Bubble and Dew Points: Identify the First New Phase

Define the Phase or Process Boundary

LearnChemE's equilibrium summary defines the bubble boundary as first vapor from liquid and the dew boundary as first liquid from vapor. Specify pressure, overall composition and direction of the temperature change. For a mixture, the start and end of a phase change need not have the same temperature.

Review a Hypothetical Comparison

Consider a fictional equilibrium diagram at one fixed pressure. Its liquid-side boundary is 78 °C and vapor-side boundary is 90 °C at a stated overall composition. Heating the initially liquid charge first produces vapor at 78 °C. Cooling the initially vapor charge first produces liquid at 90 °C. Calling both numbers the boiling temperature would erase the phase and path used to read them. These assigned values are not properties of any real solvent.

Keep the Evidence with the Decision

Annotate the starting phase and draw the temperature path on the actual diagram. Keep the pressure and composition with each boundary value. If an operating proposal uses one temperature for a mixed-phase interval, ask what equilibrium state and phase fraction that temperature represents before accepting the proposal.

This is an equilibrium reading exercise. Actual heating delay, pressure gradients, mixture nonideality and heat transfer require their own evidence; no residence time or machine setting follows from the two assigned boundaries.

Does the selected equilibrium boundary describe the first vapor from a liquid or the first liquid from a vapor?

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

Customer Questions

Primary References

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

• LearnChemE's equilibrium summary
• Reference from hmpharmamachines.com