Towards Accurate Measurement of Post-CHF Flow Boiling Heat Transfer of Water in a Circular Tube

Abstract

Experimental investigation of forced convection boiling heat transfer of water in the range from critical heat flux (CHF) to inverted annular flow film boiling (IAFFB) requires a heat transfer system with surface-temperature control, which is difficult to realize, especially, at the high heat flux rates encountered in water boiling at low pressure and mass quality. In this paper, an improved version of such a system with temperature controlled indirect Joule heating is presented which, due to rather extensive instrumentation and involved data evaluation techniques, enables simultaneous determination of both temperatures and heat fluxes at the heat transfer surface. The accuracy of measurements to be obtained by this experimental setup has been investigated using artificial data that have been taken from analytical solutions of severe steady-state test situations, and comparing both results. Largest errors are to be expected in the surface heat flux at those axial locations where large axial temperature gradients occur, but even then will typically be less than about 5 percent. The major source of error was found in the bivariate interpolation procedure applied which furnishes the input for subsequent numerical solution of the heat conduction equation to evaluate temperature and heat flux distributions at the heat transfer surface.