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General Spherical

Environmental Engineering · FE Reference Handbook section

Environmental Engineering
12 formulas
10 exam-style examples
~60 min
All Environmental Engineering lectures

Core formulas for this FE topic

Definitions, applicability, units, assumptions and worked examples for each relation.

Worked exam-style examples

The four ways this section is written on the real exam — thoughts first, then equations, then substitution.

Example 1
General Spherical (settling) — solve for settling velocity — General Spherical

general spherical particle settling velocity in a sedimentation basin Given gravitational acceleration (g) = 9.8100 m/s^2; particle density (rho_p) = 2,050 kg/m^3; fluid density (rho) = 991.5 kg/m^3; particle diameter (d) = 0.0027 m; drag coefficient (C_D) = 0.8300, determine the settling velocity (v_s) in m/s.

Given

  • gravitationalacceleration(g)=9.8100m/s2gravitational acceleration (g) = 9.8100 m/s^2
  • particledensity(rhop)=2,050kg/m3particle density (rho_p) = 2,050 kg/m^3
  • fluiddensity(rho)=991.5kg/m3fluid density (rho) = 991.5 kg/m^3
  • particlediameter(d)=0.0027mparticle diameter (d) = 0.0027 m
  • dragcoefficient(CD)=0.8300drag coefficient (C_D) = 0.8300

Find

settling velocity (v_s), in m/s

Start with the thinking

  • The governing relation printed in this handbook section is General Spherical (settling).
  • Everything except v_s is given, so isolate v_s symbolically first — never rearrange after the numbers are in.
  • Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
  • The general spherical particle settling equation gives settling velocity for particles outside the Stokes' law range.

Step-by-step solution

  1. Step 1 — State the governing relation:

    vs=4g(ρp−ρ)d3CDρv_s = \sqrt{\dfrac{4 g (\rho_p - \rho) d}{3 C_D \rho}}
  2. Step 2 — Rearrange symbolically for v_s:

    vs=4g(ρp−ρ)d3CDρv_{s} = \sqrt{\dfrac{4g(\rho_p-\rho)d}{3C_D\rho}}
  3. Step 3 — List the givens: gravitational acceleration (g) = 9.8100 m/s^2, particle density (rho_p) = 2,050 kg/m^3, fluid density (rho) = 991.5 kg/m^3, particle diameter (d) = 0.0027 m, drag coefficient (C_D) = 0.8300.

  4. Step 4 — Substitute the given values:

    vs=49.8100(ρp−991.5)0.00273CD991.5v_{s} = \sqrt{\dfrac{49.8100(\rho_p-991.5)0.0027}{3C_D991.5}}
  5. Step 5 — Evaluate:

    vs=0.2135 m/sv_{s} = 0.2135\ \text{m/s}
  6. Step 6 — Check: returning v_s = 0.2135 m/s to

    vs=4g(ρp−ρ)d3CDρv_s = \sqrt{\dfrac{4 g (\rho_p - \rho) d}{3 C_D \rho}}

    reproduces the given quantities, and both sides carry the same units.

Answer:
vs=0.2135 m/sv_{s} = 0.2135\ \text{m/s}

Why the other options are there

  • 0.4270 — kept a factor of two that cancels in the correct rearrangement.
  • 0.1068 — dropped that same factor in the other direction.
  • 0.2349 — rounded an intermediate value before the final step.

Reference: FE Handbook — General Spherical Particle Settling

Example 2
General Spherical (settling) — solve for particle diameter — General Spherical (2)

general spherical settling equation with a drag coefficient for larger particles Given gravitational acceleration (g) = 9.8100 m/s^2; particle density (rho_p) = 2,170 kg/m^3; fluid density (rho) = 997.0 kg/m^3; drag coefficient (C_D) = 4.2600; settling velocity (v_s) = 0.4575 m/s, determine the particle diameter (d) in m.

Given

  • gravitationalacceleration(g)=9.8100m/s2gravitational acceleration (g) = 9.8100 m/s^2
  • particledensity(rhop)=2,170kg/m3particle density (rho_p) = 2,170 kg/m^3
  • fluiddensity(rho)=997.0kg/m3fluid density (rho) = 997.0 kg/m^3
  • dragcoefficient(CD)=4.2600drag coefficient (C_D) = 4.2600
  • settlingvelocity(vs)=0.4575m/ssettling velocity (v_s) = 0.4575 m/s

Find

particle diameter (d), in m

Start with the thinking

  • The governing relation printed in this handbook section is General Spherical (settling).
  • Everything except d is given, so isolate d symbolically first — never rearrange after the numbers are in.
  • Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
  • The general spherical particle settling equation gives settling velocity for particles outside the Stokes' law range.

