Energy losses in fluid flow MCQs With Answer

Energy losses in fluid flow MCQs With Answer

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Energy losses in fluid flow are critical to understanding piping, pumping and process design in pharmaceutical manufacturing. This introduction explains head loss, frictional losses and minor losses in pipelines, focusing on Darcy–Weisbach, Hagen–Poiseuille and practical tools like the Moody chart and loss coefficients. B.Pharm students will learn how viscosity, Reynolds number, pipe roughness and fittings influence pressure drop, pump power and process efficiency in sterile and non‑sterile systems. Real examples include flow through production lines, filters and tubing where minimizing energy loss preserves product integrity and reduces operating cost. Now let’s test your knowledge with 50 MCQs on this topic.

Q1. What term describes the loss of mechanical energy per unit weight of fluid due to friction in pipe flow?

  • Head gain
  • Head loss
  • Specific energy
  • Pressure coefficient

Correct Answer: Head loss

Q2. Which equation gives the head loss hf due to friction in a circular pipe?

  • hf = f (L/D) (V^2/2g)
  • hf = ρ g V^2 / 2
  • hf = 8 μ L V / (π r^4)
  • hf = K (Q^2)

Correct Answer: hf = f (L/D) (V^2/2g)

Q3. The Darcy friction factor depends primarily on which two parameters?

  • Gravity and fluid color
  • Reynolds number and relative roughness
  • Temperature and pipe length only
  • Pipe slope and elevation

Correct Answer: Reynolds number and relative roughness

Q4. For fully developed laminar flow in a circular pipe, the Darcy friction factor f is given by:

  • f = 0.079 Re^-0.25
  • f = 64 / Re
  • f = 0.3164 Re^-0.25
  • f = 1 / (2 log10(Re))

Correct Answer: f = 64 / Re

Q5. Which implicit equation is used to compute the friction factor in turbulent flow for rough pipes?

  • Bernoulli equation
  • Colebrook equation
  • Hagen–Poiseuille equation
  • Continuity equation

Correct Answer: Colebrook equation

Q6. What does the Moody chart plot?

  • Head loss versus pipe length
  • Friction factor versus Reynolds number for various relative roughness
  • Velocity profile across a pipe radius
  • Pressure versus temperature for liquids

Correct Answer: Friction factor versus Reynolds number for various relative roughness

Q7. Minor losses in a piping system are caused by:

  • Only the pipe length
  • Fittings, valves, bends, sudden expansions and contractions
  • Gravity only
  • Fluid compressibility exclusively

Correct Answer: Fittings, valves, bends, sudden expansions and contractions

Q8. The head loss across a fitting is often expressed as hL = K (V^2/2g). What does K represent?

  • Loss coefficient for the fitting
  • Pipe curvature radius
  • Kinematic viscosity
  • Compressibility factor

Correct Answer: Loss coefficient for the fitting

Q9. In laminar flow, how does pressure drop scale with mean velocity V?

  • ΔP ∝ V^2
  • ΔP ∝ V
  • ΔP ∝ V^3
  • ΔP is independent of V

Correct Answer: ΔP ∝ V

Q10. The Hagen–Poiseuille equation for volumetric flow rate Q through a circular pipe (laminar) is:

  • Q = (π r^4 ΔP) / (8 μ L)
  • Q = A V^2 / (2 g)
  • Q = (π D^2 / 4) V
  • Q = f (L/D) (V^2/2g)

Correct Answer: Q = (π r^4 ΔP) / (8 μ L)

Q11. What are the SI units of head loss (hf)?

  • Pascal-second (Pa·s)
  • Meter (m) of fluid
  • Newton (N)
  • Watt (W)

Correct Answer: Meter (m) of fluid

Q12. Hydraulic diameter Dh for non-circular ducts is defined as:

  • Dh = 2A / P
  • Dh = 4A / P
  • Dh = A / (2P)
  • Dh = P / A

Correct Answer: Dh = 4A / P

Q13. Reynolds number Re for pipe flow is given by which expression?

  • Re = ρ V D / μ
  • Re = μ V / (ρ D)
  • Re = V^2 / gD
  • Re = ρ g D / μ

Correct Answer: Re = ρ V D / μ

Q14. The approximate critical Reynolds number for transition from laminar to turbulent flow in a smooth circular pipe is:

  • Re ≈ 200
  • Re ≈ 2000–2300
  • Re ≈ 10,000
  • Re ≈ 100,000

Correct Answer: Re ≈ 2000–2300

Q15. The hydraulic power required to overcome head H at flowrate Q with pump efficiency η is:

  • P = ρ g Q H / η
  • P = Q H / (ρ g η)
  • P = η / (ρ g Q H)
  • P = ρ Q / (g H η)

Correct Answer: P = ρ g Q H / η

Q16. To express a fitting loss K as an equivalent pipe length Leq, which relation is correct?

