Experimental Study on Onset of Nucleate Boiling in Vertical Annular Channel with a Short Heated Rod Under Low Pressure

The onset of nucleate boiling (ONB) in a vertical annular channel with a single short heated rod was studied by using deionized water. The experimental conditions cover a pressure range of 0.16 to 0.3 MPa, a mass flux range of 70 to 300 kg·m-2·s-1. The influence of mass flux, inlet temperature and pressure on ONB were studied, and the transition point from single phase to ONB was obtained by gradually increasing the heat flux. A high-speed camera was used to capture bubbles generating position under different heat flux. In addition, conventional correlations were evaluated for predicting the heat flux at ONB. It was found that heat flux at ONB calculated by these correlations was not consistent with the experimental data. Hence, a new correlation had been developed for predicting the heat flux at ONB. The values calculated by the new correlation had a good agreement with the experimental data.