Step-by-step solution

  1. Step 1 — State the governing relation:

    vs=4g(ρp−ρ)d3CDρv_s = \sqrt{\dfrac{4 g (\rho_p - \rho) d}{3 C_D \rho}}
  2. Step 2 — Rearrange symbolically for d:

    d=vs2 3CDρ4g(ρp−ρ)d = \dfrac{v_s^2\,3C_D\rho}{4g(\rho_p-\rho)}
  3. Step 3 — List the givens: gravitational acceleration (g) = 9.8100 m/s^2, particle density (rho_p) = 2,170 kg/m^3, fluid density (rho) = 997.0 kg/m^3, drag coefficient (C_D) = 4.2600, settling velocity (v_s) = 0.4575 m/s.

  4. Step 4 — Substitute the given values:

    d=vs2 3CD997.049.8100(ρp−997.0)d = \dfrac{v_s^2\,3C_D997.0}{49.8100(\rho_p-997.0)}
  5. Step 5 — Evaluate:

    d=0.0579 md = 0.0579\ \text{m}
  6. Step 6 — Check: returning d = 0.0579 m to

    vs=4g(ρp−ρ)d3CDρv_s = \sqrt{\dfrac{4 g (\rho_p - \rho) d}{3 C_D \rho}}

    reproduces the given quantities, and both sides carry the same units.

Answer:
d=0.0579 md = 0.0579\ \text{m}

Why the other options are there

  • 0.1159 — kept a factor of two that cancels in the correct rearrangement.
  • 0.0290 — dropped that same factor in the other direction.
  • 0.0637 — rounded an intermediate value before the final step.

Reference: FE Handbook — General Spherical Particle Settling

Example 3
General Spherical (settling) — solve for drag coefficient — General Spherical (3)

general spherical settling velocity used for grit chamber design Given gravitational acceleration (g) = 9.8100 m/s^2; particle density (rho_p) = 1,670 kg/m^3; fluid density (rho) = 996.0 kg/m^3; particle diameter (d) = 0.0020 m; settling velocity (v_s) = 0.8567 m/s, determine the drag coefficient (C_D).

Given

  • gravitationalacceleration(g)=9.8100m/s2gravitational acceleration (g) = 9.8100 m/s^2
  • particledensity(rhop)=1,670kg/m3particle density (rho_p) = 1,670 kg/m^3
  • fluiddensity(rho)=996.0kg/m3fluid density (rho) = 996.0 kg/m^3
  • particlediameter(d)=0.0020mparticle diameter (d) = 0.0020 m
  • settlingvelocity(vs)=0.8567m/ssettling velocity (v_s) = 0.8567 m/s

Find

drag coefficient (C_D)

Start with the thinking

  • The governing relation printed in this handbook section is General Spherical (settling).
  • Everything except C_D is given, so isolate C_D symbolically first — never rearrange after the numbers are in.
  • Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
  • The general spherical particle settling equation gives settling velocity for particles outside the Stokes' law range.

Step-by-step solution

  1. Step 1 — State the governing relation:

    vs=4g(ρp−ρ)d3CDρv_s = \sqrt{\dfrac{4 g (\rho_p - \rho) d}{3 C_D \rho}}
  2. Step 2 — Rearrange symbolically for C_D:

    CD=4g(ρp−ρ)d3vs2ρC_{D} = \dfrac{4g(\rho_p-\rho)d}{3v_s^2\rho}
  3. Step 3 — List the givens: gravitational acceleration (g) = 9.8100 m/s^2, particle density (rho_p) = 1,670 kg/m^3, fluid density (rho) = 996.0 kg/m^3, particle diameter (d) = 0.0020 m, settling velocity (v_s) = 0.8567 m/s.

