with same velocity? (5 points) MEEN 3242 Lab II Midterm Exam Page 2 of 6

Explanation / Answer

a) Given: Pstatic = 150 mm of water

Since the manometer is inclined, therefore,

Pressure in it will be,

Pstatic = d*g*s*sin(x)

where, x = 30 degree

d = density of water= 1000kg/m3

s = 150 mm

Therefore, on substituting these values, we get,

Pstatic = 735.75 Pa

Now, given that the velocity across the pitot tube is found to be, v = 24m/s

The velocity head contributes to the dynamic pressure head.

Therefore, Pdynamic = da*v2/2

da is the density of air which is flowing = 1.18 kg/m3

Substituting the value of v and da, we get

Pdynamic = 339.84 Pa

The total pressure head will be the sum of dynamic pressure head and static pressure head.

i.e. Ptotal = Pstatic + Pdynamic

Ptotal = 1075.59 Pa

On seeing this on an inclined water manometer, Ptotal = d*g*y*sin(x)

On substituting the valuees of d, g and x,

We get, y = 219.284 mm

This will be the total reading that we'll actually see in the manometer.

b) In this we have to calculate the dyanamic pressure head in mm of water,

Pdynamic = d*g*hw

Now, since we've already calculated the Pdynamic = 339.84 Pa

Then substituting the values if d and g,

we get hw = 34.642 mm of water, if the tube is vertical

(Otherwise, in the inclined tube, we'll get the dynamic pressure reading as 34.642/sin(x) = 69.284 mm of water)

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