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A microgravity experiment was conducted on the Space Shuttle Endeavor (STS-108) to observe sustained nucleate boiling of water. Subcooled water was boiled with a single strand and a braid of three 0.16 mm diameter and 80 mm long Nichrome resistive wires. A CCD video camera recorded the experiment while six thermistors recorded the temperature of the fluid at various distances from the heating element. This paper reports experimental results in observations, measurements, and data analysis. Bubble explosions were found to take place shortly after the onset of boiling for both the single and braid of wires. The explosion may produce a high heat transfer rate, as it generates a cloud of micro-bubbles. The number, size, and departure rate of the bubbles from the heater wire were measured and compared with theoretical models as a function of time. The temperature measurements revealed a complex temperature distribution in the fluid chamber due to bubbles ejected from the wire that carried thermal energy close to the temperature sensors. Drag forces on departing bubbles were calculated based on bubble movement and used to predict bubble propagation. Results from this experiment provided further understanding of nucleate boiling dynamics in microgravity for the eventual design and implementation of two-phase heat transfer systems in space applications.

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Boiling dynamics in microgravity need to be better understood before heat transfer systems based on boiling mechanism can be developed for space applications. This paper presents the results of a nucleate boiling experiment aboard Space Shuttle Endeavor (STS-108). The experiment utilized nickel-chromium resistance wire to boil water in microgravity, and the data was recorded with a CCD camera and six thermistors. This data was analyzed to determine the behavior of bubble formation, detachment from the heating wire, and travel in the water with effects of drag on bubble movement. Bubbles were observed to be ejected from the wire, travel through and eventually stop in the unsaturated water. The data from this experiment is in good agreement with the results of theoretical equations used to model bubble-fluid dynamics in microgravity. The primary conclusion from this experiment is that a bubble can be ejected from a heated wire in the absence of gravity, instead of the creation of a single large vapor bubble. Further conclusions from this research could be applied to the development of safe and efficient heat transfer systems for microgravity and terrestrial applications.