[ASME ASME 2013 Heat Transfer Summer Conference collocated with the ASME 2013 7th International Conference on Energy Sustainability and the ASME 2013 11th International Conference on Fuel Cell Science, Engineering and Technology - Minneapolis, Minnesota, USA (Sunday 14 July 2013)] Volume 2: Heat Transfer Enhancement for Practical Applications; Heat and Mass Transfer in Fire and Combustion; Heat Transfer in Multiphase Systems; Heat and Mass Transfer in Biotechnology - Experimental Investigation on Flow Patterns and Frictional Pressure Drop of Downward Air-Water Two-Phase Flow in Vertical Pipes