Viscosity of Solid Liquid Mixture

Design Philosophy

When solid particles are suspended in a liquid carrier, the effective viscosity of the resulting slurry is higher than that of the carrier liquid alone. Accurately estimating the viscosity of a solid-liquid mixture is essential for the hydraulic design of sludge pumping systems, screw presses, and dewatering equipment, as it directly affects pipe friction losses, pump selection, and mixing energy requirements.

This calculator uses the Thomas (1965) model, which is widely adopted in wastewater engineering for dilute to moderately concentrated suspensions (volumetric solids fraction φ up to approximately 0.25)

Density of the Mixture

The mixture density is computed from the densities and volume fractions of the constituent phases:

Conversion Between Weight and Volume Fraction

The input is accepted as percentage solids by weight (w/w), which is the standard reporting basis in wastewater practice. The weight fraction is converted to volume fraction using the individual phase densities before applying the Thomas model.

Validity Check

The calculator includes a check on the volumetric solids fraction. The Thomas model gives reliable results for φ ≤ 0.25 (approximately 25% by volume). Above this threshold, the model may underestimate viscosity significantly and the result should be treated with caution; the calculator flags this condition with an appropriate warning.

(Source: Metcalf & Eddy, Wastewater Engineering: Treatment and Resource Recovery, 5th Ed.; BWWT Course — TU Delft)

Calculator

(Note – all Yellow are user defined value, all white are fixed values, all green are calculated value, all orange is calculated not to be shown)

Instructions

Enter values highlighted in the Yellow

Green highlights are the results

In case of any invalid result of non-functioning of the calculator, please write to us at design@swaenviro.com. We will try and help you with your sizing and calculation

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