Speaker
Description
Designing efficient cooling devices is crucial in a multitude of applications. Although advanced cooling technologies have existed for decades, there is still a lack of more efficient heat dissipation methods, especially for space applications where thermal management devices must dissipate heat in reduced gravity. Flow boiling presents here a first significant improvement over traditional single phase cooling systems, as it makes use of the significantly larger latent heat of a fluid. The performance of flow boiling can even be further improved by functionalizing boiling surfaces, which is currently a key area of research. These functionalized surfaces can lead to more controlled and more dense nucleation as well as controlled rewetting of the surface, resulting in higher heat transfer coefficients, reduced flow instabilities and increased critical heat fluxes.
In this study, we evaluate the change in bubble dynamics and heat transfer performance for three different types of surface textures produced on 200 μm thick 316L SS foils using a femtosecond (fs) laser. The investigated textures include microscale grooves and conical holes with a tilted (= 45◦) geometry. In addition, we also evaluate the effect of laser-induced periodic surface structures (LIPSS), which are sub-micron scale features fabricated by fs laser processing. Results are compared between terrestrial and microgravity conditions to compare heat transfer enhancement degrees of each textured surface with respect to a plain reference surface in the same operating conditions. The fluid used is PP1, a replacement of 3M™ FC-72 in heat transfer applications. Microgravity data was gathered on the 83rd ESA Parabolic Flight Campaign. It was found that the enhancement degrees were reduced in microgravity with respect to terrestrial conditions, but overall trends remained the same for each surface, showing op to 20% improvement in HTC over a plain surface in microgravity. So, the performed experiments showed clear potential for the application and further investigation of textured boiling surfaces to be employed in microgravity flow boiling cooling systems.
