Theoretical and experimental study of the effects of spray inclination on two-phase spray cooling and critical heat flux

Experiments were conducted with PF-5052 liquid sprays impacting a 1.0 × 1.0 cm2 heated test surface at different inclination angles, flow rates, and subcoolings. Inclination angle had no noticeable effect on the single-phase or two-phase regions of the boiling curve. Maximum CHF was always achieved with the spray impinging normal to the test surface; increasing angle of inclination away from the normal decreased CHF appreciably. Video analysis showed inclined sprays produced lateral liquid film flow towards the farthest downstream region of the test surface. The film liquid provided partial resistance to dryout despite the weak volumetric spray flux in the downstream region. A new theoretical model of the spray's impact area and volumetric flux proves this decrease is the result of a sharp reduction in the fraction of the test surface area that is directly impacted by the spray. Combining the model and video results with a previous point-based CHF correlation for normal sprays is shown to accurately predict the effects of orientation angle on CHF for different nozzles and operating conditions.