EuPhO 2026, experiment — Задача 4. Task E4: Evaporation (3.0 pts)

Experimental task Language: English · 3 т.

Условие

For the remaining tasks, you will levitate liquids, which will form small droplets in the nodes. Place droplets in the levitator using the syringes (R) with needles (S). To avoid cross-contamination, use a separate syringe for each liquid. A good starting voltage for most droplet sizes is 8–12 V; at higher voltages the droplets may explode.

Warning: Avoid spilling liquids on the electronics and the transducers. Keep the metal net (L) on the bottom of the levitator; if it gets wet, remove it and let it dry. If the transducers seem to malfunction, raise your HELP sign.

The exact shape of the levitated droplets can be complicated. Moderately deformed droplets may be approximated as an ellipsoid with semi-axes $a, b, c$, which has the volume: $V = \frac{4\pi}{3} a b c \qquad (2)$

In this task, you will study the evaporation of a liquid droplet in the levitator. A simplified description for the evaporation of a droplet with equivalent diameter $D \gtrsim 1.5\ \mathrm{mm}$ is given by: $\frac{d(D^2)}{dt} = -\gamma \qquad (3)$

where $D$ is the equivalent diameter of the droplet, i.e., the diameter of a sphere with the same volume $V$ as the real droplet, and $\gamma$ is the evaporation constant. For this task, consider only liquid I and keep the voltage constant.

a) Determine the evaporation constant $\gamma$ in units $\mathrm{m^2/s}$ for droplets with an equivalent diameter $D \gtrsim 1.5\ \mathrm{mm}$. (2.5 pts) [2,5 т.]

b) Would you over- or underestimate the time it takes for a droplet to evaporate entirely, using your result from a)? (0.5 pts) [0,5 т.]

Решение

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Оригинал в Архива: eupho2026_experiment_problems.pdf · официални решения: eupho2026_experiment_solutions.pdf