Extensive research has been conducted to resolve small-scale microlayer and bubble nucleation and departure processes in flow boiling, building on controlled pool boiling studies. Large-scale two-phase flow structures, such as Taylor bubbles, are known to locally modify transport due to their wakes and varying surrounding liquid film thickness. However, the effect of interaction of such large-scale flow processes with bubble nucleation is not yet well characterized. Wakes may drive premature nucleating bubble departure, or conversely, suppress boiling due to boundary layer quenching, significantly affecting overall heat transfer. To explore such phenomena, a two-phase flow boiling visualization facility is developed to collect simultaneous high-speed visualization and infrared (IR) thermal imaging temperature distribution data. The test cell channel is 420 mm long with a 10 mm × 10 mm internal square-cross section. A transparent conductive indium tin oxide (ITO) coated sapphire window serves as a heater and IR interface for measuring the internal wall temperature. The facility is charged with a low boiling point fluid (HFE7000) to reduce uncertainties from heat loss to the laboratory environment. Vertical saturated flow boiling wake-nucleation interaction experiments are performed for varying liquid volume flow rates (0.5 − 1.5 L min-1, laminar-to-turbulent Re) and heat fluxes (0 − 100 kW m-2). Discrete vapor slugs are injected to explore interactions with nucleate boiling processes. By measuring film heater power, surface temperature distributions, and pressures, local instantaneous heat transfer coefficients (HTC) can be obtained. Results will be applied to assess simulations at matched conditions for void fraction, and size statistics of flow structures.
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The effect of bubble nucleation on the performance of a wickless heat pipe in microgravity
Bubble nucleation was investigated in a 20-mm-long, wickless heat pipe on the International Space Station. Over 20 h of running experiments using pentane as the working fluid, more than 100 nucleation events were observed. Bubble nucleation at the heater end temporarily boosted peak pressures and vapor temperatures in the device. At the moment of nucleation, the heater wall temperature significantly decreased due to increased evaporation and the original vapor bubble collapsed due to increased pressure. A thermal model was developed and using the measured temperatures and pressures, heat transfer coefficients near the heater end of the system were extracted. Peak heat transfer coefficients during the nucleation event were over a factor of three higher than at steady-state. The heat transfer coefficient data were all collapsed in the form of a single, linear correlation relating the Nusselt number to the Ohnesorge number.
more » « less- Award ID(s):
- 1637816
- NSF-PAR ID:
- 10366497
- Publisher / Repository:
- Nature Publishing Group
- Date Published:
- Journal Name:
- npj Microgravity
- Volume:
- 8
- Issue:
- 1
- ISSN:
- 2373-8065
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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