Experimental Methods
2.1 Bubble column
The bubble column was made from cast acrylic to achieve strength and
optical clarity; it was 1.2m in length with a 102mm internal diameter
(D ). Figure 1 provides a schematic of the bubble column test
facility. Tap water was passed through a cartridge filter (W10-BC,
American Plumber, Pentair Residential Filtration, LCC) with 5μm nominal
filtration. Surface tension of the filtered water and other tested
liquids were measured with a force tesiometer (K6, Krüss GmbH) and
platinum ring (RI0111-282438, Krüss GmbH). Over several days the surface
tension of the filtered water was measured to be 72.6 ±0.4 mN/m, which
is comparable to the nominal surface tension of the pure water
(~72.8 mN/m). Liquid phase temperature was measured
using a thermocouple (HSTC-TT-K-20S-120-SMPW-CC, Omega Engineering).
Figure 1 also depicts the compressed airflow control panel. Airflow
passes through a cartridge filter (SGY-AIR9JH, Kobalt, Lowe’s Companies,
Inc.) with 5μm nominal filtration. The mass flow of air was controlled
and monitored with a combination of a pressure regulator, rotameter
(EW-32461-50, Cole-Palmer), and a thermocouple (5SC-TT-K-40-39, Omega
Engineering). The rotameter measured the volumetric flow of air with an
accuracy of 2% of the full scale (FS). The thermocouple measured the
air temperature immediately upstream of the rotameter with accuracy of
±0.1°C. All tests were conducted with the air temperature between 20 °C
and 22 °C, and temperature difference between the air and liquid phase
was within ±2 °C. It is also worth mentioning that the height of liquid
in the bubble column was kept constant at 9D following
recommendations from Besagni et al.41 for studying the
void fraction and bubble size independent of column aspect ratio.