Droplet runoff

As mentioned in the previous section, the increased number of nuclei in polluted urban atmospheres can cause dense persistent fogs due to the many small droplets formed. Fog formation is very dependent on humidity and, in some situations, humidity is increased by release of moisture from industrial processes. Low atmospheric moisture content can also occur, especicilly in urban areas two causes are lack of vegetation and rapid runoff of rainwater through storm sewers. Also, slightly higher temperatures in urban areas lower the relative humidity. 

Armbruster and Mitrovic [62] observed that liquid falls from tube to tube in three patterns discrete droplets, jets or columns, and sheets, depending on the flow rate (i.e., film Reynolds number) and fluid properties. In addition, depending on the tube arrangement and spacing, the condensate may cause ripples, waves, and turbulence to occur in the film splashing may occur, as well as nonuniform rivulet runoff of condensate because of tube inclination or local vapor velocity effects. As a result, it is impossible to arrive at an analytical expression to describe these complex bundle phenomena. In general, the effect of inundation may be accounted for using... 

Measurement of runoff velocity. The runoff velocity of liquid droplets on an inclined surface coated by the superhydrophobic silica aerogel powder was quantified by recording... 

Prior to application of spray formulations, spray adjuvants are typically added to the insecticide mixture to enhance the efficacy of the active ingredient. Spray adjuvants include surfactants, compounds that impart adhesion and viscoelasticity to spray droplets (e.g., latex), compounds that provide protection from ultraviolet light and reduce volatilization, and activators. The coapplication of these compounds affects organophosphorus insecticide dissipation and transfer to surface runoff Some adjuvants and formulation ingredients are toxicologically significant themselves (e.g., nonylphenol ethoxylates). 

The problem of droplet sliding in relation to spray retention has also been considered by Tadros. Spray retention increases as the volume applied increases, up to the point of incipient runoff. Above this point, the volume of spray retained begins to decline, and retention is determined by the movement of drops on the leaf surface. Factors influencing sliding include surface roughness, presence of hairs, leaf age, position on the leaf surface, environmental conditions, surfactant incorporation and concentration, droplet size and velocity, and wind speed. 

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