Match!

Estimates of Liquid Species Diffusivities in N-Propanol/Glycerol Mixture Droplets Burning in Reduced Gravity

Published on Jul 1, 2015in Microgravity Science and Technology1.973
· DOI :10.1007/s12217-015-9455-8
C. L. Vang1
Estimated H-index: 1
(UC: University of California),
Benjamin D. Shaw13
Estimated H-index: 13
(UC: University of California)
Abstract
Results from International Space Station experiments on combustion of n-propanol/glycerol droplets are reported. The initial n-propanol mass fraction was 0.95 and droplets had initial diameters in the 2 – 5 mm range. Some droplets were fiber supported while others were free floating, and the environment was either an oxygen/nitrogen mixture at 1 atm or an oxygen/helium mixture at pressures of 1 and 3 atm. The droplets burned in a multi-stage manner where n-propanol was preferentially evaporated during the early stages of combustion. The resulting buildup of glycerol in the liquid at the droplet surface led to sudden droplet heating and flame contraction. The experimental data are evaluated to provide burning rates, radiometer outputs, and droplet diameters as functions of time. These data are used to calculate effective liquid species diffusivities, D, using asymptotic theory. The D values can be substantially larger than molecular diffusivities in some cases, indicative of the presence of strong convective mixing. It was found that support fibers can decrease D values and that high burning rates can substantially increase D. These variations are attributed to changes in droplet internal flow patterns.
  • References (47)
  • Citations (2)
📖 Papers frequently viewed together
4 Citations
4 Citations
2 Citations
78% of Scinapse members use related papers. After signing in, all features are FREE.
References47
Newest
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. ...
3 CitationsSource
#1Narugopal Ghata (UC Davis: University of California, Davis)H-Index: 3
#2Benjamin D. Shaw (UC Davis: University of California, Davis)H-Index: 13
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...
12 CitationsSource
#1Benjamin D. Shaw (UC: University of California)H-Index: 13
#2Fei Yu (UC: University of California)H-Index: 1
3 CitationsSource
Backlit droplet images are evaluated for droplet combustion experiments that have been performed on the International Space Station. The focus of the present analyses is on non-sooting or lightly-sooting droplets. The influences of diffraction, interference, and partial coherence on droplet images are considered via Fourier optics modeling. It is found that light diffraction at the droplet edge can contribute significantly to errors in droplet size measurements. Other error sources include backg...
2 Citations
Methodologies are developed for evaluating uncertainties in droplet size measurements and burning rates for droplet combustion experiments that have been performed on the International Space Station. Different uncertainty sources are considered and propagated into the combined standard uncertainties via the Taylor series method. The local polynomial method is used to provide estimates of instantaneous burning rates. Results from analyses of non-sooting (methanol) or lightly sooting (heptane) dro...
5 CitationsSource
126k Citations
#1D. Shringi (UC Davis: University of California, Davis)H-Index: 3
#2Harry A. Dwyer (UC Davis: University of California, Davis)H-Index: 25
Last. Benjamin D. Shaw (UC Davis: University of California, Davis)H-Index: 13
view all 3 authors...
Abstract Numerical calculations are carried out to study flows around liquid droplets held in place by cylindrical fibers. Two configurations were considered: (1) a droplet supported at the middle of a fiber that extends into the gas phase on both sides of the droplet and (2) a droplet suspended at the end of a fiber. Calculations are done for droplet Reynolds numbers based on droplet diameters of 0–100. The flow around a supported droplet loses its axisymmetry even for very thin support fibers....
3 CitationsSource
#1D. Shringi (UC Davis: University of California, Davis)H-Index: 3
#2Harry A. Dwyer (UC Davis: University of California, Davis)H-Index: 25
Last. Benjamin D. Shaw (UC Davis: University of California, Davis)H-Index: 13
view all 3 authors...
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...
6 CitationsSource
#1I. AharonH-Index: 1
#2V. K. TamH-Index: 1
Last. Benjamin D. Shaw (UC Davis: University of California, Davis)H-Index: 13
view all 3 authors...
Reduced-gravity experiments were performed on combustion of droplets composed of n-heptane mixed with methanol or ethanol. The initial alcohol mass fraction in a droplet was 0% (pure heptane) or 5%. The experiments were performed at 0.1 MPa and 25°C with air or with ambients of oxygen and helium with oxygen mole fractions of 0.3 or 0.4. Initial droplet diameters were in the range 0.67 mm to 0.92 mm. After considering measurement uncertainties, burning rates decreased appreciably as the initial d...
3 CitationsSource
#1Tanvir Farouk (Princeton University)H-Index: 18
#2Frederick L. Dryer (Princeton University)H-Index: 68
Droplets tethering on fibers has become a well established technique for conducting droplet combustion experiments in microgravity conditions. The effects of these supporting fibers are frequently assumed to be negligible and are not considered in the experimental analysis or in numerical simulations. In this work, the effect of supporting fibers on the characteristics of microgravity droplet combustion has been investigated numerically; a priori predictions have then been compared with publishe...
32 CitationsSource
Cited By2
Newest
#1C. L. Vang (UC Davis: University of California, Davis)
#2B. D. Shaw (UC Davis: University of California, Davis)
Combustion experiments on heptane–hexadecane mixture droplets were conducted onboard the International Space Station. The ambient consisted of oxygen mixed with either helium or nitrogen at 1 atm. Initial droplet diameters were in the 1.7–4.8 mm range with initial heptane mass fractions of 0.95 or 0.80. Because of limitations on resources, only fiber-supported experiments were possible. Vaporization of the more volatile fuel component (heptane) was favored during the droplet combustion process, ...
Source
Diffusion flames are the most common type of flame which we see in our daily life such as candle flame and match-stick flame. Also, they are the most used flames in practical combustion system such as industrial burner (coal fired, gas fired or oil fired), diesel engines, gas turbines, and solid fuel rockets. In the present study, steady-state global chemistry calculations for 24 different flames were performed using an axisymmetric computational fluid dynamics code (UNICORN). Computation involv...
4 CitationsSource