Abstract
Coalescence is a process in which two or more drops contact each other and merge to form a single daughter drop. The process may occur in a fluid medium or on a solid surface. In both instances, coalescence is an intense dynamic process during which the fluid is momentarily set into motion. The present study compares the shear rates, and hence, shear stresses generated on the wall because of the coalescence of two drops in pendant and sessile configurations. In experiments, two drops of equal volume are placed adjacent to each other till a liquid bridge is formed with the drops just touching each other. The equilibrium contact angle considered is 110o. The liquid is water placed on and underneath a textured surface. Coalescence is driven by the negative curvature of the liquid bridge, leading to a pressure difference. The contact line moves and bridge relaxes as flow takes place from a region of higher to lower pressure. The entire process has been imaged by using a high speed camera. The image sequence is analyzed to find the instantaneous center of mass of the drop, which in turn, yields the velocity components. These are used to find the time-dependent wall shear rates. Experiments show that two timescales appear during the merging of the drops. Large shear stresses are momentarily developed at the wall with a magnitude that depends on the drop volume. Oscillations in the drop shape are stronger in the pendant configuration where gravity is an additional driving force.
This is a preview of subscription content, log in via an institution to check access.
Access this chapter
Tax calculation will be finalised at checkout
Purchases are for personal use only
Abbreviations
- \(d_{1} ,d_{2}\) :
-
Diameter of larger and smaller drop respectively (m)
- \(\overset{\lower0.5em\hbox{$\smash{\scriptscriptstyle\rightharpoonup}$}} {g}\) :
-
Acceleration due to gravity (m/s2)
- L :
-
Characteristic dimension (m)
- m :
-
Mass of drop (kg)
- N :
-
Number of pixels
- t :
-
Time (s)
- U :
-
Characteristic velocity (m/s)
- \(u_{c}\) :
-
x-component of centroid velocity (m/s)
- V :
-
Volume of drop (m3)
- \(v_{c}\) :
-
y-component of centroid velocity (m/s)
- \(V_{D}\) :
-
Volume of composite drop (m3)
- \(x_{c}\) :
-
x-coordinate of centroid (m)
- \(y_{c}\) :
-
y-coordinate of centroid (m)
- \(\gamma\) :
-
Area function
- \(\dot{\gamma }\) :
-
Shear rate (s−1)
- \(\mu\) :
-
Dynamic viscosity (Pa-s)
- \(\rho\) :
-
Density of fluid (kg/m3)
- \(\sigma\) :
-
Surface tension (N/m)
References
Andrieu, C., Beysens, D.A., Nikolayev, V.S., Pomeau, Y.: Coalescence of sessile drops. J. Fluid Mech. 453, 427–438 (2002)
Aryafar, H., Kavehpour, H.P.: Drop coalescence through planar surfaces. Phys. Fluids 18, 072105 (2006)
Blanchette, F., Bigioni, T.P.: Dynamics of drop coalescence at fluid interfaces. J. Fluid Mech. 620, 333–352 (2009)
Bordoloi, A.D., Longmire, E.K.: Effect of neighboring perturbations on drop coalescence at an interface. Phys. Fluids 24, 062106 (2012)
Graham, P.J., Farhangi, M.M., Dolatabadi, A.: Dynamics of droplet coalescence in response to increasing hydrophobicity. Phys. Fluids 24, 112105 (2012)
Narhe, R., Beysens, D., Nikolayev, V.S.: Contact line dynamics in drop coalescence and spreading. Langmuir 20(4), 1213–1221 (2004)
Rykaczewski, K., Scott, J.H.J., Rajauria, S., Chinn, J., Chinn, A.M., Jones, W.: Three dimensional aspects of droplet coalescence during dropwise condensation on superhydrophobic surfaces. Soft Matter 7, 8749–8752 (2011)
Sprittles, J.E., Shikhmurzaev, Y.D.: Coalescence of liquid drops: Different models versus experiment. Phys. Fluids 24, 122105 (2012)
Thoroddsen, S.T., Takehara, K., Etoh, T.G.: The coalescence speed of a pendent and a sessile drop. J. Fluid Mech. 527, 85–114 (2005)
Wu, M., Cubaud, T., Ho, C.M.: Scaling law in liquid drop coalescence driven by surface tension. Phys. Fluids 16, L51 (2004)
Author information
Authors and Affiliations
Corresponding author
Editor information
Editors and Affiliations
Rights and permissions
Copyright information
© 2017 Springer India
About this paper
Cite this paper
Somwanshi, P.M., Muralidhar, K., Sameer Khandekar (2017). Wall Shear Rates Generated During Coalescence of Pendant and Sessile Drops. In: Saha, A., Das, D., Srivastava, R., Panigrahi, P., Muralidhar, K. (eds) Fluid Mechanics and Fluid Power – Contemporary Research. Lecture Notes in Mechanical Engineering. Springer, New Delhi. https://doi.org/10.1007/978-81-322-2743-4_4
Download citation
DOI: https://doi.org/10.1007/978-81-322-2743-4_4
Published:
Publisher Name: Springer, New Delhi
Print ISBN: 978-81-322-2741-0
Online ISBN: 978-81-322-2743-4
eBook Packages: EngineeringEngineering (R0)