Experimental studies on falling film evaporation of R134a outside horizontal tube bundle

The falling film evaporation outside seven horizontal enhanced tubes in a vertical column with various heat flux and film flow rate was experimentally investigated. The results indicated that for the constant heat flux the falling film heat transfer coefficient was greatly increased with increase of film flow rate under smaller film flow rate; with further increase of the film flow rate the falling film heat transfer coefficient tended to be constant for the tubes No. 1~3 but firstly increased and then decreased for the tubes No. 4~7. It was also found that for the film flow rate of Γ=0.159 kg·m^-1·s^-1, with increase of heat flux the heat transfer of all tubes were firstly enhanced and then deteriorated and the peak values occurred at smaller heat flux; for Γ=0.29 kg·m^-1·s^-1, with increase of heat flux the heat transfer of tube No.1 was always enhanced, that of tubes No. 2~4 was firstly enhanced and then weakened, and that of tubes No. 5~7 was always weakened. In addition the peak values of tubes No. 1~4 occurred at larger heat flux.