Research Papers: Energy Systems Analysis

A Study on the Evaporation of Water–Ethanol Mixture Using Rainbow Refractometry

[+] Author and Article Information
Jantarat Promvongsa

Joint Graduate School of
Energy and Environment,
King Mongkut's University
of Technology Thonburi,
126 Prachauthit Road, Bangmod, Tungkru,
Bangkok 10140, Thailand
e-mail: jantarat_pr@hotmail.com

Bundit Fungtammasan

Center of Excellence on Energy
Technology and Environment,
Office of the Commission on Higher Education,
Bangkok 10140, Thailand
e-mail: bundit.fun@gmail.com

Grehan Gerard

Universite de Rouen,
Rouen 76800, Saint Etienne du Rouvray, France
e-mail: grehan@coria.fr

Sawitree Saengkaew

Universite de Rouen,
Rouen 76800, Saint Etienne du Rouvray, France
e-mail: sawitree_s@coria.fr

Pumyos Vallikul

Department of Mechanical and
Aerospace Engineering,
King Mongkut's University
of Technology North Bangkok,
1518 Pracharat I Road, Wongsawang, Bangsue,
Bangkok 10800, Thailand
e-mail: pumyos@hotmail.com

1Corresponding author.

Contributed by the Advanced Energy Systems Division of ASME for publication in the JOURNAL OF ENERGY RESOURCES TECHNOLOGY. Manuscript received April 30, 2017; final manuscript received May 30, 2017; published online July 27, 2017. Assoc. Editor: Ashwani K. Gupta.

J. Energy Resour. Technol 139(6), 062002 (Jul 27, 2017) (6 pages) Paper No: JERT-17-1190; doi: 10.1115/1.4037157 History: Received April 30, 2017; Revised May 30, 2017

Evaporation of droplets of liquid mixture is a subject of interest in combustion studies, e.g., combustion of bioethanol blends. In this paper, experimental investigation, using rainbow refractometry, on the variations of droplet diameter and composition during the evaporation of water–ethanol droplet in quiescent atmosphere is studied. The droplet is suspended on the tip of 125 μm-diameter fiberglass rod. The initial diameter is around 1000–1100 μm, and the initial composition is varied from 0% to 100% of ethanol by volume. The scattered rainbow signal from the evaporating droplet is fitted to the Airy theory to extract information on the diameter and refractive index of the liquid droplet against evolution time. To determine the accuracy of droplet diameter measurements using this technique, the diameter is also measured from the shadow image of droplet simultaneously. At 0–60% of ethanol by volume, the diameter and volume fraction accuracies are within ±30 μm and 10%, respectively, even though the temperature and composition gradients inside a droplet are neglected. The results show that the water–ethanol mixture evaporates faster at the beginning due to the higher amount of the volatile component, i.e., ethanol. The D2–t curve appears as a series of two straight lines of different slopes: a steep one initially and a moderate one at later stage. The slope at the initial or the transition stage increases with the ethanol composition, while the slope at later stage (steady stage) is equivalent to that of pure water. Likewise, the refractive index decreases rapidly at the beginning and becomes steady reaching a final value of 1.333, which is close to the refractive index of pure water.

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Fig. 1

Experimental setup

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Fig. 2

The refractive index measured by Abbe refractometer versus volume percentage of E95

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Fig. 3

The series of droplet images and rainbow signals of an evaporating 50 vol % E95 droplet

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Fig. 4

The distorted rainbow signals from an 80 vol % of E95 droplet. The diameter and refractive index can be extracted only from first signal (at t = 0).

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Fig. 5

The recorded rainbow signal (top) and its intensity distribution plotted against scattering angle compared with filtered signal and Airy best fit (bottom)

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Fig. 6

(a) Comparison of extracted droplet diameter between the rainbow technique and imaging technique and (b) the difference in diameter measured from the two techniques

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Fig. 7

D2t curve obtained from the rainbow technique

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Fig. 8

The refractive index obtained from the rainbow technique

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Fig. 9

The evaporation constant (or the slope of plot in Fig. 7) at the transition and steady stages versus the volume percentage of E95

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Fig. 10

The variation of volume fraction of E95 droplets calculated from the measured refractive index

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Fig. 11

The volume fraction of E95 droplets obtained from the rainbow technique at the beginning of the measurement compared with their actual volume fraction

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Fig. 12

(a) Example of distorted rainbow signals and the corresponding droplet images of a 70 vol % of E95 droplet and (b) their extracted diameter and refractive index



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