  4. Step 4 — Substitute the given values:

    CD=49.8100(ρp−996.0)0.00203vs2996.0C_{D} = \dfrac{49.8100(\rho_p-996.0)0.0020}{3v_s^2996.0}
  5. Step 5 — Evaluate:

    CD=0.0238C_{D} = 0.0238
  6. Step 6 — Check: returning C_D = 0.0238 to

    vs=4g(ρp−ρ)d3CDρv_s = \sqrt{\dfrac{4 g (\rho_p - \rho) d}{3 C_D \rho}}

    reproduces the given quantities, and both sides carry the same units.

Answer:
CD=0.0238C_{D} = 0.0238

Why the other options are there

  • 0.0475 — kept a factor of two that cancels in the correct rearrangement.
  • 0.0119 — dropped that same factor in the other direction.
  • 0.0261 — rounded an intermediate value before the final step.

Reference: FE Handbook — General Spherical Particle Settling

Example 4
General Spherical (settling) — solve for settling velocity (case 2) — General Spherical (4)

general spherical particle settling velocity in a sedimentation basin Given gravitational acceleration (g) = 9.8100 m/s^2; particle density (rho_p) = 2,570 kg/m^3; fluid density (rho) = 996.0 kg/m^3; particle diameter (d) = 0.0039 m; drag coefficient (C_D) = 2.4700, determine the settling velocity (v_s) in m/s.

Given

  • gravitationalacceleration(g)=9.8100m/s2gravitational acceleration (g) = 9.8100 m/s^2
  • particledensity(rhop)=2,570kg/m3particle density (rho_p) = 2,570 kg/m^3
  • fluiddensity(rho)=996.0kg/m3fluid density (rho) = 996.0 kg/m^3
  • particlediameter(d)=0.0039mparticle diameter (d) = 0.0039 m
  • dragcoefficient(CD)=2.4700drag coefficient (C_D) = 2.4700

Find

settling velocity (v_s), in m/s

Start with the thinking

  • The governing relation printed in this handbook section is General Spherical (settling).
  • Everything except v_s is given, so isolate v_s symbolically first — never rearrange after the numbers are in.
  • Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
  • The general spherical particle settling equation gives settling velocity for particles outside the Stokes' law range.

Step-by-step solution

  1. Step 1 — State the governing relation:

    vs=4g(ρp−ρ)d3CDρv_s = \sqrt{\dfrac{4 g (\rho_p - \rho) d}{3 C_D \rho}}
  2. Step 2 — Rearrange symbolically for v_s:

    vs=4g(ρp−ρ)d3CDρv_{s} = \sqrt{\dfrac{4g(\rho_p-\rho)d}{3C_D\rho}}
  3. Step 3 — List the givens: gravitational acceleration (g) = 9.8100 m/s^2, particle density (rho_p) = 2,570 kg/m^3, fluid density (rho) = 996.0 kg/m^3, particle diameter (d) = 0.0039 m, drag coefficient (C_D) = 2.4700.

  4. Step 4 — Substitute the given values:

    vs=49.8100(ρp−996.0)0.00393CD996.0v_{s} = \sqrt{\dfrac{49.8100(\rho_p-996.0)0.0039}{3C_D996.0}}
  5. Step 5 — Evaluate:

    vs=0.1816 m/sv_{s} = 0.1816\ \text{m/s}
  6. Step 6 — Check: returning v_s = 0.1816 m/s to

    vs=4g(ρp−ρ)d3CDρv_s = \sqrt{\dfrac{4 g (\rho_p - \rho) d}{3 C_D \rho}}

    reproduces the given quantities, and both sides carry the same units.

Answer:
vs=0.1816 m/sv_{s} = 0.1816\ \text{m/s}

Why the other options are there

  • 0.3632 — kept a factor of two that cancels in the correct rearrangement.
  • 0.0908 — dropped that same factor in the other direction.
  • 0.1997 — rounded an intermediate value before the final step.

Reference: FE Handbook — General Spherical Particle Settling

Example 5
General Spherical (settling) — solve for particle diameter (case 2) — General Spherical (5)

general spherical settling equation with a drag coefficient for larger particles Given gravitational acceleration (g) = 9.8100 m/s^2; particle density (rho_p) = 1,580 kg/m^3; fluid density (rho) = 997.5 kg/m^3; drag coefficient (C_D) = 3.4400; settling velocity (v_s) = 0.0915 m/s, determine the particle diameter (d) in m.

