Experimental Study on Formation of Stable Flow Layer from Composite Flow Networks Using Flip-Flop Flow

利用薄膜射流的成膜技术适用于保持食品的新鲜度和保护电子系统的操作环境。这种薄膜射流可以在由多个交叉流动通道组成的常规流动网络中产生，所述多个交叉流动通道由菱形流动岛（将被称为圆柱体）形成。最近，一种新型的交叉流网络，被称为复合流网络，由一个传统的流网络叠加并流薄膜流。随后，一种不同类型的复合流网络被构造成夹在两个传统的流网络之间的薄膜流，试图稳定并因此扩展薄膜流。本研究的目的是澄清三种不同类型的流体流动特性：第一种是在常规流动网络上，第二种是在三层复合流动网络（F-A管道）上，第三种是在具有狭缝流动的三层复合流动网络（具有狭缝的F-A管道）上。研究结果表明：（1）F-A通道内对称的翻转流动振荡与下游有狭缝的F-A通道内产生的纵向涡相互干扰，产生对称的射流;（2）现有的射流束结牢固，形成层状流动。在带狭缝的F-A通道中，交叉流的存在导致下游形成稳定的流动层，并加强（拉长）了射流。

The film-forming technology utilizing thin-film jet flow is applicable in maintaining freshness in food products and protecting operational environments of electronics systems. Such a thin-film jet may be produced in a conventional flow network consisting of multiple intersecting flow passages formed by a diamond-shaped flow islands (to be called cylinders). Recently, a new type of intersecting flow network, to be referred to as composite flow network, was developed consisting of a conventional flow network superposed with a co-current thin film flow. Subsequently, a different type of composite flow network was constructed consisting of a thin-film flow sandwiched in between two conventional flow networks in an attempt to stabilizing and thus extending the thin-film flow.The aim of the present study is to clarify fluid flow characteristics of three different types : first on a conventional flow network, second on a three-layered composite flow network(F-A duct), and third on a three-layered composite flow network with slit flow(F-A duct with a slit). Each experiment consists of applications of flow visualization method and two-dimensional particle image velocimetry (PIV).It is disclosed from the study that :(1)Mutual interference between the symmetrical flip-flop flow oscillation in F-A duct and the longitudinal vortices generated in the F-A duct with a slit located downstream results in a symmetrical efflux.(2)The existing jet streams bundle up firmly and form a flow in layers. The presence of intersecting flow in F-A duct with a slit causes the formation of stable flow layer downstream and strengthening (elongating) the efflux.