Influence of Chip Size on Bubble Dynamic Behavior in Microgravity

In order to study the influence of chip size on bubble dynamic behavior in microgravity, the factor of chip size on bubble dynamics under various heat fluxes has been studied by comparison experiments. Typical isolated bubble boiling maintains on both small and large size chips in low heat flux, and the growth and coalescence rates of bubbles are relatively slow. The volume of bubble on large size chip is about 3.4 times that of the bubble on small size chip. The bubble departure could only be observed on the large chip during the experiment. Fully developed nucleate boiling are sustained in the case of moderate heat flux, the coalescence and departure frequency of bubbles is much higher than that in low heat flux, especially on large size chip. Bubbles detach more frequently on large size chip than that on small size chip. Moreover, the wake effect caused by bubble rising reduces the departure diameter of subsequent bubbles, so the formation of dry portions is effectively suppressed. For the high heat flux, obvious film boiling presents on the small size chip and the deterioration of heat transfer is observed. However, stable nucleate boiling still maintains on large size chip in the high heat flux, only the bubbles coalesce and detach more frequently. Therefore, increasing the chip size can effectively promote the bubble departure and improve critical heat flux. Film boiling is also observed as the heat flux on larger size chip is increased beyond the critical heat flux, but the heating surface could not be completely covered by the bubble, just sliding slowly on the slip, which can reduce the rising rate of temperature on chip effectively.