Given

  • gravitationalacceleration(g)=9.8100m/s2gravitational acceleration (g) = 9.8100 m/s^2
  • particledensity(rhop)=1,580kg/m3particle density (rho_p) = 1,580 kg/m^3
  • fluiddensity(rho)=997.5kg/m3fluid density (rho) = 997.5 kg/m^3
  • dragcoefficient(CD)=3.4400drag coefficient (C_D) = 3.4400
  • settlingvelocity(vs)=0.0915m/ssettling velocity (v_s) = 0.0915 m/s

Find

particle diameter (d), in m

Start with the thinking

  • The governing relation printed in this handbook section is General Spherical (settling).
  • Everything except d is given, so isolate d symbolically first — never rearrange after the numbers are in.
  • Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
  • The general spherical particle settling equation gives settling velocity for particles outside the Stokes' law range.

Step-by-step solution

  1. Step 1 — State the governing relation:

    vs=4g(ρp−ρ)d3CDρv_s = \sqrt{\dfrac{4 g (\rho_p - \rho) d}{3 C_D \rho}}
  2. Step 2 — Rearrange symbolically for d:

    d=vs2 3CDρ4g(ρp−ρ)d = \dfrac{v_s^2\,3C_D\rho}{4g(\rho_p-\rho)}
  3. Step 3 — List the givens: gravitational acceleration (g) = 9.8100 m/s^2, particle density (rho_p) = 1,580 kg/m^3, fluid density (rho) = 997.5 kg/m^3, drag coefficient (C_D) = 3.4400, settling velocity (v_s) = 0.0915 m/s.

  4. Step 4 — Substitute the given values:

    d=vs2 3CD997.549.8100(ρp−997.5)d = \dfrac{v_s^2\,3C_D997.5}{49.8100(\rho_p-997.5)}
  5. Step 5 — Evaluate:

    d=0.0038 md = 0.0038\ \text{m}
  6. Step 6 — Check: returning d = 0.0038 m to

    vs=4g(ρp−ρ)d3CDρv_s = \sqrt{\dfrac{4 g (\rho_p - \rho) d}{3 C_D \rho}}

    reproduces the given quantities, and both sides carry the same units.

Answer:
d=0.0038 md = 0.0038\ \text{m}

Why the other options are there

  • 0.0075 — kept a factor of two that cancels in the correct rearrangement.
  • 0.0019 — dropped that same factor in the other direction.
  • 0.0041 — rounded an intermediate value before the final step.

Reference: FE Handbook — General Spherical Particle Settling

Example 6
General Spherical (settling) — solve for drag coefficient (case 2) — General Spherical (6)

general spherical settling velocity used for grit chamber design Given gravitational acceleration (g) = 9.8100 m/s^2; particle density (rho_p) = 2,010 kg/m^3; fluid density (rho) = 991.5 kg/m^3; particle diameter (d) = 0.0017 m; settling velocity (v_s) = 0.2500 m/s, determine the drag coefficient (C_D).

Given

  • gravitationalacceleration(g)=9.8100m/s2gravitational acceleration (g) = 9.8100 m/s^2
  • particledensity(rhop)=2,010kg/m3particle density (rho_p) = 2,010 kg/m^3
  • fluiddensity(rho)=991.5kg/m3fluid density (rho) = 991.5 kg/m^3
  • particlediameter(d)=0.0017mparticle diameter (d) = 0.0017 m
  • settlingvelocity(vs)=0.2500m/ssettling velocity (v_s) = 0.2500 m/s

Find

drag coefficient (C_D)

Start with the thinking

  • The governing relation printed in this handbook section is General Spherical (settling).
  • Everything except C_D is given, so isolate C_D symbolically first — never rearrange after the numbers are in.
  • Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
  • The general spherical particle settling equation gives settling velocity for particles outside the Stokes' law range.

Step-by-step solution

  1. Step 1 — State the governing relation:

    vs=4g(ρp−ρ)d3CDρv_s = \sqrt{\dfrac{4 g (\rho_p - \rho) d}{3 C_D \rho}}
  2. Step 2 — Rearrange symbolically for C_D:

    CD=4g(ρp−ρ)d3vs2ρC_{D} = \dfrac{4g(\rho_p-\rho)d}{3v_s^2\rho}
  3. Step 3 — List the givens: gravitational acceleration (g) = 9.8100 m/s^2, particle density (rho_p) = 2,010 kg/m^3, fluid density (rho) = 991.5 kg/m^3, particle diameter (d) = 0.0017 m, settling velocity (v_s) = 0.2500 m/s.

