Experimental study on the critical heat flux at the operating limit of a closed two-phase thermosyphon

Flow patterns inside a closed two-phase vertical thermosyphon were visually observed in detail and the relation between the patterns and the operating limit was experimentally investigated. The parameters were the inner diameter of the thermosyphon, the properties and the fill charge of the working fluid and the system pressure. The observations showed that there were two opposite effects of liquid pool boiling in the evaporator on the operating limit due to flooding: a mild boiling delays the dryout of the evaporator wall and a violent one promotes it. Taking these effects into consideration, a correlation was proposed for the large amount of critical heat flux data obtained from many kinds of thermosyphons by using new parameters such as the height of the liquid pool and the bubble kinetic energy. The agreement of the correlation with those data is better than that of Sakhuja's, Prenger's and Imura's correlations.