Cooling High-Power Microelectronic Devices in Ground and Space Applications Using Nanofibers and Nanoparticles
Prof AL Yarin
Dept. of Mechanical and Industrial Engineering, University of Illinois at Chicago
Time & Place
Wed, 08 Jun 2016 13:00:00 NZST in Foyer of John Britten Bldg
The first part of the talk deals with drop/spray cooling of high-heat flux surfaces using electrospun polymer nanofiber mats. The nanofibers are copper- plated and resemble the appearance of a small Australian thorny devil lizard, i.e. became very rough (on the nano-scale), as well as acquired high thermal diffusivity. Drop impacts on the hot surfaces coated with copper-plated nanofibers revealed tremendously high values of heat removal rates up to 1 kW/(cm sq.). Such high values open some intriguing perspectives for cooling of high-heat flux micro-electronics and for further miniaturization of such devices, especially for such applications as UAVs and UGVs. The nano-textured coatings were tested not only in the ground (1g) experiments but also during parabolic flights at zero gravity (0g) and supergravity (1.8g). The results of the earth experiments encompass the experiments with a single needle or two needles producing drop trains or jets, with water or Fluorinert fluid FC-7300 as working fluids.
The second part of the talk deals with pool boiling on such nano-textured surfaces studied experimentally and theoretically for ethanol, water and their mixtures. The results revealed that the heat flux and heat transfer coefficient in boiling on copper-plated 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. Hence, nano-textured surfaces facilitate bubble growth rate and 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. In addition, supersonic solution blowing was used to form nano-textured copper-plated nanofiber mats with ultra-thin nanofibers of about 100 nm. In this case the pool boiling data sharply deviate from the standard boiling curve. In particular, the heat flux and the heat transfer coefficient were found to be significantly higher at low surface superheats. It was also demonstrated that the ultra-thin-nanofiber surfaces are robust and do not deteriorate after several cycles of day-long pool boiling experiments.
In the third part of the talk we explore the potential of nano-encapsulated phase change materials (PCMs) in the applications related to cooling of microelectronics using micro-channel flows. PCMs (wax or meso-erythritol) were encapsulated in carbon nanotubes by the method of self-sustained diffusion at room temperature and pressure. Such nano-encapsulated wax nanoparticles alone allow for heat removal in a relatively wide temperature range (different waxes have melting temperatures in the 40-80 C range). On the other hand, such nano-encapsulated meso-erythritol nanoparticles allow for heat removal in the 118-120 C range. The nanoparticles possess a very short response time and allow for the temperature reduction of several degrees Celsius.
This work is supported by NASA (Grant No. NNX13AQ77G) and NSF Grant CBET 1133353.