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Turbulent Flow Impeller Mixer

Environmental Engineering · FE Reference Handbook section

Environmental Engineering
4 formulas
10 exam-style examples
~53 min
All Environmental Engineering lectures

Handbook notes for this section

Definitions and conditions exactly as the handbook states them.

  • Values of the Impeller Constant KT
  • Note: Constant assumes baffled tanks having four baffles at the tank
  • wall with a width equal to 10% of the tank diameter.
  • Reprinted with permission from Industrial & Engineering Chemistry,

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
Turbulent Flow Impeller Mixer — solve for power input — Turbulent Flow Impeller Mixer

turbulent flow impeller mixer power requirement for rapid mix Given impeller constant (K_T) = 5.8500; fluid density (rho) = 995.0 kg/m^3; rotational speed (N) = 4.3000 rev/s; impeller diameter (D_i) = 0.5700 m, determine the power input (P) in W.

Given

  • impellerconstant(KT)=5.8500impeller constant (K_T) = 5.8500
  • fluiddensity(rho)=995.0kg/m3fluid density (rho) = 995.0 kg/m^3
  • rotationalspeed(N)=4.3000rev/srotational speed (N) = 4.3000 rev/s
  • impeller diameter (D_i) = 0.5700 m

Find

power input (P), in W

Start with the thinking

  • The governing relation printed in this handbook section is Turbulent Flow Impeller Mixer.
  • Everything except P is given, so isolate P 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.
  • A turbulent flow impeller mixer requires power proportional to impeller speed and diameter for rapid mixing in a basin.
turbulent flow impeller mixer basin

Figure 1 — schematic for Turbulent Flow Impeller Mixer — solve for power input — Turbulent Flow Impeller Mixer

Step-by-step solution

  1. Step 1 — State the governing relation:

    P=KTρN3Di5P = K_T \rho N^3 D_i^5
  2. Step 2 — Rearrange symbolically for P:

    P=KTρN3Di5P = K_T\rho N^3 D_i^5
  3. Step 3 — List the givens: impeller constant (K_T) = 5.8500, fluid density (rho) = 995.0 kg/m^3, rotational speed (N) = 4.3000 rev/s, impeller diameter (D_i) = 0.5700 m.

  4. Step 4 — Substitute the given values:

    P=KT995.04.30003Di5P = K_T995.0 4.3000^3 D_i^5
  5. Step 5 — Evaluate:

    P=27846 WP = 27846\ \text{W}
  6. Step 6 — Check: returning P = 27,846 W to

    P=KTρN3Di5P = K_T \rho N^3 D_i^5

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

Answer:
P=27846 WP = 27846\ \text{W}

Why the other options are there

  • 55,691 — kept a factor of two that cancels in the correct rearrangement.
  • 13,923 — dropped that same factor in the other direction.
  • 30,630 — rounded an intermediate value before the final step.

Reference: FE Handbook — Turbulent Flow Impeller Mixer

Example 2
Turbulent Flow Impeller Mixer — solve for rotational speed — Turbulent Flow Impeller Mixer (2)

turbulent flow impeller mixer design in a coagulation basin Given impeller constant (K_T) = 3.7500; fluid density (rho) = 999.5 kg/m^3; impeller diameter (D_i) = 1.0200 m; power input (P) = 33,767 W, determine the rotational speed (N) in rev/s.

Given

  • impellerconstant(KT)=3.7500impeller constant (K_T) = 3.7500
  • fluiddensity(rho)=999.5kg/m3fluid density (rho) = 999.5 kg/m^3
  • impeller diameter (D_i) = 1.0200 m

  • powerinput(P)=33,767Wpower input (P) = 33,767 W

Find

rotational speed (N), in rev/s

Start with the thinking

  • The governing relation printed in this handbook section is Turbulent Flow Impeller Mixer.
  • Everything except N is given, so isolate N 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.
  • A turbulent flow impeller mixer requires power proportional to impeller speed and diameter for rapid mixing in a basin.
turbulent flow impeller mixer basin

Figure 2 — schematic for Turbulent Flow Impeller Mixer — solve for rotational speed — Turbulent Flow Impeller Mixer (2)

Step-by-step solution

  1. Step 1 — State the governing relation:

    P=KTρN3Di5P = K_T \rho N^3 D_i^5
  2. Step 2 — Rearrange symbolically for N:

    N=PKTρDi53N = \sqrt[3]{\dfrac{P}{K_T\rho D_i^5}}
  3. Step 3 — List the givens: impeller constant (K_T) = 3.7500, fluid density (rho) = 999.5 kg/m^3, impeller diameter (D_i) = 1.0200 m, power input (P) = 33,767 W.

