1. Yung Chan, Suman Sinha Ray and Alexander L. Yarin Micro/Nanoscale Fluid Transport Laboratory Engineering Research Facility Room 1014 University of Illinois at Chicago, IL 60612 2010 NSF REU Summer Program Hydrodynamics of Drop Impact and Spray Cooling through Nanofiber Mats 1

2. Outline  Acknowledgement  Introduction  Applications  Experiments  Results and Discussions  Conclusion  Reference 2 7/29/2010 UIC-REU

3. Acknowledgement Financial support from the National Science Foundation and Department of Defense, EEC-NSF Grant #0755115 Additional financial support from CMMI-NSF Grant #1016002 Research Opportunity provided by University of Illinois at Chicago (UIC) REU organizers: Professor Takoudis Professor Jursich Advisor: Professor Yarin Mentor: Suman Sinha Ray Alex Kolbaso, Yiyun Zhang and Fady Charbel 3 7/29/2010 UIC-REU

4. Introduction  Drop impacts on dry surface exhibit more complicated flow patterns than those on the wetted surfaces Six possible outcomes of drop impacts on a dry surface   Drop impact on dry surface is a key element of a wide variety of phenomena encountered in many technical applications, including spray printing, rapid spray cooling of hot surface, ice accumulation on power lines and aircrafts 4 7/29/2010 UIC-REU

5. Applications  Spray cooling can be used to transfer large amounts of energy through the latent heat of evaporation, heat transfer rate much higher than pool boiling since the drop can be removed heat from surface more easily.  Water Spray Cooling: extremely high heat transfer (L= 2260J/g) cooling microelectronic chips, radiological elements and server room.  Semiconducting diamond devices works up to temperatures of 500 °C, and silicon devices fail at around 150 °C 5 7/29/2010 UIC-REU Use minimum amount of water to transfer maximum heat from device in shorter time. Coating that can increase the interface

6. Experiment- Nanofiber Mat Coating  Electrospinning is a process that produces continuous polymer fibers through the action of an external electric field imposed on a polymer solution.  Primary characteristic of nanofibers is the high ratio of surface area to mass.  Then polymer fiber distributed on the grounded plate  PAN (Poly-acrylonitrile) is a resinous, fibrous, and rubbery organic polymer. 6 7/29/2010 UIC-REU

7. Experiment-set up 7 7/29/2010 UIC-REU

8. Experiment 7/29/2010 UIC-REU 8 Copper Substrate at 200 C Copper Nanofiber Mat at 200C

9. Result and Discussion-1  In room temperature 9 7/29/2010 UIC-REU

10. Result and Discussion-2  In room temperature 10 7/29/2010 UIC-REU

11. Result and Discussion-3 11 7/29/2010 UIC-REU

12. Result and Discussion-4 12 7/29/2010 UIC-REU

13. Result and Discussion-5 13 7/29/2010 UIC-REU

14. Conclusion  Nanofiber mat coating: Silver > Copper > Nickel > PAN  Based on cost and heat flux rate: Copper nanofiber mat is the best coating.  Copper nanofiber mat: high thermal conductivity high interface between water and hot surface  Copper nanofiber coating may lead to a breakthrough in the development of a new generation of spray cooling process. 14 7/29/2010 UIC-REU

15. Reference Alexander L. Yarin, “Drop Impact Dynamics: Splashing, Spreading, Receding, Bouncing…” Annual Review of Fluid Mechanics, Vol. 38, pp.159-192, Jan. 2006. Darrel l H. Reneker, and Alexander L. Yarin, “Electrospinning jets and polymer nanofibers” Polymer, Vol. 49, pp.2387-2425, Feb. 2008. Andreas N. Lembach, Yiyun Zhang, and Alexander L. Yarin, “Drop Impact, Spreding, Splashing, and Penetration into Electrospun Nanofiber Mats” Langmuir Article, Vol. 26, pp.9516-9523, Feb. 2010. R. Srikar, A.L. Yarin, “ Nanofiber coating of surfaces for intensification of drop or spray impact cooling” International Journal of Heat and Mass Transfer, Vol. 52, pp.5814-5826, Sept. 2009. 15 7/29/2010 UIC-REU

16. Questions? Thank you for your attention! 7/29/2010 UIC-REU 16