Effect of the axial heat flux on the critical flux in low flow conditions with vertical annuli

An experimental study on the critical heat flux (CHF) has been performed for a water flow in vertical annuli with uniform and chopped cosine axial heat flux distributions under low flow and a wide range of pressure conditions. The effect of an axial heat flux distribution on the critical power is large at low-pressure conditions, but the effect decreases rapidly as the pressure increases. The 'overall power' hypothesis becomes more accurate as the pressure and critical quality increase, and the 'local conditions' hypothesis is not valid at high quality conditions. For a fixed mass flux and pressure, the relationship between the critical quality and the boiling length is represented by a single curve for the whole range of the present experimental conditions, regardless of the axial heat flux distributions. Smolin et al.'s F-factor and Bowring's Y parameter show good prediction results for the present CHF data. (author)