ABSTRACT
Water collection by gravity flows has been long studied in condensers cooled by contact. Such flows are different according to whether condensation is filmwise or dropwise. The different filmwise and dropwise processes on smooth and patterned substrates are addressed to determine how water can be the most efficiently collected by making use of gravity forces. When looking at dew forming on a kitchen window or on the external side of a car windshield, large edge effects can be frequently observed. Grooves are directed in the gravity direction. Although the lag time where dew accumulates on the substrate before flowing down to be collected is the most important limitation in dew collection, it has been the object of only preliminary investigations. The different situations where a water droplet can sit on an oil-imbibed microsubstrate are depicted. Depending whether lubricant has a low or moderate surface energy; oil can engulf the water droplet or form an annular ring around it.
