An experimental study of falling film evaporation on inclined plates using R-141b and R-134a

This paper discusses the effects of surface geometries and inclination angle on falling film evaporation performance. Falling film evaporation experiments were conducted on a plain plate and a finned plate using refrigerants R-141b at 15.5°C±0.5°C (59.9°F±0.9°F) and R-134a at 10.5°C±0.5°C (50.9°F±0.9°F) system temperature. Both plates were tested with an inclination angle between 10° and 40°, and the heat fluxes were varied between 17.9 kW/m² (5674 Btu/h·ft²) and 45.7 kW/m²(14486 Btu/h·ft²). The finned surface yielded better falling film evaporation heat transfer performance than the plain surface for both R-141b and R-134a. ForR-141b, the finned surface yielded 1.5-1.8 times the heat transfer coefficients of the plain surface. For R-134a, the evaporative heat transfer was enhanced 2.5-4.8-fold with the fins. The visual observation showed that bubble nucleation was more pronounced on the finned surface than on the plain surface. For the Fin-B surface in both R-134a and R-141b, the heat transfer coefficient increased as the inclination angle increased. No significant effect of inclination was found on plain surface for R-141b.