Spontaneous channeling of solitary pulses in heated-film flows

Abstract

Abstract. -We investigate the dynamics of a liquid film flowing down a uniformly heated wall. We use a four-field weighted-average model for the film thickness, the surface temperature and the two-dimensional flow rate vector. Time-dependent simulations are rationalized in a phase diagram. For small Reynolds numbers we observe regularly spaced rivulets aligned with the flow that prevent the development of hydrodynamic waves while for large Reynolds numbers, the evolution is similar to that observed in the isothermal case, i.e. wave-dominated. The transition between the two regimes is characterized by an intricate pattern formation dynamics, including regimes of quasi-2D solitary pulses riding the crests of rivulets.

Experimental investigations of liquid falling films flowing under an inclined planar substrate

“…6(b)]. Hence, as the local liquid flow rate increases, the local Re also increases, favoring the hydrodynamic instability mode[44,45]. Over the range Re = 1.4-3.5, the regular wave trains disintegrate into complex 3-D wave patterns, similar to those observed by Alekseenko and coworkers when investigating the formation of rivulets in water films falling down a vertical wall[36][37][38].…”

“…6(a)]. A rivulet evolution scenario akin to the one proposed by Scheid et al[44,45] for water films heated uniformly from the wall side could potentially account for the observed topology, with the cross-stream component of gravity(rather than the Marangoni effect) triggering the formation of rivulets upstream of the measurement location. At Re = 1.4, regular hydrodynamic waves of varying amplitude travel over the rivulet crests, but not the troughs [Fig.…”

“…This formation is manifested by a "quasisinusoidal" modulation of the interface height in the transverse direction of the flow [39][40][41][42], and has been attributed, when observed in nonisothermal falling films, to surface-tension variations induced by temperature gradients (and described by the long-wave thermocapillary Marangoni instability mechanism). Joo et al [43] proposed a mechanism for the formation of rivulets on 004000-3 the surface of a thin liquid layer falling down a heated substrate at low Re (Re ≈ 1), while Scheid and coworkers [44,45] introduced a theoretical framework for the investigation of the Marangoni-driven rivulet formation in an effort to identify possible heat-transfer enhancements in the presence of rivulets. By varying the flow Re in the range Re = 0.5-10 in water films flowing down a uniformly heated vertical wall, these authors captured numerically Marangoni-driven waves in the region where the transition from the drag-gravity to the drag-inertia regimes for isothermal flows occurs.…”

Impact of droplets on inclined flowing liquid films

“…The effects of many factors that influence the flow in falling films have been investigated, such as the effects of thermocapillarity [49], electric fields [50,51], and surfactants [52,53]. Different processes that may be involved in falling films have also been studied, such as heat transfer [54], mass transfer [55], chemical reactions [56], and phase change [57]. Even though the flow of falling liquid films has been widely studied in the literature, it still remains an important research topic and attracts the attention of researchers of various disciplines.…”

An ensemble method for sensor optimisation applied to falling liquid films

“…Effects of different influencing factors in falling films have been studied, such as the effects of thermocapillarity (Frank and Kabov, 2006), electric fields (Tseluiko and Papageorgiou, 2006), 55 centrifugal forces (Matar et al, 2005), and surfactants (Strobel and Whitaker, 1969;Ji and Setterwall, 1994). Different processes that may be involved in the phenomena have been studied, such as heat transfer (Scheid et al, 2008), mass transfer (Yang and Wood, 1992), chemical reactions (Dabir et al, 1996), and phase change (Palen et al, 1994).…”