Single- and Two-Phase Pressure Drops on a 6 × 6 Rod Bundle at 70 atm

Single- and two-phase pressure drop measurements have been carried out on a 6 × 6 rod bundle at 70 atm. Single-phase measurements have been performed with a subcooling ranging from 100 to 5°C and at mass velocities comprised between 0.5 × 10⁶ and 3.3 × 10⁶ lb/(h ft²). Two-phase measurements have been performed at steam qualities ranging from 3 to 20% and at mass velocities comprised between 0.5 × 10⁶ and 2 × 10⁶ lb/(h ft²). From the measured pressure drops, the bundle friction factor and the loss coefficient for each bundle component (bottom plate, spacer, and upper plate) have been determined. Single-phase results show that Moody’s curve for friction losses and Kays’ coefficients for form losses lead to predicted pressure drops in good agreement with the experimental ones. The two-phase loss coefficients of the spacer and the bottom plate have been compared to the slip model prediction. If, for each component, an ad hoc choice of the slip ratio is made, the calculated values can be matched to the experimental ones with good accuracy. In addition, two-phase friction losses have been calculated on the basis of the Martinelli-Nelson, Becker, and Baroczy correlations with a resulting good agreement between the predictions of the last correlation and the experimental data.