Local Heat Flux Investigation During Pool Boiling Single Bubble Cycles Under Reduced Gravity

In the present work the bubble diameter, heater surface temperature distribution, and local heat flux during different stages of single bubble cycles during pool boiling of PF-5060 at a pressure of p = 600 mbar have been investigated in several stable low g levels during the 1st Joint European Partial-g Parabolic Flight (JEPPF) Campaign. In previous parabolic flight campaigns, microgravity conditions were achieved by following a parabolic trajectory with the specially equipped A-300-Zero-G Aircraft. In this recent JEPPF campaign, the parabolic trajectories were slightly shifted, to establishapart from microgravity conditionsalso stable gravity levels of 0.16g (lunar gravity) and 0.38g (Martian gravity). High-resolution measurements of the heater surface temperature were performed using high-speed infrared thermography. An infrared (IR)-transparent sputtered heater design was employed in order to allow temperature measurements by IR thermography at a distance of approximately 800nm to the heater/fluid interface. From the acquired temperature data, the local heat flux distribution was calculated numerically. Bubble shape and interaction were recorded with a high-speed black-and-white camera. In contrast to previous investigations, the stable low gravity levels enabled performance of measurements during single bubble (ebullition) cycles without the influence of residual flows induced by boiling under a different gravity level, as is the case in the beginning of a regular microgravity parabola. The accuracy of the measurement technique could be drastically enhanced compared to earlier publications. A local temperature drop and corresponding heat flux peak have been observed close to the three-phase contact line.