Boiling bubble behaviors of fluids of different surface tensions on heating surfaces with micro/nanostructures

The use of environmentally friendly coolants with low surface tension in boiling applications holds great promise, and the implementation of micro/nanostructures is widely regarded as an effective strategy for enhancing boiling heat transfer. However, as a critical factor influencing the boiling process, the understanding of boiling bubble behavior on micro/nanostructured modified surfaces remains insufficient for the low surface tension fluids. SF-33, with its zero ozone depletion potential and extremely low global warming potential, is gradually gaining attention in the field of boiling as a representative low-surface-tension fluid. Herein, several copper heating surfaces with micro or micro/nanocomposite structures were fabricated using sintering copper mesh and thermal oxidation techniques. The bubble growth and departure phenomena during pool boiling of coolants SF-33 and de-ionized water on these micro/nanostructured surfaces were investigated and comparatively analyzed. The saturated pool boiling experiments were conducted at atmospheric pressure. It was observed that on smooth flat surface and sintered wire-mesh flat surface, SF-33 bubbles exhibited a faster growth rate, higher departure frequency, and smaller departure diameter. However, on the sintered wire-mesh flat surface with nanowires, de-ionized water bubbles demonstrated a higher departure frequency, while the growth rate and departure diameter were similar to those of SF-33 bubbles. In addition, it was found that the influence of microstructures on de-ionized water bubble behaviors is significantly lower than that of micro/nanocomposite structures, while for SF-33, increasing the microstructures alone can greatly affect bubble growth and departure, with further changes induced by the addition of nanostructures being relatively minor.