Capillary Number: Compare Viscous Stress with Interfacial Tension

Define the Process Model

Using a selected viscosity μ, velocity v and interfacial tension σ, Ca = μv/σ. COMSOL’s reference presents this dimensionless ratio. State which phase provides the viscosity and which motion supplies the velocity. A non-Newtonian material also needs a justified viscosity condition rather than an unrelated catalogue value.

Compare a Hypothetical Case

In an invented comparison, μ = 0.10 Pa·s, v = 0.020 m/s and σ = 0.020 N/m give Ca = 0.10. Increasing only viscosity to 0.20 Pa·s gives 0.20. Increasing only interfacial tension to 0.040 N/m instead gives 0.05. These cases describe the selected stress balance; they do not specify final droplet size.

Complete the Engineering Review

Keep viscosity, interface age, temperature and composition on the same comparison basis. If a process proposal quotes both Ca and We, check their separate velocity and length conventions instead of treating them as interchangeable labels. Ask what model or experiment connects the ratio to the required deformation or breakup outcome.

Use the ointment-manufacturing page with the offered mixing arrangement and actual formulation information. No critical capillary number or machine operating speed is prescribed. The worksheet is for selecting a consistent physical basis before interpreting an interface-related performance statement.

Define the phase viscosity and velocity basis before interpreting viscous-to-interface competition.

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.

• ointment-manufacturing page

Primary References

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

• COMSOL’s reference
• ointment-manufacturing page