The effect of relative humidity on dropwise condensation dynamics

Abstract

Dropwise condensation of atmospheric water vapor is important in multiple practical engineering applications. The roles of environmental factors and surface morphology/chemistry on the condensation dynamics need to be better understood to enable efficient water-harvesting, dehumidication, and other psychrometric processes. Systems and surfaces that may promote faster condensation rates and selfshedding of condensate droplets could lead to improved mass transfer rates and higher water yields in harvesting applications. In the present study, experiments are performed in a facility that allows visualization of the condensation process on a vertically oriented, hydrophobic surface at a controlled relative humidity and surface subcooling temperature. The distribution and growth of water droplets are monitored across the surface at different relative humidities (45%, 50%, 55%, and 70%) at a constant surface subcooling temperature of 15 °C below the ambient temperature. The droplet growth dynamics exhibits a strong dependency on relative humidity in the early stages during which there is a large population of small droplets on the surface and single droplet growth dominates over coalescence effects.At later stages, the dynamics of droplet growth is insensitive to relative humidity due to the dominance of coalescence effects. The overall volumetric rate of condensation on the surface is also assessed as a function of time and ambient relative humidity. Low relative humidity conditions not only slow the absolute rate of condensation, but also prolong an initial transient regime over which the condensation rate remains significantly below the steady-state value.Keywords: dropwise condensation, relative humidity, growth dynamics, droplet distribution,

Design of an environment controlled dew tracking setup to emphasize the role of the relative humidity on breath figures dynamics

“…Figure 4 shows the number of droplets as a function of time for the 45% relative humidity condition test. The three expected regions [2,18] are well defined and another can also be described -droplet appearance.…”

“…However, the given tendencies were largely approved in literature [2,15,17,18]. Figure 5 shows the three phases predicted by the theory.…”

“…Both the designed setup and the post-processing analysis were validate thanks to the work of Castillo et al [18]. Moreover, beyond their work, this paper also explains the variation of the dynamics of condensation growth with respect to relative humidity through droplet density (the number of droplets).…”

“…This mechanism is defined by a mean droplet radius growth of < R >∼ t 1/3 . The 1/3 exponent depends on the relative humidity of the air and increases with it [18]. When growing, droplets touch each other and coalesce.…”

“…Castillo et al [18] showed that relative humidity has an impact on dew formation. On coated smooth silicon samples, they demonstrated that the growth rate of non-coalescing droplets increases with RH.…”