Experimental investigations on single-phase convection and critical heat flux in vertical tubes under oscillatory flow condition

Experimental investigations on single-phase convection and critical heat flux in a vertical tube with an inner diameter of 6.0 mm under inlet flow oscillation conditions were carried out for the following range: 255 ≤ G_av ≤ 455 kg·m⁻²·s⁻¹, 0.5 ≤ P ≤ 3.0 MPa, 0 < ΔG/G_av ≤ 3.0 and 0 < τ (period of flow oscillation) ≤ 10.6 s. Single-phase convective results show that the fluctuation amplitude of single-phase pressure drop decreases with an increasing τ. Besides, there may be a critical value τ_c. The average value of wall temperature under steady state condition is smaller than that under oscillatory flow condition when τ > τ_c while the former is larger than the latter when τ < τ_c. With respect to two-phase results, the effect of flow oscillation on fluctuation amplitude of wall temperatures under flow boiling conditions is quite small. In addition, flow oscillation deteriorates flow boiling heat transfer in vertical tubes to some extent when 1.04 ≤ τ ≤ 10.6 s. The normalized periodic CHF (F_p) decreases with an increasing average mass velocity, especially for short periods of flow oscillation. In addition, the declining rate of F_p as a function of ΔG/G_av was decayed with an increasing period of flow oscillation. In a general, 2006 CHF lookup-table and Kim et al. correlation are recommended to calculate CHF under steady state condition and periodic dryout heat flux under inlet flow sinusoidal oscillation condition, respectively.