1. Chemical Engineering and Forest Products Research Centre (CIEPQPF), University of Coimbra, Coimbra 3030-790, Portugal e-mail:
2. Electrical and Computers Engineering Department, University of Coimbra, Coimbra 3030-290, Portugal e-mail:
3. Institute of Thermal Machinery, Częstochowa University of Technology, Częstochowa 42-200, Poland e-mail: