Pharos University
ME 259 Fluid Mechanics for Electrical Students
Revision for Mid-Term Exam
Dr. A. Shibl
Manometer Example
Determine the pressure at point A in the figure below if
h1 = 0.2 m and h2 = 0.3 m. Use water = 1000 kg/m3.
Solution:
P2 = P1 + Hggh2
But P1 = Patm (open to atmosphere) ==>P1 = 0 (gauge)
 P2 = Hggh2
P3 = PA + waterg(h1+h2)
We know that
P2 = P 3
(same horizontal level)
Thus
Hggh2 = PA + waterg(h1+h2)

PA = Hggh2 - waterg(h1+h2)
PA = 13.54x1000x9.81x0.3 – 1000x9.81x(0.2+0.3)
PA = 39, 848 - 4905
PA = 34.9 kPa (gauge)
Points to be selected:
1 – at the open end of the manometer
2 – at the right leg of the manometer
3 – same level with point 2 but at left leg of the
manometer
4 – same level as point A
Pressure at the points:
P1=Patm
P2 = P3
P4 = PA
2
Static Force Example
•
A rectangular gate of dimension 1 m by 4 m is held in place by a stop block at B. This block
exerts a horizontal force of 40 kN and a vertical force of 0 kN. The gate is pin-connected at A,
and the weight of the gate is 2 kN. Find the depth h of the water.
Continuity Example
• Water flows steadily through a nozzle. The
nozzle diameter at the inlet is 5 cm, and the
diameter at the exit is 3cm. The average
velocity at the inlet is 4 m/s. What is the
average velocity at the exit?
• V1 A1 = V2 A2
Bernoulli Equation
1
 v 2  gz  const [ N  m / kg ]
 2
p
• Water moving through Venture nozzle reaches a low pressure at section 1.
Nozzle dimensions are d1 = 3 mm, d2 = 9 mm, and h = 150 mm. Determine
the minimum possible water speed (V2) at the exit of the nozzle so that
fluid will be drawn up the suction tube.
Momentum Equation For Steady Flow
ΣFx= ṁ (V2—V1)x
F  
CS


V V  n dA
•
A water jet with a velocity of 30 m/s impacts on a splitter plate so that 1/4 of the water is
deflected toward the bottom and 3/4 toward the top. The angle of the plate is 45o. Find
the force required to hold the plate stationary. Neglect the weight of the plate and water,
and neglect friction.