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Influences of support fibers on shapes of heptane/hexadecane droplets in reduced gravity

Published on Dec 1, 2002in Microgravity Science and Technology1.973
· DOI :10.1007/BF02881679
Benjamin D. Shaw13
Estimated H-index: 13
(UC Davis: University of California, Davis),
M. J. Harrison1
Estimated H-index: 1
Abstract
This paper describes analytical and experimental results related to the effects of support fibers on shapes of heptane/hexadecane mixture droplets (both burning and evaporating) in reduced gravity. The experimental results were obtained from large droplets (a few mm) investigated during the MSL-1 Flight of Spacelab. Theoretical (asymptotic) analyses are developed to predict droplet shapes. These analyses, which predict droplet shapes very well, illustrate important aspects of droplet shapes in a transparent fashion. The asymptotic theory shows that for small droplet-fiber contact angles, two spatial zones exist where droplet shapes behave differently. Away from a fiber, a droplet is essentially spherical. As the fiber is approached, however, deviations from spherical symmetry are significant. Previously developed analytical theory to predict macroscopic droplet shapes also compares well with experimental results. In addition, the experiments indicate that thin liquid films can form on support fibers. In the present experiments, these films apparently lead to transient formation of small droplets/bubbles on the support fibers at locations near the surface of a droplet.
  • References (19)
  • Citations (5)
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References19
Newest
#1Benjamin D. Shaw (UC Davis: University of California, Davis)H-Index: 13
#2I. Aharon (UC Davis: University of California, Davis)H-Index: 2
Last. Forman A. Williams (UCSD: University of California, San Diego)H-Index: 54
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This paper describes reduced-gravity experiments on the combustion of droplets composed of metha-nol/dodecanol and ethanol/dodecanol mixtures. The experiments used the NASA Glenn Research Center 2·2 s drop tower as well as facilities in Spacelab during the USML-2 flight. In the drop-tower experiments, initial droplet diameters ranged from 0·8 mm to 1.2 mm, initial dodecanol mass fractions, Y, (in both mixtures) were 0·1, 0·25 and 0·5, and the ambient gas mixture was either an 02/He mixture (with...
6 CitationsSource
#1Benjamin D. Shaw (UC Davis: University of California, Davis)H-Index: 1
#2Bret D. Clark (UC Davis: University of California, Davis)H-Index: 1
Last. Difei Wang (UC Davis: University of California, Davis)H-Index: 1
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Results are presented from experiments on reduced-gravity combustion of individual heptane/hexadecane droplets. Initial droplet diameters ranged from 0.25 to 5.2 mm, and initial hexadecane mass fractions in the droplets were 0.058, 0.10, 0.20, and 0.40. Most droplets were burned in cabin air on Spacelab with an ambient oxygen mole fraction of about 0.21 and a pressure of about 0.1 MPa. Data were also obtained for small (0.25-mm) droplets in a ground-based apparatus that provides simulated reduce...
9 CitationsSource
Using an interface displacement model we calculate the shapes of nanometer-size liquid droplets on homogeneous cylindrical surfaces. We determine effective contact angles and line tensions, the latter defined as excess free energies per unit length associated with the two contact lines at the ends of the droplet. The dependences of these quantities on the cylinder radius and on the volume of the droplets are analyzed.
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#1Glen McHale (NTU: Nottingham Trent University)H-Index: 46
#2S. M. Rowan (NTU: Nottingham Trent University)H-Index: 11
Last. N.A. Käb (NTU: Nottingham Trent University)H-Index: 2
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A droplet of liquid placed on a flat high-energy solid surface spreads to give a thin film so that no macroscopic droplet shape exists. On a chemically identical solid surface with only the geometry changed to a cylinder, the same droplet can have an equilibrium conformation. When the equilibrium conformation is of a barrel type, the profile of the droplet changes rapidly in curvature as the three-phase contact line is approached and the direct measurement of the contact angle is difficult. This...
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The modeling of liquid spreading and penetration into fibrous materials requires a better understanding of the interactions of thin liquid films and small droplets with single fibers. The wetting properties of fibers may differ significantly from those of plane solid surfaces. Convex surfaces of fibers imply a positive Laplace pressure acting on the liquid-gas interface. This effect causes liquid film instability and hinders droplet spreading. Liquid films on fibers arc stable when the destabili...