  • Leq = K D / f
  • Leq = f D / K
  • Leq = K / (f D)
  • Leq = K f / D

Correct Answer: Leq = K D / f

Q17. Head loss for a sudden expansion from area A1 to A2 is commonly given by which formula?

  • hL = (V2 – V1)^2 / (2 g)
  • hL = (V1 – V2)^2 / (2 g)
  • hL = K (V1^3) / (2 g)
  • hL = 0 for expansion

Correct Answer: hL = (V1 – V2)^2 / (2 g)

Q18. A sharp-edged entrance to a pipe typically has an entrance loss coefficient Ke approximately equal to:

  • 0.005
  • 0.5
  • 5.0
  • 50

Correct Answer: 0.5

Q19. In the Darcy–Weisbach expression, what is the physical meaning of V^2/2g?

  • Viscous head
  • Kinetic head per unit weight
  • Potential head
  • Thermal head

Correct Answer: Kinetic head per unit weight

Q20. Which statement about minor losses is TRUE?

  • They are directly proportional to pipe length
  • They can be represented as a loss coefficient K multiplied by V^2/2g
  • They are significant only in laminar flow
  • They are independent of velocity

Correct Answer: They can be represented as a loss coefficient K multiplied by V^2/2g

Q21. For turbulent flow, if velocity is doubled, how does the frictional head loss change approximately?

  • It remains the same
  • It doubles
  • It quadruples
  • It increases eightfold

Correct Answer: It quadruples

Q22. The relative roughness used in Moody chart is defined as:

  • ε / D
  • D / ε
  • ε × D
  • ε + D

Correct Answer: ε / D

Q23. In laminar flow inside a pipe, the friction factor f depends on:

  • Only pipe roughness
  • Only Reynolds number
  • Both Reynolds number and roughness equally
  • Neither Re nor roughness

Correct Answer: Only Reynolds number

Q24. Which expression relates pressure drop ΔP to head loss hf?

  • hf = ΔP × ρ g
  • hf = ΔP / (ρ g)
  • hf = ΔP / μ
  • hf = ΔP / Q

Correct Answer: hf = ΔP / (ρ g)

Q25. For pharmaceutical liquid transfers, why is limiting energy loss important?

  • To maximize thermal degradation
  • To reduce pump sizing, prevent shear damage and save energy
  • To increase pressure fluctuations intentionally
  • To increase minor losses for mixing

Correct Answer: To reduce pump sizing, prevent shear damage and save energy

Q26. The symbol ε in pipe flow denotes:

  • Fluid emissivity
  • Absolute roughness of the pipe internal surface
  • Porosity of the fluid
  • Pipe eccentricity

Correct Answer: Absolute roughness of the pipe internal surface

Q27. Which equation is most appropriate for calculating pressure drop in a long, laminar flow capillary used for analytical chromatography?

  • Darcy–Weisbach with f = 0.3164 Re^-0.25
  • Hagen–Poiseuille law
  • Colebrook equation
  • Bernoulli without losses

Correct Answer: Hagen–Poiseuille law

Q28. The Colebrook equation is implicit in f. Which method is commonly used to obtain f from Colebrook?

  • Analytical closed-form solution for all Re
  • Iterative numerical methods or explicit approximations
  • Use of Bernoulli equation directly
  • Assume f=1 always

Correct Answer: Iterative numerical methods or explicit approximations

Q29. The Blasius correlation f = 0.3164 Re^-0.25 applies approximately to:

  • Laminar flow Re < 2300
  • Turbulent smooth pipe flow in the moderate Re range (≈4,000–100,000)
  • Compressible gas flow only
  • Two-phase flow only

Correct Answer: Turbulent smooth pipe flow in the moderate Re range (≈4,000–100,000)

Q30. Which parameter is most effective in reducing frictional head loss for a given flowrate in production piping?

  • Decrease pipe diameter
  • Increase pipe diameter
  • Increase fluid viscosity
  • Increase number of fittings

Correct Answer: Increase pipe diameter

Q31. The volumetric energy loss per unit time (power loss) in a pipe with pressure drop ΔP and flow Q is:

  • P_loss = ΔP / Q
  • P_loss = ΔP × Q
  • P_loss = ΔP × Q / (ρ g)
  • P_loss = ΔP × ρ g / Q

Correct Answer: P_loss = ΔP × Q

Q32. The hydraulic gradient S in a pipe is defined as:

  • S = hf × L
  • S = hf / L
  • S = L / hf
  • S = hf + L

Correct Answer: S = hf / L

Q33. Which of the following statements is correct regarding pipe roughness effect?

  • In laminar flow, roughness strongly affects f
  • In turbulent flow, increasing roughness increases f
  • Roughness has no effect at any Re
  • Roughness reduces head loss in turbulent flow

Correct Answer: In turbulent flow, increasing roughness increases f

Q34. For incompressible steady flow with energy losses, the extended Bernoulli equation includes which term to account for losses?

