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TECHNICAL PAPERS

Characteristics of Fuel Droplets Discharged From a Compensated Fuel/Ballast Tank

[+] Author and Article Information
Jerry W. Shan1

 Naval Surface Warfare Center, Carderock Division, West Bethesda, MD 20817

Paisan Atsavapranee, Peter A. Chang, Wesley M. Wilson, Stephan Verosto

 Naval Surface Warfare Center, Carderock Division, West Bethesda, MD 20817

1

Present address: Department of Mechanical and Aerospace Engineering, Rutgers—The State University of New Jersey, Piscataway, NJ 08854.

J. Fluids Eng 128(5), 893-902 (Mar 09, 2006) (10 pages) doi:10.1115/1.2234780 History: Received December 12, 2002; Revised March 09, 2006

Fuel droplets, formed by the interaction of fuel plumes with a water/fuel interface, can be discharged during the refueling of water-filled compensated fuel/ballast tanks. Motivated by increasingly stringent environmental regulations, a study was initiated to understand the physical mechanisms involved in the formation and transport of fuel droplets by complex immiscible flows inside a model tank. In particular, optical measurements were made of the size distribution of fuel droplets in water discharged from a three-bay model of a compensated fuel/ballast tank. The volumetric fuel concentration of discharge from the tank was inferred from measurements of droplet size and number. Flow visualizations inside the model were coupled to optical measurements of fuel droplets at the tank outlet to show that the presence of fuel in the discharged water was correlated to the formation of fuel plumes within the water-filled tank. The size distribution of fuel droplets at the tank exit is found to differ from the size distribution reported for the generation zone (near the fuel plumes) inside the tank. Thus, the advection of fuel droplets from the generation zone to the tank outlet is shown to affect the characteristics of discharged fuel droplets. The transport process specifically prevents large-diameter droplets from reaching the tank exit. Buoyancy tends to cause larger fuel droplets generated within the tank to rise and separate out of the flow before they can be discharged. The buoyancy time, τb(D), relative to the characteristic advection time, τa, of fuel droplets is a key parameter in predicting the fate of fuel droplets. The influence of buoyancy on the size distribution of discharged droplets was found to be modeled reasonably well by a Butterworth filter that depends on the ratio of timescales τaτb(D). This model, which relates the size distribution of discharged droplets to generated droplets, is found to produce the correct qualitative behavior that larger fuel droplets are discharged when the fuel plumes move closer to the tank exit, i.e., for decreasing advection time τa.

Copyright © 2006 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Plume of fuel in water

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Figure 2

Experimental facility and optical arrangement. Imaging arrangement shown is for low-resolution measurements; camera is closer to tank for high-resolution measurements.

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Figure 3

Flow visualization of refueling of compensated fuel/ballast tank. First fuel plume forms in Bay 2 at t≃35s.

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Figure 4

Flow visualization. Second fuel plume forms in Bay 3 at t≃70s.

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Figure 5

Sample of droplet-identification process. Left: Magnified view of typical image. Right: Identified droplets in Sobel-filtered image.

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Figure 6

Depth-of-field calibration apparatus and sample image

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Figure 7

Volumetric fuel concentration in discharge from experimental tank during refueling. Exponential decay C(t)∝e−0.03s−1(t−105s) shown in dashed line for comparison.

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Figure 8

Measured distribution of droplet sizes for fuel droplets discharged from tank. Log-normal production distribution (for droplets in generation zone) shown for comparison.

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Figure 9

Cumulative size distribution of fuel droplets discharged from the fuel tank, compared to cumulative distribution for droplets in generation zone

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Figure 10

Contribution of droplets of varying size to the fuel concentration of effluent water

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Figure 11

Increasing droplet size in discharge water over time

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Figure 12

Comparison of modeled and measured size distribution of discharged droplets for differing distances from generation zone to tank exit

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Figure 13

Comparison of modeled and measured size distribution of discharged droplets. The log-normal distribution of droplets in the generation zone (close to the fuel plume) is shown with a dotted line.

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Figure 14

Comparison of modeled and measured cumulative size distribution of discharged droplets. The log-normal distribution of droplets in the generation zone (close to the buoyant jet) is shown with a dotted line.

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Figure 15

Left: View of droplet generation zone (in the vicinity of the fuel plume). Right: Close-up of fuel droplets and oil-skin balloons formed by plume (adapted from Chang (see Ref. 5)).

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