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#1I. Aharon (UC Davis: University of California, Davis)H-Index: 1
#2B.D. Shaw (UC Davis: University of California, Davis)H-Index: 2
Abstract Experiments on combustion of heptane/hexadecane mixture droplets were conducted in a reduced-gravity environment. Initial droplet diameters ranged from 0.47 to 1.5 mm, and initial hexadecane mass fractions ranged from 0.05 to 0.4. The ambient gas was O2/He (with O2 mole fractions of 0.3 and 0.5), or atmospheric air, and pressures were varied from 0.033 to 0.3 MPa (abs). A previous asymptotic theory was extended to allow data on flame contractions to be used to estimate liquid species di...
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#1Bihai Song (Technical University of Berlin)H-Index: 8
#2Alexander Bismarck (Technical University of Berlin)H-Index: 55
Last. Jürgen Springer (Technical University of Berlin)H-Index: 27
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Abstract A generalized drop length–height method is introduced here for the determination of contact angle in the drop-on-fiber systems. This method overcomes some of the difficulties encountered in the practice by applying the common maximum drop length–height method to determine the contact angle. Furthermore, with this new generalized method a large part of a drop profile can be used in the calculation, which reduces the statistical error of the determination and improves the reliability and ...
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22 Citations
#1Glen McHale (NTU: Nottingham Trent University)H-Index: 46
#2N.A. Käb (NTU: Nottingham Trent University)H-Index: 2
Last. S. M. Rowan (NTU: Nottingham Trent University)H-Index: 11
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The measurement of the equilibrium contact angle of a small droplet of fluid partially wetting a flat solid surface provides information on the solid–liquid interfacial energy. However, if the spreading power,S= γSV− (γSL+ γLV), of the surface is positive the liquid spreads completely, no equilibrium contact angle exists, and the resulting thin film has an ultimate thickness determined by Van der Waal's forces. On a chemically identical solid surface with only the geometry changed to a cylinder ...
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The shape of a drop lying on a non-wettable solid substrate and the phenomenon of a drop jump from the substrate during the transition to weightlessness are investigated experimentally, theoretically and numerically. A mechanical model of the jump of the drop is proposed. The shape of a lying drop is calculated, and it is shown that the height of the drop depends on the volume of the drop nonmonotonically. The radius of the contact area of the drop with the substrate is calculated as a function ...
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A detailed numerical investigation of combustion of unsupported and fiber supported n-heptane droplets in reduced gravity is presented. The primary focus is on the effects of support fibers on the droplet burning rates and flame structure. A 21-step n-heptane reaction mechanism consisting of 20 species is employed to model the combustion chemistry. The volume-of-fluid (VOF) method is employed to capture the liquid-gas interface while allowing for time-dependent two-phase multidimensional flows. ...
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#1Narugopal Ghata (UC Davis: University of California, Davis)H-Index: 3
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Abstract A detailed numerical investigation of the effects of support fibers on the vaporization of a fiber-supported droplet in reduced gravity is presented. The volume-of-fluid (VOF) method was employed to capture the liquid–gas interface while allowing for time-dependent two-phase multidimensional flows. The calculations allowed for the inclusion of thermocapillary stresses at the liquid–gas interface. The study also investigated the effects of the thickness of fiber, ambient pressure, and am...
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#1D. Shringi (UC Davis: University of California, Davis)H-Index: 3
#2Harry A. Dwyer (UC Davis: University of California, Davis)H-Index: 25
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Abstract Detailed computational modeling is performed to study influences of support fibers on vaporizing fuel droplets. Droplets are supported on thin fibers and vaporize in high-temperature and high-pressure environments with cross flows that are perpendicular to the fiber. Droplet Reynolds numbers, based on initial droplet diameters are 0.1, 4, and 30. The temperature distribution inside a support fiber is almost one-dimensional with significant gradients being formed only along the fiber axi...
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#1Benjamin D. Shaw (UC Davis: University of California, Davis)H-Index: 1
#2Bret D. Clark (UC Davis: University of California, Davis)H-Index: 1
Last. Difei Wang (UC Davis: University of California, Davis)H-Index: 1
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Results are presented from experiments on reduced-gravity combustion of individual heptane/hexadecane droplets. Initial droplet diameters ranged from 0.25 to 5.2 mm, and initial hexadecane mass fractions in the droplets were 0.058, 0.10, 0.20, and 0.40. Most droplets were burned in cabin air on Spacelab with an ambient oxygen mole fraction of about 0.21 and a pressure of about 0.1 MPa. Data were also obtained for small (0.25-mm) droplets in a ground-based apparatus that provides simulated reduce...
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