George Yadigaroglu is Professor emeritus of Nuclear Engineering, ETH-Zurich and President and co-founder of ASCOMP AG, originally an ETH spin-off company specializing in Computational Multi-Fluid Dynamics simulations. Was also heading the Thermal-Hydraulics Laboratory at the national Paul Scherrer Institute (PSI) in Switzerland. Previously Professor of Nuclear Engineering at the University of California-Berkeley. Director and local organizer since 1984 of the Zurich Multiphase flow Short Courses.  Active in research and consulting on two-phase flows and heat transfer with phase change, flow dynamics and instabilities, and their applications to nuclear power plant safety. Member of several international committees dealing with nuclear safety issues. ANS Technical Achievement Award. ANS and ASME Fellow. Former Assoc. Editor of the Int. J. of Multiphase Flow. Geoffrey F. Hewitt is Professor emeritus of Chemical Engineering at Imperial College, London. Founder of the Heat Transfer and Fluid Flow Service (HTFS) at the Harwell national Laboratory in the UK. He has authored and edited many books and published over 500 papers and reports on two-phase flows and heat transfer with phase change. Former Editor of Multiphase Science and Technology and Founding Editor of the Heat Exchanger Design Handbook. Recipient of the AIChE Donald Q. Kern, the ASME Max Jacob awards, the Nusselt Reynolds Prize, the Luikov Medal, the IChemE Council and Armstrong medals, the Senior Multiphase Flow Award and the Global Energy Prize. He has Hon. Doctorates from Louvain, UMIST and Heriot Watt. Fellow of the Royal Academy of Engineering, Fellow of the Royal Society and Foreign Associate of the US Natl Academy of Engineering.