Question 1

Which of the following formula and equations are used to estimate frictional head losses in steady pipe flow?&#10;A)Bernoulli equation&#10;B)Darcy Weisbach formula&#10;C)Hazen-Williams equation&#10;D)B. and C.

Accepted Answer

Both the Darcy Weisbach formula and the Hazen-Williams equation can be used to estimate frictional head losses in steady pipe flow. The Darcy-Weisbach Formula is used to calculate pressure or head loss due to friction in a pipe system. The Hazen-Williams equation is used to take the physical properties of a pipe into account when determining the pressure drop due to friction. The Bernoulli Equation describes the conservation of energy, an important law of fluid mechanics.

Question 2

The pressure at the bottom of a 75-foot column of water with a cross-sectional area of 18 inches2 is, approximately, which of the following?&#10;A)9.1 psi&#10;B)20.0 psi&#10;C)32.5 psi&#10;D)48.8 psi

Accepted Answer

The gauge pressure that is equivalent to the static head of a 75-foot column of water is approximately 32.5 psi. Solution: Pressure = Specific Weight x Pressure Head Given Specific weight of water = 62.4 lb/ft³ Where Pressure head = 75 feet Pressure = 62.4 lbs/ft³ x 75 ft x 1ft²/144 in² = 32.5 psi

Question 3

The difference between the water surface elevations in a wet well and at a pump discharge is which of the following?&#10;A)Dynamic head&#10;B)Static head&#10;C)Velocity head&#10;D)Drawdown

Accepted Answer

The static head is the difference between the water surface elevations in a wet well and the pump discharge. The static head, therefore, is the distance that the water is lifted. The static head can be expressed by the following formula:
Static head (in feet) = Discharge head (in feet) - Suction head (in feet)

Question 4

Which of the following causes a pump to cavitate?&#10;A)Improper lubrication&#10;B)Packing glands too tight&#10;C)Elevated thrust bearing temperature&#10;D)Inadequate or restricted supply

Accepted Answer

Pump cavitation may be caused by an inadequate or restricted supply. Pump cavitation results when a pump is not fully charged with the fluid that is to be pumped. It may also be caused by air or gas that is introduced into or formed within the moving fluid. Pump cavitation, in most cases, negatively impacts pump efficiency and causes premature wear and/or damage to pumping equipment.

Question 5

Pneumatic ejectors are often used in wastewater treatment plants. Which of the following descriptions best describes a pneumatic ejector?&#10;A)A portable air compressor educator&#10;B)An air tool used to help loosen tight bolts&#10;C)A device which uses the pressure of compressed air to force a fluid to move&#10;D)None of the above

Accepted Answer

A pneumatic ejector is a device that uses the pressure of compressed air to force the movement of fluid. Pneumatic ejectors are typically used in treatment plants to raise wastewater or sludge to a higher elevation. Smaller-scale pneumatic ejectors have been in widespread use for over 140 years in sewer collection systems to move sewage from residential plumbing systems to mainline sewers.

Question 6

What is the approximate outlet velocity of a vented tank that is 15 meters high?&#10;A)4.4 meters/second&#10;B)17.2 meters /second&#10;C)47.0 meters/second&#10;D)Not enough information given

Accepted Answer

The outlet velocity of a vented tank that is 15 meters high is approximately 17.2 meters/second. Solution: Use Bernoulli equation to solve for outlet velocity. g*h¹ + (p1/p) + (V₁²/2) = g*h₂ + (p2/p) + (V₂²/2) In the case of a vented tank, the pressure inside and outside of the tank can be assumed to be the same. Bernoulli's equation can be transformed and used to solve for the outlet velocity (V₂) as follows: V₂ = (2*g*h)^1/2 Given g = 9.81 meters/second² V₂ = (2*9.81 meters/second² *15 meters)^1/2 = 17.2 meters/second

Question 7

An important law of fluid mechanics is the conservation of energy. Which of the following equations best describes this law?&#10;A)Bernoulli Equation&#10;B)Darcy-Weisbach Formula&#10;C)Hazen-Williams Formula&#10;D)None of the above

Accepted Answer

Conservation of energy, an important fluid mechanics law, is best described by the Bernoulli Equation. The Bernoulli Equation is expressed as H₂ = H₁ - h_L, where: H₁ = hydraulic head at an upstream point in a system H₂ = hydraulic head at a downstream point in a system h_L = head loss during the flow from point 1 to point 2

Question 8

With regards to energy losses caused by fittings, bends and valves in a piping system, which of the following statement is not correct?&#10;A)These losses are minor in comparison to friction losses&#10;B)The loss factor is typically provided for specific devices&#10;C)Losses are proportional to the velocity of flow and geometry of the device&#10;D)None of the above

Accepted Answer

All of the statements listed are correct with regards to energy losses caused by fittings, bends and valves in a piping system. Losses associated with fittings, bends, and valves are considered minor in comparison to friction losses, which are considered to be major. The loss factor, K, is typically provided by the device manufacturer. The velocity of flow and the geometry of a device are proportional to the losses, as demonstrated in the following equation: h_L - K (V²/2g)

Question 9

A 10-inch diameter pipe is connected to an 18-inch diameter pipe. If the average velocity in the 10-inch diameter pipe is 25 feet per second (fps), what is the average velocity in the 18-inch diameter pipe?

A)7.72 fps
B)13.89 fps
C)81.0 fps
D)None of the above

Accepted Answer

When the average velocity of a 10-inch diameter pipe connected to an 18-inch diameter pipe is 25 fps, the average velocity of the 18-inch diameter pipe is 7.72 fps. Solution: Apply the continuity equation: Area x Velocity = Area x Velocity A₁₈ V₁₈ = A₁₀ V₁₀ V₁₈ =A₁₀ / A₁₈ x V₁₀ = (D₁₀ / D₁₈)² x V₁₀ V₁₈ = (10 /18)² x 25 fps = 7.72 fps

Question 10

Which of the following is the approximate head loss in a 1,500-foot long section of 6-inch diameter galvanized iron pipe conveying water at with a velocity of 5 feet/second? (Assume friction factor of 0.02)

A)11.7 feet
B)23.3 feet
C)46.6 feet
D)None of the above

Accepted Answer

The approximate head loss in a 1,500-foot long section of 6-inch diameter galvanized iron pipe conveying water at a velocity of 5 feet per second is 23.3 feet. Solution: Use the Darcy-Weisbach equation H_L = f (L/D)(V² /2g) Given, f = Darcy friction factor = 0.02 D = 0.5 feet L = 1,500 feet V = 5 feet/ second g = 32.2 feet² /second Therefore, H_L = f (L/D)(V² /2g) = 0.02 (1,500 / 0.5) (5² /2(32.2)) = 23.3 feet

Deck 6: Hydraulics Closed