Critical heat flux under choking flow conditions Part I - Outlet pressure fluctuations

Under conditions of forced convective boiling at low pressures and high mass fluxes, beyond a certain quality, choking flow may occur at the exit of a heated channel. An experimental investigation of the influence of this phenomenon on the critical heat flux (CHF) has been carried out. An analysis of the pressure distribution downstream of the heated length as well as the behaviour of the wall temperature during CHF has shown that the occurrence of choking flow, namely outlet pressure fluctuations, does not radically influence the values of the CHF. The physical reasons for the appearance of these outlet pressure fluctuations under conditions of diabatic choking flow have been analyzed. The experimental investigation has also shown that when choking flow occurs the outlet pressure cannot be lowered below a certain value that is fixed by the flow itself. The maximum values of flow parameters attamed under choking flow conditions are presented in the Part II of this paper.