1. Postdoctorate Research Fellow, Waterpower Laboratory, Dept. of Energy and Process Engineering, Norwegian Univ. of Science and Technology, Alfred Getz vei 4, 7491 Trondheim, Norway (corresponding author).
2. Professor, Dept. of Energy and Process Engineering, Norwegian Univ. of Science and Technology, Alfred Getz vei 4, 7491 Trondheim, Norway.