# Fluid Flow

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A question pack on fluid flow in thermal dynamic systems.

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The equation of continuity (mass conservation) reduces to $\triangledown \cdot$ v = 0 for the special case of ______________.

Steady state

Constant density

Constant temperature

Constant velocity

Constant pressure

Calculate the Reynolds number for water flowing through a 2‑inch internal diameter pipe at a flow rate of 500 gallons/hour.

10

100

1000

10,000

100,000

Which group describes the ratio of inertial forces to viscous forces?

Re

Pr

Gr

St

Nu

Which group quantifies the ratio of thermal transfer and momentum transfer resistance in a fluid?

Re

St

Gr

Pr

Sc

The ratio of convective heat transfer to conductive heat transfer is commonly represented by which of the following?

Pr

St

Re

Nu

Gr

Which of the following is a state variable?

Flow rate

Diffusivity

Reynolds number

Gibbs free energy

Location

Which of the following is a form of anemometry?

Wind sock observations

Laser doppler

Particle imaging velocimetry

Hot wire

All of the above

Water flowing at 2 gallons per minute passes through a contraction from 1/2 inch internal diameter pipe to a 1/4 inch internal diameter pipe. Use Bernoulli's equation to calculate the pressure difference from immediately before the contraction to in the contraction. This pressure difference is defined as the pressure before the contraction minus the pressure in the contraction.

11 mm Hg

55 mm Hg

1120 mm Hg

‑1120 mm Hg

‑112 mm Hg

Water flowing at 10 gallons per minute passes through a contraction from 1 inch internal diameter pipe to a 1/2 inch internal diameter pipe. Use Bernoulli's equation to calculate the pressure difference from immediately before the contraction to immediately after the contraction. This pressure difference is defined as the pressure before the contraction minus the pressure after the contraction.

87 mm Hg

17.5 mm Hg

1750 mm Hg

‑17.5 mm Hg

‑175 mm Hg

Water flowing at 200 gallons per minute passes through an expansion from 2 inch internal diameter pipe to a 2.25 inch internal diameter pipe. Use Bernoulli's equation to calculate the pressure difference from immediately before the expansion to immediately after the expansion. This pressure difference is defined as the pressure before the contraction minus the pressure after the contraction.

110 mm Hg

‑56 mm Hg

‑1110 mm Hg

1110 mm Hg

None of the above

In studying Bernoulii's equation and the forms for the relationship between pressure drop and flow rate for an orifice plate and venturi meter, the results can be summarized by which of the following statements?

Q is proportional to pressure drop.

Q is inversely proportional to pressure drop.

Q is inversely proportional to the square root of pressure drop.

Q is proportional to the square root of pressure drop.

None of the above

What is the lowest absolute pressure that can exist?

14.7 psi

‑14.7 psi

‑29.4 psi

0 psi

‑1 atm

Air is flowing through a pipe with an internal diameter of 15 cm. It passes through an orifice of diameter 8 cm. The air density at the operating conditions is about 1.3 kg/m$^3$. The observed pressure difference across the orifice is approximately 100 mm Hg, and the flow coefficient for the orifice is approximately 0.7. What is the mass flow rate of air?

0.506 kg/s

0.503 kg/s

6.5 kg/s

0.05 kg/s

0.65 kg/s

Water is flowing through a pipe with an internal diameter of 15 cm. It passes through an orifice of diameter 8 cm. The fluid density at the operating conditions is about 1000 kg/m$^3$. The observed pressure difference across the orifice is approximately 100 mm Hg, and the how coefficient for the orifice is approximately 0.7. What is the mass flow rate of water?

2 kg/s

8.1 kg/s

18 kg/s

180 kg/s

81 kg/s

A liquid with 5.3 times the density of water is used in a manometer. A pressure difference of 4 psi corresponds to how many mm head of this liquid?

53

530

5.3

5300

22

A liquid with a density 8 times that of water is used in a manometer. A pressure difference of 0.25 atm corresponds to how many mm head of that liquid?

32

3200

320

‑32

3.2

Which of the following best characterizes the inner channel of a rotameter?

It is typically close to perfectly cylindrical.

It is typically tapered from top to bottom.

It is typically roughened to promote turbulence.

It is typically notched for each

None of the above

A sharp crested, contracted, rectangular weir of length 12 ft and height 1 ft exhibits a head (h0) of 2 inches of water. Calculate the water flow in ft$^3$/s. Assume the head of velocity approach is small.

0.2 ft$^3$/s

0.4 ft$^3$/s

20 ft$^3$/s

2.6 ft$^3$/s

1 ft$^3$/s

Which of the following statements about pump affinity laws is true?

Pump affinity laws describe similarity to other pumps.

Pump affinity laws describe cost versus performance.

Pump affinity laws describe relationship of geometric variables and dynamic performance.

Pump affinity laws describe dynamic head versus fluid viscosity.

None of the above

When does cavitation occur?

When vapor appears in the suction line

When the net postive suction head at the pump input is less than the vapor pressure of the liquid

When the liquid to be pumped begins to boil in the suction line

All of the above

None of the above

In considering the exits of two pumps or blowers configured in parallel, which of the following statements is true?

The flow rates from the two pieces of equipment are equal.

The total mass flow rate is the sum of the mass flow rates from each piece of equipment.

The temperatures of the streams from each piece of equipment are equal.

The pressures in the output streams from each piece of equipment are nearly equal.

Both A and C

Both B and D

In considering two pumps (1 and 2) connected in series, which of the following is true?

