Abstract
The prediction of onset of nucleate boiling (ONB) in rectangular narrow channel is very important for reactor safety design. With water as the test fluid, a series of tests are performed for ONB investigation in rectangular narrow channel with the channel size of 50mm × 3mm × 1000mm. Through monitoring the wall temperature deviation, the slope of the wall temperature deviated simultaneously with the occurrence of bubbles on the heated surface. The position of ONB is identified as the intersection of the single-phase and two-phase heat transfers. The effect of different parameters (heat flux, mass flow rate, pressure, inlet subcooling) corresponding to the ONB is analyzed. 8 existing prediction correlations are listed as well as brief assessments with the test data. The comparison results revealed that those empirical or semi-empirical correlations proposed for ONB prediction in pool boiling are not suitable for narrow rectangular channel, especially with the change of mass flow rate. The correlations developed for narrow rectangular channel could reflect the influence of mass flow rate in degree. However, the scope of application of the correlation and the prediction accuracy are still not good enough because of the limited experimental range. The derivation process of analytical solution for prediction of wall superheat in rectangular narrow channel by considering the effect of forced convection is described in detail. The new correlation is shown to provide a good prediction against the database, evidenced by more than 95% of the data falling within ±20% error bands, respectively.
