State Key Laboratory of Multiphase Flow in Power Emgineering,Xi'an jiaotong University, Xi'an 710049,China;
Faculty of Engineering, Hoddaido University, North Ward, Sapporo 060-8628,Japan;
State Key Laboratory of Multiphase Flow in Power Emgineering,Xi'an jiaotong University, Xi'an 710049,China;
natural convection; downward facing heated surface; gap size; buoyancy force;