Browsing by Author "Sheen, HJ"

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Effects of ambient turbulence and fuel properties on the evaporation rate of single droplets
(2001-12-01)
Wu, JS
;
Liu, YJ
;
Sheen, HJ
;
機械工程學系
;
Department of Mechanical Engineering
Results of the evaporation of a single liquid fuel droplet in various free-stream turbulence intensities and scales are reported. Experiments are carried out at room temperature by using n-heptane and n-decane, fuels at Re-d = 100. A low-speed vertical wind tunnel with different turbulence intensities and scales, controlled by using different sizes of disk, is constructed. The free-stream turbulence intensities are varied in the range from 1% to 60% and the. integral length scales are from 2.5 to 20 times of the initial droplet diameter. Results show that the time history of droplet diameter follows the d(2)-law in turbulent environments with generally higher evaporation rates as compared with those in quasi-laminar cases. Combined effects of liquid fuel properties and ambient turbulence properties on the evaporation rate can be reasonably well explained by the correlation of normalized evaporation rate with the effective vaporization Damkohler number, Da(v). (C) 2001 Elsevier Science Ltd. All rights reserved.
Evaporation model of a single hydrocarbon fuel droplet due to ambient turbulence at intermediate Reynolds numbers
(2003-11-01)
Wu, JS
;
Hsu, KH
;
Kuo, PM
;
Sheen, HJ
;
機械工程學系
A general evaporation model of a single liquid fuel droplet under various ambient turbulence conditions at intermediate droplet Reynolds numbers is proposed combining the current and previous experimental results. Extensive evaporation experiments of single fuel droplets are conducted at room temperature in quasi-laminar and turbulent environments at Reynolds numbers in the range of 72-333. Tested hydrocarbon fuels include by pentane, hexane, heptane, octane and decane. Flow fields, behind a perforated plate or a circular disk in a vertical low-speed wind tunnel, provide the required ambient turbulent environments for droplet evaporation experiments. The ambient turbulence intensities vary in the range of 1-60% and the integral length scales in the range of 0.5-20 times of the initial droplet diameter. Results show that normalized evaporation rate (K/K-L) decreases with increasing effective Damkohler number (0.0001 < Da(v) < 0.1) and is approximately equal to unity with further increasing Damkohler number (0.1 < Da(v) < 1). (C) 2003 Elsevier Ltd. All rights reserved.