摇摆条件下窄通道内单相水流态转捩特性

矩形窄通道广泛应用于紧凑式换热器中,其内单相流动流态转捩特性会受到摇摆运动的影响.结合流迹显示技术,对摇摆条件下矩形窄通道内单相水从层流向湍流转变临界点附近的流动特性进行了实验研究.结果表明稳态条件下临界Re为2 550左右.摇摆条件下当Re小于2 400时,流态显示为稳定的层流,Re大于3 500时,流态为湍流,摇摆对稳定的层流区和湍流区流态没有影响；Re为2400～3 500之间时流动处于过渡区,摇摆对其流态转变有一定影响.在临界点附近摇摆振幅越大,流态转捩越容易发生；摇摆周期对流态转捩影响很小.摇摆运动改变系统重位压降及产生附加压降,从而对流态转捩的影响不可忽视.

Investigations on flow regime transition characteristics of single-phase water in narrow ducts under rolling conditions

Narrow rectangular ducts have extensive application to a compact heat exchanger in which the single-phase flow regime transition behavior is influenced by rolling motion.Investigations on transition characteristics in the vicinity of a critical point from laminar to turbulent flow for single-phase water in narrow rectangular ducts with rolling motion were performed by flow resistance experiments and the technology of flow-trace display.The results show that the critical Reynolds number in the non-rolling condition has a value of nearly 2550.Steady laminar flow and turbulent flow were observed under the rolling condition with a Reynolds number of less than 2400 and larger than 3500,respectively,in which the rolling motion has no significant effect on the flow regimes.In the transition region with the Reynolds number ranging from 2400 to 3500,the rolling motion has some influence on flow regimes’ transition.The flow regime transition occurs more easily as the rolling amplitude increases.Rolling period has nearly no effect on transition of flow regimes.Rolling motion changes the system gravitational pressure drop and induces an additional pressure drop,so its effect on single-phase flow regime transition cannot be ignored.