Experimental observations of flow boiling of liquid helium I in vertical channels

Results are reported of the flow structure and pressure drop of helium 1 flowing upwards in a vertical heated circular glass tube. The experiments covered heat fluxes from 4.5 to 600 Wm-2, mass fluxes from 2 to 12 kg m-2s-1 and pressures between 1 and 1.2 atm. For the bubble flow regime the shape, size and drag coefficient of the observed bubbles are reported. Slip velocity, void fraction and pressure drop measurements are compared with generally accepted two-phase flow theories. A void fraction correlation for two-phase helium flow is proposed. (author)