Abstract

We analyze pool boiling experiments with single bubbles realized on the International Space Station (ISS) as part of Reference mUltiscale Boiling Investigation (RUBI). Fluorinert FC-72 (pure component) is used as a working liquid. For a fixed liquid pressure (here 500, 600 or 750 mbar), upon initial thermalization, a joule heater coated atop a transparent BaF2 substrate is on. Following a “waiting time” of a few seconds (here 2 or 5 s), a pre-prepared nucleation site is activated by a laser pulse. The resulting bubble growth up to a centimetric size is diagnosed for 9 s by a side-view camera (shape, contact angle) and a bottom-view infrared camera (temperature). Here, we specifically focus on “smooth growth” cases such as low heater power and near-saturation conditions inasmuch as available in RUBI. Although our 500 fps of the camera misses a “zeroth” growth stage (the bubble being of a size of hundreds of micrometers in the first image it appears), the subsequent (first, etc.) stages are well explored. Strong shape oscillations, up to detachment, due to an initial explosive growth (first stage) are followed by a quasi-spherical-cap growth (second and third stages) with different power laws. An efficient minimalistic numerical model based on a spherical-cap approximation is developed. This helps to elucidate the physics behind each observation. A strongly disproportionate contribution of a near-contact-line zone to the evaporation flux is quantified in passing. Upon a limited calibration, in conjunction with a classical “microregion” model, the simulation reproduces well the overall measurements including the evaporation-induced contact angle.

Key Points

• Bubble growth occurs on a single nucleation site near saturation conditions, indicating unique physics in microgravity.