The flow rates are the same in 1 and 2.

The inlet pressures are the same for 1 and 2.

The outlet pressures are the same for 1 and 2.

The inlet pressure of one of the pumps is equivalent to the outlet pressure of the other pump.

Both A and D

For both pumps and fans, the system resistance varies as the ______________.

Square root of flow rate

Cube root of flow rate

Flow rate

Flow rate squared

Cube of flow rate

Air is moved through a conduit at a volumetric rate of 100 m$^3$/min. The conditions are P=18 psi, T = 27°C. What is the mass flow rate of air in the conduit?

2.4 lb/min

2.4 g/s

2.4 kg/min

2.4 kg/s

2.4 kg/hr

Positive displacement pumps do which of the following?

Produce a flow rate independent of operating speed

Produce a flow rate independent of discharge pressure

Produce a flow rate independent of suction head

Usually require a relief or safety valve

Both B and D

A centrifugal pump is used to lift water at five gallons per minute against a head of 50 feet of water. The efficiency of the pump is 70%. Approximately, what is the power required by the pump?

0.7 kW

0.07 kW

7 kW

70 kW

750 kW

A centrifugal pump is used to lift water at fifty gallons per minute against a head of 75 feet of water. The efficiency of the pump is 65%. Approximately, what is the power required by the pump?

0.1 kW

0.01 kW

1 kW

10 kW

100 kW

A centrifugal pump is used to lift water at 75 gallons per minute against a head of 175 feet of water. The efficiency of the pump is 75%. Approximately, what is the power required by the pump?

0.33 kW

3.3 W

3.3 hp

3.3 tons

3.3 kw

You have a pump that is using 8.5 kW of power to pump water at about 450 gallons per minute against a head of 32 psi. What is the operating efficiency of the pump?

93%

85%

79%

74%

65%

What is the primary difference between a pump and a blower or fan?

Blowers have an unconstrained exit stream, and pumps do not.

Blowers move gases, and pumps move liquids and gases.

Pumps pressurize liquids, and blowers move gases.

Pumps operate at lower pressures than blowers.

Pumps operate on incompressible fluids, and blowers operate on compressible fluids.

One atmosphere of pressure corresponds to a water head of how many feet?

33.9 ft

3.39 ft

340 ft

3340 ft

None of the above

Water flows through a 1 inch ID 90‑degree elbow at 100 L/min. What is the pressure drop associated with the fitting?

3.3 Pa

2.2 Pa

2.2 kPa

3.7 kPa

440 kPa

Water flows through a 2 inch ID 90‑degree elbow at 300 L/min. What is the pressure drop associated with the fitting?

1 psi

2.5 psi

0.25 psi

43 psi

10 psi

A fluid with density 0.78 g/cm$^3$ and viscosity 2.3 cP flows at 1 gallon per minute through a 2 inch internal diameter pipe. The flow should be considered as which of the following?

Turbulent

Laminar

Transitional

None of the above

All of the above

For gas flow in a pipe, as the pressure decreases downstream the gas velocity does which of the following?

Remains constant

Decreases

Increases

Doubles

None of the above

A centrifugal pump can provide a flow of 20 L/min at a pressure of 20 psi above atmospheric pressure. What is the minimum pipe diameter $(\epsilon/D = 0.002)$ that can be used to carry water for 50 m?

5 cm

0.6 cm

2.0 cm

15 cm

7 cm

A centrifugal pump can provide flow of 100 L/min at 1.7 atm gauge. What is the minimum pipe diameter $(\epsilon/D=0.005)$that can be used to carry water under these conditions for 100 m?

1.4 cm

2.5 cm

3.9 cm

5.0 cm

1.1 cm

Important factors for choosing a pipe material include which of the following?

Presence/absence of organic chemicals in the pipe environment

Installation cost and lifetime

Brittleness

Ease of corrosion

All of the above

How are pipe diameters most commonly specified and tabulated?

Internal diameter

Internal and external diameter

External diameter (OD) and wall thickness

External Diameter

None of the above

A piece of analytical equipment employs very narrow diameter tubing to supply solvent (density = 0.9 g/cm$^3$, viscosity = 0.78 cP) to a workstation at a flow rate of 5 ml/min. The internal diameter of the tubing is 1000 $\mu$ m and the length of the tubing is 75 cm. What is the pressure drop in the tubing?

0.5 atm

1 atm

0.2 atm

0.02

5 atm

Water flows through a 3 inch internal diameter 75 ft long pipe at 0.1 gallon per minute. The surface roughness of the pipe is 0.02 cm. What is the pressure drop over the entire length of the pipe?

1.8 kPa

1800 Pa

17.6 Pa

1.16 Pa

0.18 Pa

Water flows through a 5 inch internal diameter pipe 50 m long at 5000 liters /min. The roughness of the pipe is characterized by $\epsilon$ /D = 0.002. What is the pressure drop over the entire length of pipe?

24 kPa

90 Pa

900 Pa

9 kPa

45 kPa

A fluid of density 0.83 g/cm$^3$ and viscosity 1.8 cP flows through a 1 inch internal diameter pipe 50 m long at 80 kg/min. The roughness of the pipe is characterized by $\epsilon$ /D = 0.005. What is the pressure drop over the entire length of pipe?

112 kPa

269 Pa

2.69 Pa

524 kPa

262 kPa

Pressure drops for elements in series are ______________.

Additive

Multiplicative

Equal

Related reciprocally

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