Mass-Transfer Coefficient and Driving Force: Keep Both in the Flux Model

Define the Process Model

COMSOL’s external-convection boundary description uses a concentration-driven flux with a coefficient kc and bulk concentration cb. For the stated molar-concentration convention, a simple relation is J = kc(cb − cs). With kc in m/s and concentration in mol/m³, J is mol/m²/s. Other conventions may use different coefficient units.

Compare a Hypothetical Case

Take an invented kc = 2×10⁻⁵ m/s and concentration difference 30 mol/m³. The model gives flux 6×10⁻⁴ mol/m²/s. Across an assumed active area of 0.50 m², the corresponding transfer rate is 3×10⁻⁴ mol/s. Doubling the coefficient while halving that concentration difference leaves the modeled flux unchanged.

Complete the Engineering Review

Write the species, direction, area and concentration convention in the same row as the coefficient. Identify how the surface or interface concentration is established, and preserve the selected model’s conditions. Keep molar flux per unit area separate from total transfer rate. A larger coefficient need not produce a larger observed rate if another input changes.

For a processing-tank project, obtain process-specific composition and interface evidence. These inputs are hypothetical and do not specify an HM mass-transfer coefficient. The worksheet provides a consistent unit and driving-force record for reviewing a transfer claim.

Which concentration difference and transfer boundary support the flux estimate?

This blank worksheet is for your own project. It contains no H M machine trial result.

Customer Questions

Related Equipment References

Review the actual offered equipment and application separately from this educational example.

• processing-tank project

Primary References

These references support the technical principles discussed in this guide. The worked examples and review questions are educational.

• COMSOL’s external-convection boundary description
• processing-tank project