Stability of axisymmetric pendant drops

This talk focuses on pendant drop experiments conducted to study the stability at Bond numbers, $0.3 < Bo = (L/\lambda_{c})^{2} < 5$, where $R$ is the characteristic length and $\lambda_{c}$ is the capillary length. To determine the characteristic length, we used needle OD for thin-walled needles and ID for thick-walled needles. The fluid drops were generated using a syringe that was mounted on a vertically oriented syringe pump. The syringe pump drove the syringe's plunger at a very low flow rate (1 $\mu$l/min - 50 $\mu$l/min). Images of a pendant drop were captured using a CCD camera. Experiments were performed at room temperature and typically lasted between 5 - 35 min, where evaporation of drops is significant. We used needle diameter of range $0.3$ mm $\leq$ $2R$ $\leq$ $7.9$ mm, and fluids water, ethanol, 5 cSt silicone oil, and glycerol for these experiments. The maximum pendant drop volume just before break-off was measured using an in-house MATLAB code. We plot dimensionless volume ($V^{*} = V/(\pi R)^{3}$) versus Bond number ($Bo$) for the performed experiments. Experiment results were also compared with drop profiles computed at their stability limit using an eigenvalue analysis. The results show good agreement.