  4. Step 4 — Substitute the given values:

    CD=49.8100(ρp−991.5)0.00173vs2991.5C_{D} = \dfrac{49.8100(\rho_p-991.5)0.0017}{3v_s^2991.5}
  5. Step 5 — Evaluate:

    CD=0.3569C_{D} = 0.3569
  6. Step 6 — Check: returning C_D = 0.3569 to

    vs=4g(ρp−ρ)d3CDρv_s = \sqrt{\dfrac{4 g (\rho_p - \rho) d}{3 C_D \rho}}

    reproduces the given quantities, and both sides carry the same units.

Answer:
CD=0.3569C_{D} = 0.3569

Why the other options are there

  • 0.7137 — kept a factor of two that cancels in the correct rearrangement.
  • 0.1784 — dropped that same factor in the other direction.
  • 0.3926 — rounded an intermediate value before the final step.

Reference: FE Handbook — General Spherical Particle Settling

Example 7
General Spherical (settling) — solve for settling velocity (case 3) — General Spherical (7)

general spherical particle settling velocity in a sedimentation basin Given gravitational acceleration (g) = 9.8100 m/s^2; particle density (rho_p) = 2,000 kg/m^3; fluid density (rho) = 993.0 kg/m^3; particle diameter (d) = 0.0041 m; drag coefficient (C_D) = 2.1300, determine the settling velocity (v_s) in m/s.

Given

  • gravitationalacceleration(g)=9.8100m/s2gravitational acceleration (g) = 9.8100 m/s^2
  • particledensity(rhop)=2,000kg/m3particle density (rho_p) = 2,000 kg/m^3
  • fluiddensity(rho)=993.0kg/m3fluid density (rho) = 993.0 kg/m^3
  • particlediameter(d)=0.0041mparticle diameter (d) = 0.0041 m
  • dragcoefficient(CD)=2.1300drag coefficient (C_D) = 2.1300

Find

settling velocity (v_s), in m/s

Start with the thinking

  • The governing relation printed in this handbook section is General Spherical (settling).
  • Everything except v_s is given, so isolate v_s symbolically first — never rearrange after the numbers are in.
  • Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
  • The general spherical particle settling equation gives settling velocity for particles outside the Stokes' law range.

Step-by-step solution

  1. Step 1 — State the governing relation:

    vs=4g(ρp−ρ)d3CDρv_s = \sqrt{\dfrac{4 g (\rho_p - \rho) d}{3 C_D \rho}}
  2. Step 2 — Rearrange symbolically for v_s:

    vs=4g(ρp−ρ)d3CDρv_{s} = \sqrt{\dfrac{4g(\rho_p-\rho)d}{3C_D\rho}}
  3. Step 3 — List the givens: gravitational acceleration (g) = 9.8100 m/s^2, particle density (rho_p) = 2,000 kg/m^3, fluid density (rho) = 993.0 kg/m^3, particle diameter (d) = 0.0041 m, drag coefficient (C_D) = 2.1300.

  4. Step 4 — Substitute the given values:

    vs=49.8100(ρp−993.0)0.00413CD993.0v_{s} = \sqrt{\dfrac{49.8100(\rho_p-993.0)0.0041}{3C_D993.0}}
  5. Step 5 — Evaluate:

    vs=0.1596 m/sv_{s} = 0.1596\ \text{m/s}
  6. Step 6 — Check: returning v_s = 0.1596 m/s to

    vs=4g(ρp−ρ)d3CDρv_s = \sqrt{\dfrac{4 g (\rho_p - \rho) d}{3 C_D \rho}}

    reproduces the given quantities, and both sides carry the same units.

Answer:
vs=0.1596 m/sv_{s} = 0.1596\ \text{m/s}

Why the other options are there

  • 0.3192 — kept a factor of two that cancels in the correct rearrangement.
  • 0.0798 — dropped that same factor in the other direction.
  • 0.1756 — rounded an intermediate value before the final step.

Reference: FE Handbook — General Spherical Particle Settling

Example 8
General Spherical (settling) — solve for particle diameter (case 3) — General Spherical (8)

general spherical settling equation with a drag coefficient for larger particles Given gravitational acceleration (g) = 9.8100 m/s^2; particle density (rho_p) = 1,740 kg/m^3; fluid density (rho) = 990.5 kg/m^3; drag coefficient (C_D) = 4.1700; settling velocity (v_s) = 0.6852 m/s, determine the particle diameter (d) in m.

