1. Mechanical Engineering Doctoral School, Szent István University, Pater K. u. 1, H-2100 Gödöllő, Hungary
2. Department of Energy Systems Engineering, Koforidua Technical University, Box 981, Koforidua, Ghana
3. Department of Physics and Process Control, Szent István University, Páter K. u. 1, H-2100 Gödöllő, Hungary