  4. Step 4 — Substitute the given values:

    N=33767KT999.5Di53N = \sqrt[3]{\dfrac{33767}{K_T999.5 D_i^5}}
  5. Step 5 — Evaluate:

    N=2.0132 rev/sN = 2.0132\ \text{rev/s}
  6. Step 6 — Check: returning N = 2.0132 rev/s to

    P=KTρN3Di5P = K_T \rho N^3 D_i^5

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

Answer:
N=2.0132 rev/sN = 2.0132\ \text{rev/s}

Why the other options are there

  • 4.0265 — kept a factor of two that cancels in the correct rearrangement.
  • 1.0066 — dropped that same factor in the other direction.
  • 2.2145 — rounded an intermediate value before the final step.

Reference: FE Handbook — Turbulent Flow Impeller Mixer

Example 3
Turbulent Flow Impeller Mixer — solve for impeller diameter — Turbulent Flow Impeller Mixer (3)

turbulent impeller flow mixer power calculation for flocculation Given impeller constant (K_T) = 2.0000; fluid density (rho) = 992.0 kg/m^3; rotational speed (N) = 0.8500 rev/s; power input (P) = 23,718 W, determine the impeller diameter (D_i) in m.

Given

  • impellerconstant(KT)=2.0000impeller constant (K_T) = 2.0000
  • fluiddensity(rho)=992.0kg/m3fluid density (rho) = 992.0 kg/m^3
  • rotationalspeed(N)=0.8500rev/srotational speed (N) = 0.8500 rev/s
  • powerinput(P)=23,718Wpower input (P) = 23,718 W

Find

impeller diameter (D_i), in m

Start with the thinking

  • The governing relation printed in this handbook section is Turbulent Flow Impeller Mixer.
  • Everything except D_i is given, so isolate D_i 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.
  • A turbulent flow impeller mixer requires power proportional to impeller speed and diameter for rapid mixing in a basin.
turbulent flow impeller mixer basin

Figure 3 — schematic for Turbulent Flow Impeller Mixer — solve for impeller diameter — Turbulent Flow Impeller Mixer (3)

Step-by-step solution

  1. Step 1 — State the governing relation:

    P=KTρN3Di5P = K_T \rho N^3 D_i^5
  2. Step 2 — Rearrange symbolically for D_i:

    Di=(PKTρN3)1/5D_{i} = \left(\dfrac{P}{K_T\rho N^3}\right)^{1/5}
  3. Step 3 — List the givens: impeller constant (K_T) = 2.0000, fluid density (rho) = 992.0 kg/m^3, rotational speed (N) = 0.8500 rev/s, power input (P) = 23,718 W.

  4. Step 4 — Substitute the given values:

    Di=(23718KT992.00.85003)1/5D_{i} = \left(\dfrac{23718}{K_T992.0 0.8500^3}\right)^{1/5}
  5. Step 5 — Evaluate:

    Di=1.8107 mD_{i} = 1.8107\ \text{m}
  6. Step 6 — Check: returning D_i = 1.8107 m to

    P=KTρN3Di5P = K_T \rho N^3 D_i^5

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

Answer:
Di=1.8107 mD_{i} = 1.8107\ \text{m}

Why the other options are there

  • 3.6215 — kept a factor of two that cancels in the correct rearrangement.
  • 0.9054 — dropped that same factor in the other direction.
  • 1.9918 — rounded an intermediate value before the final step.

Reference: FE Handbook — Turbulent Flow Impeller Mixer

Example 4
Turbulent Flow Impeller Mixer — solve for power input (case 2) — Turbulent Flow Impeller Mixer (4)

turbulent flow impeller mixer power requirement for rapid mix Given impeller constant (K_T) = 1.0500; fluid density (rho) = 995.5 kg/m^3; rotational speed (N) = 1.7500 rev/s; impeller diameter (D_i) = 1.2100 m, determine the power input (P) in W.

