Single- and Two-Phase Pressure Drops on a 16-Rod Bundle

This paper analyzes the results obtained from coolant pressure drop measurements, conducted on a test section comprising 16 rods in a square arrangement. The rod bundle, mechanically assembled by means of two end plates and five grid spacers located at different axial stations, was mounted in a vertical heat-insulated pressure vessel. The measurements, taken under isothermal and adiabatic conditions, covered the following range of coolant parameters

Relative pressure pg = 0 psi

Sub cooling: 135 and 108°F

Mass velocities between 0.5 xlO6 and 5.6 *lO6 lb/(h ft2).

Relative pressure pg = 450 psi

Sub cooling: 144 and 72°F

Mass velocities between 0.5 xlO6 and 2.5 *lO6 lb/(h ft2)

Steam quality between 2 and 22%.

The main results obtained are as follows: for single-phase flow, the continuous friction factor falls ∼ 10% short of the corresponding value predicted by Moody's correlation for smooth pipes and load loss coefficients at the constraints, i.e., end plates and spacer grid, result depending on the Reynolds number; and for two-phase flow, the continuous friction multiplier factor shows a strong dependence on the coolant mass velocity and the load loss coefficients at the constraints can be explained by a calculation model based on a slip variation hypothesis.