Hoar Frost Accretion on Organic Coatings Under Offshore Conditions

Nine organic corrosion protection coating systems are investigated according to their hoar frost accretion performance under simulated offshore conditions. A special test scenario is developed for the generation and measurement of defined hoar frost layers. Hoar frost layer thickness is estimated on newly applied coatings and on artificially aged coatings. The aging procedure refers to offshore conditions, which mainly cover low temperatures, dry–wet cycles, salt spray, and ultraviolet (UV) radiation. In average, the accreted thickness either did not change significantly or increased. Spearman's rank correlations were estimated for all surface parameters. If all measurements (new and aged) for an individual surface parameter were considered, only weak correlations were found between hoar frost thickness, static contact angle, specific surface energy, and surface roughness. The importance of UV radiation on the appearance of hoar frost is highlighted.

Estimation of a Nusselt Correlations for Numerical Prediction of Frost Thickness Growth over a Cold Cylinder

This paper evaluates numerically some of the parameters involved in modeling the process of frost formation over a cold cylinder surface subject to the flow of humid air. Was utilized for numerical predictions the empirical Nusselt correlation from the literature, obtained in experimental studies on frost formation phenomena of frost grow over a cold cylinder surface. To predict frosting process a numerical solution was utilized, and a new correlation for Nusselt number based on the experimental correlation of Kim was estimated. For the new Nusselt correlation an optimization method that adjusts the numerical solution of modeling the frost formation process with experimental results of the frost layer thickness was used. The calculation procedure allows the estimation of the parameter K of equation. The modeling process was validated by comparison with available experimental data.

Experiment Study on Unsteady Frosting of Cryogenic Vertical Plate Surface under Natural Convection Conditions

A frosting test bench was designed, and unsteady frosting on vertical plate surface was dynamically described with liquid nitrogen as working medium under natural convection conditions. The variation of frost thickness was analyzed, and the flow state of moist air and temperature distribution near the vertical plate were described. The experimental results show the unsteady frosting of vertical plate surface under natural convection and cryogenic condition actually includes several steps: formation of frost crystals, growth of frost crystals and growth of frost layer. The initial frosting rate is large, but the rate decreases as time goes on until the frost layer thickness is unchanged. Moist air conducts a top-down flow near the vertical plate, and the rest of moist air flows into the main flow. The temperature of moist air decreased systematically along the tangential direction of vertical plate from top to bottom and along the normal direction of vertical plate from far to vertical plate surface.