Given

  • impellerconstant(KT)=1.0500impeller constant (K_T) = 1.0500
  • fluiddensity(rho)=995.5kg/m3fluid density (rho) = 995.5 kg/m^3
  • rotationalspeed(N)=1.7500rev/srotational speed (N) = 1.7500 rev/s
  • impeller diameter (D_i) = 1.2100 m

Find

power input (P), in W

Start with the thinking

  • The governing relation printed in this handbook section is Turbulent Flow Impeller Mixer.
  • Everything except P is given, so isolate P 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.
  • A turbulent flow impeller mixer requires power proportional to impeller speed and diameter for rapid mixing in a basin.
turbulent flow impeller mixer basin

Figure 4 — schematic for Turbulent Flow Impeller Mixer — solve for power input (case 2) — Turbulent Flow Impeller Mixer (4)

Step-by-step solution

  1. Step 1 — State the governing relation:

    P=KTρN3Di5P = K_T \rho N^3 D_i^5
  2. Step 2 — Rearrange symbolically for P:

    P=KTρN3Di5P = K_T\rho N^3 D_i^5
  3. Step 3 — List the givens: impeller constant (K_T) = 1.0500, fluid density (rho) = 995.5 kg/m^3, rotational speed (N) = 1.7500 rev/s, impeller diameter (D_i) = 1.2100 m.

  4. Step 4 — Substitute the given values:

    P=KT995.51.75003Di5P = K_T995.5 1.7500^3 D_i^5
  5. Step 5 — Evaluate:

    P=14530 WP = 14530\ \text{W}
  6. Step 6 — Check: returning P = 14,530 W to

    P=KTρN3Di5P = K_T \rho N^3 D_i^5

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

Answer:
P=14530 WP = 14530\ \text{W}

Why the other options are there

  • 29,060 — kept a factor of two that cancels in the correct rearrangement.
  • 7,265 — dropped that same factor in the other direction.
  • 15,983 — rounded an intermediate value before the final step.

Reference: FE Handbook — Turbulent Flow Impeller Mixer

Example 5
Turbulent Flow Impeller Mixer — solve for rotational speed (case 2) — Turbulent Flow Impeller Mixer (5)

turbulent flow impeller mixer design in a coagulation basin Given impeller constant (K_T) = 0.7000; fluid density (rho) = 995.0 kg/m^3; impeller diameter (D_i) = 0.6700 m; power input (P) = 46,243 W, determine the rotational speed (N) in rev/s.

Given

  • impellerconstant(KT)=0.7000impeller constant (K_T) = 0.7000
  • fluiddensity(rho)=995.0kg/m3fluid density (rho) = 995.0 kg/m^3
  • impeller diameter (D_i) = 0.6700 m

  • powerinput(P)=46,243Wpower input (P) = 46,243 W

Find

rotational speed (N), in rev/s

Start with the thinking

  • The governing relation printed in this handbook section is Turbulent Flow Impeller Mixer.
  • Everything except N is given, so isolate N 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.
  • A turbulent flow impeller mixer requires power proportional to impeller speed and diameter for rapid mixing in a basin.
turbulent flow impeller mixer basin

Figure 5 — schematic for Turbulent Flow Impeller Mixer — solve for rotational speed (case 2) — Turbulent Flow Impeller Mixer (5)

Step-by-step solution

  1. Step 1 — State the governing relation:

    P=KTρN3Di5P = K_T \rho N^3 D_i^5
  2. Step 2 — Rearrange symbolically for N:

    N=PKTρDi53N = \sqrt[3]{\dfrac{P}{K_T\rho D_i^5}}
  3. Step 3 — List the givens: impeller constant (K_T) = 0.7000, fluid density (rho) = 995.0 kg/m^3, impeller diameter (D_i) = 0.6700 m, power input (P) = 46,243 W.

  4. Step 4 — Substitute the given values:

    N=46243KT995.0Di53N = \sqrt[3]{\dfrac{46243}{K_T995.0 D_i^5}}
  5. Step 5 — Evaluate:

    N=7.8931 rev/sN = 7.8931\ \text{rev/s}
  6. Step 6 — Check: returning N = 7.8931 rev/s to

    P=KTρN3Di5P = K_T \rho N^3 D_i^5

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

Answer:
N=7.8931 rev/sN = 7.8931\ \text{rev/s}

Why the other options are there

  • 15.7863 — kept a factor of two that cancels in the correct rearrangement.
  • 3.9466 — dropped that same factor in the other direction.
  • 8.6825 — rounded an intermediate value before the final step.

