Investigation on hysteresis effect of enhanced subcooled flow boiling by surface modification in horizontal narrow channel

This study aimed at investigating the influence of increasing and decreasing mass and heat fluxes based on modified surfaces. Test channel was 4 mm in height with a heating surface (20 × 50 mm2) settled at the bottom center. HFC245fa at a saturated pressure of 250 kPa (39.9 °C) was used as the working fluid. Thermal spray coating (TSC) and perpendicular micro-V-shaped grooves were applied. The pitch and angle of the V-grooves were 0.5 mm, and 60°, respectively. Influence of increasing and decreasing mass and heat fluxes on boiling behaviors by modified surfaces was analyzed by evaluating the heat transfer coefficient (HTC), hysteresis temperature deviation. Temperature overshoot at the onset of nucleate boiling was observed for all the surfaces by thermal history. Although V-grooved surface also enhanced the nucleation sites by increasing heat transfer area, temperature deviation was only observed on the TSC surface. At an inlet subcooling of 30 K, mass flux and heat flux were 300 kg/(m2 ∙s) and approximatively 320 kW/m2, respectively, the HTC difference was 4.58 kW/(m2 ∙K) (24%). Balance effect by mass fluxes was emphasized because bubbles departure was accelerated while the heat removed by generated bubbles was reduced due to weakened nucleation sites and bubble diameter.