What is the Hagen-Poiseuille equation used for?

The Hagen-Poiseuille equation calculates the volumetric flow rate of a viscous Newtonian fluid through a circular pipe under laminar flow conditions (Reynolds number below 2300). It relates flow rate to pipe diameter (to the fourth power), pressure drop, fluid viscosity, and pipe length.

How do I calculate heat load for a fluid system?

Heat load is calculated as Q = ṁ × Cₚ × ΔT, where ṁ is the mass flow rate in kg/s, Cₚ is the specific heat capacity in J/(kg·K), and ΔT is the temperature difference in Kelvin. For water, Cₚ ≈ 4186 J/(kg·K); for air, Cₚ ≈ 1005 J/(kg·K).

What does Reynolds number indicate in pipe flow?

Reynolds number (Re = ρvD/μ) predicts the flow regime inside a pipe. Re below 2300 indicates laminar flow, 2300–4000 is the transitional zone, and Re above 4000 indicates turbulent flow. Knowing the flow regime is essential for selecting the correct friction factor and pressure drop model.

How do I convert between pressure units like psi, bar, and kPa?

1 bar = 100,000 Pa = 100 kPa = 14.5038 psi = 0.9869 atm. The EveryEng pressure converter instantly converts between Pa, kPa, MPa, bar, psi, and atm.

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Pressure Drop ΔP

Pipe Diameter D

Dynamic Viscosity μ

Pa·s

Pipe Length L

Flow Rate Q153.3981 L/s (552233.08 L/h)

Valid for laminar flow (Re < 2300). Water at 20°C: μ ≈ 0.001 Pa·s.

Mass Flow Rate ṁ

kg/s

Specific Heat C_p

J/(kg·K)

Temperature Diff. ΔT

Heat Load Q41.860 kW (41860 W)

Water C_p ≈ 4186 J/(kg·K) | Air C_p ≈ 1005 J/(kg·K)

Point Load W

Span L

Young's Modulus E

Moment of Inertia I

m⁴

Max Deflection δ0.4067 mm

Simply-supported beam, central point load. Steel E ≈ 200 GPa (200×10⁹ Pa).

Enter any two values — the third and power are solved automatically.

Voltage V

Current I

Resistance R

ResultEnter any two values

Fluid Density ρ

kg/m³

Flow Velocity v

m/s

Hydraulic Diameter D

Dynamic Viscosity μ

Pa·s

Reynolds NumberRe = 99800 (Turbulent flow)

Water at 20°C: ρ ≈ 998 kg/m³, μ ≈ 0.001 Pa·s. Re < 2300 → Laminar.

Torque T

N·m

Rotational Speed N

rpm

Power P15.184 kW (20.363 hp)

1 kW = 1.341 hp | Typical AC motor: 1450 or 2900 rpm (50 Hz)

Value & Unit

Pa100000.00

kPa100.000000

MPa0.100000

bar1.000000

psi14.503774

atm0.986923

Driver (Input) Teeth

teeth

Driven (Output) Teeth

teeth

Input Speed

rpm

Input Torque

N·m

ResultRatio 3.000:1 | Output 483.3 rpm | Torque out 150.0 N·m

Speed and torque change inversely with gear ratio (ignoring efficiency losses).

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