Given

  • gravitationalacceleration(g)=9.8100m/s2gravitational acceleration (g) = 9.8100 m/s^2
  • particledensity(rhop)=1,740kg/m3particle density (rho_p) = 1,740 kg/m^3
  • fluiddensity(rho)=990.5kg/m3fluid density (rho) = 990.5 kg/m^3
  • dragcoefficient(CD)=4.1700drag coefficient (C_D) = 4.1700
  • settlingvelocity(vs)=0.6852m/ssettling velocity (v_s) = 0.6852 m/s

Find

particle diameter (d), in m

Start with the thinking

  • The governing relation printed in this handbook section is General Spherical (settling).
  • Everything except d is given, so isolate d symbolically first — never rearrange after the numbers are in.
  • Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
  • The general spherical particle settling equation gives settling velocity for particles outside the Stokes' law range.

Step-by-step solution

  1. Step 1 — State the governing relation:

    vs=4g(ρp−ρ)d3CDρv_s = \sqrt{\dfrac{4 g (\rho_p - \rho) d}{3 C_D \rho}}
  2. Step 2 — Rearrange symbolically for d:

    d=vs2 3CDρ4g(ρp−ρ)d = \dfrac{v_s^2\,3C_D\rho}{4g(\rho_p-\rho)}
  3. Step 3 — List the givens: gravitational acceleration (g) = 9.8100 m/s^2, particle density (rho_p) = 1,740 kg/m^3, fluid density (rho) = 990.5 kg/m^3, drag coefficient (C_D) = 4.1700, settling velocity (v_s) = 0.6852 m/s.

  4. Step 4 — Substitute the given values:

    d=vs2 3CD990.549.8100(ρp−990.5)d = \dfrac{v_s^2\,3C_D990.5}{49.8100(\rho_p-990.5)}
  5. Step 5 — Evaluate:

    d=0.1978 md = 0.1978\ \text{m}
  6. Step 6 — Check: returning d = 0.1978 m to

    vs=4g(ρp−ρ)d3CDρv_s = \sqrt{\dfrac{4 g (\rho_p - \rho) d}{3 C_D \rho}}

    reproduces the given quantities, and both sides carry the same units.

Answer:
d=0.1978 md = 0.1978\ \text{m}

Why the other options are there

  • 0.3956 — kept a factor of two that cancels in the correct rearrangement.
  • 0.0989 — dropped that same factor in the other direction.
  • 0.2176 — rounded an intermediate value before the final step.

Reference: FE Handbook — General Spherical Particle Settling

Example 9
General Spherical (settling) — solve for drag coefficient (case 3) — General Spherical (9)

general spherical settling velocity used for grit chamber design Given gravitational acceleration (g) = 9.8100 m/s^2; particle density (rho_p) = 2,030 kg/m^3; fluid density (rho) = 995.0 kg/m^3; particle diameter (d) = 0.0004 m; settling velocity (v_s) = 0.3463 m/s, determine the drag coefficient (C_D).

Given

  • gravitationalacceleration(g)=9.8100m/s2gravitational acceleration (g) = 9.8100 m/s^2
  • particledensity(rhop)=2,030kg/m3particle density (rho_p) = 2,030 kg/m^3
  • fluiddensity(rho)=995.0kg/m3fluid density (rho) = 995.0 kg/m^3
  • particlediameter(d)=0.0004mparticle diameter (d) = 0.0004 m
  • settlingvelocity(vs)=0.3463m/ssettling velocity (v_s) = 0.3463 m/s

Find

drag coefficient (C_D)

Start with the thinking

  • The governing relation printed in this handbook section is General Spherical (settling).
  • Everything except C_D is given, so isolate C_D symbolically first — never rearrange after the numbers are in.
  • Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
  • The general spherical particle settling equation gives settling velocity for particles outside the Stokes' law range.

Step-by-step solution

  1. Step 1 — State the governing relation:

    vs=4g(ρp−ρ)d3CDρv_s = \sqrt{\dfrac{4 g (\rho_p - \rho) d}{3 C_D \rho}}
  2. Step 2 — Rearrange symbolically for C_D:

    CD=4g(ρp−ρ)d3vs2ρC_{D} = \dfrac{4g(\rho_p-\rho)d}{3v_s^2\rho}
  3. Step 3 — List the givens: gravitational acceleration (g) = 9.8100 m/s^2, particle density (rho_p) = 2,030 kg/m^3, fluid density (rho) = 995.0 kg/m^3, particle diameter (d) = 0.0004 m, settling velocity (v_s) = 0.3463 m/s.

