Choked flows in open capillary channels: theory, experiment and computations

Rosendahl, Uwe; Ohlhoff, A.; Dreyer, Michael

doi:10.1017/s0022112004001041

Cited by 38 publications

(31 citation statements)

References 8 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Ichikawa et al, 2004;Jong et al, 2007;Zhu and Petkovic-Duran, 2010) and grooved/triangular (Yost and Holm, 1995;Romero and Yost, 2006;Baret et al, 2007). Moreover, the same approach has been taken for channels defined by hydrophilic paths on a hydrophobic substrate (Darhuber et al, 2001) and by the space between two parallel plates (Rosendahl et al, 2004) under the assumption of flow with low Reynolds number and liquid imbibing in a tube/slablike manner. When channels are mounted vertically gravity becomes important and exact analytical solutions for capillary imbibition are no longer possible in general.…”

Section: Introductionmentioning

confidence: 99%

Wetting considerations in capillary rise and imbibition in closed square tubes and open rectangular cross-section channels

Ouali

McHale

Javed

et al. 2013

Microfluid Nanofluid

149

View full text Add to dashboard Cite

The spontaneous capillary-driven filling of microchannels is important for a wide range of applications. These channels are often rectangular in cross-section, can be closed or open, and horizontal or vertically orientated. In this work, we develop the theory for capillary imbibition and rise in channels of rectangular cross-section, taking into account rigidified and non-rigidified boundary conditions for the liquid-air interfaces and the effects of surface topography assuming Wenzel or Cassie-Baxter states. We provide simple interpolation formulae for the viscous friction associated with flow through rectangular cross-section channels as a function of aspect ratio. We derive a dimensionless cross-over time, T c , below which the exact numerical solution can be approximated by the Bousanquet solution and above which by the visco-gravitational solution. For capillary rise heights significantly below the equilibrium height, this cross-over time is T c  (3X e /2) 2/3 and has an associated dimensionless crossover rise height X c  (3X e /2) 1/3 , where X e =1/G is the dimensionless equilibrium rise height and G is a dimensionless form of the acceleration due to gravity. We also show from wetting considerations that for rectangular channels, fingers of a wetting liquid can be expected to imbibe in advance of the main meniscus along the corners of the channel walls. We test the theory via capillary rise experiments using polydimethylsiloxane oils of viscosity 96.0, 48.0, 19.2 and 4.8 mPa s within a range of closed square tubes and open rectangular cross-section channels with SU-8 walls. We show that the capillary rise heights can be fitted using the exact numerical solution and that these are similar to fits using the analytical visco-gravitational solution. The viscous friction contribution was found to be slightly higher than predicted by theory assuming a non-rigidified liquid-air boundary, but far below that for a rigidified boundary, which was recently reported for imbibition into horizontally mounted open microchannels. In these experiments we also observed fingers of liquid spreading along the internal edges of the channels in advance of the main body of liquid consistent with wetting expectations. We briefly discuss the implications of these observations for the design of microfluidic systems.

show abstract

Section: Introductionmentioning

confidence: 99%

Wetting considerations in capillary rise and imbibition in closed square tubes and open rectangular cross-section channels

Ouali

McHale

Javed

et al. 2013

Microfluid Nanofluid

149

View full text Add to dashboard Cite

show abstract

“…Furthermore, the change in methanol flow rate cannot eliminate the effect of gravity. Moreover, research shows that the liquid/gas fluid flow in microgravity conditions is significantly different from that in normal gravity conditions because of the absence of the gravity [42][43][44][45][46]. Therefore, PEMFCs may show distinct types of behavior in a reduced gravity environment.…”

Section: Introductionmentioning

confidence: 99%

Experimental study of two-phase flow in a proton exchange membrane fuel cell in short-term microgravity condition

Guo

Zhao

et al. 2014

Applied Energy

View full text Add to dashboard Cite

h i g h l i g h t sTwo-phase flow in PEMFC cathode channels is observed in different gravity environments. The PEMFC shows different operating behavior in normal and microgravity conditions. Water tends can be removed in microgravity conditions at high water production regime. Liquid aggregation occurs in microgravity conditions at low water production regime. Effect of gravity on performance and two-phase flow at two operating regimes is studied. a r t i c l e i n f o t r a c tWater management is important for improving the performance and stability of proton exchange membrane fuel cells (PEMFCs) for space applications. An in situ visual observation was conducted on the gasliquid two-phase flow in the cathode channels of a PEMFC in short-term microgravity condition. The microgravity environment was supplied by a drop tower. A single serpentine flow channel with a depth of 2 mm and a width of 2 mm was applied as the cathode flow field. A membrane electrode assembly comprising of a Nafion 112 membrane sandwiched between gas diffusion layers was used. The anode and cathode were loaded with 1 mg cm À2 platinum. The PEMFC shows a distinct operating behavior in microgravity because of the effect of gravity on the two-phase flow. At a high water production regime, cell performance is enhanced by 4.6% and the accumulated liquid water in the flow channel tends can be removed in microgravity conditions to alleviate flooding. At a low water production regime, cell performance deteriorates by 6.6% and liquid aggregation occurs in the flow channel because of the coalescence of dispersed water droplets in microgravity conditions, thus squeezing the flow channel. The operating behavior of PEMFC in microgravity conditions is different from that in normal gravity conditions. Further studies are needed on PEMFC operating characteristics and liquid management for space applications.

show abstract

“…in Jaekle 1991Jaekle , 1993. Rosendahl et al (2004) found a flow limitation in open capillary channels which is similar to choking in compressible duct flows and open channel flows under gravity. In this work we want to expand this theory to other channel geometries.…”

Section: Introductionmentioning

confidence: 69%

Flow Rate Limitation of Steady Convective Dominated Open Capillary Channel Flows Through a Groove

Haake

Klatte

Grah

et al. 2009

Microgravity Sci. Technol.

Self Cite

View full text Add to dashboard Cite

An open capillary channel is a structure that establishes a liquid flow path when the capillary pressure caused by surface tension forces dominates in comparison to the hydrostatic pressure induced by gravitational or residual accelerations. To maintain a steady flow through the channel the capillary pressure of the free surface has to balance the pressure difference between the liquid and the surrounding constant pressure gas phase. Due to convective and viscous momentum transport the pressure along the flow path of the liquid decreases and causes the free surface to bend inwards. The maximum flow rate through the channel is reached when the free surface collapses and gas ingestion occurs near the outlet. This stability limit depends on the geometry of the channel and the properties of the liquid. In this paper we present an experimental setup which is used in the low-gravity environment of the Bremen Drop Tower. Experiments with convective dominated systems have been performed where the flow rate was increased up to the maximum value. In comparison to this we present a one-dimensional theoretical model to determine important characteristics of the flow, such as the free surface shape and the limiting flow rate. Furthermore we present an explanation for the mechanism of flow rate limitation for these flow conditions which is similar to the choking problem for compressible gas flows.

show abstract

Choked flows in open capillary channels: theory, experiment and computations

Cited by 38 publications

References 8 publications

Wetting considerations in capillary rise and imbibition in closed square tubes and open rectangular cross-section channels

Wetting considerations in capillary rise and imbibition in closed square tubes and open rectangular cross-section channels

Experimental study of two-phase flow in a proton exchange membrane fuel cell in short-term microgravity condition

Flow Rate Limitation of Steady Convective Dominated Open Capillary Channel Flows Through a Groove

Contact Info

Product

Resources

About