1. Key Laboratory of Low-Grade Energy Utilization Technologies and Systems of Ministry of Education, Chongqing University, Chongqing 400030, P. R. China
2. Institute of Engineering Thermophysics, School of Energy and Power Engineering, Chongqing University, Chongqing 400030, P. R. China
3. State Key Laboratory of Hydraulics and Mountain River Engineering, College of Water Resource & Hydropower, Sichuan University, Chengdu 610065, P. R. China