  • + hf (added to energy)
  • – hf (subtracted as head loss)
  • + μ term for viscosity only
  • No additional term needed

Correct Answer: – hf (subtracted as head loss)

Q35. Which equation is suitable for estimating pressure drop in a packed bed (e.g., spray dryer or packed column) used in pharma?

  • Hagen–Poiseuille
  • Ergun equation
  • Moody chart
  • Blasius correlation

Correct Answer: Ergun equation

Q36. The entrance length for laminar flow to become fully developed is approximately:

  • Le/D ≈ 0.05 Re
  • Le/D ≈ 10
  • Le/D ≈ 0.0001 Re
  • Le/D independent of Re

Correct Answer: Le/D ≈ 0.05 Re

Q37. For turbulent flow, which statement about the velocity profile is true?

  • Velocity profile is exactly parabolic
  • Velocity profile is flatter in the core and steeper near the wall than laminar
  • Velocity is zero at centerline
  • Velocity profile is independent of viscosity

Correct Answer: Velocity profile is flatter in the core and steeper near the wall than laminar

Q38. If two pipes of equal length carry the same flowrate but one has twice the diameter, how does its frictional head loss compare approximately (turbulent regime)?

  • It is 4 times larger
  • It is 2 times larger
  • It is about 1/16 as large
  • It is the same

Correct Answer: It is about 1/16 as large

Q39. In pharmaceutical tubing handling shear-sensitive biomolecules, which flow condition is preferred to minimize shear-induced damage?

  • High turbulent velocities
  • Laminar flow with low shear rates
  • Cavitation-prone flow
  • Intermittent slug flow

Correct Answer: Laminar flow with low shear rates

Q40. Which quantity must be known to use the Moody chart to find the friction factor?

  • Only pipe length
  • Reynolds number and relative roughness ε/D
  • Only fluid color
  • Only pump efficiency

Correct Answer: Reynolds number and relative roughness ε/D

Q41. The effect of increasing fluid viscosity, keeping flowrate constant, is generally to:

  • Decrease pressure drop
  • Increase pressure drop
  • Eliminate minor losses
  • Double the flowrate

Correct Answer: Increase pressure drop

Q42. Which of the following best describes the Darcy–Weisbach friction factor f?

  • A dimensional quantity with units of Pa·s
  • A dimensionless coefficient relating shear losses to kinetic head
  • The ratio of pipe diameter to roughness
  • The specific heat capacity of the fluid

Correct Answer: A dimensionless coefficient relating shear losses to kinetic head

Q43. What is the relation between head loss hf and volumetric flow Q in turbulent flow through a given pipe (approximately)?

  • hf ∝ Q
  • hf ∝ Q^2
  • hf ∝ Q^3
  • hf ∝ log(Q)

Correct Answer: hf ∝ Q^2

Q44. In the context of energy losses, what is an equivalent length of a fitting?

  • The physical length of the fitting
  • The length of straight pipe that produces the same head loss as the fitting
  • The diameter divided by roughness
  • The flowrate times velocity

Correct Answer: The length of straight pipe that produces the same head loss as the fitting

Q45. Which of these operations will increase minor losses in a pipeline?

  • Removing extra valves
  • Using smooth gradual bends rather than sharp bends
  • Adding sudden contractions and partially closed valves
  • Increasing pipe diameter drastically

Correct Answer: Adding sudden contractions and partially closed valves

Q46. In pharmaceutical clean-in-place (CIP) systems, why are energy losses important to account for?

  • They determine cleaning time, pump selection and effective flow distribution
  • They only affect color of the cleaning solution
  • They are negligible and ignored
  • They increase chemical reactivity

Correct Answer: They determine cleaning time, pump selection and effective flow distribution

Q47. Which of the following is a dimensionless group used to characterize flow regime affecting energy losses?

  • Nusselt number
  • Reynolds number
  • Prandtl number
  • Biot number

Correct Answer: Reynolds number

Q48. For laminar pipe flow, the pressure gradient (-dP/dx) for Poiseuille flow is proportional to:

  • Viscosity μ and average velocity V
  • Square of velocity V^2 only
  • Pipe roughness only
  • Temperature only

Correct Answer: Viscosity μ and average velocity V

Q49. Which practical method reduces both frictional and minor energy losses in a production pipeline?

  • Install many short-radius elbows and partially closed valves
  • Use larger diameter smooth pipes and minimize fittings
  • Roughen the pipe internal surface intentionally
  • Operate pumps at maximum speed regardless of need

Correct Answer: Use larger diameter smooth pipes and minimize fittings

Q50. The Colebrook equation involves which mathematical operation that makes it implicit in f?

  • Square root of f inside a logarithm
  • Simple multiplication only
  • Linear addition of f terms only
  • Exponential of f with base e only

Correct Answer: Square root of f inside a logarithm

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