Reference: FE Handbook — Turbulent Flow Impeller Mixer

Example 6
Turbulent Flow Impeller Mixer — solve for impeller diameter (case 2) — Turbulent Flow Impeller Mixer (6)

turbulent impeller flow mixer power calculation for flocculation Given impeller constant (K_T) = 3.6500; fluid density (rho) = 999.5 kg/m^3; rotational speed (N) = 3.0000 rev/s; power input (P) = 32,887 W, determine the impeller diameter (D_i) in m.

Given

  • impellerconstant(KT)=3.6500impeller constant (K_T) = 3.6500
  • fluiddensity(rho)=999.5kg/m3fluid density (rho) = 999.5 kg/m^3
  • rotationalspeed(N)=3.0000rev/srotational speed (N) = 3.0000 rev/s
  • powerinput(P)=32,887Wpower input (P) = 32,887 W

Find

impeller diameter (D_i), in m

Start with the thinking

  • The governing relation printed in this handbook section is Turbulent Flow Impeller Mixer.
  • Everything except D_i is given, so isolate D_i 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.
  • A turbulent flow impeller mixer requires power proportional to impeller speed and diameter for rapid mixing in a basin.
turbulent flow impeller mixer basin

Figure 6 — schematic for Turbulent Flow Impeller Mixer — solve for impeller diameter (case 2) — Turbulent Flow Impeller Mixer (6)

Step-by-step solution

  1. Step 1 — State the governing relation:

    P=KTρN3Di5P = K_T \rho N^3 D_i^5
  2. Step 2 — Rearrange symbolically for D_i:

    Di=(PKTρN3)1/5D_{i} = \left(\dfrac{P}{K_T\rho N^3}\right)^{1/5}
  3. Step 3 — List the givens: impeller constant (K_T) = 3.6500, fluid density (rho) = 999.5 kg/m^3, rotational speed (N) = 3.0000 rev/s, power input (P) = 32,887 W.

  4. Step 4 — Substitute the given values:

    Di=(32887KT999.53.00003)1/5D_{i} = \left(\dfrac{32887}{K_T999.5 3.0000^3}\right)^{1/5}
  5. Step 5 — Evaluate:

    Di=0.8030 mD_{i} = 0.8030\ \text{m}
  6. Step 6 — Check: returning D_i = 0.8030 m to

    P=KTρN3Di5P = K_T \rho N^3 D_i^5

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

Answer:
Di=0.8030 mD_{i} = 0.8030\ \text{m}

Why the other options are there

  • 1.6060 — kept a factor of two that cancels in the correct rearrangement.
  • 0.4015 — dropped that same factor in the other direction.
  • 0.8833 — rounded an intermediate value before the final step.

Reference: FE Handbook — Turbulent Flow Impeller Mixer

Example 7
Turbulent Flow Impeller Mixer — solve for power input (case 3) — Turbulent Flow Impeller Mixer (7)

turbulent flow impeller mixer power requirement for rapid mix Given impeller constant (K_T) = 4.9000; fluid density (rho) = 1,000 kg/m^3; rotational speed (N) = 0.9500 rev/s; impeller diameter (D_i) = 0.9900 m, determine the power input (P) in W.

Given

  • impellerconstant(KT)=4.9000impeller constant (K_T) = 4.9000
  • fluiddensity(rho)=1,000kg/m3fluid density (rho) = 1,000 kg/m^3
  • rotationalspeed(N)=0.9500rev/srotational speed (N) = 0.9500 rev/s
  • impeller diameter (D_i) = 0.9900 m

Find

power input (P), in W

Start with the thinking

  • The governing relation printed in this handbook section is Turbulent Flow Impeller Mixer.
  • Everything except P is given, so isolate P 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.
  • A turbulent flow impeller mixer requires power proportional to impeller speed and diameter for rapid mixing in a basin.
turbulent flow impeller mixer basin

Figure 7 — schematic for Turbulent Flow Impeller Mixer — solve for power input (case 3) — Turbulent Flow Impeller Mixer (7)

Step-by-step solution

  1. Step 1 — State the governing relation:

    P=KTρN3Di5P = K_T \rho N^3 D_i^5
  2. Step 2 — Rearrange symbolically for P:

    P=KTρN3Di5P = K_T\rho N^3 D_i^5
  3. Step 3 — List the givens: impeller constant (K_T) = 4.9000, fluid density (rho) = 1,000 kg/m^3, rotational speed (N) = 0.9500 rev/s, impeller diameter (D_i) = 0.9900 m.

