After midterm · Session 1 of 6 · 180 minutes
30 September 2026
How does pressure change the phase split at fixed temperature?
Write your prediction before opening the lab. By the end, support an answer with one controlled comparison and an independent check.
| Activity | Minutes |
|---|---|
| Opening question and essential concepts | 30 |
| One hand calculation | 20 |
| One lab demonstration | 20 |
| Break | 10 |
| Student pair investigation | 70 |
| Discussion and exit question | 30 |
The 70-minute investigation is student work with instructor support.
P_{bubble}=\sum_i x_iP_i^{sat} \frac{1}{P_{dew}}=\sum_i\frac{y_i}{P_i^{sat}}
Both equations are for fixed T, ideal liquid and ideal vapor. Using the same numerical composition in each equation describes different incipient-phase states.
z_i=(1-\beta)x_i+\beta y_i,\qquad y_i=K_i x_i \sum_i\frac{z_i(K_i-1)}{1+\beta(K_i-1)}=0
Here β is vapor mole fraction. In a nonideal liquid, K depends on the unknown x, so composition and phase fraction must be solved together.
Lab 01 synthetic binary at 350 K: P_1^{sat}=150 kPa and P_2^{sat}=60 kPa. Choose ideal liquid, z_1=0.5, P=95 kPa.
| Quantity | Expected result |
|---|---|
| Bubble P at x₁=0.5 | 105 kPa |
| Dew P at y₁=0.5 | 85.7143 kPa |
| Flash x₁, y₁ | 0.388889, 0.614035 |
| Vapor fraction β | 0.493506 |
The values are synthetic definitions, not real-fluid measurements.
Independently close both component balances and confirm that all phase compositions sum to one. Explain the phase state using bubble and dew pressures.
Use the synthetic ideal mixture at T=350 K, P=95 kPa and z1=0.5. Save the baseline, then change only P to 110 kPa. Predict the phase before calculating.
Keep one saved baseline for the pair investigation.
In Lab 01, save one ideal two-phase baseline and one changed pressure at the same T and z. Predict the change, report phase amounts and check one component balance by hand.
Use 20 minutes to compare results and discuss unexpected behavior.
How does pressure change the phase split at fixed temperature?
Use the final 10 minutes to explain your answer individually and name one assumption that limits it.
In Lab 01, save one ideal two-phase baseline and one changed pressure at the same T and z. Predict the change, report phase amounts and check one component balance by hand.
Assessment 1 and independent checkpoint
Retain one study JSON, one comparison and a short explanation. Continue from your classroom case. The hand checkpoint is part of this time budget.
Choose one extension: compare liquid activity models, examine zero versus nonzero virial coefficients in Lab 09, or add the energy balance in Lab 07.
Session appendix · Module reference
Learning path · Offline package
Optional work is additional. Complete the required investigation first.