  4. Step 4 — Substitute the given values:

    CD=49.8100(ρp−995.0)0.00043vs2995.0C_{D} = \dfrac{49.8100(\rho_p-995.0)0.0004}{3v_s^2995.0}
  5. Step 5 — Evaluate:

    CD=0.0408C_{D} = 0.0408
  6. Step 6 — Check: returning C_D = 0.0408 to

    vs=4g(ρp−ρ)d3CDρv_s = \sqrt{\dfrac{4 g (\rho_p - \rho) d}{3 C_D \rho}}

    reproduces the given quantities, and both sides carry the same units.

Answer:
CD=0.0408C_{D} = 0.0408

Why the other options are there

  • 0.0817 — kept a factor of two that cancels in the correct rearrangement.
  • 0.0204 — dropped that same factor in the other direction.
  • 0.0449 — rounded an intermediate value before the final step.

Reference: FE Handbook — General Spherical Particle Settling

Example 10
General Spherical (settling) — solve for settling velocity (case 4) — General Spherical (10)

general spherical particle settling velocity in a sedimentation basin Given gravitational acceleration (g) = 9.8100 m/s^2; particle density (rho_p) = 1,920 kg/m^3; fluid density (rho) = 992.5 kg/m^3; particle diameter (d) = 0.0035 m; drag coefficient (C_D) = 3.7100, determine the settling velocity (v_s) in m/s.

Given

  • gravitationalacceleration(g)=9.8100m/s2gravitational acceleration (g) = 9.8100 m/s^2
  • particledensity(rhop)=1,920kg/m3particle density (rho_p) = 1,920 kg/m^3
  • fluiddensity(rho)=992.5kg/m3fluid density (rho) = 992.5 kg/m^3
  • particlediameter(d)=0.0035mparticle diameter (d) = 0.0035 m
  • dragcoefficient(CD)=3.7100drag coefficient (C_D) = 3.7100

Find

settling velocity (v_s), in m/s

Start with the thinking

  • The governing relation printed in this handbook section is General Spherical (settling).
  • Everything except v_s is given, so isolate v_s symbolically first — never rearrange after the numbers are in.
  • Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
  • The general spherical particle settling equation gives settling velocity for particles outside the Stokes' law range.

Step-by-step solution

  1. Step 1 — State the governing relation:

    vs=4g(ρp−ρ)d3CDρv_s = \sqrt{\dfrac{4 g (\rho_p - \rho) d}{3 C_D \rho}}
  2. Step 2 — Rearrange symbolically for v_s:

    vs=4g(ρp−ρ)d3CDρv_{s} = \sqrt{\dfrac{4g(\rho_p-\rho)d}{3C_D\rho}}
  3. Step 3 — List the givens: gravitational acceleration (g) = 9.8100 m/s^2, particle density (rho_p) = 1,920 kg/m^3, fluid density (rho) = 992.5 kg/m^3, particle diameter (d) = 0.0035 m, drag coefficient (C_D) = 3.7100.

  4. Step 4 — Substitute the given values:

    vs=49.8100(ρp−992.5)0.00353CD992.5v_{s} = \sqrt{\dfrac{49.8100(\rho_p-992.5)0.0035}{3C_D992.5}}
  5. Step 5 — Evaluate:

    vs=0.1078 m/sv_{s} = 0.1078\ \text{m/s}
  6. Step 6 — Check: returning v_s = 0.1078 m/s to

    vs=4g(ρp−ρ)d3CDρv_s = \sqrt{\dfrac{4 g (\rho_p - \rho) d}{3 C_D \rho}}

    reproduces the given quantities, and both sides carry the same units.

Answer:
vs=0.1078 m/sv_{s} = 0.1078\ \text{m/s}

Why the other options are there

  • 0.2157 — kept a factor of two that cancels in the correct rearrangement.
  • 0.0539 — dropped that same factor in the other direction.
  • 0.1186 — rounded an intermediate value before the final step.

Reference: FE Handbook — General Spherical Particle Settling

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