  4. Step 4 — Substitute the given values:

    P=KT10000.95003Di5P = K_T1000 0.9500^3 D_i^5
  5. Step 5 — Evaluate:

    P=3995 WP = 3995\ \text{W}
  6. Step 6 — Check: returning P = 3,995 W to

    P=KTρN3Di5P = K_T \rho N^3 D_i^5

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

Answer:
P=3995 WP = 3995\ \text{W}

Why the other options are there

  • 7,990 — kept a factor of two that cancels in the correct rearrangement.
  • 1,998 — dropped that same factor in the other direction.
  • 4,395 — rounded an intermediate value before the final step.

Reference: FE Handbook — Turbulent Flow Impeller Mixer

Example 8
Turbulent Flow Impeller Mixer — solve for rotational speed (case 3) — Turbulent Flow Impeller Mixer (8)

turbulent flow impeller mixer design in a coagulation basin Given impeller constant (K_T) = 0.7000; fluid density (rho) = 999.0 kg/m^3; impeller diameter (D_i) = 0.7600 m; power input (P) = 49,594 W, determine the rotational speed (N) in rev/s.

Given

  • impellerconstant(KT)=0.7000impeller constant (K_T) = 0.7000
  • fluiddensity(rho)=999.0kg/m3fluid density (rho) = 999.0 kg/m^3
  • impeller diameter (D_i) = 0.7600 m

  • powerinput(P)=49,594Wpower input (P) = 49,594 W

Find

rotational speed (N), in rev/s

Start with the thinking

  • The governing relation printed in this handbook section is Turbulent Flow Impeller Mixer.
  • Everything except N is given, so isolate N 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.
  • A turbulent flow impeller mixer requires power proportional to impeller speed and diameter for rapid mixing in a basin.
turbulent flow impeller mixer basin

Figure 8 — schematic for Turbulent Flow Impeller Mixer — solve for rotational speed (case 3) — Turbulent Flow Impeller Mixer (8)

Step-by-step solution

  1. Step 1 — State the governing relation:

    P=KTρN3Di5P = K_T \rho N^3 D_i^5
  2. Step 2 — Rearrange symbolically for N:

    N=PKTρDi53N = \sqrt[3]{\dfrac{P}{K_T\rho D_i^5}}
  3. Step 3 — List the givens: impeller constant (K_T) = 0.7000, fluid density (rho) = 999.0 kg/m^3, impeller diameter (D_i) = 0.7600 m, power input (P) = 49,594 W.

  4. Step 4 — Substitute the given values:

    N=49594KT999.0Di53N = \sqrt[3]{\dfrac{49594}{K_T999.0 D_i^5}}
  5. Step 5 — Evaluate:

    N=6.5398 rev/sN = 6.5398\ \text{rev/s}
  6. Step 6 — Check: returning N = 6.5398 rev/s to

    P=KTρN3Di5P = K_T \rho N^3 D_i^5

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

Answer:
N=6.5398 rev/sN = 6.5398\ \text{rev/s}

Why the other options are there

  • 13.0796 — kept a factor of two that cancels in the correct rearrangement.
  • 3.2699 — dropped that same factor in the other direction.
  • 7.1938 — rounded an intermediate value before the final step.

Reference: FE Handbook — Turbulent Flow Impeller Mixer

Example 9
Turbulent Flow Impeller Mixer — solve for impeller diameter (case 3) — Turbulent Flow Impeller Mixer (9)

turbulent impeller flow mixer power calculation for flocculation Given impeller constant (K_T) = 3.5000; fluid density (rho) = 992.0 kg/m^3; rotational speed (N) = 0.5000 rev/s; power input (P) = 2,722 W, determine the impeller diameter (D_i) in m.

