الفهرس 
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Abstract
In the presence of an air stream a stable surface water layer with specific dimensions, on a horizontal flat plate becomes vulnerable to non equilibrium outcome of minor changes in the air stream orientation. The wall jet arising from the impingement of a plane air jet onto a horizontal flat plate is considered as an example of the air stream with possible variable orientation. This aerodynamic configuration is used in many industrial applications, most notably drying.
In this regard, an experimental study was conducted to identify and investigate the various regions and regimes of physical interaction between a two dimensional ”2D” air jet and a surface water layer on a horizontal plate, from both hydrodynamic and masstransport (evaporation) points of view. The study takes into account the effects on that issue of the angle of inclination of the air jet (wall jet in this study), the vertical distance between the jet exit lateral axis and the horizontal flat plate (offset value), the surface water layer thickness. The experimental program substantiated conducting air flow measurements that comprise jet velocity traverses, to designate the wall jet performance. Water layer visualization and meterological measurements are conducted, in presence of the air jet, throughout the different phases of jet-layer interaction. This program lead to clarify the different regions and regimes of hydrodynamic and masstransport interactions, from quasi¬static evaporation up to complete ejection and displacement characteristics of the water layer, under the effect of impinging jet.
The present study revealed that the physical hydrodynamic areas are divided into two main parts, which are the pre-displacement (pre critical region) and the displacement region itself. The first part is divided into three regions; the first is the quasi-static surface water layer (in this region the surface water layer can be aerodynamically dealt with as part of a solid surface). In this region still surface water layer evaporation experiments show that the quasi-static water layer evaporation in presence of air jet is divided into two basic regions, the first is the region where the evaporation rate is linear. This extended over about 90% of the total time of evaporation, while the second region is characterized by superfacial erosion form for the surface water layer in the direction of force, (crescent evaporation) on reaching a layer height equivalent to values that resort thin membrane. This region occupies the remaining time for complete evaporation.
The second main region is the region of appearance of minor disturbances, which appears at isolated areas of the surface water layer. With the increase of Reynolds number of the jet the minor disturbances turned to strong disturbances and these are accompanied by weakening of the static state ofthe water layer, as a result of the effective shear stress at the air-water interface. This in turn lead to the emergence of surface vortices. With increasing Reynolds number the appearance of small ripples begins in an irregular manner, followed by a state of rapid waves of notable amplitude. In the case of surface water layers with thicknesses of about 3mm these waves are found to have wave heights of about 1/3 o( the water layer thickness. The case is different with layer thicknesses of Imm and 2mm where the wave height is almost equal to the water layer height.
The third main region is the displacement region in which the front edge begins to displace (Leading edge ejection); afterward the displacement of the rear edge occurs (Trailing edge ejection). This stage ends with complete displacement of the water layerthe displacement first begins with rear edge displacement (Trailing edge ejection) followed by a displacement of the front edge (Leading edge ejection) and ends with complete displacement ofthe surface water layer (Complete ejection).