Experimental insight into the pressure drop mechanisms of hydrocarbon fuel in mini-channels: from subcritical flow boiling to supercritical pseudo-boiling under high heat fluxes

The pressure drop of hydrocarbon fuel was studied in a horizontal heated mini-channel with an inner diameter of 2.0 mm and an effective heated length of 360.0 mm. The experiments were conducted under conditions including fluid temperatures ranging from 283.0 to 674.4 K, pressures between 1.1 and 5.1 MPa, heat fluxes up to 1021.8 kW/m 2 , and mass fluxes of 312.0 and 638 kg/(m 2 ·s). The effects of operating parameters on the total, frictional, and acceleration pressure drops were analyzed under both sub- and supercritical pressures. The experimental investigations show that, under subcritical pressure, the pressure drop exhibits a distinct Λ-shaped variation near the saturation temperature, which is associated with the onset and development of two-phase flow boiling. Under supercritical pressure, a similar but smoother variation appears near the pseudo-critical temperature, reflecting pseudo-boiling and the strong variation of thermophysical properties. The large temperature rise along the channel causes a substantial decrease in fluid density, leading to a significant acceleration pressure drop. For cases with T b,out / T pc > 1, the acceleration pressure drop constitutes an average of 51.1% of the total pressure drop at subcritical pressure, and 29.2% at supercritical pressure. Based on the observed heat transfer characteristics, the flow regimes have been categorized for both sub- and supercritical states. The developed correlations were fitted for subcooled-boiling pressure drop and supercritical friction factor under high heat flux and low mass flux conditions. The proposed correlations consider the dominant effects of boiling, and property gradients, and predict most experimental data within ±20%.