Formation and breakup of compound pendant drops at the tip of a capillary and its effect on upstream velocity fluctuations
Wong, Teck Neng
Chai, J. C.
Date of Issue2011
School of Mechanical and Aerospace Engineering
In this paper, the formation and breakup process of compound pendant drops (CPDs, pendant drops with smaller drops or bubbles in them) at the tip of a glass capillary and its effect on upstream velocity ﬂuctuation are experimentally investigated. The formation process of an air/water compound drop from a CPD consists of four main stages. First, an air plug in the capillary ﬂows into the small liquid pendant drop to initialize a small CPD. Next, a liquid slug ﬂows into the CPD, and the liquid in the CPD accumulates. Subsequently, an air plug ﬂows into the CPD, and it coalesces with the existing air bubble in the CPD. The accumulation and coalescence stages repeat, until the CPD reaches a critical weight, then the CPD ﬁnally breaks up to produce a compound drop. For the air/SDS-solution system, the bubbles in the CPDs do not coalesce, and the contact line of the CPDs initially climbs along the capillary and then moves downwards with the growth of the CPDs. The upstream velocity ﬂuctuates during the periodical formation and breakup of the CPD due to Laplace pressure variation at the tip of the glass capillary. By adding surfactant into water, the ﬂuctuation of the upstream velocity decreases. The size distribution of the compound drops produced by the breakup of CPDs is quantiﬁed, and the results show that the current system is able to produce monodisperse compound drops.
International journal of heat and mass transfer
© 2011 Elsevier. This is the author created version of a work that has been peer reviewed and accepted for publication by International journal of heat and mass transfer, Elsevier. It incorporates referee’s comments but changes resulting from the publishing process, such as copyediting, structural formatting, may not be reflected in this document. The published version is available at: http://dx.doi.org/10.1016/j.ijheatmasstransfer.2011.10.008.