Tank Gravity Drain Flow Rate Calculator

Manning's Equation for Flow Rate:

\[ Q = \frac{1}{n} \times A \times R^{\frac{2}{3}} \times S^{\frac{1}{2}} \]

Manning's Roughness Coefficient (n):

Cross-sectional Area (A):

m²

Hydraulic Radius (R):

Slope (S):

Flow Rate (Q): m³/s

1. What is a Tank Gravity Drain Flow Rate Calculator?

Definition: This calculator estimates the flow rate of liquid draining from a tank under gravity using Manning's equation.

Purpose: It helps engineers and designers determine the drainage rate for tanks, reservoirs, and other gravity-fed systems.

2. How Does the Calculator Work?

The calculator uses Manning's equation:

\[ Q = \frac{1}{n} \times A \times R^{\frac{2}{3}} \times S^{\frac{1}{2}} \]

Where:

\( Q \) — Flow rate (m³/s)
\( n \) — Manning's roughness coefficient (dimensionless)
\( A \) — Cross-sectional area of flow (m²)
\( R \) — Hydraulic radius (m) [Area/Wetted Perimeter]
\( S \) — Slope of the energy grade line (dimensionless)

Explanation: The equation calculates flow rate based on channel geometry, roughness, and slope.

3. Importance of Flow Rate Calculation

Details: Accurate flow rate estimation ensures proper tank drainage times, prevents overflow, and helps design appropriate outlet systems.

4. Using the Calculator

Tips:

Manning's n: 0.013 for smooth concrete, 0.015 for cast iron, 0.022 for corrugated metal
Hydraulic radius R = Area / Wetted Perimeter
Slope S is the vertical drop divided by horizontal distance

5. Frequently Asked Questions (FAQ)

Q1: What is Manning's roughness coefficient?
A: A dimensionless value representing the channel's resistance to flow, affected by material and surface condition.

Q2: How do I calculate hydraulic radius?
A: For full pipe flow, R = D/4 where D is diameter. For other shapes, divide cross-sectional area by wetted perimeter.

Q3: What units should I use?
A: Use consistent SI units: meters for length, m² for area, and the result will be in m³/s.

Q4: Can I use this for partially full pipes?
A: Yes, but you must calculate the actual flow area and wetted perimeter for the partial depth.

Q5: What's a typical slope value?
A: For gravity drainage, slopes typically range from 0.01 (1%) to 0.05 (5%) depending on application.