How to Calculate Rate of Filtration

Filtration Rate & Flux Calculator

Milliliters (mL) Liters (L) Gallons (US) Cubic Meters (m³)

Minutes Seconds Hours

Square Meters (m²) Square Centimeters (cm²) Square Feet (ft²)

Required if you want to calculate Filtration Flux (rate per unit area).

How to Calculate Rate of Filtration

The rate of filtration determines how fast a fluid passes through a filter medium. Whether you are working in wastewater treatment, chemical engineering, or a laboratory setting, calculating the filtration rate is essential for sizing pumps, estimating process times, and monitoring filter efficiency.

This calculator helps you determine both the Volumetric Flow Rate and the Filtration Flux. While flow rate measures the total volume over time, flux measures the efficiency of the membrane or filter based on its surface area.

The Filtration Rate Formula

The basic calculation for the average rate of filtration (flow rate) is simply the volume of filtrate collected divided by the time it took to collect it.

Rate (Q) = Volume (V) / Time (t)

Where:

• V is the total volume of fluid filtered (e.g., Liters or Gallons).
• t is the time duration of the filtration process (e.g., Minutes or Hours).

Calculating Filtration Flux

In industrial and membrane filtration (like Reverse Osmosis or Ultrafiltration), the surface area of the filter is critical. This is known as Filtration Flux ($J$).

Flux (J) = Rate (Q) / Surface Area (A)

The standard unit for flux is often LMH (Liters per Square Meter per Hour). This metric allows engineers to compare the performance of filters of different sizes.

Example Calculation

Let's say you are testing a new membrane filter:

• Volume Collected: 50 Liters
• Time Elapsed: 30 Minutes
• Filter Surface Area: 2 Square Meters (m²)

Step 1: Calculate Flow Rate
Convert time to hours: 30 mins = 0.5 hours.
$Q = 50 \text{ L} / 0.5 \text{ hr} = 100 \text{ L/hr}$.

Step 2: Calculate Flux
$J = 100 \text{ L/hr} / 2 \text{ m}^2 = 50 \text{ LMH}$.

Factors Affecting Filtration Rate

Several variables can impact how quickly filtration occurs:

• Pressure Drop: Higher pressure typically increases the rate, according to Darcy's Law.
• Viscosity: Thicker fluids (higher viscosity) filter more slowly.
• Filter Resistance: As the filter cake builds up (fouling), resistance increases, and the rate decreases.
• Temperature: Higher temperatures generally lower fluid viscosity, thereby increasing the filtration rate.