Given

  • impellerconstant(KT)=3.5000impeller constant (K_T) = 3.5000
  • fluiddensity(rho)=992.0kg/m3fluid density (rho) = 992.0 kg/m^3
  • rotationalspeed(N)=0.5000rev/srotational speed (N) = 0.5000 rev/s
  • powerinput(P)=2,722Wpower input (P) = 2,722 W

Find

impeller diameter (D_i), in m

Start with the thinking

  • The governing relation printed in this handbook section is Turbulent Flow Impeller Mixer.
  • Everything except D_i is given, so isolate D_i 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.
  • A turbulent flow impeller mixer requires power proportional to impeller speed and diameter for rapid mixing in a basin.
turbulent flow impeller mixer basin

Figure 9 — schematic for Turbulent Flow Impeller Mixer — solve for impeller diameter (case 3) — Turbulent Flow Impeller Mixer (9)

Step-by-step solution

  1. Step 1 — State the governing relation:

    P=KTρN3Di5P = K_T \rho N^3 D_i^5
  2. Step 2 — Rearrange symbolically for D_i:

    Di=(PKTρN3)1/5D_{i} = \left(\dfrac{P}{K_T\rho N^3}\right)^{1/5}
  3. Step 3 — List the givens: impeller constant (K_T) = 3.5000, fluid density (rho) = 992.0 kg/m^3, rotational speed (N) = 0.5000 rev/s, power input (P) = 2,722 W.

  4. Step 4 — Substitute the given values:

    Di=(2722KT992.00.50003)1/5D_{i} = \left(\dfrac{2722}{K_T992.0 0.5000^3}\right)^{1/5}
  5. Step 5 — Evaluate:

    Di=1.4437 mD_{i} = 1.4437\ \text{m}
  6. Step 6 — Check: returning D_i = 1.4437 m to

    P=KTρN3Di5P = K_T \rho N^3 D_i^5

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

Answer:
Di=1.4437 mD_{i} = 1.4437\ \text{m}

Why the other options are there

  • 2.8874 — kept a factor of two that cancels in the correct rearrangement.
  • 0.7219 — dropped that same factor in the other direction.
  • 1.5881 — rounded an intermediate value before the final step.

Reference: FE Handbook — Turbulent Flow Impeller Mixer

Example 10
Turbulent Flow Impeller Mixer — solve for power input (case 4) — Turbulent Flow Impeller Mixer (10)

turbulent flow impeller mixer power requirement for rapid mix Given impeller constant (K_T) = 4.7500; fluid density (rho) = 993.0 kg/m^3; rotational speed (N) = 1.6500 rev/s; impeller diameter (D_i) = 0.2200 m, determine the power input (P) in W.

Given

  • impellerconstant(KT)=4.7500impeller constant (K_T) = 4.7500
  • fluiddensity(rho)=993.0kg/m3fluid density (rho) = 993.0 kg/m^3
  • rotationalspeed(N)=1.6500rev/srotational speed (N) = 1.6500 rev/s
  • impeller diameter (D_i) = 0.2200 m

Find

power input (P), in W

Start with the thinking

  • The governing relation printed in this handbook section is Turbulent Flow Impeller Mixer.
  • Everything except P is given, so isolate P 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.
  • A turbulent flow impeller mixer requires power proportional to impeller speed and diameter for rapid mixing in a basin.
turbulent flow impeller mixer basin

Figure 10 — schematic for Turbulent Flow Impeller Mixer — solve for power input (case 4) — Turbulent Flow Impeller Mixer (10)

Step-by-step solution

  1. Step 1 — State the governing relation:

    P=KTρN3Di5P = K_T \rho N^3 D_i^5
  2. Step 2 — Rearrange symbolically for P:

    P=KTρN3Di5P = K_T\rho N^3 D_i^5
  3. Step 3 — List the givens: impeller constant (K_T) = 4.7500, fluid density (rho) = 993.0 kg/m^3, rotational speed (N) = 1.6500 rev/s, impeller diameter (D_i) = 0.2200 m.

  4. Step 4 — Substitute the given values:

    P=KT993.01.65003Di5P = K_T993.0 1.6500^3 D_i^5
  5. Step 5 — Evaluate:

    P=10.9196 WP = 10.9196\ \text{W}
  6. Step 6 — Check: returning P = 10.9196 W to

    P=KTρN3Di5P = K_T \rho N^3 D_i^5

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

Answer:
P=10.9196 WP = 10.9196\ \text{W}

Why the other options are there

  • 21.8393 — kept a factor of two that cancels in the correct rearrangement.
  • 5.4598 — dropped that same factor in the other direction.
  • 12.0116 — rounded an intermediate value before the final step.

Reference: FE Handbook — Turbulent Flow Impeller Mixer

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