Pool boiling on nano-textured surfaces

Pool boiling on nano-textured surfaces was studied experimentally and theoretically for ethanol and water as working fluids. The nano-textured surfaces were copper platelets covered with copper-plated electrospun nanofibers. In addition, for comparison pool boiling on the corresponding bare copper surfaces was experimentally studied. The results revealed that the heat flux and heat transfer coefficient in boiling on the nano-textured surfaces were about 3-8 times higher than those on the bare copper surfaces. This stems from the fact that nano-textured surfaces promote bubble growth by increasing the average temperature of fluid surrounding growing bubbles, as our experimental and theoretical results show. Hence, nano-textured surfaces comprised of copper-plated nanofibers facilitate bubble growth rate and, thus, increase bubble detachment frequency. On the other hand, the critical heat flux (CHF) on the nano-textured surfaces was found to be very close to its counterpart on the bare copper surfaces. However, the heat flux on the nano-textured surfaces in transition boiling was significantly higher than on the bare copper ones, since the presence of nanofibers prevented bubble merging and delayed formation of vapor film. The wall temperature is about 10 °C lower on the nano-textured surfaces. In transitional boiling the heat flux on nanofiber mats reduces much slower than on the bare surfaces.